Southeast Missouri Pest Bulletin No. 14, August 19, 2004

INSECTS & OTHER PESTS
Insect activity has decreased somewhat over the past week in southeast Missouri. I have received reports about the following crop pests (ex. aphids, bollworms / budworms, plant bugs, stink bugs, and whiteflies in cotton; bean leaf beetle, soybean aphids in soybean) being active in the Bootheel. The latest moth trap counts are listed in Table 1. (MLB)

COTTON
Crop / Insects: Victor Roth reports that has seen a few open bolls this past week. From reports that I've received and observations we've made in the field indicate we are still seeing a mixture of various pests [i.e. aphids, plant bugs, stink bugs, caterpillars (mainly bollworms but also a few armyworms and budworms), spider mites, whiteflies] in the cotton right now. Bollworm/Budworm: Moth counts for bollworms were variable again this past week. I should point out those budworm moth counts reported in Table 1 may not be true representation of budworm activity in the area. Unfortunately, budworm moths are harder to lure to the traps than bollworm moths, and typically I'll multiple my trap counts by four to better gauge budworm moth activity. Phil Gurley reports finding fresh eggs in several fields that he scouts. I also received some larvae from Mr. Gurley that he collected from around the Campbell area, and we identified those as tobacco budworms. Since budworms are more difficult to kill with pyrethroids than bollworms, it's recommended to target ¼-inch or smaller larvae with Denim, Steward, or Tracer.

Plant Bugs / Cotton Fleahopper: Nothing new report on the on-going plant bug situation except that infestations are continuing where the cotton remains lush and green. The recent cool temperatures may have slowed down their feeding and reproduction, but they will likely remain with us for several more weeks. Once cotton bolls have accumulated 350 heat units they are generally safe from further plant bug damage and insecticide oversprays are no longer recommended in the field.

Stink Bugs: Phil Gurley reports that he is still finding stink bugs at various locations. Since stink bugs can still damage relatively mature bolls that are generally safe from others pests (ex. bollworms, plant bugs), you'll still need to protect your crop from stink bug feeding damage. The recommended action threshold for stink bug infestations is 1 or more stink bug (large nymphs and/or adults) per 6 row feet, OR when 20% of quarter-sized bolls display internal signs of damage and stink bugs are observed in the field. Since brown stink bugs are more tolerant to pyrethroid insecticides than green stink bugs, it's recommended that you use an organophosphate (ex. Bidrin, Orthene) if brown stink bugs are most prevalent in the field.

Whiteflies: Bobby Phipps wants to remind you about watching out for late-season whitefly infestations. The main threat from this pest is its honeydew production that can contaminate lint and lead to price dockage at the mills. To scout for whiteflies, examine 5 plant terminals at each of 10 locations per field. Take note of the number of whitefly colonies resting on the underside of leaves or flying about as you walk through the field.

Insecticide treatments are recommended when 50% or more of the plant terminals are infested. Recommended insecticides for controlling whitefly infestations in cotton include: acephate, Centric, and Monitor.

GRAIN SORGHUM
Headworms: Any sorghum fields that are still flowering will remain at risk from this pest. The MU action threshold for this insect is 75% of the seedheads infested with one or more larvae. You can easily sample for this insect by slapping the seedheads over a 5-gallon white bucket and counting the larvae within.

SOYBEAN
Soybean Aphid: I received a report from Brian Selle that he recently found scattered soybean aphid populations in Cape Girardeau County soybean fields. I would recommend monitoring any late-planted fields for this pest, as any young, lush growth will be most attracted to the aphids. The cooler conditions earlier this month also may have helped these insects become better established in the region. Since soybean aphids are very small, you'll need a 10X hand lens to see their black cornicles or "tailpipes" for a positive identification. Soybean aphids prefer to feed in large colonies unlike other aphid species that you may find in soybeans, and you can use this as an indirect way of locating their infestations. If you find any colonies of soybean aphids in your fields, please contact your regional extension specialist or myself so we can further document these infestations in Missouri. A recommended action threshold for this pest is 250 or more aphids per plant during the early reproductive stages when pods and seeds are still developing.

Stink Bugs: I have nothing new to report on stink bugs infesting soybean fields in the Bootheel, but I would continue monitoring any fields that still have developing seeds and are adjacent to corn fields and the insect's overwintering sites (ex. woodlots). The recommended MU action threshold is 2 or more stink bugs (large nymphs and adults) per 3-row feet as the seeds begin to fill.