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This is Jack Bacheler, Extension Entomologist at NCSU with the Cotton Insect Update. Today is Wednesday, August 4.

Stink Bugs on Cotton

Stink bugs are again our major insects of interest this week, with more cotton fields than not throughout the state exceeding the 10% internal damage threshold used during weeks 3 through 5 of the bloom period. In most cases, a pyrethroid + Bidrin tank mix is being employed because of the presence of brown stink bugs in most cotton fields.

Different approaches are being used to collect and inspect quarter-sized bolls. Some scouts are able to pick bolls and examine them while walking throughout the cotton field. Others prefer to collect the bolls into something like a nail pouch, put them into a Ziploc bag after exiting the field, and postponing their boll inspections until collections have been finished from several fields. Any of these and other boll collection methods will work fine as long as the individual bolls are examined carefully for warts or internal stained lint. A reminder that internal warts and stain may be subtle, as in many cases the stink bug damage has occurred recently. Do not count external damage or the pin prick-like dark spots in the inside of the boll wall. To count as a wart, the damaged area must be raised above the inner boll wall surface.

When a cotton field reaches the beginning of the 6th week of bloom the threshold can be raised to 20%. The following week, the use of a 30% threshold is appropriate, followed by a 50% threshold beginning at the 8th week of bloom. The raising the internal damage thresholds after the 5th week of bloom are because the boll population in cotton fields is increasingly reaching the 3.5 week “stink bug-safe” stage.

The bollworm moth flight appears to be on the moderate-plus side so far this year, with threshold levels of bollworms now possible anywhere in the state. Scouts should be reminded to only count bollworms that are 1/8 inch or larger. Those caterpillars will have survived the Bt toxin and molted to second stage larvae may well complete their development and damage bolls.

Outside of a few reports of beet and fall armyworms, in general we are apparently experiencing low levels of cotton aphids, spider mites and plant bugs this week.

Soybean Insects

We are beginning to get threshold levels of podworms in some soybean fields in our southern counties. One field in Scotland County was approximately 3-fold the podworm threshold of 1.5 podworms per 15-sweep sample in 14-inch rows with the expected price at $9.00 per bushel and the cost of control at 9.00/acre. With this many variables determining the podworm threshold for a given situation, it makes sense to use the VA Tech Podworm Threshold Calculator based on NC thresholds posted on our Cotton Insect Corner web site under “What’s New @ the Corner?” <http://www.ipm.vt.edu/cew/>. This will let you plug in your sampling device, the row spacing, the cost of control and the price of soybeans. The calculator provides you with the threshold level for the set of variables you provide.

So far, this is shaping up to be a more challenging year for worms and stink bugs on soybeans that the past three or four.