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NY Weekly Field Crop Pest Report, 2005

July 28, 2005 Volume 4 Number 15

1. View from the Field

2. Pea Aphids Come in Red and Green: Ever Wonder Why?

3. Do You Know How to Scout for Corn Rootworm?

4. Downy Mildew in Soybean

5. European Corn Borer, Armyworm and Corn Earworm Trap Counts

6. Soybean Rust Update

7. Soybean Aphid Management Guidelines

8. Clipboard Checklist

9. NYS Growing Degree Days

10. Contact Information

View From the Field

Ken Wise,

NYS IPM

Julie Stavisky

NYS IPM

Keith Waldron

NYS IPM

Soybeans: This week at the Cornell University Farm in Valatie soybean aphids ranged for 10 to 200 per plant. The average was about 75 aphids per plant. There were several ladybeetles (Adults, and larvae) feeding on the aphids. There were several lady beetle pupae on the leaves also. There were also green lacewing adults and larvae in the field. There are a few pictures of the good beasts:

Alfalfa: Alfalfa fields at the Cornell University Farm in Valatie were far about threshold for potato leafhopper. In three samples I counted 255 potato leafhopper nymphs and adults. The alfalfa was showing the traditional yellowing of the leaves that potato leafhoppers can do. Here is a picture of the alfalfa:

I've seen downy mildew in all the soybean fields I've visited recently
(Wayne, Ontario, Seneca, and Cayuga Counties).

Nancy Glazier (NWNY Team) continues to observe soybean aphid and spider
mites, particularly on drought-stressed beans, as she scouts for the
Orleans County soybean TAg program. This week she also saw phytophthora
root rot on beans in an area where there is heavy soil. The grower
indicated that there was standing water this spring.

Reports from wheat harvest have been favorable so far. Neither scab nor
sprouting has been of concern.

Jeff Miller and Kevin Ganoe both reporting soybean fields with soybean aphids approaching 250+ per plant. Yellow alert for these fields.... time to increase SBA monitoring frequency to see if populations maintain, increase or decrease. Natural enemies are present but variable in number, some fields with winged aphid forms.

Mike Hunter reports fall and armyworms in corn field causing damage. Mike says the field had an obvious giant foxtail and large crabgrass that attracted the moths to the site.

Pea aphids ­ come in red and green… Ever wonder why?

Keith Waldron, NYS IPM

NY alfalfa fields are home to resident populations of pea aphids. Close observation will detect red and green color morphs of this aphid species in the same field. What’s that all about?

Because the aphids reproduce parthenogenically, the color morphs remain distinct through the summer months. Pea aphids experience high levels of parasitism by the wasp Aphidius ervi and heavy predation by several predators, including ladybird beetles, especially Coccinella septempunctata. Both the parasitoid and the predator can have a major impact on pea aphid populations and may be important selective agents.

Research by John Losey (Entomologist now at Cornell) determined that for these aphids there was an advantage of one color over another but it varied… Think predators, think escape…

Losey and his colleagues sampled 100 alfalfa stems in eight similar locations every 6 days. They counted the number of red and green aphids, ladybugs, and the mummified remains of aphids parasitized by wasp larvae. They discovered that the predators had distinct preferences--ladybugs being partial to red aphids, and wasps to green aphids.

The result is that the two predators keep the colors balanced. With ladybugs eating the red aphids and wasp larvae parasitizing the green, neither form dominates the population and both survive. Believe it or don’t…. More information see: Nature 388, 269 - 272 (17 July 1997).

Do you know how to scout for Corn Rootworm? Ken Wise, NYS IPM

You will need to scout all corn fields that will be kept in corn next year from emergence of the tassel until pollination is complete. Pollination occurs for three weeks and monitoring takes about 20 minutes per field. You will need to monitor each field once a week until you reach a threshold or until pollination is over. Look for gravid, (i.e. mature, egg laying) corn rootworm female beetles--the ones that, when you squeeze their bodies, release white eggs from their posteriors. See: http://www.nysipm.cornell.edu/publications/crw.bro/index.html

Here’s how you scout:

  1. Are female beetles present? Mature and capable of egg laying? Conduct the squeeze test (see above) to determine if they are ready to lay eggs.

  2. Approach a corn plant carefully because the beetles will fly off if they disturbed too much.

  3. Grasp the silk with one hand.

  4. Count the beetles on the entire plant.

  5. Start counting at the top working down.

  6. Gently pull leaves away from the stalk so you count any beetles that may be hiding in the whorls.

  7. For each corn plant monitored, record the total number of beetles observed. See the sequential sampling chart below. Since western corn rootworms are potentially more damaging than their northern cousins, count each western (yellow striped) beetle observed as “one” and each northern (green type) as “1/2”.

  8. Check several plants at random (not next to each other!) in several parts of the field.

  9. Continue sampling at seven-day intervals until the ear silks are brown, approximately 3 weeks after tassels are first visible, pollination is complete or an above threshold number of beetles are found.

Using the Sequential Sampling Card for Corn Rootworm(For fields with uniform physiological crop age, for variable age fields see the CU Guide for FCrop Management “www.fieldcrops.org”)

  1. Keep a running total (RT) of the number of corn rootworm beetles you have counted on each plant. Each northern corn rootworm has half the value of each western corn rootworm. The western corn rootworm does twice the damage to corn than does the northern. So if you count 3 westerns and 4 northern (2 western equivalent) on a plant you would have a total of 5 beetles.

  2. If the number of corn rootworm beetles observed is smaller than the “N” (“Not at threshold”) number stop and scout 7 days later.

  3. If the number of corn rootworm beetles observed is larger than the “T” (“At threshold” or “Treat”) number then you need to manage rootworms next year.

