Weekly Field Crops Pest Report 2007

View from the Field

Eastern NYS-Ken Wise

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Are you Ready, Set, GO: insect pests, geese, deer, plant diseases, weeds, flies!!! This is the 7th year of the NYS IPM Weekly Field Crops Pest Report. 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.

This spring I have been evaluating Tom Kilcer’s Triticale variety trials in Columbia County. Some of the plots have snow mold and possibly Stagonospora nodorum blotch. 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 forage or grain. The photo below shows triticale plants with snow mold.

An early start on scouting wheat diseases

Julie Dennis
NYS IPM

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Wheat has only just begun to green-up in the past week or two, and in the fields I have seen, growth remains slow probably due to the continued cold nights and stubborn daytime temperatures. Even so, it isn’t too early to get out and check how the wheat is doing this spring since there are several diseases that can get an early foothold. At least we are not still buried in snow as we were last year at this time!

A fundamental concept that should underlie all management decisions is the plant growth stage. Effective management decisions are based on guidelines that refer to pest thresholds at specific crop growth stages. To identify the stage of growth of wheat, please refer to the Feekes scale. Wheat in NY is still in the tillering stages, or stage 2 & 3 on the Feekes scale. Bare spots in fields at this time of year are not unusual, and wheat diseases may be to blame. Unhealthy plants do not grow vigorously in the spring due to infection with pathogens that cause root and crown rots. Many different fungal organisms cause root and crown rot diseases of wheat, and it is often difficult to distinguish which causal agent is present. The most common organisms that cause root and crown rots include Fusarium and Pythium. Seedling blights and rots 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. Over the past winter, most areas had plenty of snow cover to insulate plants, so dormant plants were pretty well protected from the elements.

Fusarium seedling blight: Seedlings and tillering plants infected with Fusarium seedling 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 Fusarium fungi can survive in plant residue or as dormant spores in the soil for several months.

Pythium root rot: The “water mold” that causes Pythium root rot may first infect the seedlings in fall-planted wheat, though seedlings are rarely killed. The stunting of seedlings resulting from Pythium infection 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. Pythium spores survive several years in soil without a host, and spores are present in all soil types. Infection of plants is greatest in cold, wet, and clay soils.

Refuge Refresher: Bt Corn Planting

Julie Dennis
NYS IPM

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Use of Bt corn for management of corn rootworm (CRW) has become a common practice across New York State. European corn borer (ECB) is not as significant a threat as rootworm, but Bt corn is also available for this pest. Many of our hybrid choices are “stacked” - meaning they contain Bt traits to manage both of these pests. Regardless of the targeted pest or pests, a non-Bt refuge must be planted when a Bt corn crop is planted. Why is a refuge planted?

• To keep a portion of the population from being exposed to the Bt toxin
• To prevent the development of CRW or ECB populations resistant to Bt

Because the EPA requires farmers by law to plant a refuge - 20% of the acres must be planted to corn without the Bt trait. When the seed is purchased, an agreement to plant the refuge is signed.

If pests become resistant, this tool will be lost. (Remember, having more options available allows us to better implement IPM!)

Here’s a brief overview of refuge requirements for Bt Rootworm corn:

(The refuge requirements are more strict for CRW than for ECB, so if CRW requirements are followed, you’re all set for both pests)

• Plant at least 20% of corn acres with a corn hybrid that does not contain Bt technology for CRW
• The refuge can be treated with soil insecticide or seed applied insecticide, but NOT with other Bt insecticides
• Other management of the refuge field must be similar, including planting date, maturity group, and fertility program.
• Plant the refuge within the field or in an adjacent corn field (your neighbor’s corn field is NOT considered your refuge!)

Options for the configurations of a refuge include:

• Adjacent to Bt corn field (not further away than across a road, path, or ditch)
• Field end rows or field perimeter
• Strips within a field (Note that different seed companies permit different strip widths)
• Mixing of non-Bt seed with Bt rootworm seed for inter-planting is not permitted

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 is one of the possible problems that 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, the symptoms are a complex, consisting of several of the pathogens that attack 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 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 Pythium or Phytopthora root rot which attack lateral and main root systems leaving plants with limited holding power for staying in the ground. The photos shown came from a field in Freeville NY which was poorly drained and had a history of Phytopthora root rot.

Assess Alfalfa Stands for Brown Root Rot This Spring

Gary Bergstrom
Cornell and Michael J. Wunsch: Department of Plant Pathology and Plant-Microbe Biology, Cornell University

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If your alfalfa that looked great last October is slow to emerge this spring or if it has suffered apparent ‘winterkill’, brown root rot (BRR) may be one of the main contributing causes.

