Southeast Missouri Pest Bulletin No. 11, July 28, 2004

INSECTS & OTHER PESTS
Insect activity has remained steady this past week in southeast Missouri, but it will be interesting to see what effect (if any) the recent cool, wet weather has on the insects. I've received reports about the following crop pests (ex. corn borers in corn; bollworms and plant bugs in cotton) being active in the Bootheel. The latest moth trap counts for the crop pests that we're monitoring along with area consultants are in Table 1. (MLB)

CORRECTION
In issue #9 I mistakenly included an older action threshold for stink bug populations in cotton. The correct threshold is 1 or more large nymph or adult per 6 row feet. Again, I apologize for this error.

CORN
Corn Borers: David Guethle, MU Extension Specialist in Stoddard County, reports his southwestern corn borer moth counts increased again this past week; however, he did observe that the corn near his trap site is starting to dry down. At this point of the growing season, the female SW corn borer moths will most likely target late-planted corn fields or grain sorghum. The female European corn borer moths also may target late-planted corn or cotton near corn fields The MU action threshold for SW corn borers is 25% (50% for European corn borer infestations) of the plants infested with eggs and live larvae.

COTTON
Bollworm/Budworm: Bollworm moth counts continue to decline at most locations this past week. One exception was reported by Tate Castillo, MU Extension Specialist in Pemiscot County, who observed his counts around the Steele area almost doubled from last week. I have not received any reports of sprays going out just for 'worms', and the larvae that I've received from Ed Kowalski and Matt Robbins were identified as bollworms. I would continue monitoring any fields with non-Bt or Bollgard I varieties that are near corn fields. Note, that fields with Bollgard II varieties will have better protection from armyworm and bollworm feeding damage; however, plants in these fields may still sustain some damage. (MLB)

The recommended MU action threshold for bollworms and budworms in non-Bt cotton is to treat before 10% or more of the plants are infested with small larvae (less than ¼-inch in length). In Bt cotton fields a recommended threshold for bollworm control is to apply a foliar treatment when 4 or more larvae (greater than ¼-inch in length) per 100 plants are present.

Plant Bugs / Cotton Fleahopper: There is no apparent letup in plant bug infestations, and the recent rains may not help matters in the coming weeks. I'd recommend keeping a close watch on rank plant growth, since these plants will be even more attractive to plant bugs and the rank growth could decrease insecticide coverage. Reports that I've received plus observations made here at Delta Center indicate we're mainly fighting tarnished plant bugs. Cloudy plant bugs plus cotton fleahoppers are present in low numbers, and Daniel Porter reported that he is mainly seeing fleahoppers in fields that are near watermelon patches.

Spider Mites: Hopefully, the recent heavy rains will help with spider mite infestations. But, I'd caution you to continue monitoring for mite infestations as the return of hot, dry conditions will help mite populations quickly rebound.

GRAIN SORGHUM
Sorghum midge: Any late- or sequentially-planted fields plus those with uneven head emergence will be at risk from midge infestations and feeding damage. Johnsongrass infestations also can increase the risk of midge damage in your fields. The best time to scout your fields for the adult midge (small, reddish coloration) is during the morning when winds are calmer. Sample 10 heads at each of 10 locations per field to determine the extent of midge infestations. The MU action threshold is 1 adult midge per seedhead.

RICE
Rice Stink Bug: Still nothing new to report on rice stink bug infestations, but closely monitor any fields where the panicles are emerging for rice stink bugs. The MU action threshold is to treat when stink bug populations average 5 or more per 10 sweeps during the first two weeks of heading and 10 or more per 10 sweeps during the second two weeks of heading.

SOYBEAN
Sudden Death Syndrome: In New Madrid County, I've observed soybean fields with Sudden Death Syndrome (SDS) this growing season, but the disease is present in soybean production areas throughout Missouri. Sudden Death Syndrome is usually more severe under high soil moisture and below normal temperature conditions at or near blooming. The growth stage at which SDS infects soybeans is the determining factor of possible yield reductions. If the disease occurs later in a plant's development it will not cause the amount of yield reduction as if it had occurred earlier. Symptoms of SDS can appear several weeks prior to flowering but they are usually more pronounced after flowering. These include chlorotic leaves with the veins staying green, and large necrotic areas developing on the leaves causing these leaves to die and drop off the plant. Pod drop also may occur in these fields. This disease usually hits fields with high yield potential (i.e. optimum fertility, irrigation, etc.). No cure exists for SDS once it starts. Management options for SDS include selecting varieties that have shown to be less susceptible to SDS, improve drainage in fields where possible, avoid compacting soil, crop rotation, maintain crop vigor, avoid crop stress, and harvest fields in a timely manner. (JH)

Stink Bugs: I haven't received any new reports regarding stink bugs infesting soybean fields; however, I'd scout any field that is flowering and producing pods (especially fields next to corn). Several people I've spoken to indicated they are easily finding stink bugs in their corn fields. 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. If the soybeans are several weeks away from harvest, I recommend using a labeled pyrethroid insecticide; whereas, soybeans close to harvest I'd recommend treating with an organophosphate (malathion, methyl parathion) to 'cleanup' the field. Since brown stink bugs are harder to control with pyrethorid insecticides, you may need to apply a tank-mix if they are most common stink bugs in a field. (MLB)