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MANAGING INSECTS ON COTTON

Jack S. Bacheler
Entomology Extension Specialist

Cotton insects, if not well managed, can cause significant yield losses from the cotyledon stage through boll maturity. Additionally, insect pests such as stink bugs and bollworms lower lint quality directly by feeding and indirectly by causing maturity delays. However, producers can keep insect damage to a minimum by paying attention to six guidelines:

1) Recognizing the major pest and beneficial insects.
2) Following established scouting procedures.
3) Aadhering to recommended thresholds.
4) Applying insecticides in a timely manner.
5) Following recommended insecticide-use patterns designed to stall resistance to pyrethroids,
6) Use cultural and biological controls.

Presently, insect control costs in North Carolina are lower than in most other regions of the cotton belt, providing our producers with an economic advantage over their counterparts elsewhere.

The Boll Weevil Eradication Program, begun in 1978 on approximately 15,000 acres in northeastern North Carolina, resulted in the eradication of the boll weevil from the southeastern United States and most of the Mid South. However, boll weevils may still be unintentionally transported back into weevil-free areas. These "hitchhikers" are most often the result of passive transport of weevils aboard vehicles or cotton equipment, such as cotton pickers, module builders, and module haulers. The NCDA & CS manages a large-scale, pheromone trap-based Boll Weevil Containment Program that has successfully pinpoints these weevil spots, allowing these localized outbreaks or single captures to be found and eliminated. As of this writing (late December 2005), one boll weevil had been caught in North Carolina in 2005, though none had been captured in either 2003 or in 2004.

Early cotton growth was very labored this spring, but rebounded significantly during the remainder of the growing season in most areas of the state. Some cotton did suffer from lack of moisture, however final statewide average yields will likely be close to 800-plus pounds of lint per acre on approximately 806,000 acres. Bollgard cotton (including herbicide plus Bollgard stacked varieties) accounted for approximately 90 percent of North Carolina’s cotton acreage in 2005.

2006 Cotton Insect Summary

Thrips

Thrips levels were generally moderate to high in many areas of the state; however, extended cool conditions during early cotton development resulted in vulnerable seedlings for an expended period. Cotton seedlings often took up to 6 to 7 weeks to reach the “thrips-safe” stage of 5 to 6 true leaves. In two of four 2005 replicated thrips insecticide trials, lint yields in the untreated check plots were 400 to 500 pounds less than several of the better treatments. Approximately 70 percent of our state’s cotton acreage received a foliar application for thrips. Temik was used on about 75 percent of the cotton acreage, seed treatments on the remainder. Western flower thrips appeared to be a relatively minor issue in 2006, but did cause occasional headaches.

Early Tobacco Budworms

Early budworms were on the light side during the prebloom period and only developed into a minor headache in a few areas in 2006. With over 90 percent of North Carolina’s cotton acreage now planted to Bt cottons, tobacco budworms have only the remaining 10 percent conventional cotton to potentially infest.

Cotton Aphids

Aphids were generally a minor problem on most farms in 2006, with only 3.2 percent of our cotton acreage treated. Growers and consultants appear to be showing increasing confidence in the effectiveness of beneficial insects, primarily “mummies,” and in the fungus Neozygites fresenii in reducing cotton aphids to sub-economic levels in most cases.

Plant Bugs

Plant bugs were about average during the prebloom period, with approximately 7 percent of our acreage treated. Additionally, these Lygus levels did not build into a significant late season problem this past growing season.

Stink Bugs

Stink bugs and their damage were down considerably from the extensive damage of 2004, a watershed year for N.C. producers. However, stink bugs were still a significant late season pest on much of the state’s cotton acreage, causing a mean of approximately 7 percent internal damage to bolls based on our project’s annual damaged boll survey. Throughout most of the boll production period, the harder-to control brown stink bug, Euschistus servus, constituted the minor portion of the brown vs. green (mostly Acrosternum hilare) complex.

Bollworm

The major late season bollworm moth flights from corn were much later and lighter than average, even lagging behind the state’s late cotton crop. Statewide damage to bolls on conventional cotton, the bollworm/budworm complex boll damage (4.3 percent), was about par for North Carolina, as was bollworm damage to bolls on Bt cottons (1.2 percent). An average of approximately 2.3 and 1.2 late season applications were used on conventional and Bollgard cotton, respectively, in 2005.

Other Caterpillars

Other caterpillars were generally on the light side, although fall armyworms persisted, occasionally at marginally treatable levels, in a few of our eastern counties, as was the case in 2004. Beet armyworms and cabbage loopers, although detected, were again little more than curiosities in 2005. European corn borers also remained at almost undetectable levels on conventional cotton.

Cotton Acreage and Harvest

As of this late December writing, North Carolina cotton producers are expected to harvest approximately 800 pounds of lint per acre on 806,000 acres.

Bollgard Cotton

Bollgard varieties (those that have been genetically altered to express the caterpillar toxin of Bacillus thuringiensis) were planted on just over 88 percent of the state’s cotton acreage in 2005, up 8 percentage points from the prior year. Bollgard cotton was treated an average of 1.21 times, the same as in 2004. Mean boll damage to Bollgard cotton from bollworms was approximately one-third of that found in conventional cotton (1.41 vs. 4.32 percent, respectively). Stink bug (including plant bug) damage to Bollgard and conventional cotton bolls was 6.9 and 5.9 percent, respectively. This similarity in the boll damage level between conventional cotton and Bollgard cotton can be at least partially explained by the low bollworm levels and resulting fewer insecticide applications on conventional cotton in 2005.

Bollgard II and Widestrike Cotton

Bollgard II constituted the lion’s share of the two-gene Bt lines planted in North Carolina in 2005 - just over 2 percent. Overall, surveyed worm damage to Bollgard, WideStrike, and Bollgard II cotton lines were 1.41, 0.5, and 0.16 percent boll damage, respectively. Both of the latter technologies show a high level of resistance to all caterpillar species except for cutworms.

Boll Weevils

As of this writing, a single boll weevil had been found in Martin County this past October. No boll weevils were found in 2003 or in 2004.


Early Season Insect Management

Thrips

Because thrips have the potential to cause significant yield losses and maturity delays, this pest group must be controlled annually, the options being treated seed, at-planting granular insecticide, foliar application(s), or some combination of the above. Thrips damage cotton seedlings by puncturing and rasping the outer cells of young leaves and buds. Then they consume plant juices. Damage frequently results in ragged-looking plants with crinkled or "possum-eared" leaves. This damage can stunt growth, resulting in fruiting at higher positions, maturity delays, and reduced yields. Damage from thrips can also be significant when plants fail to grow because of cool conditions, as was the case in 2005. Dry weather also may inhibit the uptake of at-planting insecticides, making the seedlings more susceptible. Also, the premature drying of alternate thrips hosts (for example, various crops and weeds) during drought periods may force large numbers of flying adult thrips to abandon these plants in search of younger, greener hosts, such as cotton seedlings.

