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Weekly Field Crops Pest Report 2006

May 12, 2006 Volume 5 Number 4

1. View from the Field

2. Major Diseases of Alfalfa in NYS

3. Cereal Leaf Beetle

4. Quantifying Row Crop Plant Populations

5. Black Cutworm in Field Corn

6. Early Season Alfalfa Leaf and Stem Diseases

7. Asian Soybean Rust Status

8. Accumulated Growing Degree Day-NYS

9. Clipboard Checklist

10. Contact Information

View From The Field
Eastern NYS

Ken Wise, NYS IPM

 

 

 

 

 

 

Western NYS
Julie Stavisky, NYS IPM

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During an organic wheat TAg meeting in Essex County we discovered Stagonospora nodorum blotch on the lower leaves of hard red winter wheat. The stand of wheat did look very good and had 50 to 60 tillers per row foot. In a different hard red winter wheat there were spots of winter kill.

Alfalfa is looking good and is 8 to 12 inches tall depending on the field. I have seen only limited alfalfa weevil activity. I have only caught a few adults and 1st and 2nd instar larvae. Tip feeding is less than 5 percent.

Alfalfa Weevil Larva

Lots of people are remembering what a bad year 2005 was for flies on dairy farms, and questions started coming in this week about preventative management.  Now is the time for producers to get off to a good start with barn sanitation to prevent fly problems later.  Watch here for next week’s Clipboard Checklist for fly management tips to use when you are making farm visits. In the meantime, here’s a link to the NYS IPM Barn Flies Management Guide.

Major Diseases of Alfalfa in NY

Keith Waldron, NYS IPM

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A number of diseases can affect alfalfa yield, quality and short and long term production in New York. Diagnosing plant diseases can be challenging, but knowing what to expect and when can make a mystery ailment more identifiable. The following table outlines what diseases might be more expected in alfalfa stands based on years in production.

Disease

New Seeding

Established Stand

Verticillium Wilt

-

+++, 2nd  prod. year and older

Phytopthora Root Rot

++

+++

Anthracnose

+

++

Fusarium Wilt

+

++

Pythium

+++

-

Sclerotinia Crown /Stem Rot

++

+

Spring Black Stem

+, leaf spot

++, leaf spot, crown rot

Downy Mildew

++, systemic

++, leaf spot, systemic

Leptosphaerulina Lf Spot

+++

 

Other Leaf Spots

+

+++

Crown Rot

-

+++, older stands

+ = occasionally significant; ++ potentially significant; +++ = frequently significant, a priority for scouting; - + not expected.

More information on scouting for alfalfa diseases? More about specific alfalfa diseases will appear in future Weekly reports. In the meantime, if you want a really great visual overview of Alfalfa Diseases in NY there is a video available: “Scouting for Common Alfalfa Diseases in New York State” hosted by Cornell’s Extension Plant Pathologist, our own Dr. Gary Bergstrom. The video provides an introduction to scouting, and detecting alfalfa diseases including: Verticillium wilt; root, crown, and stem rots; and leaf and stem blights. Available through The Cornell Resource Center, Email: resctr@cornell.edu, (607)255-2080.

Additional references for alfalfa diseases and IPM: Growing Alfalfa the IPM Way.

Information on alfalfa diseases can also be found in the Cornell Guide for Integrated Field Crop Management.

Cereal Leaf Beetle

Julie Stavisky, NYS IPM

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We started observing cereal leaf beetles (CLB) last week in oats and winter wheat! Adults of the cereal leaf beetle are 3/16 of an inch long, and their wing covers are a metallic bluish black color, while their legs and front sections are reddish.  Eggs are laid on upper leaf surfaces near the midrib. Eggs are elongate, 1/16 of an inch long, and yellow-brown.  They are laid singly or end to end in short chains of 2 or 3 eggs.  Larvae are about 1/4 inch long, rounded, and usually covered with a slimy black coating.  Only one generation develops per year.

Because the flag leaf is so important for grain development and head filling, CLB larvae will be especially damaging if they feed on the flag leaf.  Larvae feed on leaf surfaces between leaf veins, giving the leaves a striped appearance. Heavy infestations give the crop a yellowish white or frosted appearance, but plants can sustain considerable damage before you see any economic losses.  And timing is everything - serious feeding damage in the late head-filling stage does not typically cause economic losses. 

