Southeast Missouri Pest Bulletin No. 8, July 7, 2004

INSECTS & OTHER PESTS
Insect activity has been light this past week in southeast Missouri. But, I have received reports about the following crop pests (ex. bollworms and plant bugs in cotton; rice stink bug in rice) being active in the Bootheel. The latest moth trap counts for the crop pests that we're monitoring along with area consultants (ex. Phil Dee Gurley, Victor Roth) are in Table 1. (MLB)

CORN
Corn Borers: Based on this week's SW corn borer trap counts at Portageville, we're definitely in the midst of the second generation moth flight. Any fields with non-Bt corn should be monitored for infestations, because this generation's feeding damage leads to the greatest yield losses. The MU action threshold for SW corn borers is 25% of the plants infested with eggs and live larvae.

COTTON
Crop Report: Cody Taylor reported yesterday that 50-60% of the cotton that he scouts should be blooming by the end of this week.

Irrigation Season Has Arrived: Cotton, like corn or grain sorghum, needs the entire growing season to achieve maximum yields. Proper irrigation will help prevent the crop from cutting out too early and reducing the final lint yield. An added bonus is that fiber length will be longer with adequate irrigation. The crop should have adequate water until August 15th, and the soil should be left wet on that date in Missouri. If this fall is dry then the crop will not become too stressed if it's wet on the 15th. On the other hand, terminating irrigation by the 15th also reduces the risk of rank crop growth should this fall be excessively wet. Generally, any bolls produced late in the season will not have enough time to mature before the first fall freeze. (BP)

Bollworm/Budworm: We've seen a dramatic increase in the number of bollworm moths in the pheromone trap at our Portageville site this week. The moth counts are still somewhat spotty as indicated by the dual counts from a couple of locations listed in Table 1. Looking at this week's counts, I'd say we are seeing the initial flight of the 2nd generation bollworm moths. Any fields that are flowering and have non-Bt or Bollgard I varieties should be scouted for eggs and small larvae. Late last week Ed Kowalski brought by some early-instar larvae, and we found they were bollworms. (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 (particularly those with Bollgard II varieties) insecticide treatments should not be based on egg counts alone. Closely examine blooms for eggs and/or any surviving larvae. A general recommended threshold for bollworm control in Bt cotton is to apply a foliar treatment when 4 or more larvae (greater than ¼-inch in length) per 100 plants are present.

Additional information on bollworm / budworm scouting, management in conventional and Bt cotton, and recommended insecticides is available on the following Delta Center webpage: http://aes.missouri.edu/delta/muguide/ctnmgtgs.stm

Plant Bugs / Cotton Fleahopper: Victor Roth reported increased plant bug (primarily adults) activity during the past few days, especially around the Bernie and Dexter areas.

Spider Mites: I've only received one recent report regarding spider mite activity. Hopefully, the recent heavy rains across the region will help suppress their populations.

GRAIN SORGHUM
Corn Earworm: As sorghum begins blooming and producing seed heads, it will become susceptible to corn earworm infestations. Seedheads are most susceptible to insect damage during the bloom to milk stages. An average of 1 larva per seedhead can potentially reduce yields by 5%. Once sorghum begins to bloom, fields should be monitored every 5 days until the hard dough stage. Randomly sample 10 plants at each of 10 locations per field by vigorously shaking the seedheads over a beat-sheet or preferably a 5-gallon plastic bucket. This method will help you detect the smaller larvae (less than ¼-inch in length). The MU action threshold for sorghum is when more than 75% of the plants are infested with 1 or more larva per seedhead.

RICE
Rice Stink Bug: Any fields that have panicles emerging should be closely monitored from now on for rice stink bug infestations. As with any crop pest, regular scouting trips across the field is the best means of locating economic infestations of rice stink bugs that can lower your crop's yields.

Early detection of rice stink bug infestations is critical so to minimize yield losses and reduced grain quality as a result of the stink bugs feeding on "milky" stage seeds. Growers can minimize stink bug infestations by NOT MOWING grassy field borders once the rice plants enter the heading stage. Rice stink bugs prefer to feed on barnyard grass, sprangletop, or other grass species unless these alternative host plants were destroyed with herbicides or a mower.

The MU action threshold is to treat with an insecticide is 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. At this time of the growing season, I'd recommend applying a pyrethroid (Karate, Mustang Max, Prolex), as these insecticides will give you the longest residual control. For more information on insecticide recommendations to control rice stink bugs, visit the following MU Delta Center webpage: http://aes.missouri.edu/delta/muguide/ricegsh.stm

SOYBEAN

Stink Bugs: I haven't received any new reports regarding stink bugs infesting soybean fields; however, I'd closely monitor any fields where the plants are producing pods. 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. Table 1. Pheromone moth counts as of July 6th.