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Weekly Field Crops Pest Report 2006

August 4, 2006 Volume 5 Number 15

1. View from the Field

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

3. Will We See White Mold in Soybeans this Year?

4. Soybean Rust Update

5. Flooding and the Risk of Disease Development

6. Soybean Aphid Populations Low Across NY So Far This Season

7. Dairy IPM Fly Report

8. Clipboard Checklist

9. NYS Growing Degree Days

10. Contact Information

View From The Field

Eastern NYS
Ken Wise, NYS IPM

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Western NY and Finger Lakes
Julie Stavisky, NYS IPM

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This week at the Cornell Research Farm in Valatie the alfalfa that had not yet been cut showed extreme potato leafhopper damage despite the fact infestation levels were low as seen in the photo below.

In past weeks potato leafhopper infestations were very high with 200+ insects per 3 samples (1 sample = 10 sweeps). This was far above the action threshold for potato leafhopper on 24-inch alfalfa. Corn looked very good even though deer have been browsing on the edge of a few of the plot areas.

The soybeans I have been monitoring in Columbia County look great! Soybean aphid infestation levels remain very low with 10 to 20 aphids per plant and beans are at the R3 stage of development.

White mold has been spotted in soybeans!  Nancy Glazier (NWNY Team) reported it in Genesee County on Monday of this week, and I observed one infected plant last Friday.  Mike Dennis (Seneca County) confirms this week that white mold is spreading already to a couple more plants since Friday. Soybean aphid numbers remain really low.  Fewer than 10 per plant were typical in Wyoming, Ontario, and Seneca Counties this week. 

From the scouting being conducted on Amish farms involved in the TAg program in Seneca County, potato leafhoppers numbers were low, and corn rootworm were below threshold.  Scouting of rootworm adults will continue next week.

In 15-inch tall alfalfa in Ontario County, I saw an increase in numbers of PLH from last week.  PLH were close to threshold, and more than half of the PLH collected in sweeps were nymphs. 

During a TAg team meeting with Amish dairy and vegetable farmers in Cattaraugus County this week, we observed some pretty good barn fly IPM.  With good sanitation, and by keeping the cows on pasture during the day, the farmer who hosted the meeting is able to keep fly numbers in the barn low.

Do you know how to scout for Corn Rootworm?

Ken Wise, NYS IPM

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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 Corn Rootworm Management in Field Corn

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 are 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 Field Crop Management.

  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

Will we see White Mold in Soybeans this year?

Julie Stavisky, NYS IPM

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The wet and humid weather conditions we’ve been dealing with this year have been ideal for white mold development in soybeans.  Since the conditions are right, will we automatically see the disease?  Well, let’s recall the disease triangle.  In order for a plant disease to occur, three things need to be present:  a susceptible host (the crop), the pathogen (the disease-causing organism), and conditions favorable for disease development.

Highly productive, dense stands of soybeans favor white mold development. The fungus survives from year to year in the soil as hard black pellets called sclerotia. Sclerotia of white mold must be present to cause the disease, though a small number of sclerotia on the soil surface can lead to significant outbreaks if wet, cool conditions are present while plants are flowering. Under these favorable conditions, sclerotia will germinate and mushroom-like structures (apothecia) will form. The apothecia produce ascospores which spread by wind and splashing rain. Ascopsores require a nutrient source to grow, and soybean flowers serve as ideal locations. The fungus colonizes dead flowers and the characteristic thick white moldy covering on stems and pods develops (see photo below). Mixed in with the white mold on stems are the black sclerotia. Plants may wilt and die as a result of infection. If white mold infection occurs late in the season, yield loss will not be as severe. Temperatures over 90 degrees will typically stop disease development. During harvest, the sclerotia on stems and pods may end up in the soil or residue, or may stay with harvested seed.  Fields where white mold has occurred in the recent past are where it will most likely occur, so these are the fields to scout the most closely for disease development.

The following photo shows the white mold infection on a plant that is starting to wilt. (Thanks go to Mike Stanyard, NWNY Team, for the photo)

A key to white mold management is to find strategies to prevent the build-up of the pathogen in a field. Rotation to crops other than soybean for at least 1 year (ideally 2 or more years) is recommended. Additionally, weed management practices that reduce weeds that serve as alternate host for white mold (for example lambs quarters and pigweed) will help to decrease build-up of the pathogen. It is also essential to avoid the planting of contaminated or infected seed, and to avoid the movement of infected soil with equipment. A strategy for preventing movement of infected soil is to harvest fields infected with white mold last. Varieties of soybeans that are tolerant or moderately resistant to white mold should be selected. Yield protection by spraying fungicides has not been documented in New York.

