Southeast Missouri Pest Bulletin No. 5, June 17, 2004

INSECTS & OTHER PESTS

It has been relatively quite this week on the insect front, but there are signs pest activity may be picking up in the coming days. I've received reports about several crop pests (ex. aphids, plant bugs, spider mites, stalk borer in cotton; Japanese beetle in corn) being active in southeast Missouri. The latest moth trap captures for the crop pests that we're monitoring are reported in Table 1. (MLB)

CORN

Japanese beetle: I recently received a report of Japanese beetle activity in a Scott County corn field. Though this exotic insect is more of a pest on ornamental plants, Japanese beetles will feed on and damage corn and soybean plants. In eastern Illinois they've found that large numbers of adult beetles (5 or more per plant) can clip silks and prevent proper pollination of the ears. Ron Hines, Univ. of Illinois Dixon Springs Agriculture Center, reported a peak adult flight this past week in southern Illinois.

Adult Japanese beetles are easily identified by their bright coloration (shiny metallic green with bronze-colored forewings). Besides feeding on the developing silks, adult beetles also 'skeletonize' the leaves. Adults usually begin emerging from early- to late-June, and the female beetles will lay their eggs in the soil through August.

Japanese beetles and corn rootworm adults will both clip corn silks; therefore, proper identification is important before deciding to treat a field. Also, adult Japanese beetles have a tendency to congregate in a small area, and this can intensify the damage in that part of a field. Thus, if you find any Japanese beetles, you also should check plants at 5 other sites within the field for the beetles and their damage before deciding to treat the entire field.

COTTON

Crop Report: Based on some information I received from two area consultants, Marilyn Atwill and Phil D. Gurley, this year's crop has greatly improved over the past week. I was struck by range of growth stages (2nd to 12th true leaf cotton) that they were finding from field to field. This may complicate pest management strategies later in the season as pest species will have wider selection of plants to infest and feed on.

Thrips: These insects will remain a threat to any late-planted or replanted cotton that has not reach the 5th or 6th true leaf stage.

Aphids: I haven't received any new reports about insecticide oversprays going out for aphid infestations; however, I'd still keep a close eye on any fields treated multiple times for thrips. It's also important to take note of the number of beneficial insects still present in these fields. A complex of different parasitoid and predatory insects are more efficient in suppressing aphid infestations than a lone group of insects (i.e. ladybird beetles). This is another advantage in selecting a neonicotinoid insecticide (Centric, Intruder, or Trimax) because they are generally 'softer' on beneficial insects than older compounds.

Plant Bugs / Cotton Fleahopper: Michael Johnson reported he has treated some of the cotton that he scouts for plant bugs (primarily the tarnished plant bug). With the favorable weather we've been having lately for crop and weed growth, I expect plant bug populations to be high again this year.

The initial MU action threshold for plant bugs is 6-8 per 100 row feet during the first week of squaring cotton, 8-10 per 100 row feet the second week, and 10-12 per 100 row feet the third week of squaring. Again, an important advantage with the newer insecticides (ex. Centric, Trimax) is each is less toxic to beneficial insects than older compounds. It's also a good idea to rotate away from acephate in case the plant bugs were previously exposed to applications made for thrips. Rotating to a different chemistry will help slow resistance by the plant bugs to acephate. One indication of poor control with any treatment application is when nymphs are still present the following week.

Spider Mites: I'm receiving reports that spider mites are still present in spite of the recent rains, and Michael Johnson reported he was using Kelthane and Zephyr to treat a few fields. To maximize your miticide treatments it's important to apply the compounds at high volumes and pressures to thoroughly coat the underside of leaves where the mites are feeding. The MU action threshold for spider mites is 50% of the plants infested with mites.

Common stalk borer: Phil D. Gurley reported he was finding common stalk borers in a few fields that he scouts. This insect is an occasional, nuisance pest in cotton. The larva is easily identified by its 5 white stripes and the black band encircling its body just behind the true legs.

Stalk borers primarily feed on grasses, but older larvae may feed on other plants (ex. cocklebur, cotton) when they outgrow their grass hosts or when these hosts have been destroyed with herbicides. More widespread infestations may result from poor grass control in no-till or conservation-till fields. As the larva tunnels into the stem, its dried droppings can be seen around the entrance hole in the stem. When the larva tunnels upwards toward the plant terminal, the upper portions of the plant above the tunneling site rapidly die. If you see this damage in the field, cut open the stem lengthwise to locate the larva. Proper identification is important because bollworm larvae occasionally cause similar feeding damage. Since stalk borer larvae feed inside the stems and infestations are generally limited to border areas of fields, a rescue treatment is rarely justified.

RICE

Miscellaneous: On the Missouri Rice webpage (http://agebb.missouri.edu/rice/index.htm), Bruce Beck, Regional Agronomy Specialist in Butler County, has information on rice production in Missouri plus links to other websites. Another website that you might find of interest, is maintained by a Texas A&M University colleague, Dr. Ted Wilson, of mine. Dr. Wilson's website (http://beaumont.tamu.edu/eLibrary/eLibrary_default.htm) has some additional information that you may find useful in your rice operation.

ACKNOWLEDGEMENTS
Photo credit - Dr. Don Steinkraus, University of Arkansas

Table 1. Pheromone moth counts as of June 14th.

Comments: Number of days refers to the last time the trap was checked since the last reporting date.CEW = corn earworm / bollworm, ECB = European corn borer, SWCB = SW corn borer, TBW = tobacco budworm

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.