"Improving People's Lives"

Southeast Missouri Pest Bulletin June 4, 2003

INSECTS
There is little news this week on the insect front. We are starting to see some movement by corn (Southwestern corn borer), cotton (thrips, spider mites, and stink bugs), and rice (rice water weevil) pests during the past few days. Cutworm moth flights have been declining; therefore, we've discontinued our trapping efforts for this insect. But, I'd still caution you to monitor for this insect, especially in burn-down situations. Since cutworms are nocturnal, recommended timing for insecticide applications is in the morning or late afternoon NOT midday. (MLB)

COTTON
Boll Weevil: All cotton fields in southeast Missouri should be monitored with pheromone-baited traps. If you find a field that does not have traps around the perimeter, inform Missouri Boll Weevil Eradication personnel about this field.

Thrips: I've received several calls the last few days regarding foliar insecticide treatments for thrips. This is a good indication thrips are starting to migrate out of the drying wheat into nearby cotton fields. It is also likely at-planting treatments on cotton planted in the first half of May are playing out. It is very important that plants be protected until they are past the 4th-true leaf stage. Foliar treatments are recommended once an action threshold of 1 thrips per plant is present in the field.

Spider Mites: Last Thursday I received a call from Victor Roth regarding a spider mite infestation on 2nd- to 3rd -true leaf cotton. Frankly, I was surprised to learn the spider mites were so abundant in this field considering all the rain we received in May.

Bt Cotton: Last week I spoke about the level of control that you obtain with 1st-generation Bt cotton varieties, but this week I'd like to briefly touch on the topic of refuge management. For 2003 there are three approved refuge options for planting Bt cotton. Option 1: With the 20% acreage refuge all Bollgard fields must lie within 1-mile of the refuge area, and this refuge area cannot be treated with foliar Bt sprays for control of tobacco budworms or cotton bollworms. Foliar insecticide treatments are recommended when 4 or more surviving larvae (1/4-inch or greater in length) per 100 plants and/or 2% boll damage is present. Option 2: With the 5% refuge option, do not control tobacco budworms or cotton bollworms in these areas with any product specially targeted at these insects. This unsprayed refuge should be at least 150 feet wide. All Bollgard fields must lie within 1/2-mile of this unsprayed refuge option. Option 3: The third option is a non-Bt embedded 5% refuge. The refuge area can be embedded within a larger field or field unit (1-mile by 1-mile), and can be treated with any insecticide used to treat the Bollgard fields within the same 24-hour period. It also can serve as a community refuge area provided the distance and other requirements are met. The importance of properly maintaining a refuge area cannot be understated. These areas are needed to produce bollworms, and particularly budworms, that are still susceptible to the Bt toxin. Insects like the budworm have a nasty history of developing resistance within a few years of an insecticidal poison's initial use.

Root-knot Nematodes: Crop-threatening levels of root-knot nematodes are present in some, but not all, cotton fields in southeast Missouri and northeast Arkansas. During a recent survey of Missouri cotton fields by University of Missouri Delta Center scientists, root-knot nematodes were found in 20%, 27%, and 43% of the fields surveyed in New Madrid, Pemiscot, and Dunklin Counties, respectively. (AW)

These nematodes can cause severe injury to cotton, and the symptoms of root-knot nematode injury will initially be visible 6-8 weeks after planting. During most years, the symptoms become visible during early- to mid-June. Unfortunately, cotton planting this year has been delayed due to bad weather, and symptoms may not become visible until late-June to early-July. The symptoms of root-knot nematode injury are stunted cotton plants, and injured plants may wilt more quickly than healthy plants during a hot afternoon. Plants injured by these nematodes also will have galls, swollen areas, visible on the infected roots.

Be cautious about diagnosing the cause of stunted cotton because other factors such as low soil pH and drought also may cause plants to be stunted. Ask your cotton scout/consultant to tell you about areas in your fields where they observe this symptom and then investigate the cause of the stunting.

For more information contact me at the University of Missouri Delta Center (Phone: 573-379-5431) or by e-mail ( wratherj@missouri.edu). Additional information on this cotton pest can be found on the University of Missouri Delta Center website (http://aes.missouri.edu/delta/).

DISCLAIMER STATEMENT
The University of Missouri does not warrant products mentioned in this publication. The use of a trade name does not constitute recommendation of one product over other (generic) products of a similar chemistry.

University Extension does not discriminate on the basis of race, color, national origin, sex, religion, age, disability of status as a Vietnam era veteran in employment or program.