Cotton Pest Management Newsletter #11
August 9, 2001

Cotton Situation: The Georgia Weekly Weather and Crops Report for the week ending August 5^th listed the crop as 90 percent setting bolls which is similar to the five year average of 92 percent. Overall crop conditions remain fair to good but some dryland fields have suffered significantly for moisture during the last two weeks. A few open bolls have been observed on early planted cotton.

Insect Situation: Boll damage from bugs varies across the state and from field to field, but in general numbers are up. Stink bug scouting should be a priority for the remainder of the season. Tobacco budworm moth activity has increased in southwest Georgia. Corn earworm moths continue to be active but numbers vary from area to area.

Tobacco Budworm and Corn Earworm: Tobacco budworm (TBW) numbers have increased during the past week, especially south and west of Tifton. Although TBW numbers have been low to date, pheromone trap captures last month would suggest that the July TBW moth flight peaked the second week of July in Tifton. TBW complete a generation in about 28 to 30 days and thus the increased activity we are seeing now is to be expected. Corn earworm moth activity continues in many areas but is sporadic. During August, it is common for fields to be infested with a mix of both TBW and CEW. For this reason it is important that scouts are observant for moths while walking fields. These "moth flushing" counts will give us an idea of which species, TBW or CEW, is most common and can aid in insecticide selection. If pyrethroid resistant TBW is suspected, non-pyrethroid insecticides such as Tracer or Steward would be recommended. When dealing with mixed populations (50:50), it is best to treat the infestation as TBW. Timing of sprays to target small larvae on non-Bt cotton is a must. Much of the April and early May planted cotton is reaching the stage of development where fields will not be attractive sites for oviposition or egg-lay. However, scouts must stay vigilant in their search for eggs and small larvae until the last boll which will significantly contribute to yield is 20 to 25 days of age. Bolls of this age are relatively safe but not immune from attack by TBW or CEW.

Stink Bugs: Stink bugs have reached treatable levels in many parts of the state based on the 20 percent internal damage threshold. As with other pests, it is not uncommon for us to observe significant variation in damage from field to field. Do not assume all fields need to be sprayed. Scout each field and treat accordingly on an as-needed basis. It is important that scouts are "calibrated" when selecting bolls to examine for internal damage. Bolls which are approximately the diameter of a quarter should be selected. Following an insecticide application for stink bugs, we normally observe a decrease in boll damage seven days after treatment when the appropriate size boll is sampled. However if a scout samples bolls which are too large, it is possible to be counting damage which occurred prior to the insecticide application and thus not see a significant reduction in the damage count. Our observations during the past few years would suggest that a follow up stink bug spray will not be needed for about two weeks. However, there are always exceptions which could be dependant upon migration into the field or the level of control achieved with the initial application. Remember that brown stink bugs are less susceptible to pyrethroids when compared with Bidrin or methyl parathion. If numerous brown stink bugs are observed, Bidrin or methyl parathion OP would provide better control. Fields which have not been treated with an insecticide that has activity on stink bugs, such as a pyrethroid, are at highest risk for stink bug infestation.

Southern Armyworm: Southern armyworm may be found on both non-Bt and Bt cotton and most often are observed in fields which have not been treated with insecticide that has activity on caterpillar pests. Typically southern armyworm will only feed on foliage, but will occasionally feed on squares. Larvae can vary in color from tan to nearly black. Several large black spots are present on the top and sides of the first abdominal segment (just behind the third pair of true legs). On small larvae, these black spots give the appearance of a band around the body. The head capsule of larvae is often a tan-orange color. Moths lay egg masses similar in appearance to beet or fall armyworm, but they are much larger, about the size of a nickel. Upon hatching the larvae feed in a group on the underside of leaves for several days similar to beet armyworms. As larvae mature they will disperse to adjacent plants.

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