An at-planting, systemic insecticide or seed treatment is recommended in cotton planted with conventional row-spacing. Even when a soil-applied systemic insecticide is used, thrips may still occur in damaging numbers, as happened in many areas in from1999 through 2003 during dry-weather periods, and to some degree in 2005 under the extended cool conditions. As mentioned above, dry weather may retard the uptake and performance of the product used. Also, extended cool weather may delay plant growth, keeping the plants susceptible longer and exceeding the time frame of the product's effectiveness. In this case, the persistence of a product's activity can be very important. When a systemic insecticide fails to control thrips, a foliar spray may be warranted. However, in some cases, a spray may give rise to other problems. Aphid populations may increase or second-generation June tobacco budworms may become established after the spraying because of the removal of beneficial insects, especially in the southern half of the state. In most cases, the use of an at-planting, systemic insecticide is successful and is recommended over a foliar-spray-only approach because it is less disruptive to the beneficial insects, far more persistent, and sometimes produces higher yields.

However, a foliar-spray-only approach may be a viable option in ultra-narrow-row (UNR) cotton, due to the greater expense of an at-planting insecticide. (The same amount per row of an at-planting insecticide would cost approximately five times more in 7.5-inch UNR rows than in 38-inch conventional rows.) Also, since UNR cotton requires about a threefold increase in the number of plants per acre, the amount of treated seed (and the expense) would be three times greater than with conventional cotton. In 1997 and 1998 tests, Temik 15 G at about 8 to 10 pounds per acre, Gaucho seed treatment plus an Orthene foliar spray, or two Orthene sprays show similar returns - the value of cotton minus the cost of thrips control (insecticide plus application costs). The value and liability of Cruiser seed treatment appears to be similar to Gaucho Grande.

Listed below are a couple of options for controlling thrips:

1. Temik 15 G—Temik at 5 pounds of product/acre generally provides good thrips control and suppression of the cotton aphid for up to 4.5 or 6 weeks, although, like other at-planting insecticides, it may show poor uptake under very dry conditions. On-farm and research station tests have shown that Temik often gave a yield advantage over other alternatives and sometimes provided earlier fruit maturity. Generally, these benefits more than offset the relatively high cost of the product on conventional row-spaced cotton. If cotton is planted after May 15 to 20, 3 pounds of Temik 15 G should suffice. The correct calibration with these at-planting insecticides is important. In rare instances, Temik at the 7.0-pound rate can show phytotoxicity symptoms.

Consult the label carefully before using this products, and adhere to the Worker Protection Standard requirements.

Temik is very toxic to humans when wet.

2. Gaucho Grande Seed Treatment - In replicated 2005 trials, Gaucho Grande provided thrips control for approximately 3 weeks. A foliar treatment for thrips is usually needed with Gaucho Grande seed and is often tank-mixed with an early herbicide in one- to two-leaf cotton. This product has not been implicated in phytotoxicity problems noted with the above material under cool, wet conditions, and Gaucho is very safe to humans and wildlife. Gaucho Grande without a follow-up spray may also fit in cotton planted after May 15 to 20, where a long residual is usually unnecessary.

3. Cruiser Seed Treatment—Cruiser seed treatment is in the same insecticide class as Gaucho Grande and shows thrips activity similar to Gaucho’s. A foliar insecticide is recommended to compensate for this product’s short residual activity, just as with Gaucho Grande.

For recommended scouting procedures for thrips and other insects, refer to the Cotton Insect Scouting Guide (ENT-COT-6 in hard copy, or on the web at http://ipm.ncsu.edu/cotton/insectcorner/scouting_guide.htm).

Plant Bugs

Prior to bloom, plant bugs, or Lygus, damage cotton by feeding in tender terminals and more commonly, directly on small squares with their needle-like mouthparts, causing the squares to abort. In pre-blooming cotton, plant bugs have required treatment on approximately 7 percent of the cotton acreage in North Carolina, averaged over the past 9 years.

When blooming begins, plant bugs continue to feed on smaller squares and also on larger squares, which causes "dirty blooms" (white blooms with darkened pollen anthers and sometimes with small circular deformities on the petals). Additionally, plant bug feeding on small bolls up to approximately 11 days old may cause stink-bug-like external boll spotting and internal boll damage, such as callous growth (warts), deformed or rotted fruit, or small boll abortion. This boll damage is often identical to that caused by stink bugs. Plant bug damage to bolls is more common in untreated or minimally treated cotton, such as Bollgard cotton. However, plant bug damage can occasionally occur in blooming cotton before the major bollworm moth flight. Plant bugs are capable of causing all of the damage symptoms shown in Table 11-1.

Early season monitoring for plant bug activity, especially retention counts of small squares (approximately 1/8 to 3/16-inches long, including bracts), is recommended. If square retention counts remain high (80 percent or more), further sampling for plant bugs is probably unnecessary. If retention rates of small, upper, and other first- or second-position squares drop below this level, further sampling for live plant bugs may be needed. Usually, one terminal square (or its missing position) and one first or second position square (or its missing position) two or three nodes from the top of the plant are inspected per plant from 25 randomly selected plants within a field (50 squares total). Sweep net sampling for plant bug adults and large nymphs typically involves the taking of 25 sweeps at 6 to 10 locations per cotton field. Be mindful of field edges along ditch banks, adjacent host plants such as weedy flowering fields, or where Irish potatoes or a substantial acreage of corn is present. These areas are often a likely source of migrating adult plant bugs.

Once blooming has been under way for 2 to 3 weeks, square retention is a less reliable indicator of possible plant bug feeding; at this point the plant will show natural square loss due to mostly weather-related reasons and energy directed to bolls. Late season damage by plant bugs may be assessed by monitoring cotton plants for dirty blooms and for small bolls with signs of internal bug damage. Additionally, live plant bugs may be monitored with a sweep net, a drop cloth, or by visual inspection of plant terminals, including upper blooms. If nymphs are also easily seen, indicating that reproduction has occurred, the population is regarded as potentially more damaging to squares and young bolls.

Table 11-1. Plant bug and stink bug damage to cotton plant.
Plant Stage Plant Part Bug Type Damage Symptoms
Prebloom Terminals Plant Bug With heavy feeding, terminals may be deformed or killed, resulting of a loss in apical dominance (crazy cotton)
Small squares Squares yellowing, turning brown, then black, and finally aborting, leaving a scar at the fruiting site.
Blooming Various Squares Small Squares, same as above; larger squares with internal damage to pollen anthers
White Blooms Darkened pollen anthers (dirty blooms); small petal deformations
Bolls Plant Bug & Stink Bug Aborted small bolls, external spotting, internal feeding "stings," wart-like growths, and stained lint, may cause boll rots, hard lock.

