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COTTON PEST MANAGEMENT NEWSLETTER #5 June 30, 2000 COTTON SITUATION: The Georgia Weekly Weather and Crops Report for the week ending June 25 listed the crop as 61 percent squaring and 18 percent setting bolls which is similar to the 5-year averages of
64 percent squaring and 11 percent setting bolls. Scattered rains brought temporary relief this week but soil moisture remains low. INSECT SITUATION:
The second generation of tobacco budworm is infesting cotton in south Georgia. Aphid populations are spreading in fields and rapidly building in some areas. Beneficial populations, especially big-eyed bugs, remain high.
Tobacco Budworm:
Tobacco budworm (TBW) eggs and small larvae have been reported in moderate numbers during the past week in southwest Georgia. This is the second generation of (TBW) to infest cotton and is a few days earlier than in past
years. Several non-Bt fields have been treated. In most areas TBW is the primary species, but a few corn earworm moths have been observed. 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 small larvae per 100 plants after the first spray. In parts of the state we have had increasing problems controlling TBW with pyrethroids due to pyrethroid resistance. If you are in an area
where pyrethroid resistance is a concern, non-pyrethroid chemistry such as Tracer would be recommended for TBW control. When using Tracer, coverage and timing of sprays is critical for a successful treatment. Tracer
efficacy, as with all insecticides, is much better when small larvae are targeted. Tracer has both contact and stomach activity, but the majority of control occurs when TBW ingest the spinosad toxin. Thus coverage is
very important. You must get the spray to the larvae. Recommended Tracer rates are 1.5-2.0 ounces per acre. The lower rate can be used on smaller cotton. Selective chemistry such as Tracer will
also have additional benefits at this time. Tracer has minimal impact on predators such as big-eyed bugs and conservation of beneficials will provide suppression of TBW, armyworms, aphids, and other pests. Additionally,
Tracer will not select pyrethroid resistant individuals and thus reduce or delay resistance development. From a resistance management standpoint, a good strategy is to rotate insecticide classes by generation. An
example would be to use Tracer now (2nd TBW generation) and pyrethroids (depending on resistance levels) on the 3rd
generation which will occur in approximately 28-30 days. We may expect to see corn earworm (CEW) activity increase in the upcoming weeks and pyrethroids have provided very good control of CEW in past years. During late July and August, we often see a mix of TBW and CEW. Pyrethroid use in August will offer control of stink bugs also.
Corn Earworm: We
should expect corn earworm (CEW) infestations to increase in upcoming weeks as corn begins to dry down. Growers will need to be prepared to treat Bt cotton if threshold levels are met (7-8 large CEW larvae greater than 1/4
inch in length per 100 plants). Scouts need to be sure to monitor the middle and lower portions of the plant on Bt cotton. In past years CEW larvae have been associated with flowers and stuck bloom tags.
Aphids: Aphid populations are spreading and building in many fields. Historically, we have treated only a small percentage of cotton in Georgia for aphids but fields should be monitored closely. 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, it will have the appearance of standing on its head with its mouthpart
stuck in the leaf. 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. 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.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 |
