Cotton Insect Newsletter Vol. 18, No. 11,  August 2, 2000 call 1-877-629-1474 for Cotton Insect Hotline

Cotton Situation: Later-planted cotton is looking good this week.   Much of the early-planted cotton has bloomed out the top, or soon will be.  Most areas of the state have received some needed rainfall during the last couple of weeks.  According to the “South Carolina Weekly Crop-Weather Report,” soil moisture ratings across the state improved slightly over the previous week to 8% very short, 46% short, 45% adequate and 1% surplus.   The overall condition of the cotton crop was judged to be 13% poor to very poor, 39% fair, 46% good and 2% excellent.  Cotton plants appear to be setting bolls 10% faster than their 1999 counterparts.  Insect Situation: We are still getting some bollworm moths visiting cotton fields here at the PDREC.   Numbers have been running from 10 to 30 per 100 plants this week, with a fairly large percentage of the eggs being laid directly on the bloom tags.  In the Savannah Valley, Mike Sullivan said that egg counts in most fields were running about 20 per 100.  One field of Bt cotton had close to 80 eggs per 100 plants.  They are still catching high numbers of bollworm moths.  Aphid numbers have been declining due to the fungus for the past couple of week, although aphid populations appear to be rebuilding somewhat in a few fields.  Stink bugs are going to be playing their games for the next several weeks.  In fields that have not been treated, keep a real sharp eye out for their damage.   I didn’t hear much about beet armyworms during the past week, but there were more sightings of fall armyworms.   Now that armyworms are showing up in cotton, it may be as good a time as any to review some information about the biology of these insects and scouting techniques.  Let’s start with beet armyworm.  This insect is not thought to overwinter in South Carolina, although we have found that pheromone traps capture moths as early as February and March.   Furthermore, larvae are often found in cotton as early as May.   So, it may well be that some beets overwinter here during mild winters.  We know that many moths make there way to South Carolina after going through a few generations further south.   There is little doubt about fall armyworms, they only overwinter in Florida and South Texas and the coastal regions of a few other southern states.   We generally never see these insects in cotton before the month of July.  In fact, it was about the middle of July before I heard any reports of fall armyworms this year.  Moths of both armyworm species lay their eggs in masses of up to 150, which they cover with scales from their bodies appearing as a whitish or grayish fuzz.   BAW moths tend to deposit their eggs on the undersides of leaves in the upper part of a cotton plant, while FAW moths deposit their eggs on the undersides of more mature leaves on the lower half of a plant.   You can’t look at an egg mass and tell if it is a beet or a fall, but if you are finding more in the upper portions of the plants they are probably beets.  If you are finding nothing but eggs, it won’t be long before the larvae tell you which species is nibbling on the cotton.  BAW’s will stay together and feed on the underside of the leaf where the eggs were  placed, whereas FAW’s split up soon after hatching, preferring to “dine alone.” When the tiny BAW’s feed on the underside of a leaf, there will be a brown spot about the size of a quarter on the upper leaf surface.  This is referred to as a BAW hit, and it will be the first feeding symptom to be observed by an observant scout.   Later, the larger worms disperse and eat more and more leaf material.  Leaves become net-veined in appearance and eventually the larvae will feed through the leaves.   Whenever a plant has evidence of leaf feeding by beet armyworms it would be counted as a hit.  Beets like to feed on square and boll bracts as well as blooms.  Generally, we do not see them feeding directly into a square or boll, although this has been observed.   To scout for BAW eggs, just bend the plant terminals over and look on the undersides of the leaves.  You can do this on the same plants that you scout for bollworms.   We don’t have a threshold as such, however 5 egg masses per 100 plants is considered to be cause for alarm.  Scouting for larvae is much easier.   Just examine plants on 100 feet of row in five different parts of a field and determine the average number of hits.  Control would be justified for 5 or more hits per 100 feet of row. FAW larvae are often mistaken for bollworms and even BAW’s in their earlier stages of growth.   The BAW will generally have a small black dot on the sides over the middle pair of true legs, while a FAW may have a similar dot on the sides of the first abdominal segment.   Unlike bollworms and BAW’s, FAW’s have three thin, white lines extending along the back from just behind the head capsule along the length of the body.   The head capsules of early instars of the FAW tend to be darker in color than bollworm or BAW.  Look for the etching marks of small FAW larvae feeding on the bracts of bolls and squares.  Larger ones will feed directly into bolls in a similar fashion to the bollworm, and they may often be seen resting in blooms.  The threshold for FAW is 10 or more worms 3/4" in length.   Boll Weevil Containment: I chatted with Randal Lynch this morning to see if they had found any boll weevils yet, and they had not.  He indicated that they were still finding some cotton fields that had not been reported.  This is a potentially dangerous situation.  If a stray weevil found her way to one of those fields and started raising a family there could be a real problem.  Her offspring might even make it to overwintering sites without being detected.  Then, after overwintering, they could infest next year’s cotton and go through 2 or 3 generations before being detected by pheromone traps.  If you see a field without traps call 1-800-269-9928 and report it.  Also, make sure trappers have access to your fields.  They are still encountering problems with locked gates.  Mitchell Roof  Extension Entomologist

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