 

Budworm and Bollworm Resistance to Pyrethroids

Unlike several Mid South and western cotton-growing states whose producers must sometimes treat portions of 3 or 4 tobacco budworm generations per year in conventional cotton, in the past seven years our growers have treated only 1 to 8 percent of their cotton acreage for the June to early July budworm generation, primarily in southern North Carolina. However, more than 95 percent of our cotton crop is treated for the major late July to early August bollworm generation and sometimes part of a late August to early September generation. Adult vial testing for bollworm resistance to pyrethroids and a decline in pyrethroid performance against bollworms have revealed the beginning of resistance to pyrethroids in scattered North Carolina bollworm populations. Fortunately, our bollworms have remained susceptible to pyrethroids for the most part.

Because of the above situation, we do not recommend the use of pyrethroids for early season (June through early July) budworm control on cotton, nor do we recommend pyrethroids on soybeans. For early budworms on conventional cotton, all treatments should be held to a minimum and based on need. It is imperative to (1) use the higher, early season budworm thresholds (see “Thresholds” section below) to minimize the acreage treated; (2) limit this treatment, if needed, to a single application of an effective pyrethroid alternative; and (3) avoid unnecessary routine treatments for other “pests” that often serve to increase the likelihood of early season tobacco budworm sprays. Although pyrethroids are the most economical class of insecticides used against budworms (though no longer the most effective), the use of pyrethroid alternatives, including transgenic Bt cotton, Tracer 4 SC, or Steward 1.25 SC, should reduce the probability of pyrethroid resistance and/or slow its development. According to research conducted here in the 1990s, treatment for June to early July (prebloom) budworms seldom pays due to plant compensation for early square loss. Retaining pyrethroids to control later budworm/bollworm generations is of utmost importance to North Carolina cotton producers in their conventional cotton acreage.

 

Mid Season Insect Management

Although technically beginning at first bloom in late June to early July, the start of the major mid July to early August bollworm (corn earworm) moth flight usually signals the onset of our most critical insect control period. The bollworm-tobacco budworm complex, typically composed of mostly bollworms, is the primary target for foliar insecticides in conventional cotton. However, European corn borers (ECB) and fall armyworm (FAW) also can inflict significant boll damage in some years, and stink bugs can be moderate to serious pests in low bollworm treatment situations, as is often the case in Bollgard, Bollgard II, or Widestrike cotton. Stink bugs, and to a lesser degree plant bugs, are now the dominant late season pest in Bt cottons. Because of the potential for severe boll damage from one or more of the above pests and because cotton damaged at this time of year usually compensates little for boll damage, insect damage to bolls must be minimized during all or part of late July through mid-to-late August in North Carolina.

Bollworm

The first two generations of bollworms occur primarily on field corn. Third-generation (sometimes referred to as the second field, or F2 generation) moths usually emerge in large numbers from mid July to early August when corn is drying, and they fly to the more attractive, blooming cotton.

Systematic, regular weekly scouting of non-Bt cotton for the bollworm and its cousin, the tobacco budworm, should begin in early to mid July. Weekly scouting is adequate until egg laying or light-trap catches increase, although light traps are ineffective in monitoring budworm moths. (Check with your county Extension agent for possible light-trap counts for the major bollworm moth flights; additionally the light counts from approximately 30 traps were available online during the moth flight in 2005 at http://ipm.ncsu.edu/cotton/insectcorner/blacklight/).

At the beginning of the major bollworm moth flight, fields should be scouted twice a week, with the emphasis on finding eggs and small worms, until insecticide treatments begin. After the onset of the moth flight and initial application(s), a 4- to 7-day scouting schedule usually will suffice for conventional cotton, depending on the insecticide rate used, the egg pressure, and the susceptibility of the cotton plants. A 4- to 5-day scouting schedule is suggested in conventional cotton for standard industry use rates of pyrethroids and a 5- to 7-day schedule for high rates. Employing an egg threshold remains the most profitable way to manage this generation of bollworms in conventional cotton. Once the egg threshold has been met and treatment(s) made (see "Thresholds" section), the primary focus of scouting shifts toward finding small bollworms feeding on squares and bolls, including those under pink flowers and bloom tags. Eggs should also be monitored, however, particularly down in the plant canopy or in yellow, pink, and dried flowers and on stems.

At times, tobacco budworm populations persist into the beginning of the major bollworm moth flight period. Because tobacco budworm adults are not readily attracted to black-light traps and because they sometimes begin laying eggs on cotton before the bollworm egg threshold is met, occasional fields may reach a 3 percent larval threshold on conventional cotton before bollworm treatment begins. Deploying tobacco budworm pheromone traps, especially clusters of 5 to 10 traps on a farm, and correctly identifying adult tobacco budworm moths within fields can help you recognize this situation. However, pheromone traps are not always a reliable indicator of moth levels and attract only males, so one should be cautious in their interpretation.

Another option in identifying the potential presence of tobacco budworms was the use of an egg kit. Although the present Agdia egg kit is somewhat expensive and time-consuming to use, knowledge of the relative proportion of bollworm vs. budworm eggs early in the bollworm moth flight can be valuable. If the proportion of eggs present is composed of more than 20 to 25 percent budworms, pyrethroids may be ineffective, and the use of either Steward or Tracer may be more valuable for the initial application. Unfortunately, beginning in 2006, these kits will be available only in commercial lots of 500 or more. In the past, North Carolina growers and consultants have used less than 1/10 of this number per year.

After the upper bolls that will be harvested have become difficult to cut with a pocketknife, the field is normally safe from further bollworm attack. Fields are also normally safe from further bollworm establishment when blooms and/or non-terminal squares are less than one per 1 to 2 row feet, or more. Bollworm scouting can normally be stopped at that time—usually in late August to early September. Spot scouting for FAW in conventional or Bollgard fields should continue through early September, especially in fields of late-maturing cotton or in green areas, if this species is present. Because FAW are migratory pests, in some years this species does not reach North Carolina cotton fields in appreciable numbers, particularly in the more northern counties.

European Corn Borer

Larvae of the European corn borer damage cotton by feeding on medium and large bolls of conventional cotton from early August through mid September. This species causes very little damage to Bollgard, BG II, or Widestrike cotton. In rank or late-maturing cotton, this damage can be significant. An earlier tunneling type of damage may occur within stems and leaf petioles, usually in mid July through late August. Although this damage looks serious, with wilting and eventual death of the tissue above the feeding site, it causes no known economic loss.

The major moth flight peak for the ECB usually occurs a few days to 3 weeks later than the peak of the major bollworm flight. The female moths lay small, flat, scale-like egg masses that contain 15 to 75 eggs each on the underside of cotton leaves deep within the canopy. At first, early instars feed within the leaf petioles and stems, but then they begin to enter and feed on large bolls, sometimes within 48 hours, particularly after mid August. Although the caterpillars of this species generally do not feed as extensively within the bolls as do bollworms, most infested bolls are destroyed.

