Cotton Insect Newsletter Vol. 20, No. 14, August 21, 2002 Call 1-877-629-1474 for Cotton Insect Hotline

COTTON SITUATION: Much of the cotton crop in South Carolina is showing severe signs of moisture stress at this time.   Rain will be needed in a hurry to get some of the later maturing cotton back on track.   Many fields are now littered with small squares and bolls that have been aborted due to high temperatures and dry soil conditions.  According to South Carolina Agricultural Statistics, the expected yield is now 504 pounds per acre; down 182 pounds from last year.  INSECT SITUATION: The bollworm flight is continuing to bring fairly heavy egg lays in some of the more robust cotton.  Where cotton has reached cutout, plants should no longer be as desirable to the moths that are searching for the best places to deposit eggs.  A small worm, hatching from an egg deposited on an old leaf with no small squares in reach, will have little chance of surviving.  Also, egg mortality often occurs at higher rates this time of year.  A tiny parasitic wasp called Trichograma will lay its own egg within a bollworm egg.  As the wasp develops, the egg turns black and is killed.   From here on out, let bollworm counts and square or boll damage determine the need to apply insecticides for control--not eggs.  Also, don't forget to consider the yield potential of the crop and the cost of the chemical when debating the need to make an application.  If you are spending $7 to $10 per acre to control an insect, you need to have a reasonably good chance of getting your money’s worth.   For example, if your proposed treatment may only protect a few “iffy bolls” in the tops of the plants, you would be hard pressed to pay for treating 3 worms and/or 5% square damage.  You could probably triple or even quadruple this threshold under such conditions.  On the other hand, 3 worms and/or 5% square damage in actively fruiting cotton planted on June 1 would more than likely warrant a treatment because you would be protecting the meat of the crop, the lower and middle bolls.  This same argument can be made concerning armyworms and other insect pests. Speaking of armyworms, the beet armyworm continues to rear its ugly head in many areas of the state.   The hot, dry conditions and open canopies in cotton fields have been ideal for the establishment of this insect.  Now they are being joined by cabbage loopers and soybean loopers in some areas.  Throw in a few fall armyworms and an occasional bollworm and you have a very wormy situation.  Thank goodness, we now have materials like Intrepid, Tracer and Steward that will provide pretty good control of most of these species. Soybean loopers have shown up in fairly large numbers in some fields.  These are the loopers often referred to as the “black-footed loopers.”  It's true that soybean loopers frequently have black legs, but not always.  Cabbage loopers, on the other hand, will always have green legs.  The two species are often found in mixed populations.  Cabbage loopers are fairly easy to control with pyrethroids, but soybean loopers are resistant to the pyrethroid insecticides. Both soybean and cabbage looper moths lay white eggs one at a time on the undersides of cotton leaves.  Their eggs are slightly larger than bollworm eggs and somewhat flattened in appearance.  The green-colored soybean loopers have only two pairs of abdominal prolegs, so they walk with a looping motion.  They are strictly leaf feeders, often defoliating cotton from the bottom up.  This sometimes is not so bad in cotton where you are ready for this to happen, but if you still need those leaves to make a crop, it can be devastating.   In a cotton field where I saw the loopers yesterday, they were actually feeding mostly on the top leaves, because the lower leaves were either falling off, or were badly wilted.   Whiteflies are showing up in many fields.  I have not yet seen what I would call an economic infestation, but they still need to be watched.  Whiteflies excrete a sugary substance (honey dew) that creates problems when it falls on exposed lint. BOLL WEEVIL CONTAINMENT:  I wish to caution growers once again to please communicate to farm workers the importance of the boll weevil traps.  Downed traps need to be set up.  Destroyed traps need to be replaced.  All fields should now have some traps around them.  If you have problems notify Randal Lynch at 1/800-269-9928. END OF NEWSLETTER SEASON: This will be the last regularly scheduled newsletter of the season.  You may continue to get information on “Cotton Insect Blurbs” or by calling the Cotton Insect Hotline number shown in the header.    Mitchell Roof  Extension Entomologist

This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. Brand names of pesticides are given as a convenience and are neither an endorsement nor guarantee of the product nor a suggestion that similar products are not effective. Use pesticides only according to the directions on the label. Follow all directions, precautions and restrictions that are listed. The Clemson University Cooperative Extension Service offers its programs to people of all ages, regardless of race, color, sex, religion, national origin, disability, political beliefs, sexual orientation, marital or family status and is an equal opportunity employer.  Clemson University Cooperating with U.S. Department of Agriculture and South Carolina Counties.  Issued in Furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of May 8 and June 30, 1914.  Public Service Activities