FIELDAND
FORAGE
CROPS
FIELD
The information and recommendations in this newsletter are applicable to
North Carolina and may not apply in other areas.
Thrips should remain our only potentially-significant insect problem from cotton plant emergence through early to mid-June. All county Extension agents should have received a copy of a recent article on at-planting options for thrips control via Keith Edmisten's Cotton Notes. You might also refer pages 131-133 of 1997 Cotton Information for additional information. Thrips scouting information also can be found in the Cotton Insect Scouting Guide on page 4. I will provide more information on scouting and symptoms of damage in the coming weeks.
Valent is no longer making Payload 15G at-planting insecticide (because of the bridging problems with this formulation). Therefore, supplies may be limited and available for only the coming year.
If using Gaucho-treated cotton seed, I would suggest that growers and consultants inspect seedling cotton particularly carefully for immature thrips and thrips damage. Although this product has shown yields similar to Temik in extensive testing in North Carolina for the past 2 years, these tests have generally been conducted under much lighter thrips pressure than is often observed in our state, and, in replicated tests, the seedlings in the Gaucho-treated plots have often shown much higher thrips levels than in the other treatments evaluated.
Foliar applications for thrips following an at-planting insecticide
should be made with discretion and based on need, as these
treatments can greatly increase the probability of having to also
treat for June tobacco budworms or bollworms, particularly in the
southern half of the state (except with B.t. cotton which is
extremely resistant to budworms).
Within a few weeks, I should begin receiving information from Florida and Georgia regarding their insect populations. Thrips, early tobacco budworms, plant bugs and cotton aphids will be of interest; I will try to pass some of this information along. General trends for insects in the Southeast sometimes become established early.
For our later, economically-damaging insect pests, primarily
bollworms and European corn borers, the weather between now and the
major moth flights and the attractiveness of the cotton crop will
largely determine the extent of potential damage. Very little can
be predicted now; however, it can be noted that our 1997 cotton
crop is slightly behind schedule.
I am currently scheduling cotton insect scouting schools. Our
school for the Scotland/Hoke/Robeson County area has been set for
June 12, 1997 at the O.P. Owens Agricultural Center in Lumberton,
beginning at 10:00 a.m. I will keep you posted as other schools
are scheduled. Dr. John Van Duyn, Extension Entomologist, Vernon
James Center, Plymouth, will be organizing the sessions in the
northeastern region of North Carolina.
Black cutworms appear to be more abundant than usual in fields of seedling field corn. I have received reports from across the lower Coastal Plain of infestation, damage, and insecticide treatment for black cutworms. County Extension agents and growers should be alert to the possibility of attacks on newly-emerged stands of corn and take the necessary measures to keep losses within tolerable limits.
No-tillage corn has greatly increased in recent seasons; it appears to be widely practiced this year. No-tillage is a positive factor for cutworm survival. Tillage directly kills cutworm larvae and is usually performed several weeks before the newly-planted crop emerges, thereby depriving the caterpillars of their food. Thus, conventionally-planted corn has a lower probability of economically-damaging cutworm infestations. Conventional tillage does not eliminate cutworms and it is not unusual to find economically-damaging black cutworm populations in conventionally- tilled corn. Do not assume that conventionally-tilled corn is entirely safe from black cutworms.
No-till corn planted into no-tilled soybeans in wheat stubble residue tends to be more favorable for cutworms than most other situations, especially if the residue is thick. If burndown herbicide has been applied well in advance of planting, cutworm populations may have declined due to starvation or migration from the field. Without a long delay between the killing of existing vegetation and emergence of corn seedlings, caterpillars will remain in the field and be very hungry when the seedlings emerge. Damage is also more severe on slow-growing seedlings, another negative effect of no-till/cutworm situations where soils warm more slowly.
Scouting for cutworms can be done quickly since fields are easily traversed. However, cutworm occurrence can be spotty and scouting requires thorough coverage of fields. The threshold is set at 5 percent severely-damaged plants, but in reality must be considered with existing plant stand (it is not how many plants are eaten but how many remain). The goal is to retain a full yield plant stand. Therefore, counts of the plant stand must be made and converted to plants per acre to compare with the farmer's target plant stand. If stands are below the target stand, then little additional plant loss can be tolerated.
Damage from black cutworms can have a dramatic range. If larvae are small, then leaf feeding will be the most common damage. Large larvae cut the plants if the stem diameter is small or eat a hole into the side of larger plants. Newly-emerged seedlings may show leaf feeding or be cut above the growing tip, in which case the plants will recover. Injury to the growing tip will kill the plant. Evidence of cutworm infestation includes cut-off plant stumps, cut plants pulled into ground tunnels, leaf bits from mostly consumed plant tops, and mole cricket-like tunneling just below the soil surface (you can see the tunnel routes). Digging around cut plants will often reveal the dark colored caterpillar, which can be rather large (e.g., the size of a large corn earworm). In dry, loose soil, cutworms may be subterranean and little above ground evidence of infestation will show. In these cases, plants will seemingly have disappeared and digging for evidence to positively identify the pest is a must.
Effective insecticides for treating cutworms are listed in the
North Carolina Agricultural Chemicals Manual. If cutworms are
worse than usual in corn, no-tillage cotton will also be at risk of
damage.
Cereal leaf beetle populations continue to cause concern with county Extension agents, consultants, and growers. Populations of the insect vary widely in intensity and stage of development. In general, populations range from a few (especially in early-planted wheat) to well above threshold (especially in thin, later-planted wheat). In the mid section of the Coastal Plain (e.g., Greenville and to the south) above-threshold populations should have been treated by now, in most cases. Above-threshold fields are suffering, or have already suffered, excessive defoliation. At the latitude of Plymouth, most populations above threshold have been treated, but some populations still remain at a treatable state (not to late). However, above the Albemarle Sound populations are now at a treatable stage, or soon will be in the case of the counties in the far northeast. Cereal leaf beetle infestations will soon be over and if anything is going to be done, it needs to be done immediately.
Most comments on the new threshold and scouting procedure have been positive. So far we have done a much better job of treating in a timely fashion. Early spraying with both Karate and malathion has worked well, as best as I can determine. Consultants have told me that scouting eggs and small larvae has not been a burden.
Regarding insecticide treatment, malathion is cheaper than Karate and will work well if the bulk of the population is in the larval stage. Very early treatment gives an edge to Karate, due to its longer residual. However, populations comprised mostly of larvae do not require residual control and malathion can be used. Malathion would be the choice when spraying around waterways or dwellings.
I am very interested in hearing from county agents regarding the
new threshold, scouting, and earlier insecticide treatments.
Contact me by electronic mail at john_vanduyn@plymouth.ces.state.nc.us.
Web page last updated on April 28, 1997 by Stephen J. Toth, Jr..
