Cotton Pest Management Newsletter #9
August 1, 2002

Cotton Situation: The Georgia Weekly Weather and Crops Report for the week ending July 28^th listed the crop as 89 percent setting bolls. Eighty-seven percent of the crop is rated fair or better.

Insect Situation: Mixed populations of tobacco budworm and corn earworm infestations continue to be reported. Mixed populations should be treated as a TBW infestation. Insecticide selection and timing of application will be critical for success. Low numbers of armyworms and soybean loopers have also been reported. Silverleaf whiteflies have been observed in localized fields near Tifton.

Boll Weevil Eradication Program: Boll weevil traps should be installed on all cotton fields at this time. If you have a field which is not being trapped be sure to contact the BWEP so traps can be installed. The first cycle of checking traps has been completed and no boll weevils were found. As we begin to prep field borders for harvest, be careful to avoid traps. Traps which are knocked down are not functional. If a trap is accidentally destroyed, contact the BWEP so new traps can be installed. The potential for re-infestation of boll weevils exists. During 2001, four boll weevils were captured in Georgia which was the fewest number captured per year since the program began. Boll weevils may be reintroduced into Georgia in several ways such as movement of pickers or module trucks from boll weevil infested areas. Care should be taken that such equipment is boll weevil free.

When is a Boll Relatively Safe from Insect Damage? Some fields in the state are approaching the stage at which a decision to terminate insecticide applications for some pests exists. This decision has already been made on some early dryland fields. Often the insects will help us make this decision. Tobacco budworm (TBW) and corn earworm (CEW) moths will often select more suitable host sites such as later planted or green lush cotton compared with fields which have cuttout and have few squares. Number and size of TBW and CEW larvae must be considered when terminating insect control. Will larvae be able to size on developing squares and small bolls and move down the plant? Generally, TBW and CEW will have difficulty establishing on plants when few squares (2-3 per plant) are found. Developing bolls remain susceptible to TBW and CEW until about 20 days of age (fully sized boll). Although bolls of this age are not immune from TBW and CEW attack, damage is much less likely to occur. Fall armyworm larvae are capable of damaging bolls for a more extended time frame. Data suggests that bolls 25 days of age are not likely to incur yield loss from stink bug feeding. Excessive foliage feeding by soybean looper or beet armyworm can affect yield until bolls are mature as foliage is needed for bolls to properly fill. Honeydew producing insects such as whiteflies and aphids must be monitored and controlled until defoliation as honeydew may potentially accumulate on open bolls.

Silverleaf Whitefly: Low populations of silverleaf whitefly (SLWF) have been observed on cotton in Tift County. Historically SLWF has been a localized pest in Tift and surrounding counties. Infested fields should be monitored closely. Rainfall events will generally suppress populations, but if we encounter dry conditions in the coming weeks, the risk of whitefly buildup will increase.

Adult SLWF is a small (about 1/20 inch in length) moth-like insect with solid white wings. Eggs are oblong, pointed, and yellowish brown. Newly hatched SLWF or "crawlers" move about the undersides of leaves searching for a suitable site to attach. Once attached, SLWF will complete its life cycle feeding on plant sap as a flattened oval nymph. The pupal stage has prominent red eye spots. As little as 18 days is required to complete a generation. Both adult and immature SLWF feed on the lower leaf surface by sucking plant sap. Whiteflies produce honeydew similar to aphids. In addition to problems associated with honeydew and sooty mold on foliage and open bolls, premature defoliation may occur when high populations are present.

Cultural practices such as destroying crop residues which harbor SLWF will help reduce overall population buildup. Conserving natural enemies (predators and parasites), planting smooth leaf varieties, and avoiding late planting are ways to reduce the risk of whitefly problems. However, when and if the problem develops, insecticides will be needed to reduce yield loss.

Knack insect growth regulator has been the most consistent treatment for management of SLWF. Knack has a long residual and is slow acting (i.e. it must be put out early for optimal performance). Female SLWF treated with Knack will lay sterile eggs. Knack will control immature SLWF when they pupate (red-eye stage), however established nymphs will continue to feed until pupation. If five immatures can be found on a square inch area anywhere on the underside of leaves, treatment would be suggested. Knack will not provide good control when applied as a rescue treatment on an out-of- control population.

Additional options for SLWF control include contact insecticides. Tank mixes of Danitol or Capture plus Orthene can provide temporary relief. Thiodan will also provide temporary knock down of adults. During 2000, Assail (i.e. Intruder) looked promising in a SLWF insecticide efficacy trial. Multiple applications will be needed as re-infestation of fields occur.

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