Southeast Missouri Pest Bulletin No. 6, June 23, 2004

INSECTS & OTHER PESTS
Well, insect activity has started to pickup during the past few days. I just hope this isn't the calm before the storm! I've recently received reports about the following crop pests (ex. plant bugs, saltmarsh caterpillars, spider mites, in cotton; grasshoppers, stink bugs in soybean) being active in southeast Missouri. (MLB)

COTTON
Crop Report: The latest DD60 data based on Portageville weather information indicates we are way ahead of last year. As of June 21st, we've accumulated 775 heat units (vs. 485 in 2003) since May the 1st.

Irrigation: Remember if your crop wilts it has already been injured. This results in reduced yields, short staple length and premature cutout. The staple within a boll is determined within the first 3 weeks after flowering, and water stress during this period will shorten the fiber since plants use water to swell and elongate the fiber. If the crop has a tendency to get too tall due to irrigation, mepiquat chloride or mepiquat pentaborate should be used. (BP)

The appearance of the soil surface can be very deceiving. Use a soil probe to observe the soil below the surface where the roots are located to get the true story. Adequate irrigation will prevent the crop from cutting out too early. In Missouri we want the crop to cutout on August 10th. Cutout before this date will reduce yields, and thereafter upper bolls may not have enough time to mature.

Plant Bugs / Cotton Fleahopper: Ed Kowalski reported he has observed an increasing number of adult plant bugs in fields that he scouts. I've also observed that daisy fleabane and plains coreopsis are supporting high numbers of tarnished plant bugs plus cotton fleahoppers that can further add to field infestations. The MU action thresholds for plant bugs (# / 100 row ft.) are as follows: 6-8 the first week of squaring cotton, 8-10 the second week, 10-12 third week, and 15 or more the fourth week of squaring. Besides taking note of the number of plant bugs present in your fields, it's also important to keep track of square retention. Ideally, you'd like to have 80% or greater retention of the first position fruiting forms. (MLB)

Spider Mites: I'm still receiving reports that spider mites are persisting and that populations are building once again. Heavy rainfall can help reduce spider mite problems, but the recent rains have been too spotty to help much. The MU action threshold is 50% of the plants infested with mites.

Saltmarsh caterpillar: Ed Kowalski also reported he was seeing a lot of egg lays by saltmarsh caterpillars. Though these insects are considered a minor pest on cotton, they can cause significant defoliation damage when populations are concentrated in an area. These large, hairy (red or black) caterpillars are yellow, brown, or almost black in coloration with yellow lines.

These insects tend to migrate into cotton fields from border vegetation to feed on young cotton seedlings as well as older plants. Saltmarsh caterpillar defoliation damage is similar to that of looper larvae. The larvae initially remove the green tissue from the leaves, and damaged leaves typically have a "window-pane" appearance. As the larvae increase in size and appetite, they'll consume all the tissue between the leaf veins.

Missouri has no set threshold for saltmarsh caterpillars; therefore, I'd recommend using the looper threshold of 25% defoliation while bolls are still developing. Studies conducted at Mississippi State found that the insect growth regulator Intrepid 2F (methoxyfenozide) at two fluid ounces per acre to be effective in controlling saltmarsh caterpillars.

RICE
Rice stink bug: Nothing to report about field infestations for this rice pest, but I did want to remind you about mowing around your fields as it relates to this insect. If you're incline to mow around rice fields, do so before the rice panicles emerge. Once the panicles appear you don't want to flare stink bug infestations by eliminating their weed hosts. Also, carefully watch any fields where grass weeds (ex. barnyardgrass) are present because stink bug infestations are more likely in these fields.

SOYBEAN
Stink Bugs: This week I've received a couple of calls regarding stink bugs in soybeans. I cannot recall addressing stink bug problems this early in soybeans; however, with more plantings of Group III soybean varieties in the Bootheel, I'm not surprised to learn about stink bugs in these fields. Jeff House, MU Regional Extension Specialist, also reported he easily observed adult stink bugs feeding on pods in fields behind the Mississippi River levee. If you've booked your soybeans early to take advantage of high market prices, NOW is the time to scout your early soybeans once the plants are blooming and producing pods.

Both brown and green stink bugs can be significant pests of soybeans. Fortunately, the information I've received at this time is that green stink bugs are mainly present in these Group III soybeans. Green stink bugs tend to be easier to control with insecticides. Stink bugs primarily use their piercing-sucking mouthparts to remove plant fluids from pods and seeds. Their feeding punctures are identifiable by the presence of small brown or black spots. Stink bug feeding damage can certainly reduce your soybean yields by causing seeds to abort or shrivel, but keep in mind that you can be docked several cents to the bushel should seed quality (discolored, deformed) also be affected. Stink bugs also can delay plant maturity and cause abnormal production of leaflets and pods. This condition is referred to as the "green bean effect". Indirectly, high numbers of stink bugs mixed in with the harvested soybeans can result in further price dockage at the elevator.

To sample soybeans for stink bug infestations, I'd recommend using a sweep net since it's a quicker and easier to use in drilled fields. It's important to sample several different spots in a field, because stink bugs lay their eggs in masses. Initially, this means their infestations are 'clumped' along field edges, and then the infestations will gradually spread across the field as the populations increase.

Control Decisions:

1. Before applying an insecticide take note of the percentage of parasitized eggs (darker than normal) and predators present in the field.
2. Treatment is recommended once infestations reach 2 or more stink bugs (large nymphs and adults) per 3-row feet as the seeds begin to fill.
3. If green stink bugs are present, then a pyrethroid insecticide (ex. Asana, Baythroid, Karate, Mustang Max, Prolex) will be sufficient; however, if a significant level (25% or more) of brown stink bugs also are present, then you might consider adding in an organophosphate (ex. methyl parathion) insecticide to improve control of the brown species.

ANNOUNCEMENTS
Dr. Andy Kendig has scheduled his 2004 Delta Center Weed Tour for Thursday, July 15th, at 9:30 AM. The weed tour will be held at the Rone Exhibit Hall at the MU Delta Center Lee Farm. The farm is 8 miles southeast of Portageville at the intersection of highways T and TT. He asks that you contact him at (573) 379-5431 so you can preregister. Typically, 2 hours of CCA credit are available for this weed tour.

DISCLAIMER STATEMENT
The University of Missouri does not warrant products mentioned in this publication. The use of a trade name does not constitute recommendation of one product over other (generic) products of a similar chemistry.