Limiting bolls damage from ECB can be difficult. The small, flat egg masses, located on the undersides of leaves, are hard to find, even by trained scouts searching a moderately infested field. By the time the larvae are found feeding on or within bolls, insecticidal treatments are usually ineffective. However, scouting to detect the caterpillars is advised, particularly if stem tunnel penetration and the associated "sawdust"-like frass (droppings) is noted. If small larvae are present (3 percent or more associated with bolls), treatment may be indicated if an active flight is confirmed—that is, ECB moths around or within cotton fields. Treatment at this time is targeted at trying to prevent or minimize further establishment of ECB larvae.

Because finding the egg masses is virtually impossible and the live, penetrating caterpillars are spotted too late to achieve effective control, no control threshold has been developed for the ECB. Growers instead must depend on another observation as a trigger for directing insecticides against this pest. Fortunately, because egg laying of the corn earworm (from its major flight) usually occurs somewhat earlier than the ECB flight, employing the egg threshold for bollworm control usually works well for ECB if treatments are extended into the ECB infestation period. An insecticide should be selected that is effective against both insects (see recommendation tables in the North Carolina Agricultural Chemicals Manual).

If the major part of the ECB flight occurs after the bollworm flight has subsided and spraying has been completed, fields can be particularly susceptible. Under this condition, additional application(s) may be required for adequate suppression. This approach is recommended only where late rank growth points toward a high probability of ECB damage. Finding moths of this species in local light or pheromone traps, or flushing the adults from around or within cotton fields, can help confirm the need for this extended treatment.

Generally, ECB has been a very minor pest of cotton in North Carolina for the past 10 years.

Stink Bug

In situations of low insecticide use, often the case with Bollgard, BG II, and Widestrike cotton, the green stink bug and the brown stink bug have become more abundant and damaging. Stink bugs often invade cotton fields in early to mid July and may reach damaging levels from this time through late August and sometimes into September. However, in 2004, stink bug levels were already high in many cotton fields at the onset of blooming during the last week of June. Stink bugs damage cotton by puncturing the carpal walls of bolls with their "beaks" and feed primarily on the soft, developing seeds. Heavy feeding sometimes completely destroys small bolls, causing them to abort. These small, dead, dry, brown bolls are then either shed or remain on the plant. When stink bugs feed on slightly larger to medium-sized bolls (up to about 3 to 3.5 weeks), they often introduce boll-rot pathogens, resulting in partially or entirely destroyed locks, hard-lock, and a lower grade of harvested cotton.

External boll damage is characterized by small, round, shallow, purplish depressions, usually in the 1/32- to 1/16-inch range. These spots tend to be larger than the tiny spots usually seen on maturing bolls. Internally, the damaged bolls will often have a yellowish to tan to brown stain in the seed areas, often, but not always, under the external feeding spots. Other damage symptoms include small wart-like growths and/or dark "pin prick" spots on the inside of the boll wall. Internal boll damage may be present without obvious external evidence.

Stink bug damage is more prevalent in fields where bollworm treatments have been minimal (that is, none or one), although significant stink bug damage may occasionally occur prior to applications for bollworms. Where the bollworm population is high enough that the field has been treated twice or more (as is often the case with conventional cotton), stink bug numbers will usually, but not always, be reduced enough to limit damage to low levels. Because stink bug and plant bug damage symptoms are often indistinguishable, damaged boll levels may sometimes be the result of feeding by both kinds of bugs. At present, stink bug damage to bolls is more common than plant bug damage in most areas.

The distribution of stink bugs and plant bugs in a cotton field may be uneven, with bug numbers and damage higher at field edges and in rank areas, but also dispersed in a clumpy manner throughout the cotton field. Do not oversample these unrepresentative areas; however, they should be noted.

In Bollgard, BG II, or Widestrike cotton, or in conventional cotton in areas with a history of stink bug damage or light bollworm pressure, a sample of 25 to 50, quarter-sized boll should be sampled at each scouting session, beginning at early boll development.

In conventional cotton, in the course of regular bollworm scouting for 50 to 100 bolls of representative sizes, if more than 2 percent stink bug-damaged bolls are found (internal damage present), the further sampling of 25 more medium-small bolls (approximately quarter-sized) for stink bug damage is recommended.

To determine if a boll has been damaged by stink bugs, the quarter-sized bolls should either be crushed by hand or cut open into all locks with a knife to reveal possible internal damage. Count all internal boll damage, including stained or spotted lint and callous growth or inner boll wall warts. If all bolls are less than approximately 3 to 3.5 weeks old (the age at which a boll is no longer susceptible to bug damage), use an initial treatment threshold of 10 percent. As the ratio of larger, “safe” bolls to smaller, susceptible bolls increases, the threshold should may be raised (Table 11-2).

A BollChecker, any flat material (such as thin plywood or Plexiglas®) with a 1 1/4- inch diameter hole cut in it can help determine the ratio of larger, safe bolls (cannot pass through the hole in the BollChecker) to smaller, susceptible bolls (will pass through the BollChecker). There are some differences in the diameters of bolls at the “safe” 21- to 24-day age, however. Boll growth may be affected by variety, fruiting position, moisture availability, age of the crop at boll initiation, fertility level, and other factors. The impact of these factors in boll size is presently being investigated. The accuracy and utility of this BollChecker method of sizing bolls for use in threshold adjustments is still under investigation. This approach is only a suggestion at this time.

Table 11-2. Suggested Damaged Boll Thresholds for Stink Bugs*
Boll Ratio Threshold (%)
Susceptible "Safe" (Too Large)**
1 0 10
1 0.5 15
1 1 20
1 1.5 25
1 2 30
1 3 40
1 4 50

* To be used with BollChecker; this approach based only on preliminary information, and is presently under study.
** Boll diameter approximately 1.25 inches or larger.

If two or more consecutive scouting checks reveal stink bug damage at approximately two-thirds of the threshold level, treatment may be justified. Additionally, 2004 and 2005 initial research on the relationship between stink bug damage to bolls and yields suggest that the cotton yields are not impacted as significantly during the first two weeks of blooming as during weeks 3 through 6.

