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Weekly Field Crops Pest Report 2007

July 31, 2007                Volume 6 Number 14

1. View From the Field

2. Soybean Foliar Fungicides, Yield Benefit or an Extra Expense?

3. Corn Rootworm Scouting Tip (Are They Gravid?)

4. Downy Mildew in Soybeans

5. Soybean Rust Update

6. Soybean Aphid Update

7. Clipboard Checklist

8. Upcoming Events

9. Contact Information

View From the Field

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Eastern NYS
Ken Wise

Soybean aphid populations were low this week in the soybean sentinel plot field in Columbia County. The grower had sprayed for the aphids when they were at 600 aphids/plant. Many of the plants show yellowing starting from the margin of the leaflet progressing into the midrib. The new growth on these plants does not show the yellowing and is the typical green. Oneida County (Jeff Miller) reports that aphid populations have been increasing dramatically over the week. Some of the fields have been treated with insecticide for soybean aphids in this county. Anita Deming reports that in organic soybeans in Essex county have remained at low infestation levels in fields.

Potato leafhopper infestation levels remain low at the SUNY Cobleskill farm. It was hard to find even a few leafhoppers in the sweep net. The Cornell Research Farm in Valatie did have high populations of potato leafhopper. Fields are over threshold and alfalfa has the typical V-shaped yellowing on the tips of the leaflets.

At the SUNY Cobleskill Farm one corn field I looked at had extremely high populations of Corn Rootworm. It had and average of 5 beetles per plant.

Western NY and Finger Lakes Region
Julie Dennis

Bruce Tillapaugh, CCE Wyoming County, reports that there was a severe infestation of spring black stem in alfalfa.  Also in Wyoming County alfalfa, populations of potato leafhopper are below threshold in Julie Hansen’s variety tests.

The only thing certain about soybean aphids this year is that they are unpredictable! While aphid numbers are on a steady rise in some fields, scouting in nearby fields show few aphids, or that crashes in aphid populations have already occurred.  Population crashes are associated with predators, parasitoids, and perhaps even fungal pathogens.  During scouting this week, aphid populations in the Cayuga County soybean TAg team participant fields range from just a few per plant to 1,400 per plant.  Nancy Glazier reports that SBA’s are on the increase in western Monroe County, but so are predators.  Nancy continues to see just a few aphids in Ontario County TAg fields.  Mike Dennis reports a severe aphid outbreak in Seneca County this week. See Keith’s article below for more detailed information on statewide soybean aphid occurrence.

Kristen Bossard, Oneida County Soil and Water, provided the following photo showing sooty mold resulting from a severe soybean aphid infestation:

Sarah Woodard, Cayuga CCE scout, reports that spider mites continue to increase in one soybean field.

Soybean Foliar Fungicides, Yield Benefit or an Extra Expense?

Julie Dennis
NYS IPM

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In 2005, soybean producers in NY began asking questions regarding the use of foliar fungicides.  The purported benefits of protectant fungicide application during the early reproductive stages (R1-R4) were protection against potential soybean rust attack and the general improvement of “plant health”.  In some field situations, use of strobilurin fungicides was seen to result in a “yield bump” due to increased plant health.  Replicated on-farm NY field data was not available to assist growers in making educated economic choices regarding a calendar spray of fungicides in the absence of Asian soybean rust. 

In 2006, Preventative soybean fungicides Headline and Quadris were applied to soybeans at the R3 growth stage at 2 on-farm research sites in Seneca County. Results indicate that the amount of disease present did not justify fungicide application for disease control, and fungicides did not reduce disease incidence or severity of Septoria brown spot or downy mildew.  Partial budget analysis showed a net loss in profit per acre when fungicides were applied as a preventative tactic.

Replicated University trials from across the soybean growing regions of the US continue to show that there is rarely a yield or economic advantage to the use of protectant fungicides in the absence of significant disease pressure.

Please visit Soybean Foliar Fungicides: Yield Benefit or an Extra Expense?, a report from the 2006 NY study, for more information.  This project was funded by the NYS IPM Agricultural Grants Program.

What if soybean rust were to occur in our area?  Fungicide recommendations can be found in the Soybean section of the 2007 Cornell Guide for Integrated Field Crop Management

Corn Rootworm Scouting Tip (Are They Gravid?)

Ken Wise
NYS IPM

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Remember, when taking beetle counts you are monitoring to assess the potential that CRW's will lay enough eggs in the field to cause damage to next year's corn crop. Taking beetle counts is important but make sure you stop to check a portion of the female western CRW's for the actual presence of eggs. Squeeze the abdomens of the yellow and black striped CRWs and look for the small yellow - white eggs. It takes CRW about three weeks from the time the adult beetles emerge from the soil and mate until the time the females are gravid. In this time period you may find high CRW numbers in a field but since the females are not yet capable of laying eggs they are not causing an economic problem. This is the reasoning behind sampling the same field 2-3 times before making the management decision. Being pollen feeders and highly mobile, CRW's may relocate to another pollinating field during the 3 week period. Comparing the two types of fields, the second field is at greater risk from subsequent CRW damage since females (and their eggs) will have matured and are ready for deposit.

When is the best time to control corn rootworm if a field exceeds the action threshold?

  • The following year!

If there is a field over the action threshold what are the options for control next season?

  • The best option to control corn rootworm is crop rotation. Corn after corn is prime habitat for corn rootworm and will increase infestations from year to year.

  • Crop rotation is not always possible so ....... The second management option is the use of a soil-applied insecticide at planting. To select an insecticide registered for corn rootworm, please consult the Cornell Guide for Integrated Field Crop Management.

