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Weekly Field Crops Pest Report 2006

August 18, 2006 Volume 5 Number 17

1. View from the Field

2. What Pest Problems to Consider When Planting Wheat

3. How Important is European Corn Borer in Field Corn?

4. Check for Stalk Rots

5. Soybean Aphid Update

6. Soybean and Alfalfa Disease Update

7. NYS Growing Degree Days

8. Clipboard Checklist

9. Contact Information

View From The Field

Western NY and Finger Lakes
Julie Stavisky, NYS IPM

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Eastern NYS
Ken Wise, NYS IPM

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Reports of white mold are coming in, but they are not as numerous or as severe as many of us feared, given the wet conditions in July.  During a soybean TAg team meeting in Genesee County this week, the host producer showed a field where he planted the same variety but in different row spacing - one area drilled in 14 inch rows, and the other area planted in 30-inch rows. There was sporadic white mold in the beans in 14-inch rows, and none in the 30-inch row beans.

Nancy Glazier reports that many corn fields enrolled in the Yates County TAg team are over threshold for corn rootworm.

While walking through corn fields for corn rootworm sampling, I have seen very few European corn borer infested plants so far this year, and I’ve been hearing the same reports from many other observers.

Brian Aldrich (Cayuga County CCE) observed very high numbers of white dwarf soybean aphids in a small field of soybeans at the R-4 stage.  There were an average of 1,000 aphids per plant, with some plants exceeding 2,000 white dwarfs.  He also observed many lady beetle adults and larvae.

This week at the Cornell Research Farm in Valatie potato leafhopper were not to be found. In all of the alfalfa fields I did not find a single potato leafhopper. Corn look very good and no pest pressure with the exception of deer feeding along the edge of the corn plots. Soybean aphids have increased over the last week. I was finding about 200 per plant. This was below threshold but an increase from the previous week. About 80 to 90% of the aphids were the white dwarf that Keith Waldron has been discussing over the last few weeks.

What pest problems to consider when planting winter wheat

Ken Wise, NYS IPM

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There are several factors to consider when planting winter wheat. The first is to never plant wheat in the same field two years in a row. By rotating you reduce the risk of several diseases like eyespot foot rot, powdery mildew, leaf rust, stagonospora nodorum blotch, glume blotch and more. The second item to consider is what winter wheat variety to plant. Of course you will look at potential grain yield, grain test weight and straw quality. It is also important to consider resistance to diseases in the varieties you select. Diseases of particular concern are wheat spindle streak mosaic virus, soil borne mosaic virus, yellow dwarf virus (formally called “barley yellow dwarf virus”), powdery mildew, leaf & stem rust and/or other disease problems your farm has had in previous years.  For a list of potential wheat varieties consult your Cornell Guide for Integrated Field Crop Management (available online at www.fieldcrops.org). Next, remember to plant AFTER the Hessian fly free date. By doing so, not only are you avoiding infestations of Hessian fly but also certain aphids that can transmit yellow dwarf virus. The following figure shows the “Hessian Fly Free Dates” in NYS:

The use of certified wheat seed should be considered. When seed is certified you can be confident of the quality and it is void of diseases and weed seed. Next is to remember to always use a fungicide seed treatment to protect the crop from certain seed and seedling related diseases. Another core consideration is having a sound fertility program. When a plant is healthy it can complete with weeds and may tolerate more insect pest pressure and still maintain good yield.

How important is European Corn Borer in Field Corn?

Julie Stavisky, NYS IPM

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Last year at this time, catches of European corn borers (ECB) in pheromone traps were still rising dramatically.  But as of the latest statewide reports, ECB trap catches are down from last week at most locations.  The trapping data is available from The Sweet Corn Pheromone Trap Network, coordinated by Abby Seaman with the NYS IPM Vegetable program. We are probably past the peak of the second generation of ECB for this year.

While ECB causes much less worry in field corn than in sweet corn, concern about severe ECB infestations and the disease problems that may follow requires our attention.  The primary injury from the second generation of ECB is caused by the larvae tunneling into stalks and ear shanks (see photo), which can result in poor ear development, broken stalks (see photo), and dropped ears. The later in the kernel-filling period that an ECB infestation starts, the lower the yield impact will generally be.

To scout for ECB in August, look for egg masses on the undersides of leaves near ear level on the plant. Tunneling larvae can be found by looking for areas of frass (insect droppings) at the point of entry into the stalk. 

