Southeast Missouri Pest Bulletin No. 13, August 12, 2004

INSECTS & OTHER PESTS
Insect activity has increased within the past week in southeast Missouri. I've received reports about the following crop pests (ex. bollworms, plant bugs, and stink bugs in cotton; bean leaf beetle, Dectes stem borer, and stink bugs in soybean) being active in the Bootheel. The latest moth trap counts are listed in Table 1. (MLB)

COTTON
Insects: From reports that I've received and observations we've made in the field indicate we have a mixture of various pests [i.e. plant bugs, stink bugs, caterpillars (mainly bollworms but also armyworms), spider mites] in the cotton right now. Ed Kowalski reports that in several fields he scouts the individual pests may not be at their threshold levels; however, the cumulative damage from all these pests is still requiring insecticide applications. I cannot say this is unexpected this late in the season, and I would recommend monitoring any late-maturing cotton for these pests (particularly defoliators and stink bugs). We'll also have to see how the current cool spell will affect the crop's maturity as it relates to insect damage.

Bollworm/Budworm: Moth counts for bollworms were variable this week with some locations' counts decreasing whereas at other sites they remain steady. Phil Gurley reported another large bollworm flight in the Peach Orchard area, and again we caught several hundred more moths at our Portageville site. Several consultants report that they have treated more fields within the past week for bollworms. Most of the larvae that I've received from Michael Johnson and others for identification were bollworms.

Plant Bugs / Cotton Fleahopper: The plant bug problem continues unabated based on information that I've received from several consultants. Again, I'd closely monitor fields with rank plant growth, since these fields will be most attractive to plant bugs and the rank growth could decrease insecticide coverage. Once cotton bolls have accumulated 350 heat units they are generally safe from further plant bug damage.

Stink Bugs: Phil Gurley reported that he has recommended treating a few more fields this past week for stink bug infestations. Keep in mind that stink bugs can still damage relatively mature bolls that may be safe from others pests (ex. bollworms, plant bugs). The recommended action threshold for stink bug infestations is 1 or more stink bug (large nymphs and/or adults) per 6 row feet, OR when 20% of quarter-sized bolls display internal signs of damage and stink bugs are observed in the field. Since brown stink bugs are more tolerant to pyrethroid insecticides than green stink bugs, it's recommended that you use an organophosphate (ex. Bidrin, Orthene) if brown stink bugs are most prevalent in the field.

GRAIN SORGHUM
Headworms: This is the same insect as the bollworm or corn earworm, and the adult moths will continue migrating out of corn fields into neighboring sorghum fields that are still flowering. The MU action threshold for this insect is 75% of the seedheads infested with one or more larvae. You can easily sample for this insect by slapping the seedheads over a 5-gallon white bucket and counting the larvae within.

SOYBEAN
Bean Leaf Beetle: Jeff House, MU Extension Specialist in New Madrid County, reports finding substantial populations of bean leaf beetles in several fields (especially those behind the Mississippi River levee). Earliest planted soybeans should be 'safe' from this pest; however, any soybeans with developing pods may be at risk. This time of the year the adults (coloration - red to tan, markings - black triangle at the base of their wings) will feed on the leaves (small, round holes between the major leaflet veins) and pods (outer green tissue removed but seeds are not feed upon). Generally, the pod damage is considered more economically important. The recommended Missouri threshold from blooming until maturity is 10 or more adults per row foot and 20% defoliation OR 15 or more adults per row foot and 10% pod damage. Any of the labeled pyrethroid insecticides will control this soybean pest.

Dectes Stem Borer: Anthony Ohmes, MU Extension Specialist in Mississippi County, reported finding Dectes stem borers in a few fields near the Mississippi River. Again, this insect occasionally damages soybean plants, and infestations are usually most severe in fields with a history of cocklebur and ragweed problems. You are most likely to notice the lodging damage by this insect in the fall. Timely harvest will help minimize lodging damage caused by this insect, and disking under the larval-infested stems will help increase larval mortality this winter.

Soybean Podworm: I've received a couple of reports of podworm activity in soybeans. Any fields where the plants are still blooming will be potentially attractive to the female moths. Soybean plants are most susceptible to podworm damage during peak flowering to early pod-fill stages.

A beat-sheet is usually recommended to detect podworms, but it's impractical to use in drilled-seeded soybeans. Instead, I'd recommend using a sweep net and beat the plants over the net. You can also use the sweep net handle to push over the plants and visually check for any pod damage. You should check 10 locations (20 beat net samples is roughly equivalent to 25-row feet per location) per the field for the larvae and any pod damage. The University of Missouri action threshold for insecticide treatments is when podworm populations exceed 1 larva per row foot (or 25 larvae per 20 beat-net sample) and pod damage is 5% or greater. Target mid-sized larvae since they are more exposed on the plant than smaller ones and less resistant to insecticides than larger larvae.

Stink Bugs: I still haven't received any new reports regarding stink bugs infesting soybean fields; however, I would continue monitoring any fields that still have developing seeds and are adjacent to 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.