Cotton Insect Newsletter Vol. 21, No. 13, August 13, 2003 Call 1-877-629-1474 for Cotton Insect Hotline

Cotton Situation:  Most of the crop is setting bolls now.  More and more fields are now showing blooms all the way to the tops of the plants.  In the latest-planted cotton fields, there are only a couple of good weeks left for setting bolls that will contribute much to harvest.  Soil moisture has been adequate throughout most of this crop year.  Now we could certainly use some bright sunny days!  Cloudy days cut down on the rate of plant photosynthesis, therefore the supply of  carbohydrates available for small bolls will also be reduced.  Since the more mature fruit is first in line to be fed, the small bolls will suffer and some will be shed.  There is also an abundance of vegetative growth in some fields, so carbohydrates that could have been put into fruit production will end up in leaves and stems.  Another potential problem associated with rank growth is boll rot.  The warm, damp and shady conditions that flourish in the canopies of rank fields will definitely promote the fungi and bacteria that cause boll rot.  Insects are also an important factor in the equation.  A few years ago, Dr. Bruce Martin and I looked at boll rot in relation to insect damage.  Of the bolls affected by boll rot, most were also damaged by insects.  When insect pests eat through the protective covering afforded by the carpal wall, they provide an open door for microorganisms.  Some insects may actually reduce the incidence of boll rot.  Dr. Phil Roberts, who is an Extension Entomologist, recently reported that they were finding several fields infested with soybean loopers in Georgia.  These insects may feed extensively on lower leaves, thereby increasing the flow of air and sunlight to the bolls that are most susceptible to disease.  When these insects feed on leaves subtending bolls that are still developing, it's not a good thing.  The full-service pest manager must take all of these factors into account when deciding whether or not to spray for loopers or other defoliators. Insect Situations: The Hel ID tests conducted by Candy Roach continue to show that a high percentage of larvae in cotton have been tobacco budworms.  A field in Darlington County was 36% and on into Dillon County was 27% budworms.  I don't know where the moths are hiding because we are still not seeing moths in the fields and the pheromone traps aren't catching many.  I checked larvae that came from some fields where there were control problems on Tuesday.  Fields in Williamsburg County were 40% budworms, and in Dillon County I found 67% budworms.  There were also a couple of fall armyworms from the Dillon County field.  Worms have been surviving up to 3 or 4 pyrethroid applications--most at medium to medium-high rates.  One grower also applied Tracer after pyrethroids and came back again with pyrethroids, but he was still having control problems.  On Tuesday, I had several calls concerning problems controlling worms.  I can't help but think that rains have been implicated in some of the failures.  There also could be problems of obtaining adequate coverage in some fields that have gone a little rank.  Budworms are a somewhat harder to control anyway, and there might even be some resistance involved.  We are in the process of getting some pyrethroid-treated vials to run a few resistance tests.  How are we going to control these worms?  If budworms are the problem, it would make sense to switch to Tracer or Steward (if you can get it).  At National Cotton Pest Management Seminars held from 1999 to 2002, the entomologists rated Tracer as the standard for control of budworms.  Steward was rated as equal to Tracer while Larvin and Denim were rated fair.  As you would expect, Bollgard cotton was rated standard+, since it controls close to 100% of budworms.  But be they bollworms or be they budworms, when they get to be 3/4 to 1 ½ inches long, you aren't going to kill too many.  As I mentioned earlier, there is also a possibility of some fall armyworms winding up in the mix of worms on cotton.  Small ones can easily be confused with bollworms, but by the time they are a half inch or better in size, they can be distinguished by the three thin white lines that run from just behind the head to the tail.  You will also notice the skin is quite smooth and often more grayish in color compared to the bollworm which is much more hairy and variable in color.  With fall armyworms, we don't have any real good insecticides although we have heard of some decent results at times with Tracer, Steward, Denim and Intrepid.  Although I don't have any first-hand experience, I have heard that Intrepid does well against FAW when applied in combination with pyrethroids.  By the way, the plant-back restriction has been lifted from Intrepid and you can plant soybeans, corn and wheat the year following its usage.  The stink bugs seem to be turning green.  Not really, but it may appear that way.  Here at the PDREC, we are seeing a lot more green stink bugs moving into fields and the browns may be moving out or moving over to soybeans.  Species determinations will affect the way you spray your cotton.  The pyrethroids, Bidrin or methyl parathion should do a good job on greens and southern greens.  Pyrethroids alone won't do much better than 40-50% on browns, so if you are just going after browns, use 6-8 ounces of Bidrin or 12 ounces of Orthene.  You can cut the Bidrin rate to 4-5 ounces when applying it with a pyrethroid for bollworm control.  You do not have to mix Bidrin with a pyrethroid to control stink bugs, it is a good material by itself.    Mitchell Roof  Extension Entomologist

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