Once the damaged-boll threshold has been met, it may be helpful to determine if the brown stink bug (Ecschistus servus) or green stink bugs (usually Acrosternum hilare or Nazara veridula) is the predominate species group, as brown stink bugs are difficult to control with pyrethroids. To discover which stink bug it is, make general observations while scouting (in the case of high population levels), sample with a beat cloth (six 6-row-foot samples or more until adequate stink bug numbers are observed), or using a sweep net (six 25-sweep samples or more until adequate numbers of stink bugs are observed) is advised. Since these observations or samples are conducted solely to determine if the stink bugs are brown or green, they may be done quickly. For beat cloth sampling, a 3-by-3-foot beat cloth is unfurled between two adjacent rows, and the cotton plants in the two adjoining rows (6 row feet) are beaten, or shaken over the cloth, causing the large nymphs and adults to fall onto the cloth so they can be counted. Count any adult stink bugs seen flying if the color can be distinguished. In sweep net sampling, individual sweeps should be made with firm, pendulum-like motions (handle up, net down), swinging down with both hands through the upper middle canopy while walking down the row. If the sweeping motion is correct and vigorous enough, some bolls and leaves usually will be knocked into the net. In either of the above approaches of assessing live stink bugs, count adults and large nymphs. This quicker sampling may be stopped once an adequate sample (approximately 10 stink bugs) has been counted. As the proportion of large “stink bug safe” bolls increases relative to the smaller susceptible bolls during the end of July and throughout August and early September, the threshold may be raised. Twice a week scouting for stink bugs on Bollgard (or minimally treated) cotton is recommended under heavy stink bug pressure.

With the help of the North Carolina Agricultural Crop Consultants Association and a Cotton Incorporated Southeast Regional Project grant, investigations into more effective methods of assessing stink bug levels, stink bug damage, and appropriate action thresholds are under way. Refinements in scouting procedures and thresholds can be expected.

Transgenic Bt Cotton

Bollgard varieties and other Bt cultivars (such as Bollgard II, Widestrike, and VIP [due out in 2007]) will not control noncaterpillar pests, such as boll weevils, thrips, cotton aphids, plant bugs, and stink bugs. Also, different caterpillar pests are not controlled to the same degree. For example, field tests have shown that tobacco budworms attempting to feed on Bollgard varieties essentially will die (zero survival). However, bollworms will be able to damage squares and bolls, though generally at a low rate. Fall and beet armyworms are not controlled by Bollgard and can easily become established. In BG II cotton, unless bollworm pressure is very high and chemical disruption has occurred (e.g., an overspray with Bidrin or Orthene just prior to bollworm egg lay), sprays for bollworms will probably not be needed; they are less likely to be needed on Widestrike than on Bollgard cotton.

Because beneficial insects are not adversely affected by Bollgard cotton, their abundance and impact have increased in situations where disruptive insecticide applications are either less frequent or not made. Higher beneficial insect numbers have led to somewhat more effective suppression of third-generation bollworms and other caterpillars in Bollgard cotton.

Bollgard Efficacy

The effectiveness of the Bollgard gene against North Carolina’s major cotton pests is influenced by a number of factors, including the pest in question, the level of supplemental beneficial insect “help,” and the phenology or maturity of the cotton crop. A summary of research collected to date and of producer experiences in North Carolina with Bollgard cotton from 1996 through 2005 suggests that Bollgard cotton, if treated when needed, will provide better bollworm control than that provided by insecticides in conventional cotton under most grower circumstances. Under irrigation, and/or if a beneficial-insect-reducing spray is applied just before or early in the bollworm moth flight (for example, a spray for stink bugs), moderate to occasionally heavy bollworm establishment may occur with associated significant yield reductions. Less than 4 percent of North Carolina’s cotton acreage is presently irrigated, and disruptive insecticide sprays made just before the major mid to late July to mid August bollworm moth flights are not common. Nevertheless, bollworm damage and damage from other pests such as stink bugs mean that Bollgard cotton often requires supplemental insecticide protection. Additionally, in 2003 and 2004 (and to a lesser degree in 2005), a number of Bollgard cotton fields were severely damaged by bollworms.

Information collected in North Carolina from 1996 through 2005 shows stink bug damage in typical grower-managed Bollgard cotton fields is 2 to 10 times greater than the levels found in grower-managed conventional cotton fields. Also, plant bugs have become a common late-season pest in Bollgard cotton, resulting in damage to small and large squares, blooms, and small bolls in the postbloom period. However, the Bollgard toxin effectively controls European corn borer, judging from data collected on ECB main-stem penetration, boll damage, and larval establishment. Also, Bollgard cotton, treated approximately an average of 1.2 times by our producers from 1996 through 2005, has shown somewhat lower fall armyworm damage to bolls than pyrethroid-protected conventional cotton fields in this same period. Both fall and beet armyworms are typically infrequent pests in North Carolina cotton fields, especially in the more northern counties.

A large-scale comparison of insect damage in Bollgard vs. conventional cotton (pyrethroid-protected fields under producer conditions) was undertaken beginning in 1996, the first year of commercial Bollgard cotton use. Approximately 75 pairs of Bollgard and conventional cotton fields have now been assessed annually through 2005 for late-season boll damage from bollworms, European corn borers, fall armyworms, and stink bugs. During this time, a survey of insecticide use also was undertaken so that the spray requirements and cost-effectiveness of the two technologies could be compared. From 1996 through 2005, conventional and Bollgard cotton fields were treated approximately 2.7 and 0.8 times per year, respectively. Most of these treatments were for bollworms—though more treatments have been made for stink bugs and plant bugs during the past two years.

Table 11-3 gives information on the damage by these significant late-season insects in both Bollgard and conventional fields. Presented first is historical boll damage data on conventional cotton from 1985 through 1995. Then Bollgard vs. conventional cotton is compared for 1996 through 2005, in which 662 pairs of Bt vs. 747 conventional cotton fields were monitored.

Table 11-3. Bollgard vs. Conventional Cotton: Damaged Boll Survey, North Carolina, 1996 to 2005
Category Mean Percentage of Damaged Bolls
Bollworm ECB FAW Stink Bug Total Damage
Historical Ave.: 1985-1995 (n=2,514 Fields) 4.0 1.5 0.7 0.6 6.8
1996-2005 Conventional (n= 662 Fields) 5.12 0.18 0.32 2.10 7.72
1996-2005 Bollgard (n= 747 Fields) 1.51 0.01 0.16 4.62 6.30

Bollworm damage in the Bollgard fields was approximately a third of that found in the conventional fields. However, stink bug damage to Bollgard fields was about 2.5 times higher than in conventional fields. ECB and fall armyworm boll damage in the Bollgard fields was approximately 10 and 50 percent of the damage found, respectively, in the conventional fields. Overall protection for both systems, including stink bugs, favored the Bollgard fields, 6.30 percent damage versus 7.72 percent over the conventionally protected fields. Additionally, the higher stink bug damaged bolls in the Bollgard cotton fields should be discounted by approximately 60 to 70 percent because bolls damaged by stink bugs have less of an impact on yield than do bolls damaged by bollworms or other caterpillars.

