Cotton Insect Newsletter Vol. 22, No. 5, June 16, 2004

Cotton Situation:  There are lots of cotton fields with squaring plants this week.  We haven't seen any general rains for sometime, but at least, there have been scattered showers for the past several days, and these should continue through the weekend.  In the “South Carolina Crop and Weather Report” for the week ending June 13, soil moisture ratings were 8% very short, 34% short, 56% adequate and 2% surplus. Insect Situation:  I have heard several reports of early worms in cotton during the past week.  Eggs and small worms are being found as well as flared squares in non-Bt cotton fields.  More than likely, these are tobacco budworms.  The threshold for treating budworms in non-Bt cotton before first bloom is 15 small larvae or 20% square damage.    Thrips should no longer be a problem in cotton.  Where damage has occurred, it will just take time for the plants to grow out of it.   Cotton fleahoppers appear to be more numerous in cotton fields than we have seen for several years.  These insects are true bugs with piercing, sucking mouthparts, which they use to penetrate and suck juices from terminal buds and pinhead squares.  Scouts should monitor pinhead-square set and estimate the numbers of fleahoppers (and/or tarnished plant bugs) per row foot.  An insecticide treatment may be warranted when 1 or more plant bugs are found per row foot and 25% or more of pinhead squares have been shed.     I'm still getting a few reports of grasshoppers in cotton.  Some farmers have spot-sprayed their fields and have had relatively good success with pyrethroids.  Keep in mind that we could have some hoppers hatching out over the next couple of weeks. Stink bugs have been seen in cotton fields already, although I have never seen them doing any feeding on plants prior to boll set.  It does appear that stink bug numbers are going to be fairly high this year, judging from the numbers seen in corn and on some of their wild host plants. Insecticide Treatments Don't Always Pay:  Insecticides applied to cotton from this point on have the capacity to flare problems with tobacco budworms or bollworms by reducing numbers of beneficials that have found a home on your cotton plants.  That's why it is so important to avoid applying insecticides, unless you are fairly certain that an insect pest is really going to cause economic damage.  In other words: Will the cost of not spraying be more than the cost of applying an insecticide?   For example, there are some late-planted fields where thrips damaged plants are fairly obvious, but plants have five leaves or more.  You would kill some thrips by applying an insecticide, but there would probably be no economic benefit.  The cost of treating would be considerably more than any damage you might avoid by killing thrips.   Furthermore, killing beneficials might allow budworm or bollworm numbers to increase greatly and cause some real economic damage.  Beneficials usually provide a great service to cotton growers in June by keeping worms in check in most cotton fields.  Scouting Bt Cotton: In Bt cotton, there should not be a problem with budworms, since the Bt toxin has proven to be totally effective against them.  We don't usually see cotton bollworm problems either, before plants have begun setting blooms.  I'm not really concerned about bollworms prior to blooming.  When small bollworms feed on squares and terminal buds, the titer of the Bt toxin is usually adequate to kill them.   The blooms and dried bloom tags are the “Achilles heel” of Bt cotton.   When eggs are laid on or near these sites, small bollworms are often able to feed on flower parts until they become large enough to bore their way through the tips of small bolls.  When they go in under the bloom tags, inexperienced scouts will often be unaware of what has happened.  If they fail to look inside purple blooms and under bloom tags, their first inkling of a problem will be when they see the large bollworms coming out of small bolls and attacking larger bolls.     Mitchell Roof  Extension Entomologist

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