FIELDAND
FORAGE
CROPS
FIELD
The information and recommendations in this newsletter are applicable to
North Carolina and may not apply in other areas.
Most of the cotton in North Carolina is currently past the stage at which feeding by thrips can cause enough damage to effect maturity or yields. A few late or replanted cotton fields which still have only one to four true leaves should still be monitored for deformed young leaves and terminals and the presence of immature thrips. Even though this cotton should quickly outgrow potential thrips damage, it can not afford maturity delays. Therefore, thrips at levels exceeding threshold should be treated quickly. Be aware, however, that treatments at this time of year have the potential for increasing tobacco budworm damage due the to destruction of beneficial insects.
Tobacco budworm moth egg laying and young larvae have increased sharply this past week in our southern and southeastern counties. A number of fields in Scotland and Robeson counties are in the range of 20 to 60+ percent eggs per 100 terminals, and first instar budworms in terminals are running from 1 to 2 percent up to 6 to 8 percent in terminals. Reports from the area including Jones, Craven and Onslow counties also indicate the presence of budworm eggs, but at lower levels. At this point, budworm larvae are still below threshold in all areas reporting, but levels are considerably higher than in past few years. Budworms should now be a focal point of scouting through the central cotton-growing area of North Carolina.
In general, scouts should examine 50 terminals and 100 squares for small budworms. Remember not to count damaged terminals or squares toward the treatment thresholds. The very tiny budworm hatchlings are very difficult to find when feeding on or with the fuzzy terminals. A hand lens is very helpful. With beneficial insects on the rise, heavy mortality of budworms in terminals is common. This will probably not occur if the field has been sprayed with an insecticide for thrips or plant bugs in the past 7 to 10 days.
Remember to observe the new, higher thresholds for budworms (i.e., 15 percent budworms per 100 terminals, or 8 percent live budworms on or in squares). These higher thresholds will still provide plently of protection from delays in maturity and yield loss, given the amount of square compensation which consistantly occurs at this time of year. Do not spray insecticide for this generation on the basis of egg levels. However, egg levels can help to determine the scouting frequency (normally every 5 to 7 days).
At this point, corn earworm (bollworm) moths have been a greater component of these tobacco budworm moth flights than normal. Earworm moths will decline sharply in cotton as more field corn begins to silk. Earworm eggs and young larvae on cotton along with budworms will not change the method of scouting or the thresholds. If scouts or consultants notice more corn earworm moths than budworm moths within or around cotton fields, a single application of Tracer (spinosyn) at the industry rate (2.0 oz. per acre or 0.067 lb. of active ingredient per acre) may be in order for threshold levels of larvae. Tracer at this rate will cost about $12 per acre, so banding may be needed to make it affordable. The low rate of Tracer (0.045 lb. of active ingredient per acre) shows good efficacy against budworms, but is mediocre on bollworms. Pyrethroid insecticide applications should be kept to an absolute minimum at this time of year. If budworm moths predominate (this should generally be the case), the lowest rate of Tracer (0.045 lb. of active ingredient per acre) is a good choice, as it spares most beneficial insects and does not contribute to pyrethroid resistance.
Generally low levels of plant bugs are currently present in a large number of fields. Before monitoring cotton fields for the plant bugs themselves (which is time-consuming), calculate the percent square retention by inspecting a terminal and a lateral square of about 1/8 inch in total length in the upper 3 nodes of the plant. Count missing squares or discolored squares (yellowish to brown or black) as absent, and attached green squares as being retained. If 80 percent or more of the squares in a field are being retained, look no further. With less than 80 percent square retention, sweeping for live plant bugs will be necessary. See 1998 Cotton Information or the Cotton Insect Scouting Guide for details. Even with the elevated plant bug levels present in 1997, approximately 1 field in 30 was treated. Generally, cotton will be most susceptible to plant bug injury during the first 3 weeks of squaring.
Cotton aphid numbers have increased this past week in a number of fields, though levels are far behind last year's populations. Producers are urged to rely on predators, parasites (particularly the mummifying wasps) and fungi. Chemical control is seldom effective against cotton aphids.
Peanuts are beginning the transition from early-season to the mid-
season pest problems. Many peanut growers choose to apply
insecticides for rootworms during flowering rather than at pegging.
Before making a decision to treat with insecticide, consider the
risk of rootworms to each field. Fields with very light, sandy
soils have little risk from rootworms, but are most likely to
suffer from spider mites. Rootworm insecticide treatments can
increase the likelihood of a spider mite outbreak. Treating in
such areas can cause secondary problems.
Web page last updated on June 24, 1998 by Stephen J. Toth, Jr..
