Cotton Insect Newsletter Vol. 19, No. 10, July 18, 2001 Call 1-877-629-1474 for Cotton Insect Hotline

Cotton Situation:  Believe it or not, some of this early-planted cotton has just about reached the end of the line--cutout.  I have cotton planted May 1 that has 3-5 nodes above white bloom.  Cotton planted the middle of April in lighter soil has blooms in the top.  The plants were under some drought stress in May and early June, but since then they have received a fairly good supply of rain.  Plants are a little on the short side, however, a high percentage of fruiting positions are filled.  I looked at several fields in Lee, Darlington and Williamsburg County yesterday.  Some plants were starting to show signs of stress from lack of moisture, but in general the crop was still looking good.  The July 16 edition of the South Carolina Weekly Weather and Crop Bulletin characterized the condition of the cotton crop as 3% poor, 26% fair, 62% good and 9% excellent.  They indicated that 22% of the crop had set bolls compared with a 5-year average of 31%. Insect Situation:  Bollworm egg counts were on the way up the Hampton County area on Saturday.   Over the weekend, egg counts of 20-25 per 100 plants were showing up in some fields below the lakes and I'm sure they are even higher now.  There were a few fields above the lakes with increases in egg counts, but as of Tuesday, July 17, there had not been much increase in activity here at the PDREC.   The numbers of bollworm moths caught in pheromone traps in the Pee Dee area had increased slightly.  When 13 bollworm moth traps were checked on July 16 and 17, an average of about 6 moths per trap (4-day period) were found.  This doesn't sound like a lot of moths, but it does represent a 4- to 5-fold increase over the previous week's catch.  Scouts should be checking cotton fields on a twice-per-week basis or at least a 5-day cycle now.  If you scout on a 7-day cycle, you can easily be there one or two days too late.  For example, a field was checked on Wednesday afternoon and the egg count was 5/100 plants.  Since this is below the economic threshold in both Bt and conventional cotton varieties, you wouldn't be too concerned about applying an insecticide.  Now, let's suppose that moths really begin moving into that same cotton field during the next couple of days.  Egg counts went up dramatically and, if the field had been scouted on Saturday or Sunday, there would have been 80-100 eggs/100 plants.  The farmer would have been alerted and an insecticide treatment could have been applied based upon egg numbers.  In Bt-cotton 75 eggs would have triggered an application, and in conventional cotton 25 eggs would have been a trigger.  Unfortunately, in this story the scout did not return until the following Wednesday.  Eggs laid on Wednesday and Thursday nights had already hatched (it takes only about 3 days in July) and  there were 3- to 4-day old worms chomping away in terminals and squares in conventional cotton and in blooms and small bolls in the Bt-cotton.  The farmer was alerted, but was unable to treat that day, so it was the following Thursday before the sprayer entered the field.  By then, 1/4-1/2 inch worms were feeding under bloom tags, in large squares and in small bolls.  A pyrethroid insecticide applied at a moderately high rate failed to rescue the cotton crop from the large bollworms--50-60% control was not enough.  Another pyrethroid application was not enough.  By then, the large worms had penetrated 15-20% of the bolls, and the farmer was beginning to think that pyrethroid resistance was showing up.  His third application with a non-pyrethroid insecticide seemed to do the job, as the most of the large worms were gone.  Actually, they had pupated in the soil and there was already another flush of eggs and small worms coming on.  If this story sounds familiar, you may want to reconsider the way your scouting program operates.  With pyrethroid-resistant bollworms showing up in South Carolina, it has become more important than ever to be timely with treatments.  We just don't get the residual activity that we used to get with pyrethroids, so we need to hit the bollworm in the eggs stage or as first-instar larvae.  A 7-day scouting cycle may get you by in some fields, but it will eventually hurt you in others.   Like anything else that you do with more intensity, it will cost more money, but it will be money well spent. Cotton aphids are being devastated by the fungus Neozygites fresenii throughout the state.  Hopefully, the onslaught of this disease will save you the expense of an insecticide treatment.  I first reported that the fungus had shown up in two fields when aphids were collected on July 3.  Of the four fields checked that day, one field had 4% of the aphids infected and the other had 10% infected.  Last week, the fungus was showing up in all four fields in Lee, Darlington and Williamsburg Counties.  When I collected aphids from the same field yesterday, it was hard to find live aphids.  In other words, aphid populations in all four fields had crashed.  The plants in the Williamsburg-County field had really begun to grow out of the aphid infestation and were no longer showing many wilted, yellowed leaves. I saw only one field yesterday that had economic damage from stink bugs (green and brown), and it was a field with some 18-day old bolls.  A few green stink bugs were found in other fields which had just begun to bloom, but no damage could be found.  If you don't have quarter-sized bolls, it's pretty hard to assess damage.  Stink bugs will penetrate and feed upon smaller bolls, and it's quite possible for the small bolls to be aborted.  Our threshold is based upon % damage in quarter-sized bolls.  When you find 15% damage, then an insecticide treatment is recommended.  Boll Weevils:  All traps should be up now.  If you find a field without traps, please report it by calling 1-800-269-9928.   Mitchell Roof  Extension Entomologist

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