Cotton Pest Management Newsletter #6
July 5, 2001

Cotton Situation: The Georgia Weekly Weather and Crops Report for the week ending July 1^st listed the crop as 60 percent squaring and 16 percent setting bolls. Scattered showers were received in parts of the state and most of the crop is rated fair or better. Producers continue to clean up weed problems and make side-dress nitrogen applications. The National Agricultural Statistics Service released the first planted acreage estimates on June 29, 2001. The Georgia cotton acreage for 2001 is estimated at 1,6000,000 acres.

Insect Situation: Aphids are spotty and continue to build in parts of the state. Where high populations have been observed, the naturally occurring fungus which causes populations to crash is also being observed. Tobacco budworm and corn earworm eggs and small larvae are being reported but infestations are light in general. This is the time of year we expect worm numbers to increase so scouts need to watch fields closely. We have received a few reports from scouts of stink bugs in fields.

Aphids-Fungus: Aphid numbers are light in general but populations are building in some fields. We continue to receive reports of the naturally occurring fungus which causes populations to crash. Typically we need good numbers of aphids before we see the epizootic or populations crash. Very few if any fields have been treated for aphids.

Stink Bugs: We have received several reports of sting bugs, both adults and nymphs, in cotton. Stink bugs can feed on squares and other plant parts, but the primary damage we have observed occurs to developing bolls. The presence of stink bugs in cotton at this time should be an early warning of potential problems once plants begin to set bolls. It is imperative that all fields are scouted for stink bugs. Stink bug scouting should be initiated by the second week of bloom, i.e. 10-12 day old bolls present. Although it is only early July, some early planted fields may reach economic levels in the next week or so. In recent years we have conducted numerous field demos and research plots and it is not uncommon for thresholds to trigger a stink bug spray in July. Although we have three primary species of stink bugs, the behavior and life cycle is somewhat similar. Stink bugs have five immature or nymphal stages. First instar, just hatched, stink bugs do not feed on plant tissue and remain clustered around the egg mass. Second and third instars also remain clustered but will feed on plant tissues. Research has shown that the larger or later instars cause greater damage to developing bolls. Significant damage from fourth and fifth instars feeding on bolls will occur. Fourth and fifth instars as well as adults disperse widely. The life cycle of stink bugs is about 40 days from egg to adult. Approximate development times include: eggs hatch: 4-5 days, first instar: 4 days, second instar: 4-5 days, third instar: 5 days, fourth instar: 7-8 days, fifth instar: 12 days, and adults may live for 30-60 days. Scouting for stink bugs should be a priority as plants enter the second week of bloom and begin to set bolls. In addition to being observant for nymphs and adult stink bugs, scouts should assess stink bug populations by quantifying the percentage of bolls with internal damage or using a drop cloth. Estimating boll damage has proven to be a reliable technique for assessing damage and timing insecticide applications when needed. To quantify the percentage bolls with internal damage bolls which are approximately 12 days of age ( the diameter of a quarter) should be examined. Bolls of this age can be squashed easily in the palm of your hand. It is important that bolls of this age (soft) are selected. Bolls are considered damaged if stained lint is observed or a warty growth is present on the inner surface of the boll wall. Our recommended economic threshold using internal boll damage is when 20% of medium sized bolls display internal signs of stink bug feeding and stink bugs are observed in the field. A second method for scouting stink bugs is to sample stink bugs with a drop cloth. The cloth should be carefully placed between two rows so as not to disturb the bugs and then the plants shaken vigorously to dislodge stink bugs. At each stop shake three feet of row on two adjacent rows. Report the number of stink bugs as the average per six row feet. Our recommended economic threshold when a drop cloth is used is 1 stink bug per 6 row feet.

Tobacco Budworm and Corn Earworm: Scouts are reporting observations of both tobacco budworm (TBW) and corn earworm (CEW) moths in the field. We typically would expect TBW to be the predominant species of the two in southwest Georgia and expect CEW numbers to increase in mid-July. Corn earworm is generally the predominant species during July in east Georgia. To date egg and small larvae counts are low but this could change in a matter of days. Bt cotton should provide excellent control to TBW, but supplemental insecticides may be needed for control of CEW. As CEW numbers increase it is important that scouts examine blooms and bloom-tagged bolls for eggs and larvae (be sure to look under bloom tags for larvae). Historically a high percentage of CEW escapes on Bt cotton have been found in the middle part of the canopy associated with bloom-tagged bolls or blooms. Scouts should examine at least one bloom, one bloom tagged boll, and a boll lower in the canopy after searching the top third of the plant on cotton that is in bloom.

Beneficial Numbers Good: We are still observing good numbers of beneficials. When estimating beneficials, scouts should be especially observant for big-eyed bugs and minute pirate bugs which are two of our more important predators.

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