Soybean Rust Update

Gary Bergstrom, Cornell University

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Weekly scouting is occurring on 19 sentinel plots located in Cayuga, Chautauqua, Chemung, Chenango, Columbia, Genesee, Herkimer, Jefferson, Montgomery, Oneida, Onondaga, Ontario, Seneca, Tompkins, Wayne, and Wyoming Counties. Plant growth stages in NY state have been reported to range from V5-R3. Low levels of Septoria brown spot continue to be found in several of the sentinel plots.  In addition, we have found low levels of downy mildew and bacterial pustule.  The current risk of soybean rust infection in New York is extremely low. Future risk in New York will depend on rust build-up in the southern U.S., especially in commercial soybean fields. To date, in 2006, soybean rust has been reported in five counties in Alabama, 12 in Florida, one in Texas, five in Georgia, and two in Louisiana. Currently, there are no known reports of rust on commercially planted soybean in 2006. Dry to very dry conditions prevail in the spore source regions and movement to new areas has been slow. There is virtually no chance that rust will cause yield loss to soybean in New York in 2006. Last updated (July 19, 2006)

New York State Soybean Rust Information Center

Flooding and risk of disease development

Keith Waldron, NYS IPM

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Many areas of NY have experienced significantly heavy rains in the past several weeks. In some areas flooding has been a serous issue. For fields that have been subjected to flooding or standing water soybean and alfalfa field monitoring should include observations to detect presence of root rot diseases such as Phytopthora.

When soils are saturated for 3 or more days, carbon dioxide builds up and suffocates and kills the roots. These conditions are also favorable for Phytopthora root rot infection. Watch for signs of yellow, stunted plants. Plants showing symptoms would correspond to a field's drainage pattern. Affected plants would show signs of brown, necrotic roots.

Soybean aphid populations low across NY so far this season

Keith Waldron, NYS IPM

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Reports this week from across the state indicate soybean aphid (SBA) populations are generally very low. This season, SBA numbers have been consistently well below the 250 SBA's per plant action threshold. Low SBA populations have also been reported by our neighbors in Ontario and Ohio. Soybean fields in NY are generally at early to mid stages of pod fill.

Many regions within NY have recently experienced heavy rains.  For SBA management this could be good news or bad news. The good news for growers is that rains can literally knock down SBA populations, physically forcing aphids to the ground where they are prey to ground dwelling natural enemies such as ground beetles. The possible bad news is that SBA's have been known to travel on weather patterns and be deposited by rain storms.

Some midwestern states are reporting scattered areas of high SBA populations. While it is still perhaps to early to call, it appears that most areas of New York will likely escape economic populations of soybean aphids this season. In previous years, soybean aphids have tended to be an issue in relatively few fields in NY. How will you know if your field is at risk? The best way is still the old fashioned way. Continue to monitor fields for soybean aphid and diseases such as white mold, Phytopthora root rot, foliar diseases and soybean rust.

While scouting for soybean aphids be on the look out for small white aphids mixed in with the usual soybean aphid forms. There have been several reports in western NY of these white dwarf aphids being found in and amongst the usual larger “mountain dew” green colored soybean aphids.

Regarding these little white aphids, the August 12, 2005 (Issue 20) of the Purdue Pest and Crop Newsletter states: “These ARE soybean aphid. They ARE NOT all “baby” aphids. They ARE NOT diseased aphids. In literature they are referred as “white dwarfs.” Aphids of many different species do this in response to change. With soybean aphid, this change morphology may be due to hot temperatures, higher humidity, shorter day-length, nutritional quality, predator populations, etc. In short, we do not know what is causing this. We do know that they are living, feeding, and reproducing aphids. They should be included in the total plant population count when determining treatment. (NY IPM suggests keeping track of normal SBA’s vs white dwarf SBA’s). It is true that they likely do not feed as heavily as the “normal” green/yellow aphid. It has been noted that because of their size and color, many are missed when making aphids/plant counts.

We are interested in tracking these soybean aphid morphs in NY, if you are finding populations of “white dwarf” soybean aphids in your fields, drop a message to Keith @ jkw5@cornell.edu. Thanks…

SBA threshold guideline - 250 per plant with increasing populations on 80% of the plants up to the R5 growth stage of soybeans. This action threshold should be based on an average of aphids per plant over 20-30 plants sampled throughout the field. Regular field visits are required to determine if aphid populations are increasing. Midwestern research has found that treating earlier than this threshold in most cases does not pay for itself.  But if you have aphids at flowering, and the SBA population is increasing (no natural enemies of insufficient numbers), then yield loss is to pod abortion and once pods are gone, there is no recovery of yield other than getting seed a bit bigger. This recommendation has held up well over the past 5 years.

