Cotton Insect Newsletter Vol. 20, No. 8, July 10, 2002 Call 1-877-629-1474 for Cotton Insect Hotline

Cotton Situation: Much of the cotton crop is hurting from drought stress this week.  In some of the worst areas of the state, you may see fields of 12- to 16-inch cotton plants blooming out the top.  When it starts raining again, these plants will produce a small crop of bottom half bolls, and hopefully, will still have time to build a second crop of bolls in the tops of the plants.   One of the worst things about this scenario is that having such a time lag between the two crops will prevent a “once-over-harvest.”  Also, the differences in maturity between the two crops of bolls will cause some problems in timing applications of defoliants.    Insect Situation: Tommy Walker called on Monday and indicated that he had found a field in the Lena area of Hampton County where there were up to 100 bollworm eggs/100 plants, and 20 small worms.   James Thomas reported finding 15 eggs and 10 or more small worms per 100 plants in the Hunter's Chapel area of Bamberg County.  Reports from Lee and Sumter County indicated that bollworm egg counts were up in some fields, and there were enough small worms in a few fields of conventional cotton to begin spraying.  It appears that infestations are spotty right now, but this generation is coming on a little earlier than expected.   I was in Marlboro and Darlington Counties on Tuesday and checked a number of cotton fields.  I didn't see many eggs or small worms, but from the number of bollworm moths that I flushed while walking through cotton fields, the egg business will be picking up very shortly.   The female bollworm moth is tan in color and about an inch in length.  Budworm moths are slightly smaller and have oblique bands across the front wings. No one has yet devised a threshold for moths, but when you see them when you walk through a field, you can be pretty sure they are going to be laying some eggs.  Every scout is interested in quantifying the numbers of eggs in a field.   It's also a good idea to qualify the eggs as to relative age.  The eggs that are creamy white in color were put there by the moths the previous night.  When they get to the stage where they appear more tan in color, a closer examination will reveal the eggs are in the “red-ring stage,” or in the 2-day old class.  By the third day, eggs will appear grey in color, as the darkened head capsule of the enclosed larva is visible through the egg shell.  Sometime during the third day, the 1st-instar larva will nibble its way through the egg's shell and begins to search for an edible part of the plant.  Terminals are usually very tasty for the young larvae and they can be found there in some of the younger plants.  After plants have begun squaring, the small squares will provide food and protection for the developing larvae.   Larger larvae will eventually start feeding on bolls where they will complete their developmental process.   Larvae will undergo about 5 molts and 6 instars on cotton plants.  The fully grown larvae will move off of the cotton plants and dig into the soil to a depth of 2 inches or more, where pupation occurs.   Inside a pupa, a bollworm becomes an adult moth during a period of 12 to 14 days.  The moth must find its way back out of the hole that was originally dug by the larva, so it is possible that heavy rainfall and standing water would prevent this.  It looks like the moths won't have any trouble getting out of the ground this year.   It takes a few days for mating and egg production to occur, and then the moths start laying their eggs thereby beginning a new generation.  The entire process may occur in as little as 28 days at this time of year.  In cotton plants that are blooming near the top, and even where blooming may have just begun, a fairly large percentage of the eggs are going to be laid down in the middles of the plants.  Stems, blooms, bloom tags, squares, and bolls (and bracts) all may be targeted by the moths.  Scouts need to be looking closely at those parts of the plants, just because you aren't finding eggs in the terminals doesn't necessarily mean there are no eggs there.  It's possible that most of the eggs will be further down on the plants under these hot, dry growing conditions.  Make sure you are familiar with the thresholds for bollworm control in both conventional and Bt cotton, as they are not the same.  In conventional cotton, the egg threshold for this generation of bollworms is 20 eggs per 100 plants.   Controls are also advised for 3 small worms (less than 1/4-inch in length) or 5% damaged squares.  In Bt cotton, a treatment is recommended for 75 eggs or 30 small worms (less than 1/4-inch in length).  Furthermore, a treatment is recommended in Bt cotton when 5% of small bolls are damaged or there are 3 large worms per 100 plants.    Stink bugs are showing up more in cotton now as small bolls are forming.  We have some purple-hulled peas that serves as a trap crop for stink bugs in a test at the PDREC.  I noticed that the numbers of stink bugs have really increased this week as the bean pods have become more desirable.  There were also a number of nymphs that had hatched out during the last few days.  Aphid are still increasing and I'm not seeing many parasites yet, and very little of the fungus.  One aphid sample, which was collected in Hampton County on July 5 by Tommy Walker, had 16% infected with the fungus, but aphids collected in other counties have failed to show evidence of Neozygites. Boll Weevil: I see that most of the pheromone traps are up now, and July 10 was the date they had hoped to complete this task.  Keep an eye out for fields without traps, and if you see one, call the Boll Weevil Office at 1-800-269-9928.  I see some traps being knocked down, so please impress on your workers how important this program is to you.   Mitchell Roof  Extension Entomologist

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