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NY Weekly Field Crop Pest Report, 2005

April 18, 2005 Volume 4 Number 1

1. View from the Field

2. Alfalfa Winter Kill, Root Diseases and Frost Heaving

3. Wheat Root and Crown Rot

4. Snow Mold-Small Grains

5. Insecticide Seed Treatment for Seed Corn Maggot-Field Corn

6. Soybean Rust Center

7. Clipboard Checklist

8. Contact Information

View From The Field

Ken Wise-NYS IPM

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"Seasons Greetings". Spring is finally here and time to start a new growing season. This year the Weekly Field Crop Pest Report has a new look and will have a statewide focus. Julie Stavisky, Keith Waldron and I are excited about this new venture and will be collaborating to prepare this weekly report. We need your help to make this both timely and useful. Please feel free to share your field crop pest observations and concerns with us as we try to pool and summarize each week’s significant pest related information. Hopefully, this shared information will help each of us learn about, and better anticipate, emerging problems and stimulate improved discussion regarding pest management. We look forward to hearing from you.

Signs of spring are everywhere. Alfalfa fields are slowly greening up and wheat has started to tiller, hardware in the field and land preparation has begun on many fields this last week. This nice dry weather is starting to dry out fields enough to work the soil. Can planting be far behind? Before we know it pests will once again be emerging and making their presence known. It is a good time to prepare for the coming season. Remind growers that by watching and monitoring fields for certain pest like potato leafhopper, corn rootworm, soybean rust, and so on; they can avoid economic losses now and in the future.

Alfalfa Winter Kill, Root Diseases and Frost Heaving

Ken Wise-NYS IPM

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There are many potential causes of alfalfa winter kill often involving some type of root disease. Crown rot, one of the possible problems can occur in older fields with a history of stress, heavy traffic or grazing, poor drainage, fertility and pH problems, previous insect damage, etc. Plants exhibiting crown rot appear stunted and have few stems. Crown rot progresses slowly in the crown and taproot area of the plant. In many situations, crown rot cannot be attributed to a single pathogen. Several fungi (Fusarium spp., Phoma, Pythium, Rhizoctonia) as well as some bacteria, have been implicated in the disease. Often, a complex consisting of several of the pathogens attacks the plant. The way to tell if a plant has the disease is to dig up (not pull up) a plant showing symptoms. Then use a knife to split open the crowns and roots. Healthy tissue should be white, moist, and firm. Rotted tissue usually has a black or brownish- red color, but the color may vary from yellowish to pinkish or gray.

Another common alfalfa problem observed this time of year is frost heaved crowns. Low areas of the field that tend to accumulate water are sites worth checking for this ailment. Frost heaving may indicate potential disease problems such as Pythiumor Phytopthoraroot rot which attack lateral and main root systems leaving plants with limited holding power for staying in the ground. The photo shown came from a field in Freeville NY (Year 2004) which was poorly drained and had a history of Phytopthora root rot.

Wheat Root and Crown Rot

Julie Stavisky-NYS IPM

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Root and crown rot diseases of wheat are caused by many different fungal organisms, and it is often difficult to distinguish which causal agent is present. The most common organisms which cause seedling blight include Fusariumand Pythium. Seedling blights are more likely to be severe under excessively wet conditions and when soil temperatures are too low for good growth. Plants injured from frost heaving, resulting from repeated freezing and thawing, are especially vulnerable.

Fusariumseedling blight: Seedlings and tillering plants infected with Fusariumseedling blight are generally stunted and yellow, and the crown, roots, or lower stem take on a brown to reddish-brown water-soaked rotten appearance. If plants survive, they have a brittle, stunted appearance and are paler green than healthy plants. Plant death can result in patchy stand reduction. The Fusariumfungi can survive in plant residue or as dormant spores in the soil for several moths.

Pythiumroot rot: The “water mold” that causes Pythiumroot rot may first infect the seedlings in fall-planted cereals, though seedlings are rarely killed. The stunting of seedlings resulting from Pythiuminfection may go unnoticed until other plants in the field begin healthy, vigorous growth in the spring. Roots of infected plants begin to turn brown then disintegrate beginning at the root tips. Plant mortality can occur if infection is severe enough for the rotted roots to break away from the crown. Pythiumspores survive several years in soil without a host, and spores are present in all soil types. Infection of plants is greatest in cold, wet, clay soils.

Snow mold-Small Grains

Ken Wise-NYS IPM

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Pink snow mold (Fusarium nivale) and speckled snow mold (Typhulaspecies) are the two main fungi that cause this disease. Pink snow mold is by far more common than speckled snow mold. Many times snow mold occurs in patches in the field after the snow melts. You will observe a fungal mass on the leaves that appears pinkish, whitish or gray. Many times the leaves will have brown-black fungal bodies which are called sclerotia. The leaves could be partly or entirely killed. If snow mold infects the crown it will kill the plant. If the crown is not infected most likely new leaves will grow back and the plant should produce grain.

Insecticide Seed Treatments for Seed Corn Maggot-Field Corn

Ken Wise-NYS IPM

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During the last few years I have been in a few corn fields where seed corn maggot infestations have reduced plant populations by 5,000 to 6,000 plants per acre. This reduction can translate to a loss of 1 to 2 tons of corn silage per acre. This pest is, however, easily and inexpensively controlled by using an insecticide planter box seed treatment or insecticide pretreated seed. Prevention is the key to controlling seed corn maggot!

Seed corn maggot (SCM) is an insect pest that feeds on large seeded crops like corn and soybean. In the early spring, the female SCM fly searches fields with high organic matter (decomposing plant material, fields with manure, etc.) for soil cracks and germinating seeds in which to lay their eggs. Maggots hatch from the eggs and feed by burrowing into germinating seeds. These maggots are tapered, legless, appear to be headless, pale yellowish-white, and reach a length of about a 1/4 inch long. Symptoms of SCM damage may show as skips in the corn rows. In bean crops, such as soybeans and drybeans, SCM damaged seedlings may appear as "snake heads" i.e. seedlings without cotyledons. Proper diagnosis requires some digging in the gaps within a row to check for seeds and on seed health. For more information on SCM management check out Early Season Insect Pests of Corn

Soybean Rust Center

Julie Stavisky-NYS IPM

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The New York State Soybean Rust Information Center is now available online! This will be our best first resource as things develop in the soybean crop this year

Clipboard Checklist

Ken Wise-NYS IPM

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Check alfalfa and wheat stands for overwintering success
Treat corn seed with an insecticide for seed corn maggot
Treat corn seed with an insecticide for seed corn maggot
Treat corn seed with a fungicide for seed and seedling diseases
Watch for alfalfa weevil damage as the weather continues to warm
Watch for early season weeds: field penny cress, shepherd's purse, giant ragweed, lambsquarters, Pennsylvania smartweed, common sunflower