Careful field monitoring for numbers of larvae present is the only reliable way to determine if insecticide application will be cost-effective.  Periodic monitoring should begin now and continue through early heading stages. To monitor a field, carefully inspect 30 stems throughout a field for the presence of eggs and larvae.  The economic threshold is three or more eggs and larvae per stem before the boot stage, or one larva per flag leaf after the boot stage.  If mostly eggs are observed, come back and scout again in about 5 days.

Use of insecticides is generally not warranted because natural enemies, including beneficial parasitic wasps and predators (such as lady beetles) generally keep populations in check.   It is important to remember that if insecticides are sprayed unnecessarily or excessively, our allies, the natural enemies, will be killed before they can do their job. 

Overall, when sound agronomic practices are used to ensure a healthy crop, impact from cereal leaf beetle will be minimized.

Cereal Leaf Beetle Adult
Cereal Leaf Beetle Larva

Quantifying Row Crop Plant Populations

Keith Waldron, NYS IPM

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Proper pH? – Check. N-P-K matched to soil test recommendation? – Check. Nice seedbed preparation? – Check. Timely planting? – Check. Plant Population? – Check?

How many corn seeds did you plant and what did you get?

It’s important to evaluate stands early to determine if the optimal plant population has been achieved. A good stand or a replant situation? One EZ method for determining plant populations is to count the number of plants per 1 / 1,000th of an acre. Use the table below to determine the length of row you’ll need to count plants in for a particular row spacing. Then determine the average of three sets of emerged plant counts found at several locations throughout the field to get the average number of plants per acre. Finally, determine the average number of plants found in the length of row sampled and multiply by 1,000 to get the average plant population.

Locate wheel tracks and make observations for each row planted. Check at least three areas within the field for consistency and to determine if all planter boxes were operating well.

Row Width (in)

Length of Row per 1/1,000 of an acre

 

Feet

Inches

7

74

8

15

34

10

28

18

8

30

17

5

32

16

4

36

14

6

A 10% reduction in number of plants observed vs number of seeds dropped is not uncommon. Large deviations from what was expected can signal a variety of potential problems. If your plant population counts are not up to snuff, sometimes waiting a few days and re-doing the estimate can make a difference if there is uneven germination from cool temps or variations in seeding depth. Other potential problems can be related to poor seed germination, planter calibration, performance and planting associated problems, poor soil conditions, seed rots or seedling diseases, seed corn maggot, wireworm, white grubs, birds, mice, and other factors.

Black Cutworm in Field Corn

Ken Wise, NYS IPM

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There have been signs of migrating cutworm moths to the south and southwest of NYS.  Since they ride storms that bring the adult moths from the south to the Northeast we should watch our corn for signs of feeding. Weedy grasses, winter annual broadleaves, and chickweed are favorite targets. If cutworm moths lay eggs in the field and the field is treated with an herbicide, hatching cutworm larvae bail off the dying weeds and look for greener food sources such as emerging corn seedlings. Cutworms can be an annual problem in some fields; particularly those with a history of poor weed control or have low wet areas in the field. Field margins, especially those next to ditch banks, grassy lanes, and hay fields are potential sites for infestation. Doing an early season plant population count is a good way to check corn fields for cutworm damage and other corn emergence problems.

Black Cutworm larvae vary in color from light gray to black with a pale brown to black head. Larvae have a greasy, shiny appearance with coarse granules present over their body. During the day larvae burrow into the soil next to the corn plant. These larvae curl into a C shape when disturbed. Symptoms of damage are leaf feeding, irregular holes in stems, notched and cut or missing plants. No-till fields and those with a lot of grass weeds are at particular risk to black cutworm. Monitor fields to find cutworm larvae when they are less than 1/2 inch long. If there are sufficient numbers and damage present, an insecticide could be justified. Treat only the affected area and a 20 to 40-foot border around the infestation. Rarely does a whole field need to be treated for cutworm. Larger cutworm larvae, greater than 1/2 inch long, are much more difficult to control. If the majority of cutworm larvae are 1/2 inch long or larger their damage is already done. These large larvae are also more tolerant of insecticides, reducing the effectiveness and economic viability of this option. Check out our on-line publication, Black Cutworm in Field Corn Management Guide.

