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This is Jack Bacheler, Extension Entomologist at NCSU with the Wednesday cotton insect update. This is Wednesday afternoon, July 22, 2009.

We have finally arrived at the beginning of crunch time for sting bugs on cotton. That is, much of our cotton crop has now reached the beginning of the 3 to 5 week of bloom period when cotton plants are most vulnerable to stink bug damage. Additionally, we are seeing stink bug damage to quarter-sized bolls in the 6 to 30% range in our threshold tests, in Scotland, Union and Wayne counties. Once at the 3rd week of bloom, our threshold recommendation for the next three weeks remains at 10% internal damage to quarter-sized bolls. Although we recommend a sample size of 25 to 50 bolls for small and larger cotton fields, respectively, smaller sample sizes may also be appropriate if fields will be grouped for spraying purposes. Where possible, fields should be treated individually as thresholds are reached. To assist scouts in confining their inspections to quarter-sized bolls, any material, such a Plexiglass or thin plywood, into which a 1-inch diameter hole has been drilled, can serve as a template to judge the correct boll size to sample.

In treatment situations in which brown stink bugs outnumber greens, with the bollworm moth flight either underway in our most southern counties or within a week of arrival in other areas, a Bidrin plus pyrethroid tank mix is probably appropriate. Endigo and Leverage are co-pacs of a pyrethroid plus either the active ingredient in Centric or Trimax Pro, respectively. These insecticides may be cost effective in situations in which cotton aphids are also present at treatable levels along with economic levels of stink bugs and the threat of bollworms. Both products will provide some additional control of stink bugs, but Bidrin may still be needed in the tank if brown stink bug levels are high.

At the 5th or 6th week of bloom, many bolls on the cotton plant will no longer be susceptible to stink bug damage, and the internal boll damage threshold can be raised to 30%. Please check out NCSU’s Cotton Information booklet or our Cotton Insect Corner web page via Google to find scouting and threshold details.

We continue to receive calls of some treatable levels of cotton aphids, plants bugs and spider mites, so be on the alert for these less commonly treated pests.

Although the bollworm moth flight is underway in the southern counties, so far numbers of moths are only low to moderate. Some Scotland County cotton fields were reported to have some fields with significant levels of bollworm eggs being deposited down in the plants as opposed to the easy to find terminal eggs. With essentially all of our cotton now either Bollgard, BG II or WideStrike technology, look for 1/8-inch or larger bollworms as a spray trigger. Tiny hatching bollworms must eat the plant toxin to be killed, and 1/8-inch or larger bollworms indicated that the first stage caterpillars have survived the toxin.

The status of the bollworm moth flight will become much more apparent in the coming week, as will how this year’s stink bug levels may be impacting our cotton crop.

Finally, please feel free to call or email us about what’s happening in your area.

See you next week on July 29.