In North Carolina, the economic advantage of one insect management system over the other varies by area and circumstance. Over the nine years in which Bollgard cotton has been commercially available, the technology fee (which averages about $19-20 per acre based on producers’ row spacing and seeding rate) and the somewhat lower late-season boll damage have allowed producers to more than break even, compared to conventionally protected cotton with its slightly higher boll damage and higher insect protection costs (Table 11-4). In general, economics would favor planting Bollgard cotton in situations in which producers now treat their conventional cotton three or more times. However, other factors must also be weighed, such as the varieties of available conventional and Bollgard cotton, the activity of Bollgard in rainy conditions (more often than not a help when growers cannot treat conventional cotton), and the ability of scouts to properly assess stink bug and plant bug damage.

Table 11-4. Bollgard vs. Conventional Cotton:
Insect Control Costs and Damage ($/acre),
1996 to 2005 (n = 1,409 total fields)

Item

Bollgard

Conventional

Ave. Tech Fee1

$20.00

 $ 0.00

Insect Control Cost2

    6.98 (0.93 apps.)

  19.50 (2.56 apps.)

Insect Damage3

  22.41

  43.98

Scouting 4

- - -

- - -


Total

$49.39

$63.48

1 Varies according to seed rate and row spacing.
2 Control Costs = Insecticide + application ($7.50).
3 Damage: 1% boll Damage = 12 lbs. lint / acre; cotton = $0.65 / lb.
(stink bug damage to bolls sometimes less than that caused by caterpillars, so Bt cotton damage to bolls may be somewhat lower than stated.
4 Correct scouting of Bt. cotton should be more labor intensive.

Scouting Transgenic Bt Cotton

Because a number of aspects of scouting Bt cotton are different from those of scouting conventional cotton, the Cotton Insect Scouting Guide was revised in 2005 to include guidelines on monitoring insects in transgenic cotton. A few of the more significant changes follow:

1. Utilization of a very high egg threshold for the major bollworm generation: Because bollworms must hatch from eggs and consume enough of the Bt toxin to be killed, neither the egg stage (except under unusually high egg lay, and here only on Bollgard cotton, not Bollgard II) nor the small, soon-to-die, first instar bollworms are now used as the basis for the treatment threshold in Bt cotton (see “Thresholds”). This threshold should be disregarded with BG II cotton and perhaps with Widestrike cotton.

2. Use of "multiple pest thresholds" is encouraged: If sub-threshold levels of different pests add up to or exceed a one-pest threshold, treatment is advised (for example, 60 percent of the bollworm threshold, 30 percent of the plant bug threshold, and 40 percent of the stink bug threshold equal 130 percent, or 1.3 times the treatment threshold).

3. Focus on economic bloom tag or boll damage and second instar bollworms: The point at which Bt cotton may require a supplemental insecticide for caterpillar control will be the point at which either bollworm establishment or fruit damage occurs at a potentially high enough level to cause economic loss. Thus, it will be essential both to recognize the difference between first and second bollworm stages and to identify the difference between insignificant, superficial square damage and damage that will cause the square to abort.

4. A high proportion of the bollworms that become established often do so under red flowers and bloom tags. This is a very common "trigger" for treatment: In monitoring blooms and bloom tags, however, remember to raise the 3 percent bollworm treatment threshold according to the ratio of total bolls to bloom-tagged bolls. For example, if bloom tags represent 10 percent of the sampled boll population in the field, if a bollworm is present under each of these bloom tags, and if no bollworms are found on the remaining (non-bloom-tagged) sampled bolls, then sampling only bloom tags (100 percent bloom tags) would result in overestimating the bollworm population in the field tenfold. In this case, the treatment threshold for this sample containing only small bolls with bloom tags should be raised from 3 percent to 30 percent. On the other hand, the threshold for bollworms on Bollgard is low—it takes very few worms under bloom tags in late July to mid August to justify treatment.

5. Scouting for other insects: Some insects, such as stink bugs and plant bugs, will, in the absence of insecticides directed toward bollworm, budworm, and ECB, become more numerous and require more intensive scouting than they would in conventional, more often-treated, cotton. Twice per week scouting is recommended for Bollgard, BG II, and Widestrike cotton, at least on a representative portion of the acreage, especially during weeks 3 through 6 or 7. Producers should expect to pay more for properly scouted Bollgard cotton.

6. Beneficial insects: Beneficial insects will likely be more abundant in untreated or less-treated Bt cotton, and their identification and population levels should be at least informally monitored.

7. Platoon scouting: Because the scouting of conventional and Bt cotton is likely to have different requirements, consultants and producers may elect to deploy separate groups of scouts who specialize in the scouting of these two different plant systems. For example, the scouting of conventional cotton will likely require the monitoring of second-generation budworms, an emphasis on the egg threshold for bollworms, monitoring for ECB, a more relaxed approach after the initial insecticide application(s), and less emphasis on stink bugs in fields that have received two or more insecticide applications. Bollgard and other Bt cottons cotton will require no scouting for second-generation tobacco budworms, an emphasis on the appearance of second instar bollworms, and major emphasis on stink bugs and plant bugs as the trigger for foliar insecticide treatment. Bollgard and other Bt cottons (except for VIP cotton) likely will not require scouting for ECB.

Late-Season Insect Management and Miscellaneous Insects

Aphids

Cotton aphids are an occasional headache in a number of North Carolina cotton fields. Due to resistance development, treatment with organophosphates is often ineffective. The pyrethoid Capture also has succumbed to aphid resistance. Chloronicotinoid insecticides that provide good aphid control are now available, but they are costly. Additionally, because all of the new insecticides are of the same class, aphid resistance to this new, effective class of insecticides is a major concern.

Fortunately, high levels of aphid mummifying parasites and fungi that, in most cases, usually hold or reduce aphids to low, subeconomic numbers often characterize our region. The combination of predators, parasites, and fungi, along with ineffective insecticides, usually justifies our general recommendation NOT to treat cotton aphids, especially in early to mid season, except under dry, stressed conditions, very high aphid levels, and little evidence of mummies or the fungus. In opening cotton, aphid-caused sooty mold or sticky cotton (from the heavy presence of honeydew) may become a problem, thought not typically in the Southeast. After the defoliant has been applied, however, cotton aphids are typically only at very low levels.

Aphid Rating Scale

 0.      No aphids.

 1.     Occasional plants with low numbers of aphids.

 2.      Plants with low numbers common; heavily infested plants rare; honeydew visible occasionally.

 3.     Most plants with some aphids; occasional plants heavily infested; honeydew visible in most areas of the field.

 4.     Heavily infested plants common; aphids clumped on upper leaves; honeydew common; cotton under stress.

 5.     Many heavily infested plants; infestations are on most plants in large areas of the field; cotton under stress.

On the Aphid Rating Scale, a level of 4 or higher in cotton just before opening, plus honeydew presence along with low levels of mummies or the fungus, may be a good indicator of the need to treat (see Aphid Rating Scale below). Treatments for cotton aphids have been very rare for the past seven years.