  • Additional CRW management technologies are now available. You can use insecticide treated seed to control moderate populations of corn rootworm infestations

  • You can also use Bt hybrids now for CRW.

How to Monitor for Corn Rootworm

Downy Mildew in Soybeans

Julie Dennis
NYS IPM

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I have only heard a few reports of downy mildew so far this season on soybean foliage in New York State, but where rain is catching up, many plant diseases may become more likely. This fungal disease is generally observed on leaves in the middle and upper canopy. Downy mildew can be identified by the pale yellow or greenish irregular areas on upper leaf surfaces (see photo below). 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. Soybean productivity is generally not significantly affected by downy mildew in NY.

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.

Downy mildew on the upper leaf surface:

Soybean Rust Update

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NY SBR Information Center

Soybean rust on Weekly scouting is being conducted in twenty New York State sentinel plots located in the following counties: Cayuga, Chautauqua, Chemung, Chenango, Columbia, Cortland, Jefferson, Monroe, Oneida, Onondaga, Ontario, Oswego, Otsego, St. Lawrence, Seneca, Steuben, Suffolk, Wayne, and Wyoming. Plant stages in these plots reported to date range from V-3 to R-2. Septoria brown spot is present at low levels in some of these plots.

Soybean rust has recently been reported in commercial fields in eight new counties in Texas including Hunt, Fannin, Ellis, Dallas, Collin, Jackson, Fort Bend and Austin counties as well as in Acadia Parish in Louisiana. Reports of disease severity as high as 40% were noted in a commercial field in Rapides Parish, LA where the disease was first reported on June 21, 2007.

To date in 2007, soybean rust has been detected in ten counties in Florida, five counties in Georgia and Alabama, six Parishes in Louisiana, fifteen counties in Texas and one county in Mississippi. Continued scattered showers in parts of the Southeast keep conditions favorable for rust development.(Updated July 20, 2007 )

Soybean Aphid Update

Keith Waldron
NYS IPM

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Soybean sentinel site - Soybean aphid update - as of July 27, 2007.

Sentinel site soybean fields reporting 7.23-27.07 have reached the reproductive growth stages.  Soybeans generally 15-24 inches.

Soybean aphid monitoring indicates significant differences in population levels across sites contributing information this past week. The value of individualized field by field monitoring is apparent as SBA infestations on some adjacent fields have been found to be significantly above or below threshold. Several fields above SBA threshold are showing symptoms of potassium deficiency.

Reports from Monroe, Onondaga, Ontario, and Wyoming counties all well below the 250 SBA / plant threshold.  Fields in Cayuga, Chemung, Columbia, Cortland, and Oneida county were treated within the past 10-14 days for above threshold SBA populations.

Natural enemy populations vary across monitored fields, however, beneficial insect numbers generally appear to be increasing since last week. High numbers of lady bugs, parasitized aphids, are syrphid fly larvae beginning to more numerous. Orius spp and predaceous stink bugs also being found.

Reports last week did not indicate an appreciable amount of entomopathogenic fungal epidemics affecting SBA populations. Wyoming county did, however, report a significant drop in pea aphid populations in alfalfa as the apparent result of a fungal disease. Growers are advised to continue monitoring fields for SBA's, crop condition and growth stage and diseases. If fields reach the 250 SBA / plant threshold, resample fields within a week to re-evaluate the population level before taking action.

For assistance on soybean growth stages and soybean aphid decisions see: "Reproductive Soybean Development Stages and Soybean Aphid Thresholds"

Thanks to: P. Barney, J. Degni, J. Dennis, K. Ganoe, N. Glazier, J. Lawrence, M. Hunter, J. Miller, B. Tillapaugh and K. Wise for sharing their soybean aphid observations.

For more on the current national Soybean aphid perspective see the USDA Public PIPE website.

Clipboard Checklist

Keith Waldron
NYS IPM

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

Established Alfalfa & Hay:
* Monitor for crop growth and condition, potato leafhopper and nutrient deficiencies.
* Monitor for diseases, particularly Verticillium wilt, record information on type and location for future cropping decisions.

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.

Small Grains:
* Watch grain moisture. Be ready to combine at 18 percent.
* Adjust combine in preparation for winter grain harvest (late-July) or spring grain Harvest (early to mid-August). Contract custom-operation if necessary.
* Clean grain storage areas.

Corn:
* Monitor for crop growth and condition, European corn borer, armyworm, foliar and stalk rot diseases, vertebrate damage, nutrient deficiencies.
* Monitor corn rootworm adults at silking.
* Observe corn for weeds and fertility

Soybeans:
* Monitor for crop growth and condition, soybean aphids, and other insects, including bean leaf beetle and natural enemies such as ladybird beetles, vertebrate damage, nutrient deficiencies.
* Monitor for diseases including white mold, foliar and stem diseases.
* Check droughty fields for presence of spider mites

Livestock:   
* Continue manure management and release of biological control agents (parasitic wasps) for house fly and stable fly control.
* 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.

Equipment:
* Note any repairs to harvesting equipment as they are cleaned and lubricated.
* Repair forage harvest equipment as needed
* Ready combine for small grains or finalize arrangements for custom harvest

Upcoming Events

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Empire Farm Days 
August 7, 8, & 9, 2007
Rodman Lott & Son Farms, Seneca Falls.
For more information, visit the Empire Farm Days website or call 877-ny-spuds.

Contact Information

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Julie Dennis: Western NY Area IPM Educator, Livestock and Field Crops
Phone/Fax: (315) 252-5440
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