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NY Weekly Field Crop Pest Report, 2005

July 1, 2005 Volume 4 Number 11

1. View from the Field

2. What Diseases can Cause Wheat to Lodge?

3. Western Corn Rootworm or Striped Cucumber Beetle?

4. Do Insect Defoliators Impact Soybeans Profits?

5. Soybean Rust Update

6. Growing Degree Days in NYS

7. Clipboard Checklist

8. Contact Information

View From the Field

Western NYS Julie Stavisky

Eastern NYS

Ken Wise

Keith Waldron, NYS IPM

Most soybean fields that I visited had low soybean aphid numbers. For example, one field in Wayne County at the 4th leaf stage had aphids present but not abundant 2 weeks ago, while this week, aphids were difficult to find. Lady beetle pupae, on the other hand, were numerous. All except one of the soybean fields that Nancy Glazier (NWNY Team) is scouting as part of a TAg team in Orleans County were under the threshold of 250 soybean aphids per plant. But one field had as many as 300 aphids per plant. Mike Dennis (Seneca County) reports that aphids are widespread but below the threshold of 250 per plant. Mike Stanyard (NWNY Team) reported a field in Wayne County with up to 400 aphids per plant on beans with 3 fully expanded trifoliates. Natural enemies were not numerous. Septoria brown spot has been reported to be widespread in the state. This foliar fungal disease of soybeans is generally non-economic when beans are in the early vegetative stages. It is encouraging to be getting many questions about Septoria -people are alert for fungal diseases in their soybeans! Grasshoppers were a major threat in a soybean field that Mike Stanyard visited this week. During the early vegetative stages, soybeans can tolerate 30-50% defoliation. Feeding injury caused by grasshoppers appears as ragged holes on the leaf margins. Grasshoppers are likely to be more of a threat during dry weather. Many infestations start in field edges where dense weeds are present. Spider mites have been reported on soybeans in Ontario County

In a couple of corn and soybean fields, I observed snails on lowest leaves.

There was an increase in the infestation of potato leafhoppers in alfalfa this week at the Valatie Cornell Farm. While it was below threshold they increased from the previous week. Most likely the increase was due to hot weather we have been receiving. Soybean aphids in the soybean plots were at very low in numbers this week. Aphids ranged for 0 to 5 per plant on V3 staged soybeans beans.

While conducting an Organic Field Crops TAg meeting in Essex County we monitored glume blotch on hard white wheat. In some fields there was infection on every head. There was no sign of Fusarium head blight (Scab). During the same meeting we found a few soybean aphids in organic soybean fields. These fields had been row cultivated the previous week and seemed to have good weed control. We also viewed a soybean field that had been blind cultivated with a tine-weeder twice this season and had excellent weed control.

Soybean aphid populations in most of our production areas appear to be stable and well below the 250+ SBA’s per plant action threshold. In central NY a few young soybean stands (4-5 leaf stage) have gone over threshold. Opportunities for Treat / No Treat insecticide comparisons are being sought. Michigan reports presence of winged SBA’s suggesting the potential of an influx of aphids into eastern US and Canada should the right weather pattern occur. I.e. should we get storms in the next week watch field for presence of newly deposited winged SBA’s.

What diseases can cause wheat to lodge?

Julie Stavisky, NYS IPM

I observed a winter wheat field this week where a small section of plants in a low spot in the field had lodged. Too much nitrogen fertilizer was applied, right? Not necessarily! There are a couple of fungal diseases that can cause wheat plants to lodge during grain fill despite balanced fertilization.

Strawbreaker, or eyespot foot rot, causes plants to break off about an inch above the soil line. Diamond shaped lesions (like a cat’s eye) appear on lower stems (see photo). As the disease progresses, the lesions take on a charred appearance. The development of the disease is favored by dense stands, high soil moisture, and high humidity. Aside from the possibility of causing lodging, foot rot can reduce the quality of grain by inhibiting the flow of nutrients up through the damaged portion of the stem to the filling kernels.

If instead of breaking off above the soil surface the wheat plants fall over at soil level, the culprit may be another fungal disease, take-all. With take-all, a plant’s roots are blackened and rotten. Lower stems are blackish in appearance. When the lowest leaf sheath is pulled back, the infected area is shiny black. If the infestation of take-all is severe, grain heads of infected plants will appear white. The presence of shriveled kernels can lead to a decrease in yields. Take-all is favored when the soil pH is high.

A good test to distinguish between eyespot foot rot and take-all is to give a tiller a gentle tug. If the plant is easily pulled out of the ground, it is likely to be take-all. If the roots are strong enough to hold the plant in the ground, the root system remains relatively healthy and eyespot foot rot is the more likely culprit.

So upon closer examination of the field with lodged plants I observed this week, lesions were present on the lower stems. Thus, the field I looked at was suffering from eyespot foot rot.

Both of these diseases reside in the soil and are encouraged by having a continuous grass host. Rotation to a non-grass crop for 2 years is the primary means of reducing the likelihood of crop infection.

