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Southeast Missouri Pest Bulletin July 22, 2003

INSECTS & OTHER PESTS
I've received several calls over the past few days regarding infestations in cotton (bollworm/budworm, plant bugs, spider mites), grain sorghum (corn earworm), and rice (rice stink bug) fields. Moth counts (Table 1) have again increased this past week for several species. (MLB)

CORN
Corn Borers: I've received a few calls the past few days regarding Southwestern corn borer infestations. Looking at local and regional moth trap captures, we are definitely in the middle of another moth flight. Now is the time to intensify your scouting efforts in non-Bt corn fields.

COTTON
Crop Report: Because of the frequent early-season rains and soil compaction, we have observed that the soil is not absorbing irrigation water as well as normal. Thus, more frequent irrigation may be required in order to keep the crop adequately supplied with water. (BP)

I have heard that some growers are planning to withhold water now because of the reduced yield potential of the crop. This year's crop needs to be pushed with irrigation until August 15th so flowers that are produced on or before August 10th will have a chance to produce adequate lint. The August 10th flowers should not stress before September 1st at which time the bolls should be full size and the fiber length is established. At that time water requirements by the crop will be greatly reduced.

Pushing the crop with irrigation also may require the use of a growth regulator such as mepiquat chloride. If the crop is stressed then use of any growth regulator may not be necessary. Do not guess if it is needed, but check the length of the internode between the fourth and fifth nodes from the top of the plant.

The latest DD60's for this year versus those received in 2002 are reported in Table 2.

Aphids: I have not received any more reports regarding insecticide treatments for aphids. Last week someone asked about the presence of the aphid fungus in Missouri; however, I know of no confirmed cases of it in the state. In Arkansas, the fungus still has not been observed in the northern parts of the state. (MLB)

Bollworm/Budworm: We observed a slight jump in budworm moth captures in pheromone traps this past week, and I would expect those numbers to increase in the coming days. Michael Johnson reported finding larvae behind an insecticide treatment in two Stoddard County fields. All six larvae collected yesterday from the fields were identified as budworms.

Again, I encourage you to intensify your scouting efforts in non-Bt fields so you can target eggs and ¼-inch or smaller larvae if threshold levels are present. If you have any larvae that you need to have identified, my students and I as well as your local extension specialist can assist you. The recommended University of Missouri action threshold for bollworms and budworms in non-Bt cotton is to treat when around 10% of the plants are infested with small larvae.

Plant Bugs: I've received a couple of reports that plant bug infestations are holding steady over the past week. With this late crop plant bugs also may feed on early blooms as well as squares and small bolls. The Missouri action thresholds for rescue treatments are: 6-8 plant bugs per 100 row feet during the 1st week of squaring, 8-10 per 100 row feet the 2nd week, 12-15 per 100 row feet the 3rd week, and 15 or more per 100 feet during the 4th week.

GRAIN SORGHUM
Corn Earworm: I've received a couple of more calls regarding sorghum fields being infested and seedheads damaged by corn earworm moths. A sweep net or a white 5-gallon bucket (not visual examination) is my recommended means of sampling the seedheads. The Missouri action threshold for sorghum is when more than 75% of the plants are infested with one or more corn earworm larvae per seedhead.

RICE
Rice Stink Bug: Fields that were planted on time should have panicles emerging, and now is the time to begin scouting these fields for rice stink bug infestations. Overall, stink bugs are relatively abundant this year, and the rice stink bug is no exception. As with any potential crop pest, regular scouting trips across rice fields are the best means of determining if economic infestations of rice stink bugs exist in your fields.

Rice stink bugs become a problem once the panicles start to emerge from the head. Early detection of stink bug infestations is critical so to minimize yield losses and reduced grain quality as a result of rice 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 are unavailable or were destroyed.

To determine if an economic rice stink bug infestation is present in your fields, take 10 sweeps with a heavy-duty sweep net at each of 10 locations per field. Generally, the stink bugs are less active and easier to catch in the morning. The University of Missouri action threshold 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 (Fury, Karate, or Mustang Max) 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