Cotton Insect Newsletter Vol. 22, No. 7, June 30, 2004

Cotton Situation: Since my last newsletter thunderstorms have been widespread, and they appear to be staying around for the next week or so.  The crop has responded well to the increased moisture and appears to be off to a very good start.  Ratings for the cotton crop for the week ending June 27 were 3% poor, 29% fair, 65% good and 3% excellent, according to the “SC Crop and Weather Report”.  At least 75% of the cotton crop is squaring and 10-15% will be setting bolls by the end of the week.  Insect Situation:  Fran reported seeing fairly high numbers of bollworm moths in cotton plots here at the PDREC this week.   Budworm moths are scarce and do not appear to be a factor even in conventional cotton at this time.  As you all know, however, conditions vary between different areas of the state and it's still possible to have budworm problems in fields planted with non-Bt seed. Aphids are building up in high numbers in some fields this week.  We are seeing more beneficials, such as lady beetles, that have been attracted to cotton fields to feed on aphids.   I refer to one of these lady beetle species as the “false mealy bug”. They really aren't mealy bugs, but are instead the nymphs of small, dark-brown lady beetles of the genus Scymnus.  The white, waxy covering can be scraped away to reveal the small nymphs that are shaped similarly to their larger cousins.   These insects will usually be found in association with aphids, which they love to eat.  Scouts should also see some parasitized aphids.  They may not see the tiny, black, Lysiphlebus wasps, but they should see the parasitized aphids.  Affected aphids will be tan colored and much larger than the normal aphids.  These parasitized aphids are called “mummies”.  They become mummified after the parasitic larvae have consumed their vital organs.  About 2 weeks after a female wasp laid her egg within the body of an aphid host, the new adult wasp cuts through the upper surface of the mummy, leaving a circular hole.   This parasite is not as effective in killing aphids as the fungus, Neozygites fresenii, but it does add to the death toll.  Brown stink bugs are more numerous than usual in cotton.   They are infesting cotton fields that have not started blooming.  We don't know of any damage they do to pre-squaring cotton, so maybe they are just setting there waiting for the bolls to show up.   Last year, brown stink bugs were more numerous in cotton in June and July, but by August the green and southern-green stink bugs were “out-bugging” them in some fields.  There are still some grasshoppers in cotton this week.  For the most part, infestations of grasshoppers are not high enough to cause problems in cotton.  They are doing some foliage feeding, but the rapidly growing plants are not being hurt. Japanese beetles are also hitting cotton field in fairly high numbers in Darlington, Dillon, Florence, Marion and Marlboro counties.  I would not expect to see any economic damage from these insects, although they can look rather intimidating in small areas of fields. New Insecticide:  Crompton Corporation/Uniroyal Chemical has announced that EPA has approved a new insecticide for cotton.  The new product is called Diamond, and it has been registered to control plant bugs, stink bugs, bollworm/budworm and foliage feeders.  This material interferes with synthesis of chitin, which is a component of the insect exoskeleton.  Larvae/nymphs are unable to molt and develop to the next stages.  It is active only on immatures and should not be used for control of adults. I have looked at Diamond for the last few years on conventional cotton.  It has performed moderately well on bollworms under medium pressure at the 12 oz rate.  It needs to be applied before hatch out, or if worms are present, they should be less than 1/4 inch long.  It should perform fairly well on fall armyworms, beet armyworms, and soybean loopers.   If immatures are the main targets, Diamond will control plant bugs and stink bugs, however, don't expect to take out adult populations. Diamond will provide at least 14 days residual activity and it is rain fast on plant tissue.  It is easy on mammals, birds, and beneficial insects; including bees.    Mitchell Roof  Extension Entomologist

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