Western Corn Rootworm or the Striped Cucumber Beetle?

Ken Wise, NYS IPM

Have you ever gotten western corn rootworm confused with the striped cucumber beetle? Do you know the difference between corn rootworm and striped cucumber beetle? 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. The adult beetle starts appearing 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. Adults start appearing in mid to late July

Female Western Corn Rootworm

Striped Cucumber Beetle

Insect Markings

Stripes are less distinctive and do not extend to the tip of the abdomen

Both sexes have stripes, are clearly defined, and extend to the tip of the abdomen.

Insect size

5/16 inches long

1/4 inch long

Host range

Primarily Corn
Secondary Cucurbits

Primarily Cucurbits
Secondary beans, corn, potatoes and other crops

Emerge

July

June

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

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

Learn more about the differences between Western Corn Rootworm and Striped Cucumber Beetle:
Cucumber Beetles, Corn Rootworms, and Bacterial Wilt in Cucurbits

When do Insect Defoliators Impact Soybeans Profits?

Ken Wise, NYS IPM

Japanese beetle and Mexican bean beetle are the main defoliators of soybeans in NYS. While they are minor pests, defoliation of soybeans sends up many red flags by growers. The question normally is how much leaf defoliation is too much in soybeans? The good thing is that soybeans can withstand much defoliation without losing yield. The soybean defoliation threshold is 35 percent of leaf area eaten or missing from V1 to just before bloom. During blooming through pod-filling stages, the threshold is 20 percent defoliation. The following pictures are a guide that depict 10, 20, 30 and 40 percent defoliation:

10 percent defoliation 20 percent defoliation

30 percent defoliation 40 percent defoliation

(Source: Purdue University Field Crops Pest Management Manual, 1/92)

Soybean Rust Update

Keith Waldron, NYS IPM

USDA national and state commentaries report today that Soybean rust has been confirmed on soybeans in AL, GA and FL. The Alabama and Florida finds were in sentinel sites, while the Georgia find was on volunteer soybeans which have since been destroyed. The soybean sentinel plot in Marion County, FL is in the same county where rust was found on kudzu earlier this year. See map of SBR confirmed areas at http://www.sbrusa.net/. The NYS soybean rust website states: “Scouting and spore trapping continues throughout the soybean production areas of the U.S. Sentinel plots in New York State were scouted this week and no soybean rust was found. (Last updated 6/30/05)”. http://www.ppath.cornell.edu/soybeanrustny/default.htm.

Soybean Rust in US - 6.30.05

Growing Degree Days for NYS

Keith Waldron, NYS IPM

March 1 - June 29, 2005

Location

Base 48 F

Base 50 F

Batavia

921.4

799.4

Chazy

759

653.7

Clifton Park

1178.5

1025.3

Geneva

923.2

795.7

Ithaca

850.4

731.2

Mexico

527.3*

444.9 *

Prattsburg

775.3*

666.4*

* Missing data

Source: http://newa.nysaes.cornell.edu/base5005.htm

Note: Alfalfa weevil expected growth stages (Accum GDD@48F): pupa (725), adult emergence (815)…. Alfalfa weevil season ends for 2005.

Clipboard Checklist

Keith Waldron, NYS IPM

General:

• Maintain crop production activity records by field, including harvest date, pesticides used, nutrient inputs including manure, etc.

Alfalfa & Hay:

• Continue monitoring for potato leafhopper- harvest early or spray on basis of need.

• Monitor for diseases, particularly Verticillium wilt, record information on type and location for future cropping decisions.

Small Grains:

• Prepare for grain harvest: combine ready?, check and disinfect inside, under and around grain bins.

• Watch wheat grain moisture. Be ready to combine at 18 percent.

Corn:

• Monitor for foliar and stalk diseases, nitrogen and other nutrient deficiencies, European corn borer, weeds.

• Monitor corn rootworm adults at silking.

Soybeans:

• Monitor for soybean aphid, soybean rust, foliar diseases.

Livestock:

• Continue livestock facility sanitation management (manure, feed bunks and storage areas, waterers, etc.). A cleaner barn means less fly production

• Initiate integration of biological control agents into house fly and stable fly management program.

• Mow around facilities to minimize rodent habitat.

• Monitor young stock for cattle lice and mange mites

• Check condition of pastures and animals on pastures

- Evaluate need for face fly and stable fly control measures

- Check and clean pasture water supplies.

Contact Information

Julie Stavisky: IPM Area Educator, Livestock and Field Crops, Western NY
Phone: (315) 331-8415
Fax: (315) 331-8411
Email: js38@cornell.edu

Keith Waldron: NYS Livestock and Field Crops IPM Coordinator
Phone: (315) 787 - 2432
Fax: (315) 787-2360
Email: jkw5@cornell.edu

Ken Wise: Eastern NYS IPM Area Educator: Field Crops and Livestock
Phone: (518) 434-1690
Fax: (518) 426-3316
Email: klw24@cornell.edu