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NY Weekly Field Crop Pest Report, 2005

May 26, 2005 Volume 4 Number 6

1. View from the Field

2. Alfalfa Weevil Biological Control, Continued

3. How Do You Monitor Alfalfa Weevil

4. Seed Corn Maggot in Soybeans

5. Fusarium Head Blight May be Coming to a Field Near You!

6. Growing Degree Days in NYS

7. Clipboard Checklist

8. Contact Information

View From the Field

Western NYS

Julie Stavisky, NYS IPM

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Poplar Ridge Road, Aurora, NY
Thursday, June 2, 2005
Coffee at 9:30 AM
Program 10 AM to Noon

This last week I found a few alfalfa weevil larvae. There were a few signs of feeding on the leaves. The field I was looking in is right about 310 growing degree days (base temperature 480F). This is when about when you start to see larvae in the fields. How do you monitor for alfalfa weevil? Read on… more information in this issue….

Alfalfa weevil larvae have been seen, but they are few and far between. Occasional cereal leaf beetle eggs are present, but I haven’t seen any larvae yet.

Carl Albers has seen the first signs of alfalfa weevil feeding in Steuben County this year. Also in forage news from the Southern Tier, Carl reports confirmed cases of brown root rot in alfalfa and trefoil. Rough stalked bluegrass and henbit are abundant in alfalfa.

Alfalfa Weevil Biological Control, Continued

Julie Stavisky, NYS IPM

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In addition to the parasitoids we talked about a couple of weeks ago, another biological control friend in alfalfa is an entomophagous fungus. Yes, it’s an insect-feeding fungus. Its only choice for breakfast, lunch, and dinner is the alfalfa weevil. The rain that has been falling on and off for the last week may provide a big advantage for keeping alfalfa weevil larva numbers in check. With the cool temperatures keeping alfalfa growth slow so far this spring, we’ll take all the help we can get for protecting alfalfa.

The fungal pathogen, Zoophthora phytonomi, is always present in low levels in and around alfalfa fields. Under the right cool, wet conditions, an epizootic, or outbreak, of the fungal pathogen can occur. Infected larvae lose their normal light green color. The pale yellow infected larvae become less active and usually die within a few days.

Zoopthora phytonomi first appeared in Ontario, Canada in 1973, and now commonly occurs throughout the weevil’s range in the Midwest and northeast. Although there are several theories about where the fungus might have come from, its origin remains a mystery.

Here’s a photo showing what you may see.

How do you Monitor Alfalfa Weevil.

Ken Wise, NYS IPM

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Monitor alfalfa weevil weekly from mid to late-April through June. Because weevil populations can build up over the life of the alfalfa stand, monitoring fields that are two or more years in production is critical to determine infestation levels. Start weekly field sampling in fields at about 350 degree-days (base temperature 48F) which is about mid to late April in most years, but not this year!

  • Pick 50 alfalfa stems at random throughout the field.

  • Look for the small "shot holes" in the leaves that indicate that larvae are feeding.

  • Record the percentage of alfalfa stems that show the "shot hole" feeding damage in the top 3 inches of the canopy.

Before the first cutting, if 40% of the stem tips show feeding damage, you are at the "action threshold". The good thing is that alfalfa weevil can generally be controlled by harvesting. If you reach an action threshold within a week of your normal 1st cutting date, early harvesting will help avoid economic, yield, and forage quality losses. Alfalfa weevils only have one generation per year and are typically not a problem after first harvest. Occasionally, weevil can damage alfalfa re-growth after harvest. This damage may be more evident in the windrow areas, and can be more noticeable under cool or droughty weather conditions. If you find that 50 percent of the new growth is damaged, with many small larvae present, a chemical control may be warranted. For more information on alfalfa weevil checkout our online publication: http://www.nysipm.cornell.edu/publications/alfweevil.pdf

Seed Corn Maggot in Soybeans

Julie Stavisky, NYS IPM

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Seed corn maggots occasionally attack soybean seeds and seedlings before plants emerge from the soil. Generally, stand reduction does not impact soybean yield potential as directly as corn yield potential is impacted because of the ability of the remaining soybean plants to compensate and fill in gaps. Rarely is damage severe enough to warrant re-planting.

Sources of fresh organic matter draw in the adult female flies. The adults look like a small, slender version of a house fly (they’re about half the size of the house fly). They lay eggs in fresh organic matter, including weeds on the soil surface (or recently incorporated into the soil), recently applied manure, or debris left on the soil surface in a no-till situation.

The seedcorn maggot is a small, yellowish-white, headless, legless larva. The body is tapered in the front with two small black mouth hooks. The maggots seek out seed, then feed directly on the seed before it germinates, and may additionally attack stems on seedlings before they push through the soil. These seedlings seldom survive. Delays in germination resulting from cool weather give seed corn maggot more time to find a seed and do damage before the plant is vigorously growing.

Here’s an image of seed corn maggot in a soybean seed

What is our job now? It’s time to scout newly planted fields as seedlings emerge. Look first for gaps in the stand. Then, focus on plants at several locations in a field, and assess the color and growth stage of the plants. Plants that have a yellowish coloration or appear stunted or wilted may be injured. If cotyledon-stage plants show signs of damage, dig up the soil around the plants to detect the presence of the maggots.

Fusarium Head Blight (Scab) May be Coming to a Wheat Field Near You

Julie Stavisky, NYS IPM

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One of the most devastating diseases of wheat is Fusarium head blight, or scab. The disease reduces yield by decreasing the number of viable kernels, but the more significant impact is that a mycotoxin may be produced by the fungus in diseased kernels.

Scab is caused by airborne spores of the fungus Fusarium graminearum that dwell in nearby crop debris, including corn stalks and wheat straw. This is the same fungus that can cause root, stalk, and ear rots of corn. Since the fungus is very widespread, likelihood of exposure is generally not reduced by crop rotation or other cultural practices. Extended periods of warm, moist weather at crop flowering can cause the anthers to be infected just after their emergence, killing the florets so kernels do not develop. Symptoms of scab become visible on emerged heads soon after flowering. During early grain fill, the disease shows up as pink to salmon orange on infected kernels. As kernel fill progresses, the infected kernels appear bleached. Spikes that are infected later than flowering will produce diseased kernels that are shriveled in appearance.

Stay tuned for more information on Fusarium and prediction models next week!

Growing Degree Days for NYS

Keith Waldron, NYS IPM

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March 1 - May 24, 2005


Base 48 F

Base 50 F







Clifton Park















Data from: http://www.nysipm.cornell.edu/newa/index.html

Clipboard Checklist

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Update field records: variety, planting date/rate, pesticides used, nutrient inputs including manure, other important field observations, etc.

Is hay harvesting equipment ready to go in next 2 weeks?

Note any repairs to corn planters, other spring machinery, and harvesting equipment as they are cleaned and lubricated.

Repair forage harvest equipment as needed

Pest Monitoring Priorities:


alfalfa weevil, weeds, crown rot, leaf spot diseases

Small Grain Cereals:

Winter Wheat: Cereal leaf beetle, virus diseases, weeds, powdery mildew

Spring Grains: Cereal leaf beetle, seedling diseases, weeds

Field Corn:

Monitor corn for weeds, note presence of triazine resistant annual broadleaf weeds. Cultivate or treat if necessary.

Check corn emergence, take stand counts/plant populations, check for signs of damping off / seedling blights, seed corn maggot


Small Grain Management Field Day, Robert Musgrave Research Farm, June 2

Contact Information

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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