  4. If the number of corn rootworm beetles observed fall between “N” and “T”, continue sampling additional plants until you finally go over or under.

  5. In a very low or very high rootworm population a sampling decision can be made in sampling as few as 3 to 8 plants. For moderate populations more samples may be necessary to insure accuracy.

Sequential Sampling for Corn Rootworm

Downy Mildew in Soybean

Julie Stavisky

NYS IPM

Downy mildew is showing up on soybean foliage in New York State. I’ve observed this fungal disease frequently on leaves in the upper canopy. Downy mildew can be identified by the pale yellow or greenish irregular areas on upper leaf surfaces. These spots show through to the lower leaf surface, where the affected areas are grayish. Under humid conditions, grey tufts of the fungus are apparent on these spots on the underside of leaves (see photo below). Soybean productivity is generally not affected by downy mildew.

On a severely infected plant, downy mildew also can affect soybean seed. While pods show no symptoms, seeds inside can be covered with white fungal mycelia. If this infected seed were planted, stunted seedlings with mottled leaves would result.

The fungus that causes downy mildew can survive on infected leaves and seed. A key management strategy for downy mildew is to not plant contaminated seed. Rotation to a crop other than soybean or tillage that deeply buries infected crop residue effectively control downy mildew.

European Corn Borer, Fall Armyworm, Corn Ear Worm ­ Trap Catch Info

Keith Waldron, NYS IPM

Two calls this week about potential armyworm / fall armyworm issues in corn and mixed alfalfa grass stands. Positive identification still pending. Either species could be possible this time of year. Trapping networks reporting such data indicate low FAW counts. ECB counts have been moderate. If you are looking for the latest information on trap catches for these lepidopteran pests in NY check the Sweet Corn PheromoneTrap Network for Western NY, Report for 7/12/05

http://www.nysipm.cornell.edu/scouting/scnetwork/index.html.

This trapping network is gathered by Abby Seaman of the NYS IPM Program.

For information on trap catches for these insects in the states to our south go to the PestWatch web site.

Soybean Rust Update

Keith Waldron, NYS IPM

From: http://www.ppath.cornell.edu/soybeanrustny/default.htm Soybean rust on soybeans has been reported in Florida , some adjacent counties in Alabama and Georgia as well as Mississippi. The most recent finds in Mississippi and Georgia were in sentinel plots. The most recent find in Alabama was the first detection in a commercial field in 2005. Scouting and spore trapping continues throughout the soybean production areas of the U.S. Scouting of sentinel plots in New York State continues this week and to date no soybean rust has been found. The risk of soybean rust infection in New York is currently considered to be low and no fungicide application for soybean rust is advocated at this time. Septoria brown spot is the most prevalent foliar disease in all 10 of the research protocol sentinel plots in New York State over the past two weeks. Bacterial blight has also been observed and soybean aphid populations are increasing. Growth stages in New York State sentinel plots range from V5 to R2 stages and several are flowering. (Last updated 7/27/05)

Soybean Aphid Management Guidelines

Keith Waldron,

NYS IPM

Expect soybean aphid populations to rise over the next week or so as “cooler” temperatures (in the 80’s F) occur over our region.

Guidelines for management? A short review of guidelines. Adapted from: http://www.plantpath.wisc.edu/soyhealth/aglycine.htm

Pay particular attention to late-planted fields, or fields under moisture stress. Examine the entire plant, particularly the new growth at the top and side branches.

Use an action threshold of 250 aphids per plant if populations are actively increasing. This action threshold should be based on an average of 250 aphids per plant over 20-30 plants sampled throughout the field. Regular field visits are required to determine if soybean aphid populations are increasing.

In replicated research trials, in the Midwest , this threshold have worked well in R1 (right at first bloom) to R4 soybeans. This threshold incorporates an approximate 7-day lead-time between scouting and treatment to make spray arrangements or handle weather delays. Spraying at or beyond R6 has not been documented to increase yield.

Like more discussion? See “Soybean Aphid Management Recommendations (Consensus recommendations developed by Ontario and U.S. researchers, Jan. 2004)”

Research to enhance Soybean aphid management guidelines continues. Data (SBA counts, growth stage, yield, etc.) from Treat ­ No treat fields is in “short supply”. If you have a situation that will be treated and have the ability to collect information including yield checks please consider doing trial. More SBA data will help us all. For more information contact jkw5@cornell.edu.

Clipboard Checklist

Keith Waldron, NYS IPM

General:

• Maintain crop production activity records by field, including harvest date, pesticides used, nutrient inputs including manure, etc.

Alfalfa & Hay:

• Continue monitoring for potato leafhopper- harvest early or spray on basis of need.

• Monitor for diseases record information on type and location for future cropping decisions.

Corn:

• Monitor for foliar and stalk diseases, nitrogen and other nutrient deficiencies, European corn borer, weeds.

• Monitor corn rootworm adults at silking.

Soybeans:

• Monitor for soybean aphid, soybean rust, foliar diseases.

Livestock:

• Continue livestock facility sanitation management (manure, feed bunks and storage areas, waterers, etc.). Cleaner, less fly production

• Mow around facilities to minimize rodent habitat.

• Monitor young stock for cattle lice and mange mites

• Check condition of pastures and animals on pastures

- Evaluate need for face fly and stable fly control measures

- Check and clean pasture water supplies.

NYS Growing Degree Days

Keith Waldron, NYS IPM

March 1 - July 27, 2005

Location

Base 50 F

Batavia

1406.6

Chazy

1248.75

Clifton Park

1734.9*

Geneva

1487.44*

Ithaca

1368.8

Prattsburg

1310.3

*missing data

Source: http://newa.nysaes.cornell.edu/

Contact Information

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