Cotton Insect Newsletter Vol. 17, No. 6, June 16, 1999

Cotton Situation      Rain at last!  We had a nice shower here yesterday, but not nearly enough.  By the time you read this, you should have had some relief from the drought.      Cotton will start growing rapidly in response to this moisture.  It has been hanging in there quite well, although the leaves on many plants are somewhat small in relationship to their growth stages.  By this morning, plants here at the PDREC were already looking greener and more vigorous.

Squaring should begin in a large percentage of cotton fields this week.  In this picture, you can see the pointer directed at the first square.  The square is located in the leaf axil (point of attachment of the leaf petiole to the main stem).       By the time plants have produced six true leaves, scouts should begin looking for those first squares.  It’s always good to determine the node where the first squares are formed in each field.  Plants that don’t begin squaring until the ninth node or higher might have had too much nitrogen, or plant populations may be excessive.  It’s always good to have this information available at the end of the season in case a little investigative work is needed to determine what might have gone wrong, or better yet, gone right, to result in such a fantastic yield!       Examine at least 10 plants that are representative of a particular field to determine the average node where squares are being set.  If there are plants present in two or more distinct growth stages, be sure to select some plants representing each stage.  When plants have begun squaring freely, determine the percentage of squares set on 25 or more plants.  Determine percentage set for the first 3 weeks of squaring.  Damaged squares will appear discolored or they will be dislodged by a light touch.  If a square has already dropped off, you will see the scar where it was formerly attached.  Examine the square at the base of the same sized leaf on each of the plants.  For example, you could check for the presence or absence of a square at the base of a leaf the same size as the one shown in the photograph.  If squares are being lost at this stage, it is usually as a result of insect injury.  Ten percent square loss would be a warning sign to check for the presence of plant bugs.  This is explained further in the next section. Insect Situation      As I mentioned last week, thrips damaged leaves are still noticeable in many fields, but there’s not much you can do about it.  By now there should not be any foliar sprays going out for thrips control.  Insecticide treatments applied from this point on can be very risky.  They can decimate populations of beneficials such as big-eyed bugs and damsel bugs.  This can trigger infestations of tobacco budworms in the conventional cottons, and other pests in Bt cotton.      Speaking of budworms, Fran Arnette found a fairly heavy egg lay here on the station this morning.  Since we also have a few budworms in a pheromone trap nearby, I assume these are budworms.  There should be no problems with budworms in Bt cotton.  In conventional cotton, the treatment threshold is 15 small worms (<1/4 inch) or 20% damaged squares.  There is no egg threshold for June infestations of budworm/bollworm.      False chinch bugs were present in a few fields last week.  We treated a few small plots of strip-till cotton that were infested with false chinch bugs last Thursday.  By the next day, numbers were greatly reduced by both Orthene 75S @ 8 oz/acre and Fury @ 3 oz/acre in comparison to the untreated cotton.  When I checked the field again on June 15, most of the remaining bugs were on the ground.  They were not doing any further damage.  We also saw an infestation in strip-till soybeans (along with 2 or 3 bean-leaf beetles per plant).  Cultural controls may be the answer to managing this insect.  It is apparently a general feeder, and just happened to be feeding on wild host plants that were present before planting.  These plants could be burned down 3-4 weeks ahead of planting to prevent the problem from developing.      Plant bugs may be showing up in cotton fields that are beginning to square.  When 10% or more of the squares in a field are being shed, a scout should begin to check for tarnished plant bugs and cotton fleahoppers.  A beat cloth can be used for this.  Just lay the cloth (36 inches long and up to 40 inches wide) between the rows and shake the plants on 3 feet of row over the cloth.  Count all plant bugs that land on the cloth.  Do at least 10 shakes in different areas of a field.  The treatment threshold for plant bugs in 25% square shed and one plant bug per row foot. Section 18 for Pirate      Don Adams informed me today that EPA has granted South Carolina a Section 18 for the use of Pirate to control beet armyworms in cotton.  The treatment threshold will be an average of 5 beet armyworms/100 row feet.  Pirate may not be used on any field until the threshold has been reached in four non-adjacent cotton fields in an area.  EPA initially wanted to mandate this trigger for each county.  Now I’m proposing that the four-field trigger apply to three areas in South Carolina.  Those areas are (1) Pee Dee, (2) Savannah Valley, and (3) the Piedmont.  Once the threshold has been met in four non-adjacent fields in an area, Pirate could be used on an area-wide basis.      There will be some further restrictions that apply to aerial application on the label.  To protect certain endangered species of birds, the product may not be applied aerially in certain counties.  For example, to protect pollinators of the American Chaffseed, Pirate may not be applied by aircraft within one mile of native vegetation in Clarendon, Florence, Horry, Sumter, and Williamsburg counties.  As always, it will be the responsibility of the applicator to read and heed label directions.  It’s essential that we use this product as directed, or it may not be around another year. Coming Events      Be on the lookout for budworm eggs and first instar larvae.  Determine percentage square set and check for plant bugs if 10% or more of squares are being shed.  There may be a few yellow-striped armyworms or even beet armyworms around.  Beneficials such as big-eyed bugs, damsel bugs, spiders, and minute pirate bugs should be moving into fields that are starting to square.  Strip-till fields are often loaded with fire ants.  Yes, Virginia, even these little varmints can be beneficial. 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.