Cotton Pest Management Newsletter #9
July 26, 2001

Cotton Situation: The Georgia Weekly Weather and Crops Report for the week ending July 22^nd listed the crop as 93 percent squaring and 65 percent setting bolls. Cotton growth and development ranges from 4-5 leaf cotton planted in late June to cotton planted in April which is cutting out. Welcome rains were received in many areas this week but some areas are dry.

Insect Situation: Not much change in the insect situation since last week. Corn earworms are being reported from various areas at light to moderate populations. Treatable populations are present in some areas but are sporadic in nature. Stink bug scouting should be a priority in fields which are setting bolls. To date, insects have not caused many problems but we do not need to drop our guard.

Corn Earworm: Corn earworm (CEW) infestations are spotty and sporadic. Treatable infestations are being found in individual fields. Eddie McGriff in Decatur County reported CEW egg deposition in the middle part of the plant on bracts, bloom tags, and stems. He also indicated that large larvae CEW counts are appearing in some fields when previous scouting reports failed to detect similar numbers of eggs and small larvae (we missed them but they were there). Scouts be sure to look closely at the middle part of the plant in both Bt and non-Bt cotton. As a reminder, scouts should examine the top 1/3 of the plant and at least one bloom, one bloom tagged boll (be sure to look under tag for small larvae boring into the tips of bolls), and a small boll lower in the canopy for eggs and larvae. Also be observant for fall armyworm in blooms or etching boll bracts low in the canopy. Richard McDaniel in Burke County reported an increase in CEW activity but again treatable infestations are spotty. If economic CEW infestations are observed, pyrethroids would be a good treatment. Historically, pyrethroids have provided very good control of CEW and will also control bugs which are continuing to build in some fields.

Tobacco Budworm: Tobacco budworm (TBW) moth activity continues to be low. As we enter August we would expect TBW numbers to increase. In recent years, we often contend with mixed populations of TBW and CEW during August, especially in southwest Georgia.

Stink Bug Scouting: Stink bug scouting should be a priority on cotton which is setting bolls. Scouting should be initiated during the second week of bloom and continued until harvestable bolls have attained 25 days of age. Once a boll is 25 days from white bloom, the likelihood of suffering significant yield loss from stink bugs is greatly reduced. Recommended treatments include several pyrethroids and the OPs, Bidrin and methyl parathion. Vydate was also recently labeled for control of green and southern green stink bugs. In some fields, scouts and consultants are seeing fairly high numbers of brown stink bugs. However in most situations, southern green will be the predominant species. Brown stink bugs are more tolerant to pyrethroids than green and southern green. Bidrin and methyl parathion would be preferred treatments if brown stink bug is the primary species.

"Bug" Damaged Boll Threshold: During 1999 and 2000, Drs. Gary Herzog and Jeremy Greene coordinated research addressing economic thresholds for stink bugs. Five trials were conducted in Bt cotton fields. Treatments included Bidrin (8 ozs/a) sprays at various threshold levels (10, 20, and 30 percent internal boll damage, 1 stink bug per 6 row feet, and an untreated). Plots were scouted weekly and each treatment was treated on an as-needed basis. Highest yields (+109 lbs lint/a) were obtained in the 20% internal damage threshold plots which required two applications of Bidrin. Similar yields were also produced using the 10% damage threshold but with the expense of two additional Bidrin sprays. The 30% damage threshold and 1 stink bug per 6 row feet treatments required one or fewer Bidrin sprays and did not result in significant yield increases compared with the untreated. Because plants were exceedingly tall at several sites, bugs were difficult to detect in the elevated canopies using the drop cloth technique. This could have resulted in undetected densities exceeding threshold, fewer insecticide applications, more boll damage, and reduced yields. Based on these studies, managing stink bugs using the 20% internal boll damage threshold returned a net gain of $48.48 to the grower (All Fields Should Be Scouted For Stink Bugs). Net gain was calculated with yield gain at $0.60 per lb of lint minus $8.31 per Bidrin acre application ($5.31 for insecticide plus $3.00 application costs). Two on farm trials were also conducted in Irwin County with Gibbs Wilson. Treatments included a pyrethroid treatment at the 20% internal damage threshold and an untreated. One application was needed at each location and yields were increased 122 and 56 lbs lint/a when stink bugs were managed.

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