At times, a large infestation of ECB may cause a localized problem. Late harvesting and/or adverse weather conditions that cause plants to break at the points of injury may exacerbate those losses. Although the ECB damage can be conspicuous on an occasional plant, it does not generally cause significant yield losses in NY in corn harvested for grain or silage. Another reason to be concerned with an ECB infestation is that stalks or ears injured by ECB can be the entry point for disease-causing organisms. For more information, keep reading....

Check For Stalk Rots!

Ken Wise, NYS IPM

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It is important to monitor your fields for stalk rots as you start thinking of your corn harvest. If you have an infection of stalk rot it can cause the plant to die early losing grain or silage yields. Stalk rots are caused by many different fungi that enter the plant. They occur when the plant is under stress or when it may be injured by insect pests, hail, deer and bird damages, drought or soil saturation, lack of sunlight, extended cool weather, and the lack of fertility. The following are symptoms of specific stalk rots:

Anthracnose stalk rot symptoms may appear after tasselling as vertical, tan to reddish brown, water-soaked lesions (streaks) in the stalk rind. Lesions become large, dark brown to shiny black. Fields with high amounts of anthracnose leaf blight (both diseases have the same causal agent) should be checked for indications of anthracnose stalk rot.

Diplodia stalk rot symptoms may appear as numerous black pycnidia in the lower internodes of the stalk. The black dots are the size of a pinhead or smaller. When conditions are wet a white mold may develop on the stalk surface.

Fusarium stalk rot normally starts just after pollination and symptoms appear later in the season. When you cut open the stalk, the pith appears as a whitish to pink (salmon) color. There are also distinctive brown streaks on the lower internodes.

The first symptom of gibberella stalk rot is the onset of grayish-green color of the leaves. The stalk will turn dark green to tan near the base of the plant. The pith of the stalk becomes soft and will appear as a red to pinkish color.

Pythium stalk rot normally appears as a decay of the first internode above the soil. The pith will become soft, turn brown and appear water-soaked. Many times the stalk can twist and/ or lodge. Even though it may have lodged the plant will stay green for several weeks because the vascular tissue is not destroyed.

If you discover certain stalk rot diseases make notes of the hybrid, tillage methods, rotation history, and planting date. By doing this you be able to avoid the disease occurrence in the future. The following is the effectiveness of specific management practices for stalk rots:

Corn Disease
(Stalk Rots)

Resistant Variety

Crop Rotation

Clean Plow Down of Residues

Fungicides

Anthracnose

1

1

1

4

All other

2

3

3

4

1= highly effective, 2= moderately effective, 3=slightly effective, 4= not effective, 5 = not usually economical,
Reference: Purdue University Field Crops Pest Management Manual

As with most diseases that attack corn, if you can reduce stress on the plants you most likely can reduce the occurrence of certain stalk rots. Having a sound fertility program based on soil testing is important for keeping a corn plant healthy. Select a hybrid with resistance to certain diseases and good standability that is adapted to your region. Some of these stalk rots can produce mycotoxins that can be toxic to livestock. You should consider having silage tested for certain mycotoxins if you had fields with stalk rots this season. For more information on corn diseases checkout our online publication, Diseases of Corn Management Guide.

Soybean Aphid Update

Keith Waldron, NYS IPM

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Soybean aphid (SBA) populations continue to remain low (0-60 SBA’s per plant average) in most SBR sentinel plots being monitored across NY. In general, relatively few soybean fields have been treated for SBA in NY this season. Winged (alate) aphids are beginning to be observed. Soybeans are typically at R4-R6 growth stage.

Some sites in central (Finger Lakes) and western NY regions have reported the presence of “white dwarf” soybean aphids among the normal SBA forms. In most instances these populations have also been low. Recently, however, some fields in central NY have been found to exceed the 250 aphids per plant threshold, with several fields having SBA populations over 1000 per plant, the majority of those aphids being the "white dwarf" type.  Several of these fields have been treated with an insecticide.

“White Dwarfs” are very tiny forms of the soybean aphid about 1/2 the size (nymphs smaller) still..) of the normal “mountain dew” green colored normal aphids. These minute milky-white colored live moving aphids, are not the molted (dead) skins of aphid nymphs or diseased aphids. Why SBA populations may shift to these “white dwarf” forms is not well understood. Some entomologists suggest this may be due as a response to hot temperatures, higher humidity, shorter day length, nutritional quality, or predator populations. White dwarfs appear to feed less than the "normal" green/yellow aphids, primarily due to their smaller size. Plants infested by white dwarf aphids may not exhibit the presence of sticky honeydew or sooty mold discolored leaves often associated with high soybean aphid populations. The very small size of the white dwarf forms can make them difficult to detect.