Early Season Alfalfa Leaf and Stem Diseases!

Ken Wise, NYS IPM

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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.

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. When observed through a hand lens, tiny raised, light brown disk-shaped fungal fruiting bodies are visible in the center of mature lesions. See photo at: Common Leaf Spot

Leptosphaerulina Leaf Spot (aka “Lepto”): 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

Downy Mildew: causes leaves to become blotched or chlorotic (light green or yellow). Many times young leaflets can become distorted. Often a dark purplish-gray fungal mat covers the underside of the leaves. This disease is common early in the spring.

While alfalfa leaf spots may be easily found in most stands the real impacts for this harvest would be if 30% or more of the leaves on plants were shed as the result of infection.

For more information see Diseases of Alfalfa (Leaf Spots) Management Guide.

2005 Asian Soybean Rust (SBR) Update

Gary Bergstrom, Cornell University Department of Plant Pathology

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From: NYS Soybean Rust Information Center

At this early point in the growing season, the potential for early and severe soybean rust in the northern states in 2006 is unclear.  The 2006 North American epidemic is starting from over-wintered rust on kudzu in a somewhat broader and more northerly area than in spring 2006, yet early pockets of rust from Florida to Alabama are scattered and of low severity.  Recent rains across destroyed and no new rust has been found in Texas.  Scouting on kudzu patches continues throughout the southeastern U.S. expanding northward to southern Illinois, and westward to Texas. Many of the soybean sentinel plots have been planted in most southern and some mid-western states. Soybeans in sentinel plots have emerged as far north as central Illinois.  We are finalizing plans for approximately 20 sentinel soybean plots in New York to be scouted in cooperation with soybean producers and Cornell Cooperative Extension Educators. Sentinel plots are planned for locations in Cayuga, Chemung, Chenango, Genesee, Jefferson, Montgomery, Oneida, Onondaga, Ontario, Orleans, Seneca, Steuben, Tompkins, and Wayne Counties.

National Map Commentary, from USDA Soybean Rust Website.

Alfalfa Weevil and Growing Degree Days in NYS

Ken Wise and Keith Waldron-NYS IPM

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Growing degree Days for peak (50%) Occurrence of Alfalfa Weevil growth stage:

Stage or Event

Accumulated growing degree days (48F base temperature)

Eggs hatch

280

Instar 1

315

Instar 2

395

Instar 3

470

Instar 4

550

Cocooning

600

Pupa

725

Adult Emergence

815

(Note: for alfalfa weevil predictions use Base Temp of 48F)

Accumulated Growing Degree Days for March 1 to May 9

Location

Base 48 F

Base 50 F

Batavia

204

163*

Chazy

178

144

Clifton Park

330

278*

Geneva

221

176

Ithaca

200

159

Mexico

167

135*

Prattsburg

167

133*

Redhook

379

321

*indicates missing data

Do you know the number of growing degree-days in your region today? Check this website: NY Growing Degree-Day Tracker Base Temp. 50F.

Clipboard Checklist

Keith Waldron-NYS IPM

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General:

• Walk fields to check tile flow, check and clear drainage outlets.

• Maintain crop records by field, including variety, planting date, pesticides used, nutrient inputs including manure, etc.

• Watch for early season weeds, any patches of herbicide resistant weeds?

Corn:

• Finish corn planting by May 15

• Use corn insecticide seed treatment in the planter box

• Monitor for weeds, note presence of “who”, “how many” and “where”

• Adjust post emergence weed control actions

• Determine corn plant populations, make notes on germination problems

Small Grains:

• Monitor winter grains for crop stage, insect and disease problems

      - assess crop for adequate stand and plant vigor

Alfalfa & Hay:

• Monitor alfalfa seedings for weeds, insects & diseases.

• Check established alfalfa stands for alfalfa weevil, weed and disease problems.

• Timothy stands: check fields for symptoms of cereal rust mite

Soybeans:

• Field preparations, planter ready, Rhizobium inoculum?

Equipment:

• Note any repairs needed for corn planter, seeding equipment, alfalfa harvesting equipment, and tillage implements as they are cleaned and lubricated.

• Service corn planter as needed.

• Soybean planter ready?

• Calibrate manure spreaders - maintain records on amount spread per field

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