Cotton Insect Newsletter Vol. 22, No. 11, July 28, 2004

Cotton Situation:  Some cotton fields are showing signs of moisture stress this week.   Rains have been spotty during the last 10 days, and cotton plants growing in lighter soils are having trouble finding that 0.25-inch of moisture needed per day during the blooming period.   As blooms reach toward the top of a cotton canopy, plants will begin to shed large numbers of squares and small bolls.  Close to 85% of bolls will be set during the first 3 weeks of blooming.   The remaining 15% will be set during weeks 4-7, and lots of failed bolls will fall to the ground.   But don't assume that all the bolls on the ground are there for physiological reasons.   Insects are also one of the primary causes of small boll abortion. Insect Situation:  Bollworm/budworm egg counts are down this week.  Older fields, where blooms are showing up near the tops of plants, have fewer eggs in the terminals.  Younger cotton plants will be more attractive to the moths that are still in the market for places to lay eggs.  We saw from 2X to 3X more eggs in late-planted cotton here at the PDREC, than in cotton planted 3 weeks earlier.   This is also the time of year when moths tend to lay their eggs lower on the plants.   Cotton that is still young and tender will attract moths to terminals, but as plants begin to load up with bolls, terminals lose their attractiveness.  Scouts need to be doing whole-plant searches for eggs.  Continue to check terminals, but also look at stems, bracts, blooms and dried blooms.   During the whole plant searches you will also be more likely to find fall armyworms.  FAW moths tend to lay their egg masses on the undersides of leaves in the middle third of a plant.   Small larvae may be found in white blooms.  As they get larger, they can be found feeding on the bracts of bolls (middle third of a plant).   Small larvae will feed on the exterior surface of a boll, and as they get larger, they will fully penetrate the boll wall to feed on lint and seeds.  Their favored site of penetration is often at the base of a boll.  Reports of fall armyworm problems have come mostly from the Pee Dee area this week.  Scouts are still finding small worms in white blooms, but have also begun to report bract etching and exterior boll feeding damage.   As these worms begin to increase in size, expect to see some bolls being penetrated.   There have been a few reports of farmers treating their cotton fields for FAW.  Tracer has been used at 2.5 oz/acre, although this may be a little too pricey.  Steward at 9.2 to 11.3 oz/acre is recommended, and it will not be cheap either.  Denim at 10 oz/acre is probably good, but it may not be readily available.  The Dow people are saying that 4 oz Intrepid + a low rate of pyrethroid will be good, but we don't have any SC data to support that combination.  To be quite honest there is very little hard data to support any recommendation on FAW.  We also recommend Larvin, but this material is weaker than those previously mentioned, and it can be readily washed off the plant by rainfall.  The threshold for treating cotton fields is 10 or more fall armyworms that are ¾” in length or smaller per 100 plants.  Keep in mind that one bollworm has the potential to damage more bolls than one fall armyworm. Mike Sullivan filed the following report on July 26:  “Short update on our cotton insect situation in Barnwell/Bamberg counties.  Most conventional cotton treated 2X for bollworm; one report of difficult to kill worms (3X treated with pyrethroid in conventional); we are going to collect worms for ID.  On Bollgard, most all has been treated 1X for piercing/sucking bugs (mainly the lygus).  We have not seen many stinkbugs in cotton yet BUT the numbers started edging up last week.  Lygus numbers are going down. This is very similar to last year.  Aphids are making a return visit but with the disease present, they should not be a problem.  I have not found any significant numbers of armyworms to date.” Stink bugs should be high on everybody's hit list this week.  Keep checking those quarter-sized bolls and keep looking for the bugs.  It's important to know if you have brown stink bugs, because they are less susceptible to the pyrethroids than the greens and southern greens.  If you can't find stink bugs and suspect tarnished plant bugs (but you can't find those either) look for “dirty blooms.”   Tarnished plant bugs fed on the floral parts within the square, and when blooms open, these parts will have dark brownish discolorations.   Stink bugs don't feed on squares and they don't produce dirty blooms.   Mitchell Roof  Extension Entomologist

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