Cotton News Letter Vol. 18, No. 6,  June 28, 2000

Cotton Situation:  There have been some more general rain showers during the last couple of weeks, but some areas of the state remain extremely dry.  Where moisture has been adequate, cotton is growing well and squaring freely in most fields.  Randy Cubbage said that he received a report of blooms last week, and my scouts found the first blooms here at the PDREC last Monday in some cotton planted April 15.  As cotton begins to bloom, the moisture requirements will be increasing up to about 0.25 inch per day.    Insect Situation:  Bollworm and budworm moth counts have been lower in most areas this week.  Egg counts are also down.  In conventional cotton, there have been a few larvae in terminals, but most reports have indicated that numbers have been sub economic.  Bt cotton has been clean, with nothing much happening besides the buildup of beneficial insects and spiders.  Our beet armyworm traps captured more moths this week than the previous week, but the average was only about 3 moths per trap for a week's time.  My scouts found a few beet armyworm egg masses on cotton plants here at the station.  It's too early for any economic problems from beets in cotton.  Most of our economically important infestations will occur in August and September.  A few aphids were found this week on some scattered plants.  Tarnished plant bug numbers have been low in the Savannah Valley area according to Mike Sullivan.  We have also seen very few plant bugs in the Pee Dee area.  The biggest problem now could be the misidentification of false chinch bugs as plant bugs.   In the past, there have been cases where these critters were assumed to be plant bugs, because of their general appearance and because they were sometimes found in squares.  They are actually members of the lygaeid family, which includes the true chinch bug (not found in cotton) and the big-eyed bug.   Of course, the big-eyed bug is a predator and it has a head much wider than the FCB.  Tarnished plant bugs (mirid family) are a brownish color with yellow markings, and FCBs are gray in color and more narrow bodied than TPBs.  False chinch bugs may be found crawling all over squaring cotton plants, but they do not cause economic damage. Stink bug activity will be picking up in cotton once it begins to bloom.  Scouts should begin sampling small bolls to determine if there is stink bug damage during the first week in July.  Last year, when boll samples were taken from fields throughout the state, there appeared to be much more stink bug damage than would have been predicted based upon scouting reports.  During the Ag Expo, we discussed our thresholds in a group that included Extension and research entomologists and private consultants.  We agreed that scouting for stink bugs by shaking the plants on a beat cloth laid on the ground had not done a good enough job of detecting potential problems.  Last year, the threshold of 1 stink bug per 6-row feet of cotton, or 20% damaged small bolls, was used as the treatment threshold.  Those of us who reviewed this threshold agreed that we needed to concentrate more on damaged bolls.  There was also some discussion about lowering the damage threshold.  After consulting with other entomologists and looking at research data gathered by Dr. Jeremy Greene when he worked at the Edisto REC, the threshold for damaged bolls was reduced to 15%.  In scouting for stink bug damage, one should select at a random sample of at least 25 bolls.  Make sure that the bolls are all similar in size with a diameter close to that of a quarter.  Each time that you check a field, select the same sized bolls.  If you looked at larger bolls the next week, you might be assessing some of the same damage that occurred the previous week, and it wouldn't tell you what had happened more recently.  Open the bolls by squeezing between your thumb and forefinger, then examine the inner linings of the bolls and look for penetration points or warty growths that would signify stink bug damage.  Before making a treatment decision based upon the percent damaged bolls, I would certainly expect to at least see some stink bugs as well.      Pyrethroid Resistance Management:  I believe most farmers are now aware of the importance of staying away from pyrethroids in June.  We have found pyrethroid-resistant bollworms and budworms in South Carolina.  When these insects build up to economic levels in June and you apply a pyrethroid insecticide to a field, it's somewhat like throwing gasoline on a fire.  Although you would be killing the majority of the worms, you would be subjecting them to more selection pressure to develop resistance.  With most of the susceptible bollworms gone, the few resistant female bollworms would become adults, and they would have a good chance of pairing with resistant male moths thereby producing resistant offspring.  If the field were treated with Tracer or Larvin, however, there would be more pyrethroid-susceptible moths to mate with the few resistant ones, and the offspring would most likely be susceptible.  We are assuming that resistance is a recessive character and, when resistant and susceptible moths mate, the offspring is also susceptible.  This is an oversimplification, but I'm just trying to explain why it's so important to minimize selection pressure for resistance.  Larvin and Tracer are Resistance Management Tools:  Unfortunately, Tracer was left out of the recommendations in IC-97 for control of budworm and bollworm larvae at mid season.  Tracer is a very important insecticide for us, since we have documented cases of pyrethroid resistance in both bollworm and budworm.  Either Larvin and Tracer should be used at this time in situations where control problems have been experienced with pyrethroids, and resistance is suspected in both conventional and Bt cottons.  The suggested rates are Tracer @ 2.2 oz/acre or Larvin @ 24 oz/acre. 2000 Pest Management Handbook:  The omission of Tracer from IC-97 brings up an important point.  The latest Cotton Insect Control Recommendations are available on the internet.  If you have questions about any recommendation for insecticides, herbicides or fungicides in field crops and elsewhere, just check this web site: http://cufan.clemson.edu/pestmgmtguide/.  Anytime I need to update a recommendation, I can do it that day.        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.