Brown root rot, caused by the fungus Phoma sclerotioides, is a cold-weather disease affecting the roots and crowns of alfalfa during the dormant period when plants are not actively growing. April through early May is the best time to assess over-wintered alfalfa plants for the symptoms and signs of BRR. It is difficult to diagnose BRR in dead plants, but characteristic lesions can be discerned on the roots and crowns of plants showing slow regrowth of shoots from the crown buds in spring. You will need a good shovel or trowel to dig up plants and a bucket of water to rinse off adhering soil for a closer inspection. A pocket knife is useful for slicing through roots to determine the depth of lesions. BRR lesions vary in appearance, but they are generally light to dark brown, often with a darker border. BRR lesions that girdle the upper tap root or the crown result in winterkill. BRR lesions that girdle the lower tap root or affect just part of the root or crown, can lead to reduced plant vigor and slow emergence of alfalfa in the spring. You can be fairly certain that BRR was a factor in poor winter survival and reduced plant vigor when you see characteristic root symptoms on a high percentage of plants in early spring and there are winterkilled plants interspersed with slowly emerging plants in patches scattered across the field. The severity of brown root rot increases as the plants age and experience more winters.

Absolute confirmation of brown root rot requires a molecular laboratory test that is recently available from the Cornell University Plant Disease Diagnostic Clinic for $40 per composite field sample. The result will be yes/no whether the BRR fungus was present at any level in the overall sample. We suggest you call the clinic at 607-255-7850 prior to submission of samples for diagnosis.

First confirmed within New York in Clinton Co. in 2003, BRR is now known to occur throughout New York, Vermont, New Hampshire and Maine. In New York, high incidence levels of the disease have been observed in alfalfa production fields across western, southern tier, and northern parts of the state. The disease is most severe in regions with harsh winters such as in northern New York and northern New England. Many other stresses to alfalfa plants interact with BRR to cause plant death. Winterkill is not a new problem for New York alfalfa producers. The brown root rot fungus may not be new either though our recognition of it in the Northeast is very recent. The widespread finding of BRR in association with winterkill represents an opportunity to reverse one of the main factors that reduces the productivity and longevity of alfalfa in our region. There is no action that an alfalfa producer can take currently to control BRR, but we hope that ongoing research at Cornell University and elsewhere will change that. With support from the Northern New York Agricultural Development Program we are assessing alfalfa varieties adapted to this region in BRR-infested soils in order to identify varieties that may perform better than others in the presence of the BRR fungus.

Figure 1. Range of typical brown root rot symptoms in alfalfa. Note the light to dark brown lesions and the flaky epidermal tissues within the lesions. Photos by Kent Loeffler, Cornell University.

Soybean Rust Center

Gary Bergstrom
Cornell University Plant Pathology,

On April 10th, all green tissue from a soybean rust-infected kudzu vine in Mobile, Alabama was removed. This was the only "known" rust-infected site in Alabama. At this time the disease can only be found in Florida. Soybean rust is still active on kudzu in six counties in Florida. Soybean sentinel plots are beginning to be planted in some of the Gulf Coast states. Kudzu is also greening-up rapidly in this region of the country.

NYS Soybean Rust Information Center

National Soybean Rust Website

Clipboard Checklist

Keith Waldron
NYS IPM

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General
*Walk fields to check tile flow, check and clear drainage outlets. Look for line breaks.
*Observe wet areas and plot on aerial photo of farm for future drainage considerations and crop decisions
*Maintain crop records by field, including variety, planting date, pesticides used, nutrient inputs including manure, etc.
*Watch for early season weeds: winter annuals, chickweed, henbit, field penny cress, shepherd's purse, giant ragweed, lambsquarters, Pennsylvania smartweed, common sunflower
*Store snow shovel, "summerize" sno-blower?

Alfalfa and Small Grains:
*Monitor alfalfa for Alfalfa Snout Beetle (In Oswego, Jefferson, Cayuga, Wayne, Lewis, St. Lawrence, Clinton, Essex, and Franklin counties)
*Monitor alfalfa for Alfalfa weevil as weather continues to warm
Evaluate established legume stands for winter damage (thinning stand, frost heave), determine average alfalfa stand count, adjust crop plans if necessary
*Monitor winter grain fields for over wintering survival, virus disease symptoms, goose damage

Corn:
*Pre-plant weed evaluation
*Prepare land for corn if it is dry enough and begin planting the last week of April if it is dry (even if it is cold!)

Pastures:
*Check and mend fences as needed.
*Check crop growth
*Review/Plan rotation system

Equipment:
*Arrange for custom weed control or check your own application or cultivator equipment for repairs.
*Check nozzles, pumps, etc., recalibrate pesticide application equipment regularly before use.
*Calibrate planting equipment - maintain records on crop planting rate per field
*Calibrate manure spreaders - maintain records on amount spread per field

Storage:
*Check forage allocation and anticipate feed program adjustments as forages from previous year are used up
*Plan where forages should be stored for optimum allocation next feeding season

Contact Information

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Julie Dennis: 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