Not familiar with soybean growth stages? See Soybean Growth and Management Quick Guide, Reproductive

Soybean Reproductive Stages
R1. Beginning Bloom (R1)
R2. Full Bloom (R2)
R3. Beginning Pod (R3)
R4. Full Pod (R4)
R5. Beginning Seed (R5)

For the latest updates on NY and national soybean aphid observations see the USDA Public PIPE website.

Dairy IPM Fly Report

The Cornell University Veterinary Entomology Program

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The increased moisture from the summer rain and following heat has provided ideal conditions for fly breeding.  Maggots, the precursor to the mahogany brown capsule-like fly pupae (see photo) and ultimately flies, prefer wet conditions.

Fly pupae collected from calf stall

Using gravel in calf greenhouses and barns appears to retard and even prevent the fly life cycle because the gravel retains less moisture as compared to traditional wood shavings.  Keeping barn shavings or gravel as dry as possible will alleviate some of the fly burdens affecting regional herds.  These moist areas are likely to be localized around water and feed buckets, just outside calf stalls, or waste piles.  Avoiding small behaviors like dumping out extra calf milk substitute near the barn or dragging leaky or running water hoses between buckets will help reduce numbers both inside and outside the barn.   Removing wet bedding as opposed to covering it with dry bedding is also advised.  Based on comments by local farmers, stable and house flies are now causing significant irritation within the barns.  By keeping barns clean and thus reducing fly numbers, the animals expend less energy fending off flies and more energy is invested into milk production and higher feed conversion rates.

Horn flies have come out this week in full force.  With their V-shaped wings, the horn flies aggregate predominately on the back and sides of cattle in an upside down position where they impart painful bites. See photo of angus cattle heavily infested with horn flies:

Horn flies on angus cattle in North Carolina

(Action threshold for horn flies is an average of 50 per animal side (dairy cattle), 200 per animal side (beef cattle). 

Face flies are also out in large numbers, with some dairy cows carrying the burden of 45 to 50 flies feeding on their facial secretions. (Action threshold is an average of 10 per animal face)  Stable flies, as consistent with last week, are still out in peak populations. (Action threshold is an average of 10 per animal) See photo:

Stable flies on calf leg

The early July flooding had noticeably decreased the dung beetles populations in pastures.  A generation of dung beetles could have been flooded out, but this week resurgences in dung beetle numbers is noted.

Growing Degree Days in NYS

Keith Waldron NYS IPM

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Accumulated Growing Degree Days for March 1 to August 2

Location

Base 50 F

Batavia

1232*

Chazy

1478

Clifton Park

1884*

Geneva

1514

Ithaca

1391*

Prattsburg

1257*

Redhook

1980

*indicates missing data

Source: NEWA

Clipboard Checklist

Keith Waldron-NYS IPM

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General:

* Maintain crop records by field, including crop condition, inputs, observations, issues, concerns, etc.

* Storage areas cleaned and ready to accept wheat harvest? Check and disinfect inside, under and around grain bins.

* Mow around barn and farm facilities

* Clean and store weed sprayers. Flush tanks, booms, nozzles.

Established Alfalfa & Hay:

* Monitor for potato leafhopper- harvest early or spray on basis of need.

* Monitor for diseases, particularly Verticillium wilt, record information on disease species and location for future cropping decisions.

* Monitor for Phytopthora root rot in fields recently flooded or subject to ponding.

Alfalfa Seedings:

* Continue monitoring for potato leafhopper, weeds and diseases.

* Monitor fields for weeds and diseases: record information on type and location for future cropping decisions.

* Monitor for Phytopthora root rot in fields recently flooded or subject to ponding.

Summer Forages:

* Plant birdsfoot trefoil by end of July.

Small Grains:

* Check grain storage bin for temp, moisture, air flow, drying conditions.

Corn:

* Monitor corn rootworm adults at silking.

* Observe corn for crop growth and condition, weeds, foliar diseases and fertility

Soybeans:

* Monitor for crop condition and growth stage, soybean aphids, natural enemies, foliar diseases, soybean rust

* Monitor for Phytopthora root rot in fields recently flooded or subject to ponding.

Livestock:

* Continue manure management and release of biological control agents (parasitic wasps) for house fly and stable fly control in barns

* 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; adjust paddock rotation as needed.

Equipment:

* Provide annual maintenance to fertilizer and pesticide application equipment,

* Note any repairs to harvesting equipment as they are cleaned and lubricated.

* Ready combine for small grains or finalize arrangements for custom harvest

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