"Improving People's Lives"

Southeast Missouri Pest Bulletin June 10, 2003

INSECTS & OTHER PESTS
There has been a slight increase in the activity of crop pests this past week. We continue to see some movement into corn (corn earworm, Southwestern corn borer), cotton (thrips, spider mites, and stink bugs), and rice (rice water weevil) fields. Moth trap counts for several crop pests have declined slightly and are reported in Table 1. (MLB)

Even though I haven't received any reports of this crop pest appearing in Missouri, slug infestations have been observed by University of Tennessee extension specialists in no-till cotton and soybean fields. Slugs will damage cotyledon leaves and clip plants like cutworms.

CORN
Corn Borers: Reports have been coming from surrounding states of increased corn borer [particularly the Southwestern corn borer SWCB)] activity. We've also been observing more moths in our pheromone traps, and Bill Emerine reports finding more SWCB moths in his light traps in Sikeston and Vanduser sites.

Any non-Bt corn fields should be closely monitored for SWCB egg masses and hatching larvae. Early detection is the key to timing insecticide applications and minimizing corn borer damage. Once the larvae bore into the plant they are next to impossible to kill. The recommended action threshold for European corn borers (ECB) is 50% or more of the plants infested with egg masses and small larvae; whereas, with the SWCB it's 25% infested with egg masses and small larvae.

For more information on scouting procedures for both borer species, obtain a copy of MU guidesheets G7111 (SWCB) and G7113 (ECB) at local MU extension office, here at the MU Delta Center, or from MU Extension Publications (800-292-0969).

COTTON
Crop Report: The first twenty days of May were very warm in 2003, but the last ten days of the month and the first week of June have been very cold with only 115 DD60's accumulated. Last year we had colder weather with a low of forty-two on May 18; however, this year we have not had the 90 degree weather that was observed last year. Rainfall amounts have much greater this year in some areas and definitely were a factor in the crop looking so poor in the last week of May. A comparison of DD60's for this year's crop versus the 2002 one is reported in Table 2. (BP)

Thrips: It is important to closely scout fields for any rapid increase in thrips infestations in coming days as the wheat continues to mature. I cannot emphasize enough that this early protection is needed with this year's later-planted crop. The presence of immature (wingless) thrips in your fields is an indication that at-planting treatments are no longer effective in controlling thrips infestations. Insecticides such as Bidrin, Orthene, and several pyrethroids are available for treatment once an action threshold of 1 thrips per plant is present in the field. (MLB)

Spider Mites: If we don't receive any significant rainfall within the next few days, I would expect to see an increase in spider mite infestations. As with thrips infestations, you can ill afford any delay in this year's crop because of mite feeding damage. The recommended action threshold is 50% of the plants infested and mite populations are increasing.

Plant Bugs: These insects can be so erratic when infesting cotton fields; therefore, any fields close to squaring should be closely monitored in the coming days for plant bug infestations and damage. If the cotton is more succulent than their weed hosts, then plant bugs will likely infest these fields. Protection of early fruiting positions will be essential to an early-maturing crop. This will help minimize the impact on yields should we experience another bollworm/budworm outbreak or the onset of an early fall.

Bollworm/Budworm: There are reports coming out of Arkansas of bollworms and budworms infesting pre-squaring cotton. I also observed a similar occurrence several years ago near Kennett. This an unusual time for these insects to be infesting cotton, but it isn't a complete surprise considering last year's big outbreak and this year's early moth captures. Unlike fruit damage, the cotton crop should be able to tolerate more terminal damage. The University of Missouri has no threshold for this type of damage, but the University of Arkansas Extension Service is recommending an insecticide overspray if 20% or more of the plants have terminal damage.

Stink Bugs: Last week I received a report from Ed Kowalski that he was finding adult stink bugs and their egg masses (barrel-shaped eggs) in pre-squaring cotton. This is also early for these insects to be infesting cotton, but they may occur in no- or reduce-till fields when alternative weed hosts are killed. To best of my knowledge, stink bugs are not an economic threat unless large squares and particularly bolls are present in the field.

RICE
Rice Water Weevil: If adult weevils are present and leaf scar counts are 50% or higher, then a pyrethroid insecticide like Karate (1.6 - 2.56 oz/acre), Fury (3.4 - 4.3 oz/acre) or Mustang Max (3.2 - 4.0 oz/acre) should be applied within 10 days after permanent flood in drilled-seeded fields. A foliar spray should not be required if the rice seed was treated with Icon prior to planting. Additional information on rice water weevil management is available on the MU Delta Center website: http://aes.missouri.edu/delta/muguide/ricegsh.stm