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Southeast Missouri Pest Bulletin August 13, 2003

INSECTS & OTHER PESTS
I've received several calls over the past few days regarding infestations in cotton (armyworms, bollworm/budworm, plant bugs), grain sorghum (corn earworms, midge), and soybean (stink bugs) fields. Moth counts (Table 1) have remained high this past week for corn earworms but have fallen for southwestern corn borers. (MLB)

COTTON
Armyworms: I've received a couple more calls about fall armyworm (small larvae are white with black heads; whereas, larger ones are dark, smooth skinned, and have an inverted "Y" mark on their cream-colored heads) infestations in both Bt and conventional cotton fields. Most fall armyworms are initially being found in the blooms before boring into the base of the bolls.

To scout for fall armyworm infestations, examine 5 plants at each of 10 locations per field for egg masses, larvae, and/or damage. Insecticide treatments are recommended when 4 or more larvae per 100 bolls or blooms are present. Keep in mind that Bt cotton fields may still require an insecticide overspray for fall armyworms, and that pyrethroid insecticides are not recommended for controlling this pest. Recommended insecticides for controlling fall armyworm infestations in cotton include: Curacron, Confirm, Intrepid, Lannate, Larvin, Steward, and Tracer. Newer chemistries like Steward and Tracer should only be targeted at ¼-inch or smaller larvae.

Bollworm/Budworm: Moth trap captures remained high this past week in several locations for cotton bollworms. As I stated last week, cotton fields (even those with Bollgard I varieties) remain vulnerable to bollworm infestations. Victor Roth also reported he is mostly finding tobacco budworms in egg kits that he conducted this past week. If you have any eggs that want you tested, I have five Heli-ID egg kits available here at the MU Delta Center.

I recently saw a report by Glenn Studebaker, University of Arkansas Extension Entomologist, of poor bollworm control in Bt cotton fields. As he stated in his report, coverage was an issue as the larvae were feeding beneath bloom tags when the fields were treated. Keep in mind that Bollgard I cotton varieties do not produce as much Bt toxin in the flower pollen versus that in other parts of the plant. This will enable some bollworms to survive exposure to the toxin and continue feeding.

European Corn Borer: With more corn fields rapidly maturing and becoming less attractive to egg-laying moths, watch for European corn borer infestations in nearby cotton fields. Labeled, recommended pyrethroids used for bollworm control also should control European corn borer infestations if the applications are properly timed.

Plant Bugs, Plant Bugs, Plant Bugs!: Infestations of this pest group remain persistent in many locations, and I've also noticed a resurgence of nymphal counts in my research plots since last week's rains. Ed Kowalski reported finding plant bugs even after fields were treated multiple times, and similar accounts also are coming out of Arkansas. This could be due to a combination of pest resistance to insecticides, poor spray coverage, and/or rapid reinfestation of treated fields. If you've already used an insecticide twice in a field for plant bug control, I strongly advise you to switch to another insecticide of a different chemistry class. As I've stated before, the tarnished plant bug has a history of developing resistance to insecticides (ex. Orthene) during the course of a field season. Increasing the application rate to 15 GPA and the pressure also can help improve coverage on larger plants.

RICE
Rice Stink Bug: Closely monitor any fields where the panicles are still emerging for rice stink bug infestations. Rice stink bugs cause the greatest yield loss during the milky to soft dough stages.

SOYBEAN
Soybean Aphid: I've seen several reports out of Illinois that soybean aphid infestations are higher this year, and that the aphid is now being observed south of I-64. I have not received any reports thus far of soybean aphid infestations in southeast Missouri, but you may want to monitor any double-cropped and/or late planted soybeans for this pest.

Soybean aphids usually prefer feeding on young trifoliate leaves in the terminal before moving to the stems and older leaves lower on the plant. Soybean aphids are small with yellowish coloration, and you'll need a 10X hand lens to see the black cornicles or "tailpipes". Soybean aphids also prefer to feed in large colonies, and an indirect way of detecting these soybean aphid infestations is by the presence of large numbers of ladybird beetles attacking the aphids.

If you find any colonies of soybean aphids in your fields, please contact Dr. Wayne Bailey (MU State Extension Entomology Specialist, 573-882-4264) or myself so we can further document these infestations in Missouri.

Stink Bugs: Early-planted fields with developing pods should be closely monitored for stink bug infestations. Insecticide treatments are recommended once infestations reach two or more stink bugs (large nymphs and adults) per 3-row feet (roughly equivalent to 17 or more stink bugs per 20 sweeps). Before applying an insecticide take note of the percentage of brown versus green stink bugs in the population. Brown stink bugs are more tolerant to pyrethroid insecticides than green stink bugs. If the infestation is largely comprised of brown stink bugs, then an organophosphate like methyl parathion is recommended. For more information on stink bug biology and management in soybeans, obtain a copy of MU guidesheet G7151 at your local extension office, the MU Delta Center, or from MU Extension publications (800-292-0969).