Cotton Pest Management Newsletter #6
July 11, 2002

Cotton Situation: The Georgia Weekly Weather and Crops Report for the week ending July 7^th listed the crop as 87 percent squaring and 46 percent setting bolls. Crop conditions were generally listed fair to good, but some areas remain dry. Early planted dryland fields are cutting out in dry areas.

Insect Situation: As a whole, insects are more active than during recent years. Tobacco budworm has been difficult to control with pyrethroids in some areas. Beet armyworms continue to infest many fields, but the number of fields requiring treatment has been low. Aphid populations have crashed in most areas. Boll feeding bugs have reached treatable levels in some early planted fields.

Tobacco Budworm: Tobacco budworm (TBW) moth activity continues to be reported from various areas in the state. Populations are variable depending on location but are generally light to moderate with a few hot spots. In the central part of the state (Dooly County area), control of TBW with pyrethroids has been difficult. Poor control has been observed in numerous fields even when timely pyrethroid sprays were made. Larval collections were made from a problem field and lab studies will be conducted on pyrethroid susceptibility in the coming months. Pyrethroid resistance is suspected. Producers should use non-pyrethroid chemistries such as Steward or Tracer for TBW control. Both Steward and Tracer must be used in a timely fashion, targeting small larvae, for optimum results. The adults or moths of TBW and corn earworm (CEW) are easy to distinguish, but species identification of the larval stage requires the use of magnification. See the following website for additional information on differentiation of TBW and CEW larvae (http://www.gaipm.org/cotton/larvaid.html).

Corn Earworm: Corn earworm (CEW) pheromone trap captures have increased in many areas. Typically, mid-July is when we see CEW movement from corn into cotton.

Don't Zig when you should Zag (Insecticide Selection): Insecticide selection will be very important to manage TBW and CEW efficiently. When pyrethroid resistance is a concern, Steward or Tracer should be used to control TBW. If CEW is the predominant species, a pyrethroid would be the treatment of choice from both an efficacy and economic standpoint. We normally observe TBW during early July and transition into CEW during mid-July. During late July and August we may have either or a mixed population. Mixed populations should be treated as TBW. We can estimate species makeup of field populations by moth counts while walking fields. Egg identification kits are also available (AgDia).

Bt Cotton: Bt cotton has provided excellent control of TBW. Historically, Bt cotton has provided good control of CEW but, in some situations, supplemental treatment with insecticide is needed to control escaped CEW. Pyrethroids typically provide good control of CEW in Bt cotton and will also control stink bugs and other boll feeding bugs (plant bugs, leaf-footed bugs, etc.). We have received a few reports of CEW treatments in Bt cotton. Scouts should be sure to monitor blooms and bloom tagged bolls closely for CEW in Bt cotton. The recommended threshold for CEW in Bt cotton is when 7-8 larvae (1/4 inch or greater in length) are found per 100 plants.

Fall Armyworm: A few reports of fall armyworm (FAW) have been received from southernmost Georgia. We have not had much FAW pressure since 1997. Falls are difficult to control with insecticide, especially once greater than 1/2 inch in length. Scouts should be observant for small FAW feeding in blooms or etching the inner surface of boll bracts in the middle and lower part of the plant canopy. The threshold for FAW is about 2X that of CEW/TBW. Pyrethroids provide good suppression of FAW less than 1/8 inch in length.

Stink Bugs: Treatment for boll feeding bugs (stink bugs, plant bugs, etc.) has been needed in various parts of the state based on the 20% internal damage threshold. Scouts should begin monitoring medium sized bolls (the diameter of a quarter) for internal signs of feeding. Internal signs of feeding include stained lint and/or wart or callous growths on the inner surface of the boll wall. The wart or callous growth on the inner surface of the boll wall is visible within 48 hours of feeding by the bug. Scouts should also be observant for stink bugs and plant bugs when walking fields to determine which bug is causing the damage. Plant bugs will damage small bolls less than 10 days of age. Stink bugs may damage bolls up to 25 days of age. Bolls damaged by plant bugs and stink bugs can not be distinguished. Pyrethroids provide very good control of green and southern green stink bugs. However, control of brown stink bugs is less, about 50%. If brown stink bugs are the primary species infesting a field and numbers are high, the use of an organophosphate should be considered.

Spider Mites: Spider mites have been observed in some areas. Early symptoms of a mite infestation include stippling or small bleached or yellow spots that are visible on the upper leaf surface. Initially these symptoms are concentrated along primary leaf veins or folds in the leaf. A hand lens should be used to verify the presence of mites on the underside of suspect leaves.

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