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NY Weekly Field Crop Pest Report, 2005

April 26, 2005 Volume 4 Number 2

1. View from the Field

2. Watch for Virus Diseases of Winter Wheat

3. Alfalfa Weevil Creeps into Fields

4. Winter Annuals in Winter Wheat

5. Clover Root Curculio

6. Cereal Leaf Beetle

7. Importance of Fungicide Seed Treatments-Corn

8. Clipboard Checklist

9. Contact Information

View from the Field

Julie Stavisky, NYS IPM

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Winter wheat is growing and tillering actively. The first cereal leaf beetle adults were seen by Nate Herendeen this week. Now that they are out and about, cereal leaf beetles will be ready and waiting for the emergence of the many fields of spring grains that were planted in the last week or two. Alfalfa weevil adults have been spotted in a couple of locations in western New York!

Watch for Virus Diseases of Winter Wheat

Julie Stavisky, NYS IPM

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With the dry conditions of the past 2 weeks, winter wheat stands are vigorously growing and generally free of stand-reducing diseases. But this is the prime time to monitor fields for wheat spindle streak mosaic and yellow dwarf.

Wheat spindle streak mosaic virus(WSSMV) symptoms are yellow-green dashes or streaks with tapered ends, running parallel to the leaf veins. A soilborne fungus that attacks the roots of wheat in the fall transmits WSSMV. Symptoms often show up on plants in wet soils, but excessive moisture in the spring is not required for infection to occur. Cool spring temperatures encourage continued development of WSSMV. As temperatures warm, plants usually outgrow the disease. For photos of WSSMV, follow this link: Wheat spindle streak mosaic virus

Yellow dwarfsymptoms include yellowing of leaf tips, sometimes progressing to red or purple colors. Several species of aphids common in New York transmit yellow dwarf. If winter wheat was planted too early in the fall, aphids may have had time to infest and infect plants. If yellow dwarf infections occur in the spring, instead, symptoms will appear later. Stay tuned to the Pest Report for updates. Photos of symptoms can be seen at: Yellow dwarf field effects andYellow dwarf: healthy vs diseased plant

Rescue treatment options to eliminate infections from viral disease are not available. However, scouting now for these diseases, and submitting suspicious samples for correct identification has the value of verifying the presence of these diseases. Next time wheat is planted in the same field, preventative management, such as planting a resistant cultivar, becomes an easy choice.

Alfalfa Weevil Creeps into Fields-Alfalfa

Ken Wise, NYS IPM

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This week a few observant people discovered adult alfalfa weevils. While they found adults no eggs were located in the stems. 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.

Do you know your the growing degree days for your area from March 1 to April 24?

Accumulated Growing degree days (48F Base)
Batavia: 64.7
Chazy: 26.7
Clifton Park: 105.0
Geneva: 69.4
Ithaca: 55.1
Mexico: 32.6
Prattsburg: 40.7

Winter Annual Weeds in Wheat

Julie Stavisky, NYS IPM

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Most of the problem weeds in winter wheat are winter annuals. The “usual suspects” include henbit, purple deadnettle, common chickweed, and corn chamomile. The life cycle of winter annuals matches the life cycle of wheat: they germinate in the fall, overwinter as seedlings, and flower and go to seed in the spring.

Wheat is now actively growing, and the winter annual weeds are actively competing for nutrients and moisture. If scouting indicates that herbicides are necessary, applications should be made no later than the fully tillered stage of wheat development.

Let’s highlight a couple winter annuals to watch for while scouting:

Corn Chamomile plants are currently still in the rosette stage. The rosettes are small and low to the ground, with finely divided foliage. The small daisy-like flowers may be seen starting in late May. For a photo: View Corn Chamomile

Henbit is already flowering! The small tubular pink to purple flowers are seen in the upper whorls of leaves. Stems are square, as is typical of the mint family. Lower leaves are heart-shaped, while the upper leaves are deeply lobed. Follow this link for a photo:

View Henbit

Purple deadnettle also has a square stem and small tubular flowers that appear in the upper whorls of leaves. Leaves are triangular in shape and less deeply lobed than henbit. The upper leaves of purple deadnettle are purple, and the flowers are pale purple. Photos can be seen at: View Purple Deadnettle

More information on weed management options in wheat can be found in the small grains section of the online version of The 2005 Cornell Guide for Integrated Field Crop Management

Clover-root curculio

Ken Wise, NYS IPM

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While scouting last week I found a few clover-root curculio adults. These adult weevils are 1/8 inch long and 1/16 inch wide with short, broad snouts. The adult weevil is brownish-black and covered with grayish hair and scales. Adult curculios chew the margins of leaves leaving C shaped notches. Clover-root curculio larvae feed below-ground on nodules, small rootlets, and chew out portions of the main root. As a result of larval feeding on roots, diseases such as fusarium crown and root rot can enter the plant. Clover-root curculio will feed on several types of clover and alfalfa.

Cereal Leaf Beetle

Ken Wise, NYS IPM

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Cereal leaf beetle eggs can be found on the upper surface of the leaves near the midrib. Eggs are elongate, yellow to brown about 1/16 inch long, and are laid in chains of two or three. Small black slug-like larvae emerge from the egg and reach about a 1/4 inch long. Larvae feed on the leaf surface, leaving long narrow white strips between the veins. The adults are 3/16 inch long with metallic bluish-black head and wing covers. Cereal leaf beetle is more of a problem in oats but can occasionally reach threshold levels in wheat.

The threshold for cereal leaf beetle is three or more eggs and larvae per stem before the boot stage of oats or one or more larvae per flag leaf after the boot stage. Check 30 stems distributed throughout a field to determine if the field are at an action threshold.

Importance of Fungicide Seed Treatments-Corn

Ken Wise, NYS IPM

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Prevention is the key to control early season corn diseases! Using a fungicide planter box treatment will help prevent corn seed from many different early season diseases. Sound planting practices, such as use of certified seed, good seed bed preparation, good seed soil contact, and appropriate planting depth, help promote stand establishment and help avoid seedling blights and emergence diseases. Watch for foliar diseases in continuous corn fields if contaminated residue from last season is present.For more information on early season disease management visit our web page on Field Corn Diseases.

Clipboard Checklist

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Monitor new seedings closely to determine need and timing of weed control activities.
Monitor alfalfa for Alfalfa Snout Beetle (In Cayuga, Clinton, Essex, Jefferson, Lewis, Oswego, St. Lawrence, Wayne counties)
Top dress winter grain fields, pastures, and grass hay fields.
Scout for cereal leaf beetle in newly emerging spring grains and in winter wheat
Scout winter wheat for virus diseases and weeds
Begin scouting for alfalfa weevil
Watch for frost heaving and winter killed alfalfa
Keep track of growing degree days in your area
Remember fungicide and insecticide seed treatments
Arrange for custom weed control or check your own application or cultivator equipment for repairs.
Recalibrate pesticide application equipment regularly before use.