Cotton Insect Newsletter Vol. 20, No. 10, July 24, 2002 Call 1-877-629-1474 for Cotton Insect Hotline

Cotton Situation:  It's looking a lot like rain as I write this letter.  In fact, we were thinking about spraying an insect control test, and decided to wait for a day or two.  It's going to take a large amount of rain to break this drought that has so severely impacted the production of crops in the Southeast.  The Crop and Weather Report put together by our State Statistician for the week ending July 21 declared that only 18% of the cotton crop was considered to be in good condition--67% was fair, 12% poor and 3% very poor.  Although North Carolina is currently experiencing serious drought conditions, the condition of their crop sounded better than ours--they stated that 4% of their cotton crop was in excellent condition, 50% was good, and 41% fair.  Only 5% was classified as poor or very poor.  Georgia reported 11% of the cotton crop in excellent condition, 41% good, 35% fair and 13% poor to very poor.   Insect Situation:  There are still plenty of bollworms and bollworm eggs in cotton this week.  This has probably been the heaviest moth flight that we have experienced above the lakes for several years.  Still, there are fields of cotton that seem to have “dodged the bullet,” even some conventional fields that haven't had any serious problems.     Most of you are aware now that we advise spraying Bt cotton when you have 75 eggs or 30 small worms (< 1/4 inch in length) per 100 plants during the initial moth flight in July.   You can count on the Bt toxin killing nearly 100% of the budworms, but bollworm control may only be in the range of 75 to 90%.  Usually the July infestations will be comprised of 80 to 95% bollworms.  If we assume that natural causes might get about 30% of the 70 eggs, that would leave about 50.  If you get 75 to 90% control of the worms that hatched out with the Bt toxin, then you still have 5-10 worms that might potentially penetrate small bolls.  From this scenario, you could easily end up with 3 large worms, which is the threshold for both Bt and conventional cotton.  Now if you have the luxury of a scout that can come back in a field within a couple of days and can look to see if there are large worms in dried blooms or in tips of small bolls, then a farmer might want to wait and see.  Also you have to go somewhat on experience.  Has bloom-tagged boll damage been a problem before?  Perhaps you have been seeing high egg numbers, but no worms, and very few escapes.  You may want to adopt a more liberal approach and wait for 3 large worms and 5% damage.   But how far down the road should we go with this threshold?  Surely, you wouldn't want to use an egg threshold in mid August in a cotton field where the plants had blooms in the tops.   Of course it would be unlikely that such a field would attract enough moths to lay that many eggs, but with insects, anything could happen.   It would be a waste of money to spray such a Bt-cotton field in the middle of August just because you found 75 eggs or 30 small worms.  There wouldn't be many 1st instar bollworms that could make it to 2nd instars under such conditions.  In other words, a lower percentage of the worm would survive than would be the case where cotton plants had several nodes above white blooms.  Now if you were to find 7 or 8 large worms (> than 1/4 inch in length), a treatment might be beneficial.    Beet armyworm egg masses were showing up in some field this week.  The moths will generally lay their eggs on the undersides of leaves in the upper 1/3 of the plants.   Fall armyworms tend to lay egg masses that are very similar in appearance to BAW’s in the middle 1/3 of the plants.   Moths of both species lay egg masses with an average of 80 or more eggs per mass, which are covered with scales that the females remove from their own bodies. Infestations of aphids appear to be hanging on in some fields although the fungus has been showing up all across the state during the last three weeks.   I saw more evidence of parasitism by a wasp called Lysiphlebus testaceipes this week.  The aphid “mummies” will appear enlarged and tan in color.  The wasp lays its eggs within the body of an aphid and when the larvae has digested enough of the vital organs of the aphid, it will die.  The larvae then pupates, and a few days later a wasp emerges through an exit hole cut along the back of the aphid mummy. Keep an eye out for leaf-footed bugs on cotton bolls.  They are dark brown in color, 1/2 inch in length and have leaf-like projections on the hind legs.  I saw a few of them on small bolls this week and when the bolls were opened, the carpal walls had been penetrated and warts had already formed.  The damage will look just like what you would expect from stink bugs, which seem to be increasing in cotton fields this week.      Boll Weevil Traps:  Keep an eye out this week for fields that have no pheromone traps around them.  It's the time of year that boll weevils start moving, and in the event that an infestation were to occur, it would be extremely important that the pheromone traps were there to capture some of them before they could make their way to overwintering sites.  If a field were not trapped, it is quite possible that an infestation could occur, and weevils could be spread over a much larger area.  Next spring, the boll weevils could become established in more fields before any would be captured during the July trap run.   I also see a lot of traps that have been destroyed by equipment.   Please impress upon your workers the importance of the pheromone traps in keeping South Carolina free of boll weevils.  We were weevil free last year, and with your help, we can do it again.   Error in last week's newsletter:  Double Threat is an insecticide that combines Capture and Tracer, not Fury and Tracer.   Mitchell Roof  Extension Entomologist

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