Cotton News Letter Vol. 18, No. 5, June 21, 2000

Cotton Situation:  There are areas of South Carolina, mostly below the lakes, that are still struggling with a severe drought.  The SC Weekly Weather and Crop Bulletin reported moisture deficits from January 1 ranging from about 4 inches to as much as 12 inches.  If the state were to receive adequate rainfall from here on out, much of the cotton could still produce abundant yields.  There are plenty of fields, however, with poor stands and drought-stunted plants where farmers are  going to be forced to give it up.  The intended acreage reported to FSA was over 340,000 acres, but now it looks like farmers will be hard pressed to come up with 300,000 acres for harvest.  About 50% of the cotton crop is squaring, with the older cotton getting close to bloom.  A pinhead square will develop into a white bloom in about 21 days.  The first few weeks of squaring are a critical period in the life of a cotton plant.  The squaring rate should increase about 11/2 to 21/2 fold through the fourth week of squaring.  By the fifth or sixth week the rate should begin to level off, and will drop sharply between the seventh and ninth week. Insect Situation:  We have seen some activity by both budworm and bollworm this week.  Egg counts have generally been in the range of 10 to 50, with a few reports of up to 20 or more small worms in conventional cotton varieties.  Plant bugs have been reported in a few fields, but I haven't heard any reports of economic damage.   Beneficial counts are good in most unsprayed fields, with big eyed bugs, fire ants, minute pirate bugs and lady beetles as the predominate species. The following discourse will apply mostly to bollworm,(Helicoverpa zea), but the developmental cycles of the two species are about the same.   Host plants may differ somewhat.  For example, budworm (Heliothis virescens) moths are not attracted to corn like bollworm moths.  And it's primarily the budworm infesting tobacco.  There are also differences in their preferences for wild host plants.   Also remember that the bollworm is the same insect as the corn earworm that is found in corn.  The bollworm overwinters as a pupa in the soil, so after it warms up in the spring the adults emerge and lay eggs in April and May.  This first generation will usually occur on corn and some wild species of plants.  What we have now in corn (earworm), cotton and tobacco (principally the tobacco budworm) is the second generation.  In July, it will be the third generation (primarily bollworm) infesting cotton and then soybeans.  A fourth generation of bollworms will occur in August, and a fifth generation will occur in September.  Bollworm moths are currently being attracted in a big way to corn that is tasseling.  Eggs are laid on the silks and small worms begin feeding on the silks and gradually eat there way down to the developing kernels.  In the corn fields that I have checked this  week, less than 25% of the ears had any damage from corn earworm (bollworm).  If numbers of corn earworms remain low there could be some relief from the bollworm problem in cotton.  From the time the corn earworm moth lays on egg on a cotton terminal it takes about 3 days to hatch and for the tiny first-instar bollworm to begin feeding in the terminals of cotton plants.  The bollworm will actually feed for 14-16 days on terminal growth, squares, blooms and bolls.  When the larva is fully developed it will leave the plant and burrow in the soil to pupate.  After 10-12 days in the soil the moths emerge, mate and begin to lay eggs.  The entire life cycle takes only about 30 days during June, July and August.  When temperatures are cooler, development will proceed at a slower rate, so the process would require more time in May and September.  Five or six generations of bollworms will occur in a typical growing season.  The July generation is the most feared because of the potential of this insect to develop large populations on corn and other hosts prior to infesting cotton. Last year bollworm populations were at extremely low levels throughout most of the southeast U. S. Does that mean we shouldn't worry about them this year?  I'm afraid it's not that simple.  You would think with extremely low numbers going in to the fall and winter of 1999 there would be low numbers  to  overwinter and begin the reproductive spiral in 2000.  However, our pheromone traps have all been capturing bollworm moths during the last couple of weeks.  In fact, these numbers look very similar to the numbers of moths captured in  years prior to 1999.   The bollworm is a survivor.    Pyrethroid resistant bollworms should be on every farmer's mind.  I will be focusing on this in a future newsletter.  We didn't learn much about pyrethroid resistance last year, but you can be sure that it won't just go away.  Please don't even think about applying pyrethroids in June. The tarnished plant bug is showing up in cotton fields throughout the state.  I have heard rumors of a field or two being sprayed, but none that I am personally aware of.   Our economic threshold is one or more plant bugs per row foot when square retention is 75% or less.   Cotton fleahoppers are also plant bugs, so individuals of this species should be counted when scouting for plant bugs.  We recommend using a drop cloth (about 3-ft square) to place between the rows.  Shake all the plants on 3 row feet over the cloth and count adults and nymphs that land directly on the cloth.  Check at least 10 different places in a field and determine numbers of plant bugs per row foot.  Bidrin, Orthene, Provado, Lorsban and dimethoate are recommended for control.  Of these materials, Provado may offer the best protection for beneficials, but it will kill some of them.  If you have a question about whether you may need to treat for plant bugs, I would advise erring on the side of conservation of natural enemies.  We are fast approaching the time when beneficials will be an important factor in preventing economic damage from bollworm in Bt cotton. Hotline: Remember that we have a Cotton Insect Hotline now sponsored by the SC Cotton Board.  It was down last Friday and Monday, but should be functioning for the remainder of the season.   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.