Spider Mites

Spider mite damage, rare in North Carolina in most years but sometimes more common on cotton in the northeastern peanut-production counties, can occur almost any time during the season, is usually more prevalent during dry conditions and on sandy soils, and may be more common following seed treatments with follow-up foliar sprays for thrips. Mite damage appears as a slight yellowing of the leaves, which later changes to a purplish or bronze color. Mite damage also can be recognized by the presence of fine webbing on the underside of the affected leaves. This webbing often traps blown sand grains. In severe infestations, the damage can cause widespread leaf yellowing and defoliation, beginning with the lower leaves.

Visual spot checks for mites can be made while scouting for other pests. Initial mite infestations often occur at field borders adjacent to drying corn, weeds, or mowed ditch banks or roadways. Even with obvious yellowing and defoliation, the presence of an active mite population in the field should be confirmed before treating. A hand lens of 10x magnification or greater is indispensable when scouting for these tiny arthropods and their eggs. In treating for mites, two expensive applications with excellent coverage are sometimes required for only fair to effective control. A fungus that preys on mites is often present, particularly under rainy or humid conditions, and may greatly reduce mite numbers while the damage symptoms are still present. Do not spray if rain is likely.

Fall Armyworms and Beet Armyworms

The presence of fall armyworms and their damage are recorded as part of bollworm scouting. Additional samples are usually unnecessary. However, if fall armyworms are found, noting and recording egg masses on the undersides of leaves in the upper third of plants and checking flowers for FAW are helpful. Because FAW migrate into North Carolina from farther south, their numbers vary greatly from year to year and normally reach higher levels in the southern and southeastern counties. Fall armyworms have been an occasional complicating factor in the bollworm fight in a number of cotton fields in the southeastern counties for most of the past nine years, sometimes requiring the addition of a nonpyrethroid, such as Larvin, Curacron, or Lorsban, to achieve effective control of small FAW. Tracer and Steward insecticides also show fall armyworm activity, but they have received only limited testing on this pest in North Carolina through 2005. Control of medium-sized to large FAW is at best mediocre with all labeled insecticides. Bollgard II and Widestrike cotton lines appear to offer excellent resistance to FAW.

Fall armyworms prefer blooms and bolls of all sizes. These caterpillars can be extremely damaging if present in moderate to large numbers, and they can become established late in the season, though rarely after September 1. They can feed on mature bolls normally resistant to bollworm penetration. Because the insecticides that control bollworms do not always control FAW effectively, it is very important that they be identified correctly. Also, because fall armyworms are difficult to control with insecticides, treatments are best applied at an early boll bract feeding stage. Be on the alert if scouts find egg masses, particularly if the small, posthatching larvae are dispersing from the egg masses. Fall armyworms have a more difficult time becoming established under a bollworm spray regime with certain pyrethroids.

Beet armyworms are rarely cotton pests in North Carolina, although a few are noted on cotton almost every year. When BAW occur initially, their population levels are usually low, and feeding is typically confined to leaves. When BAW are present in higher numbers and the larvae attain some growth, they often begin to feed on squares and blooms and, into small developing bolls. At times defoliation can be substantial. Early stage larvae tend to feed in groups on leaves and are often associated with webbing. These hatching egg masses with their initial feeding are called “hits.” Initial spotting of a potential beet armyworm infestation is best accomplished by the finding and examining of brownish areas on the undersides of leaves, particularly at row ends or in plant skips in the field.

Tracer 4 SC and Steward 1.25 SC usually provide acceptable to good control of BAW at high rates, while Intrepid most often offers good to excellent activity. No other presently labeled bollworm insecticides in North Carolina will control beet armyworms; however, Bollgard II and Widestrike cotton lines provide excellent BAW resistance.

Loopers

Cabbage and soybean loopers rarely damage cotton in North Carolina because they prefer foliage, are prone to virus attack (less so with the soybean looper), and occur sporadically. Observing foliage during routine late season scouting for other pests in most cases suffices for looper monitoring. However, with more cotton being grown in the far eastern counties, migratory, insecticide-resistant soybean loopers may occasionally be a problem and could warrant closer attention. If significant leaf feeding is seen, the average percentage of defoliation across the entire field should be recorded. As a general rule, if defoliation exceeds 30 percent in cotton with a significant portion (25 percent or more) of the bolls still immature and filling out, treatment may be needed. Soybean loopers, however, are very difficult to control with insecticides. Steward and Tracer insecticides appear to offer good control of soybean loopers, unlike our other labeled materials. Because foliage feeding typically begins at the bottom of the cotton plant and proceeds upward and out, foliage feeding may be beneficial in preharvest cotton that has begun to open. The brownish larval frass can be plentiful and temporarily stain opening cotton; however, this is not thought to be an economic problem.

Bollgard II and Widestrike cotton lines provide excellent resistance to loopers.

Beneficial Insects

About a dozen beneficial insects are commonly found in North Carolina cotton; ambush bugs, big-eyed bugs, damsel bug, minute pirate bugs, green lacewings, two species of ladybird beetles, and several types of spiders. They are of two types: (1) predators that prey upon an insect pest or (2) parasites that live within the host insect. These insects, particularly the predators, reduce the number of eggs and larvae of bollworms and other caterpillars, as well as cotton aphids. Because these allies lessen the impact of pest insects, common sense dictates that producers use them as a management tool. Their presence often means that growers can delay - and, on occasion, eliminate - some insecticide applications, particularly early season tobacco budworm or aphid treatments.

Many complex factors are involved in determining just how many of each beneficial insect species are needed to influence a given level of pests. Therefore, it is usually not practical to assess the value of these insects except in a very general way. That is, if relatively high numbers of beneficial insects are consuming a large proportion of aphids or bollworm eggs and larvae, the treatment threshold will be reached later than would otherwise be the case, reducing the number of insecticide applications needed. By the same token, beneficial insects in conventional cotton are often overwhelmed by the third generation (second field generation) of bollworms, and spraying becomes necessary. Presently, the careful observation of sound economic thresholds offers the producer the best odds of balancing beneficial insect numbers against damaging insects. Cotton aphid infestations are usually best managed by avoiding insecticides and allowing beneficial insects and fungi to limit populations.

Cultural Control of Cotton Insects

Fortunately, most of our agronomic and weed management recommendations geared toward providing the cotton crop a fast start, rapid development, and early maturity also aid in the management of late season insects, particularly bollworms, European corn borers, and stink bugs. Practices that encourage early maturity, such as avoidance of late planting, render the cotton plant less attractive to moths and less susceptible to injury. In our fall boll-damage surveys, late rank plants often sustain 2 to 4 times the damage of those that mature early. A few of these recommended practices are listed below:

1. Matching varieties to soil type—Some mid and late season varieties can grow excessively large, rank plants, precipitating late season insect problems; reserve these varieties for earlier planting and/or sandy soils.

2. Avoidance of late planting—While employing the earliest possible planting date is not critical, avoiding late planting (after the third week in May) can have a dramatic effect on minimizing late season insects. This is the single most important cultural factor in reducing late season insect damage.

