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Eastern New York Field Crops Pest Report, 2004

This is a seasonal scouting report giving growers in the Eastern New York area information on the presence of agricultural pests. The report is written by Ken Wise, IPM Extension Area Educator for Livestock and Field Crops.

For 5/5/04:

Note: All Eastern New York Extension Educators who wish to contribute their pest monitoring observations to the Eastern New York Field Crops Pest Report, are invited to do so and join in the fun.


Leaf Spots on Alfalfa

Our cool, moist early season weather has provided great conditions for several leaf spot diseases. Three of the more common you might find while walking fields are spring black stem, common leaf spot, and Leptosphaerulinaleaf spot.

Spring Black Stem: is favored by cool and moist weather in early spring. Symptoms appear as irregularly shaped brown to black spots that can merge to form a larger blotch. This disease can infect the petiole, form elongated blackened areas on the stems, and may be a contributor to a crown rot.

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Common Leaf Spot: proliferates when the weather is cool and wet. This disease first develops on the lower leaves near the soil surface and then progresses upward through the canopy. Common leaf spot appears as small, circular, dark brown to black spots, about 1/16 inch in diameter. Tiny, raised, light brown disk-shaped fungal fruiting bodies visible when a hand lens can be observed in the center of mature lesions. See photo at: Common Leaf Spot

Leptosphaerulina Leaf Spot: is also favored by cool and moist weather in early spring and late summer to early fall. The lesions usually start as small black spots and enlarge to oval or round “eyespots” 1/16 to 1/8 inch across. As lesions develop they become light brown or tan with dark brown borders; often surrounded by a chlorotic (yellow) area. This disease primarily attacks young leaflets but may also attack petioles and other plant parts. See photo at: Leptosphaerulina Leaf Spot

Management of leaf spots on alfalfa: If infections are severe in fields, early cutting generally is recommended to avoid defoliation damage. Sound crop management limits the development and impact of diseases. Any practice that reduces crop stress (biotic or abiotic) and promotes vigor will help extend the productive life of the stand. This becomes even more critical in the presence of serious disease organisms. In the unlikely event that severe foliar infections cause 25% or more defoliation, early harvest is generally recommended to avoid further losses. Check out our on-line publication: IPM for Alfalfa Diseases: Leaf Spots

Alfalfa Weevil Creeps into Fields, but No Eggs to be Found!

Last week (April 29), I discovered a few adult alfalfa weevils. I looked far and wide for eggs in stems of alfalfa and did not find any. Do you know what the eggs look like when the adult female weevil lays them in a stem? Weevils chew a hole and lay up to 25 eggs at one time into an alfalfa stem. Each female weevil can lay from 500 to 2000 eggs during the growing season. When eggs are first deposited into the stem they are yellow and then turn darker as they develop. First instar larvae hatch from eggs at about 280 growing degree-days (48F base temp). Here is a website with great pictures of alfalfa weevil egg development: Alfalfa Weevil Eggs. Check out our on-line publication, IPM for Alfalfa Weevil.

Winter kill or Alfalfa Snout Beetle?

Alfalfa snout beetles (ASB) are root-feeding weevils found only in northern New York State, southern Ontario and central Europe. Lucky us, eh? For those unfortunate NY counties along Lake Ontario and the St. Lawrence (Clinton to Cayuga) where ASB infestations have been confirmed, winter killed alfalfa may really be an indication of ASB damage.

ASB’s are mottled gray, humpbacked, 1/2 inch long, do not fly, and are all females. Adults emerge in the spring to feed on new shoots from the alfalfa crown. Spring ASB emergence occurs about the time the shadbush (Amelanchier sp., aka Juneberry, Serviceberry) blooms. When adults emerge in the spring they migrate in mass numbers often in a northeast or northwest direction. Note: above ground migrations can be just the tip of the alfalfa damage “iceberg”. ASB larvae live about 2 years feeding on roots. Larvae are legless, white, 1/2 inch long, and can be found feeding on alfalfa roots within a foot of the soil surface in mid to late summer. Larvae feed on side roots, and girdle the main taproot causing death to the plant. In early fall the larvae move deeper in the soil where they spend the winter. The following spring the larvae move 10-12 inches from the surface, pupate by mid-summer and become inactive adults, which remain in the soil until the following spring. ASB damage in the spring looks similar to winter killed alfalfa with plants failing to “green up”. ASB is one of the few pests that can completely destroy an alfalfa field, almost literally overnight. Some growers have been forced to grow other forages than alfalfa because of the destructive damage by this insect to alfalfa and clover.

