Cotton Pest Management Newsletter #10
August 2, 2001

Cotton Situation: The Georgia Weekly Weather and Crops Report for the week ending July 29^th listed the crop as 78 percent setting bolls which is slightly behind the five year average of 86 percent. Crop conditions are generally fair to good but some dryland fields have cuttout early.

Insect Situation: As a whole, we continue to be in good shape concerning insects. Some treatment of corn earworm has occurred during the past week but infestations continue to be spotty. Stink bug sprays are being made in some areas and scouting for bug damage should be a priority for the remainder of the season. A few reports of tobacco budworm moth activity were received this week and spider mite infestations have been observed in isolated fields.

Corn Earworm: Corn earworm (CEW) infestations continue to be spotty and sporadic. This year is a good example of why we scout all fields. It has not been uncommon for one or two fields on a farm to require treatment while others may never reach threshold. Larvae are generally being found in the middle part of the canopy associated with blooms and stuck bloom tags. In some situations this has made control difficult, especially in densely canopied fields. Good coverage is critical for control. The insecticide must penetrate the canopy to where the larvae are feeding. Pyrethroids should provide good control and also offer some control of bug pests.

Tobacco Budworm: Eddie McGriff in Decatur County reported tobacco budworm (TBW) moth activity. Numbers are low but this could be the start of the August generation. Bt cotton should provide very good control of TBW. On non-Bt cotton, it is important that scouts observe moths while walking fields. If TBW is the primary species, non-pyrethroid insecticides such as Tracer and Steward should be used in areas where pyrethroid resistant TBW is suspected.

Stink Bugs: Stink bug scouting should be a priority on all fields which are setting bolls and should be continued until the last harvestable boll has attained 25 days of age. We have had a few calls concerning the presence of brown stink bugs following a pyrethroid application. Brown stink bugs are more tolerant to pyrethroids compared with southern green which is typically the primary stink bug species found in cotton. Drs. Gary Herzog and Jeremy Greene conducted laboratory bioassays during 2000 looking at insecticide susceptibility of southern green and brown stink bugs. Mortality of field collected southern green adult stink bugs 48 hours after exposure to various pyrethroids ranged from 83 to 94 percent. In a separate test, mortality of field collected brown stink bug adults 48 hours after exposure to various pyrethroids ranged from 21 to 64 percent. Mortality after exposure to 8 ozs of Bidrin was 97 and 96 percent for southern green and brown stink bug in each test respectively. The complete report of "Efficacy of selected cotton insecticides on brown and southern green stink bugs" can be found in the Cotton Research-Extension Report for 2000 on page 223. Insecticide selection can be very important when treating stink bugs. Consider the following: What proportion of the stink bug complex is brown? The use of a drop cloth would aid in this decision. Often southern green is the predominant species. Are corn earworms also present in the field? If you have a mixed population of larval pests and bugs, a pyrethroid would be a good treatment. What is the stage of plant development? In general, we would typically delay use of OPs such as Bidrin or methyl parathion to late in the year when the fear of flaring other pests such as corn earworm or armyworms has been reduced. Pyrethroids will also disrupt beneficials, but a single application of a pyrethroid would not be as disruptive as a Bidrin spray. In summary, it is important that scouts are checking all fields for stink bugs and internal boll damage. Not all fields will require treatment, but if thresholds are exceeded (20% internal boll damage and stink bugs observed in the field) treatment would be recommended.

Spider Mites: Spider mites have been observed in a few fields. Although typically a dry weather pests, some infestations are present in fields which have not suffered for moisture. Initial infestations are generally spotty and are often observed near field borders or weedy areas in a field. In time, these areas may spread. Mites are very small and feed on the underside of leaves near the leaf veins of folds in the leaf. The upper surface of the leaf will be yellowish or red and appear freckled in localized areas above the infested portion of the leaf. If this damage is observed, a hand lens should be used to verify the presence of mites which are very small.

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