3. At-planting application of Temik—The use of Temik at recommended insecticide rates in conventional cotton often promotes accelerated growth, earlier maturity, and increased yields, thereby controlling thrips and helping late season insect management, although the new seed treatments at the present rates, coupled with a thrips spray at about the first true leaf stage, offer similar growth rates and yields.

4. Adherence to recommended nitrogen levels—High levels of nitrogen, particularly when coupled with late planting and favorable rainfall patterns, can trigger rank cotton growth and high bollworm and European corn borer populations on conventional cotton and higher stink bug and plant bug levels on Bt cottons.

5. Directed application of herbicides—Applications of Roundup prior to the 5-leaf cotton window can minimize fruit loss and the associated maturity delays, making the crop less vulnerable to late season stink bug and bollworm damage (Roundup Flex cotton lines are expected to eliminate the above problem).

6. Use of PGRs—The use of mepiquat chloride and other similar products on fields with either a history of rank growth or a propensity for fast plant growth hastens maturity and may facilitate late season insect control.


Thresholds

A threshold is the level of plant damage or the number of insects at which treatment is recommended—that is, the level at which treatment will pay for itself. Threshold numbers are usually expressed in terms of the percentage or number of insects or instances of damage observed per 100 forms inspected. Based on years of research, these thresholds form the basis for sound treatment decisions. Thresholds, however, are only general guidelines applicable to the entire state. A knowledgeable consultant or advisor may be able to modify the threshold, depending on the region of the state, its history of insect problems, and the amount of risk that the consultant and the farmer are willing to take. Also, these thresholds are refined periodically on the basis of new research or changes in the status and behavior of the various pests.

Current thresholds for the important cotton pests are as follows:

Thrips

On cotton from the cotyledon to the 5 true leaf stage:

An average of 2 immature thrips per plant.

Alternatively, an average of 1 immature thrips per plant for each true leaf.

Timing of thrips applications, especially following seed treatments, is often best targeted at the 1st true leaf stage.


Plant Bugs

Prebloom thresholds to be used when square retention rate drops below 80 percent.*

From initiation of squaring until the first or second week of blooming:

8 plant bugs per 100 sweeps.

* The sweep net threshold may be raised to 10 if fruiting begins on nodes 4 through 6 or lowered to 6 to 7 if fruiting begins on node 8 or higher. Thresholds also may be lowered somewhat in stressed cotton.

Postbloom thresholds**

15 percent dirty blooms. Count any brown anthers as damaged.
or
10 percent internal damage to quarter-sized bolls (assessed as overall bug damage).

** Use sweep net or beat cloth to confirm presence and size (number of adults vs. nymphs) and to determine potential presence of stink bugs.

Cabbage and Soybean Loopers

30 to 35 percent defoliation and presence of more than 25 percent immature bolls.

Spider Mites

General leaf discoloration (chlorosis, bronzing, or both), plus live mites over most of the field and defoliation from mites in 25 percent or more of the field. (If rain is imminent, delay treatment and reevaluate three to four days after the rain. If a miticide is used, two applications are often necessary.)

Stink Bugs

Damaged Bolls (primary threshold)

10 percent stink bug internal damage to quarter-sized bolls (see Table 11-1), plus presence of stink bugs. Thresholds may be adjusted upward to reflect advancing boll maturity (see Table 11-2)

Beat Cloth (shake cloth) and Sweep Net (15-inch diameter)

These devices should be used to confirm presence of green vs. brown stink bugs, and are thus technically no longer employed to determine if threshold levels are present.

Conventional Cotton - Bollworms & Tobacco Budworms

Pre-bloom (normally used only in southern North Carolina on part of the acreage; limit this treatment to one well-timed application of a non-pyrethroid, such as Tracer 4 SC, Steward 1.25 SC, or Larvin 3.2 F. Treatment before bloom seldom pays, however.)

15 budworms per 100 terminals.
or
8 budworms per 100 squares.

Egg Threshold (after the onset of the major bollworm moth flight)

10 or more eggs per 100 terminals.
or
2 eggs per 100 fruiting forms.

Postbloom or Larval Threshold (usually after the egg threshold has been employed; but also used after blooming begins and before major bollworm flight, particularly if tobacco budworms are present)

3 live worms per 100 fruit (squares, blooms, or bolls).

Transgenic Bt Cotton - Bollworms & Tobacco Budworms (used against the major bollworm generation)*

Larval:

3 second-stage (1/8 inch or larger) bollworms per 100 squares or bolls. Pay particular attention to bollworms in or under yellow, pink, and dried blooms, but sample only in proportion to their occurrence.
or
2 second-stage bollworms (as above) on 2 consecutive scouting trips.
or
1 second-stage bollworm (as above) on 3 consecutive scouting trips.

Egg:**

75 to 100 eggs per 100 terminals. (Do not use egg threshold in Bollgard II cotton).
or
15 to 20 eggs per 100 fruit (blooms, tags, and bolls).
(Do not use egg threshold in Bollgard II cotton).

*Scouting Bt cotton for other insects will be similar to scouting conventional cotton, although population levels of some pests, and thus scouting emphasis, may be different.

**These egg thresholds, met only following very high egg deposition, should not be used within a week or less of an insecticide application.

Fall Armyworms

Same as the postbloom larval threshold for bollworm but may be revised upward late in the season (after September 1). The fall armyworm is primarily a late-season cotton pest. Pay particular attention to the small, grayish, fuzzy egg masses deposited on the undersides of leaves and to "windowpaning" in the bracts of lower bolls and blooms for the presence of larvae. Correct identification is critical; many bollworm insecticides are ineffective against fall armyworms. Large FAW are very difficult to kill with insecticides.

European Corn Borers

Use of the bollworm egg threshold will often control much of the late ECB generation. Follow the more detailed guidelines in the Cotton Insect Scouting Guide (ENT-cot-6).

Beet Armyworms

• 10 percent live beet armyworms in squares, blooms, or small bolls in
blooming cotton.
or
• 10 beet armyworms per foot of row later in the season (when squares and
blooms will not produce harvestable bolls).
or
• 15 percent of blooms with one or more live larvae.

Cotton Aphids

Using the Aphid Rating Scale, treat at a rating of 4 in opening cotton (15 percent open bolls or greater) or 5 in pre-opening cotton if plants are under stress or stunted and if aphid mummies and fungi are at low levels.

Treatment is discouraged under most circumstances because of its deleterious effect on beneficial predators and parasites that attack aphid populations. In opening cotton, treat only if plants are heavily infested and honeydew is detected in significant portions of the field. The Aphid Rating Scale may help define situations where treatment may be indicated.

Recommendations

A complete listing of recommended insecticides for use in controlling cotton insects is found in the North Carolina Agricultural Chemicals Manual.