Management Alternatives for Alfalfa Snout Beetle
  • To combat the ASB the 1st line of defense is to practice intensive crop management.

  • Rotation with susceptible and non-susceptible crops is very important.

  • Rotation limits the ASB from developing large infestations in field. ASB has host plants other than alfalfa that make eradication impossible.

  • Host plants for ASB are alfalfa, red clover, dock, wild carrot, quackgrass, and white clover.

  • Non-host cultivated crops for ASB are corn, wheat, oats, soybeans, potatoes, and birdsfoot trefoil.

  • Growers should plan to crop alfalfa for 3-4 seasons, using clear seedlings, and then rotate with non-host cultivated crops for 2 or 3 successive years.

  • New infestations can result from transporting ASB infested equipment, hay bales, gravel and soil to other locations. Take precautions to limit transport of these unwanted hitchhikers by cleaning equipment between fields and farms.

  • Use of insecticides is not an effective control for ASB.

Field Corn

Black Cutworm alert in the Mid-West: Several areas of the Mid-West are reporting a large number of black cutworms moths captured in light traps. This does not mean that they will be a problem but maybe potential for damage. Why should we be concerned with black cutworm here, while they are in the middle of the country? Adult moths ride storms from the south and mid-west moving north looking for fields to eat! More on black cutworm next week; STAY TURNED! Check out our on-line publication, Black Cutworm in Field Corn Management Guide 912K pdf file

When do weeds wakeup in the spring?
It is a good idea to know when certain weeds wakeup in the spring! By knowing when certain species of weeds emerge, selection of the best control measures can be employed. We can break weeds down into the accumulation of growing degree-days (48F Base Temp.) as a means to know when plants might start to emerge:

Group 0 (Emergence occurs in fall or early spring)
Winter annuals normally complete emergence prior to planting of corn.
Examples: horsetails (mares tail), white cockle, field penny cress, shepherd's purse

Group 1 (Emergence begins several weeks prior to corn planting, GDD <150)
Examples: giant ragweed, lambsquarters, Penn. Smartweed, common sunflower

Group 2 (Emergence begins soon, before or at corn planting, GDD 150-300)
Examples: common ragweed, green foxtail, velvetleaf

Group 3 (Emergence begins at the end of corn planting season, GDD 250-400)
Examples: yellow foxtail, black nightshade, common cocklebur, wild proso millet

Group 4 (Emergence begins after corn emergence, GDD 350 >)
Examples: large crabgrass, fall panicum, waterhemp, morning glory species

(Source: Purdue Field Crops Pest Management Handbook)

Do you know the number of growing degree-days in your region today?
(Base Temp. 50F)

For more information, check out our on-line publication, Weeds in Corn-Management Guide, 1Mb pdf file

Small Grains

Stagonospora nodorum blotch

At the Cornell Research Farm in Valatie, I discovered stagonospora nodorum blotch on the lower leaves in Tom Kilcer’s triticale plots. Splashing rain or thunderstorms can move spores from field surface to the plant wheat seed can be contaminated from spores when it is harvested. This disease may also be in the residue on the surface of the field. Greatest yield losses occur when the flag leaf and the next two lower leaves become infected by the time the wheat flowers in late May. Symptoms usually appear within two or three weeks of head emergence. Leaf lesions begin as very dark brown flecks or spots, sometimes with a yellow halo. These small irregular lesions expand into oval light brown lesions with dark brown centers. On wheat heads the lesions begin as either grayish or brownish spots on the chaff, usually on the upper third of the glume. As lesions enlarge, they become dark brown and the centers turn grayish-white in color as tiny brown or black dots (pycnidia) develop within them.

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Pests to watch this week: Alfalfa weevil, cereal leaf weevil, more pigweed emergence, (other weeds?)


Ken Wise

Thanks to this week’s contributors: Keith Waldron and Julie Stavisky (NYS IPM).