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Eastern New York Field Crops Pest Report, 2002

For 6/28/02:

Eastern New York Weed Day
Where: CORNELL/VALATIE RESEARCH FARM, Valatie, NY (State Farm Road off Route 9 just north of Valatie)
Time: 9:30 a.m. Registration
10:00 - 12:00 p.m. Field Crop Weed Control (Hahn)

Note: CCA and DEC Credits have been requested
Why Come: You can learn and see the newest strategies for controlling weeds in field corn!


General: The SUNY Cobleskill fields were 10 to 25 inches tall, but much of the alfalfa has lodged, due to thunderstorms and heavy rain.

Alfalfa Weevil: Alfalfa weevil tip feeding dramatically declined this week (June 27). I did not find any larvae in the 5 fields monitored this week, while last week there were 50 per 10 sweeps with the net. Where did they go? They all pupated! What does this mean? It means the potential for alfalfa weevil damage to occur this year is over.

Check out our on-line publication, IPM for Alfalfa Weevil. 1.2 Mb pdf file

Alfalfa Weevil and Parasitoids: Alfalfa weevils have many natural enemies. One group of these are tiny beneficial wasps called parasitoids. Some parasitoid species attack weevils in their egg stage, other types attack larvae, and still other types attack adults. A common weevil parasite (Bathyplectes spp) lays it‚s eggs in late instar larvae just before they pupate. The parasitoid egg hatches and the young wasp feeds on the developing pupa effectively killing the weevil before it completes it‚s development. If you find a weevil cocoon and instead of a healthy green to brown weevil pupa you find a small dark brown egg-shaped structure about 1/8 inch long you have found the cocoon of a Bathyplectes parasitoid. The natural predator has devoured the alfalfa weevil pupa. Biological control in action!

Potato Leafhopper: I found moderate levels of potato leafhopper in 5 alfalfa fields at the SUNY Cobleskill farm this week. While there were no fields over threshold the number of potato leafhoppers is increasing (June 27). Keep those nets sweeping fields!

Check out our on-line publication, Potato Leafhopper Management in Alfalfa

Field Corn

General: Corn growth ranged between the V1 and V4 stage at the SUNY Cobleskill farm this week (June 27). The latest herbicide application on cornfields controlled the weeds that were present last week.

Western Corn Rootworm Vs Striped Cucumber Beetle: Who knows the difference between corn rootworm and striped cucumber beetle?

Pete Carey (Sullivan County) pointed out to me that there is conflicting information about the difference between the two beetles on the World Wide Web. Striped Cucumber Beetle and Western Corn Rootworm look similar but are two different species of insects.

Striped Cucumber Beetle, Acalymma vittatum
The Striped Cucumber Beetle adult is about 1/4 inch long and the upper body surface is about equal black and yellow, the folded wing covers forming three longitudinal black stripes. Adult beetle starts appear on several vegetable crops starting in mid-June.

Western Corn Rootworm, Diabrotica virgifera virgifera
Female Western Corn Rootworm is 5/16 inches long with three black strips alternating with yellow. Male Western Corn Rootworm is mostly black with a small area on the poster end that is yellow-green.

Differences between the two insects:

Female Western Corn Rootworm:
Insect Markings: Stripes are less distinctive and do not extend to the tip of the abdomen.
Insect size: 5/16 inches long
Host range: Primarily Corn, Secondary Cucurbits
Emerge: July
Life cycle:
1. Over-winter as eggs in the soil in the field
2. Eggs hatch and larvae feed on the corn roots starting in late May
3. Adults emerge at time of corn pollination. Males emerge first.
4. Adults lay eggs in cornfields mid to late pollination
5. Adults die, eggs overwinter.

Striped Cucumber Beetle:
Insect Markings: Both sexes have stripes are clearly defined and extend to the tip of the abdomen.
Insect size: 1/4 inch long
Host range Primarily Cucurbits, Secondary beans, corn, potatoes and other crops
Emerge: June
Life cycle:
1. Over-winter as adults in woodland litter or in the soil.
2. Lay eggs at the base of the plant in mid-June through mid-July
3. Larvae develop for 2 to 4 weeks on the roots, pupate in the soil.
4. Adults appear in early to mid-August
5. Adults produced this season overwinter

Refer to the following website on differences between Western Corn Rootworm and Striped Cucumber Beetle: Cucumber Beetles, Corn Rootworms, and Bacterial Wilt in Cucurbits

Is the western corn rootworm the only corn rootworm in New York? See next week's report for the answer.

Black Cutworm: I saw minor patches of cutworm damage in a no-till field this week at the SUNY Cobleskill farm (June 27). Corn is vulnerable to cutworm feeding until about the V6 growth stage. Pay particular attention to no-till or reduced till fields and those fields with poor weed control. Cutworm moths are attracted to grasses and also seem to like laying their eggs on chickweed.

For more information on Black Cutworm in Field Corn, check out our on-line publication (912k pdf file).

Weed Quiz

Are there certain species of weeds resistant to triazine herbicides in New York?
If so, what are they? See next week's report for the answer.

Grass and Pasture

True Armyworm: Lisa Fields, (Schoharie County) reports low captures of true armyworm moths (June 27).


General: Soybean growth ranged between the VE to V3 stage in central NY fields.

Slugs: Holes in soybean leaves? Slime trails may lead to culprit hiding in soil cracks or field residue. Slug damage to young soybean plants is easily found in 5-10% of plants in central NY. Economic impacts not generally expected at low levels observed.

Soybean aphids: Soybean aphids have recently been found in soybean fields in central NY. If soybeans are grown in your neighborhood, field Scouting is recommended. Read about the biology and life cycle of soybean aphids here.

Happy Scouting!