Cotton Pest Management Newsletter #5
June 28, 2001

Cotton Situation: The Georgia Weekly Weather and Crops Report for the week ending June 24^th listed the crop as 47 percent squaring and 9 percent setting bolls which is slightly behind the five year average. Producers are busy with herbicide and side-dress nitrogen applications. Scattered showers were received in parts of the state. Cotton growth and development is progressing rapidly in the presence of good moisture and high temperatures.

Insect Situation: Aphids continue to build but early reports of the naturally occurring fungus which causes populations to crash have been received. Tarnished plant bugs continue to be reported from various parts of the state and retention varies from very good to average. We should anticipate increases in tobacco budworm this week. Beneficial numbers remain strong.

Aphid Fungus Observed: Several county agents and consultants are participating in a Cotton Aphid Fungus Sampling Service being coordinated by Dr. Don Steinkraus of the University of Arkansas in cooperation with Cotton Incorporated. During most years, a naturally occurring fungus causes aphid populations to crash in early July. This service will actually detect the presence of the fungus before we can observe diagnostic symptoms in the field. Once an aphid is infected with the fungus, mortality occurs in about three days. This service actually looks for fungal spores on the aphids. When the aphid is killed by the fungus, the dead aphid will have the appearance of standing on its head with its mouthpart stuck in the leaf (a hand lens will help here). In a couple of days, a secondary fungus will invade the aphid cadaver. This fungus will grow and the aphid will quickly be covered by a brown or grayish green fungal mass ("fuzzy" aphids). Once these symptoms are observed, the aphid infestation will generally crash within a week. Two samples were submitted for diagnosis from the CPES in Tift County and both were positive for fungal spores. Results of samples sent from Georgia and other states will be posted on a web site by the University of Arkansas (http://www.uark.edu/misc/aphid/). Additionally there is information on the life-cycle of the aphid fungus, Neozygites fresenii, and how this service works. We also have reports of visual observation of the fungus in Colquitt and Decatur Counties. Scouts should be observant for fungal symptoms and treatments should be delayed if the fungus is present. Historically, a healthy population of aphids is needed before the epizootic or "crash" of the aphid population occurs. The fungus appears to be about 7 to 10 days earlier than in previous years.

Plant Bugs: Plant bug numbers continue to be higher than in previous years and isolated fields or farms have required treatment. It is likely that higher populations of plant bugs are being observed due to spring rainfall. We have had an abundance of alternate weed hosts for plant bug populations to build and potentially these populations could invade cotton. Be sure scouts are monitoring retention and being observant for plant bug adults and nymphs. Although we recommend examining one fruiting position in the top of plants when making retention counts, scouts must not ignore other areas of the plant. If damage is consistently observed at other fruiting sites, this should be quantified and reported.

Tobacco Budworm: Scouts should anticipate tobacco budworm (TBW) numbers to increase in the next week or two. Although the June generation was light, we typically expect higher pressure in early July. In southwest Georgia, TBW will likely be the primary species, but a few corn earworm moths have been observed recently. Bt cotton should provide very good control of TBW, but growers, scouts, and consultants should be monitoring non-Bt fields closely and reacting promptly (within 24 hours) if an insecticide application is required. Our threshold for TBW is 7-8 small larvae per 100 plants prior to the first insecticide application and 5 per 100 plants after the first spray. If you are in an area where pyrethroid resistance is a concern, non-pyrethroid chemistry such as Tracer or Steward would be recommended for TBW control. When using Tracer or Steward, timing and coverage are extremely important. Both of these products are selective in that minimal disruption of beneficials occurs following use. Lady beetles would be an exception when Steward is used.

Two New Insecticides: Two new insecticides, Steward (DuPont) and Centric (Syngenta), have been labeled for foliar use on cotton. Steward is labeled for most caterpillar pests in cotton and also for tarnished plant bug. Steward has a novel mode of action (new class of insecticide) and thus would be a good choice where insecticide chemistries are being rotated or where pyrethroid resistant tobacco budworm is suspected. Applications targeting tobacco budworm and corn earworm must target small larvae. If you have experience using Tracer, Steward should be timed in a similar fashion. Steward is very active on foliage feeders such as loopers and beet armyworm. I would not consider Steward the product of choice if plant bugs were heavy, but data suggests it can offer some help on light to moderate populations of plant bugs. Centric is labeled for control of several sucking pests (aphids, whiteflies, thrips, tarnished plant bug, and cotton fleahopper) which infest cotton. Centric is in the same chemical class as imidacloprid (Provado). Centric would be considered one of the better aphicides available based on our experiences. We have less experience with Centric on plant bugs. As with any new technology, we would encourage growers and ourselves to gain experience with these products on small acreages initially.

Boll Weevil Traps: Recently Boll Weevil Eradication Program (BWEP) personnel began installing boll weevil traps. Plans are for all fields to have traps installed by July 13. In order for traps to be functional, they must be standing. If traps are accidently knocked down, please stand them back up.

Insect Updates: Check the Cotton Insect Hotline (1/800-851-2847) for updates on current insect conditions. The Cotton Pest Management Newsletter is also posted on the Internet at www.gaipm.org and then click on "cotton."

Sincerely,

Phillip Roberts
Extension Entomologist