Management Guidelines:

Current management guidelines for soybean aphids, including white dwarfs, have been developed by entomologists in the Midwest. These guidelines are based on a large body of collaborative research and trials over the last 5 years. SBA management is recommended when an average of 250 SBA’s are found per plant with increasing populations on 80% of the plants up to the R5 growth stage of soybeans. Note SBA threshold guidelines are designed to minimize risk of injury at vulnerable crop stages up to R5. Action threshold based on an average of aphids per plant over 20-30 plants sampled throughout the field. Additional considerations may include crop condition (drought, other stresses, etc.) and abundance and diversity of natural enemies.

Include “white dwarf” aphids in any monitoring counts, threshold and decision making.

The good news for most NY producers is that many soybean fields are maturing and will soon be at less risk for SBA injury.

A description of soybean aphid threshold guidelines related to crop growth stage (including pictures) can be found in the factsheet “Reproductive Soybean Development Stages and Soybean Aphid Thresholds” by Fischer, DW and J. Fanta. 2004. U of Wisconsin Extension Circular X-1134 at: www.uky.edu/Ag/IPMPrinceton/SoybeanAphid/soybean%20stages.pdf

Information from a portion of that factsheet follows.

Soybean aphid Threshold Guidelines:
R4 Stage soybean plant (full pod)

Pod is 3/4 inch long at one of the four uppermost nodes on the main stem with a fully developed leaf. The most critical time for soybean yield: Stress at this time can not be recovered and results in more yield loss than at any other time. Stage length 4 to 26 days: average 9. SBA thresholds not currently determined, but populations exceeding 250/plant and actively increasing need monitoring and treatment at grower discretion.

R5 Stage soybean plant (beginning seed)

Seed is 1/8 inch long in the pod of one of the main stem with a fully developed leaf.

Stress continues to be a major concern in soybean yield. Stage length 11 to 20 days: average 15. SBA thresholds not currently determined, however actively increasing populations exceeding 250 aphids/plant need monitoring and treatment at grower discretion.

R6 Stage soybean plant (full seed)

Pod containing a green seed that fills the pod cavity at one of the four uppermost nodes on the main stem with a fully developed leaf. At the end of this stage full yield potential has been realized, future yield losses are the result of harvest difficulty and not yield potential. Stage length 9 to 30 days: average 18.

Spraying for SBA after R6 has not been documented to protect yield.

R7 Stage soybean plant (beginning maturity)

One normal pod at any node on the main stem has reached its mature (brown or tan) pod color. Plants will continue to lose leaves and dry down as the season progresses. Stage length 7 to 18 days: average 9. Spraying for SBA at this time has not been documented to protect yield.

Soybean and Alfalfa Disease Update

Gary Bergstrom, Cornell University

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Thanks to Mike Stanyard's eagle eye, we have recorded two new 'firsts' for New York in terms of soil-borne soybean diseases.  The find of sudden death syndrome (incited by the soilborne fungus Fusarium solani f. sp. glyines) was in the sentinel soybean plot in Wayne Co. and the find of brown stem rot (incited by the soilborne fungus Phialophora gregata f.sp. sojae) was in a commercial soybean field in Yates Co.  We have long suspected both diseases to be present here as both are extremely common in midwestern soybean production.  Both provide us added incentive to rotate for two years between soybean crops in the same field to limit the impact of diseases on yield.

More information and excellent photos are available at the University of Wisconsin Soybean Health Website:

Sudden death syndrome

Brown stem rot

The foliar symptoms (pronounced necrosis of the inter-veinal panels of leaves) are nearly identical for the two diseases.  See the attached jpeg photo of foliar symptoms of SDS.

Brown stem rot is distinguished by a brown internal discoloration of the stem that can extend the length of the plant.

This is a good time to scout for these two diseases and learn how extensive their distribution may be in New York State.  Please contact Mary McKellar (mem40@cornell.edu) before sending us plant samples for confirmation, other than those from the cooperative sentinel plot program.

Growing Degree Days in NYS

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Accumulated Growing Degree Days for March 1 to August 2

Location

Base 50 F

Batavia

1591*

Chazy

1707

Clifton Park

2078*

Geneva

1741

Ithaca

1604

Prattsburg

1498*

Redhook

2269

*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.

* Check grain storage bins for temperature, moisture and air flow.

* Mow around storage bins, barn and farm facilities

Established Alfalfa & Hay:

• Harvest third cutting of alfalfa about 40 days after second harvest.

• Record hay yields by field; take samples for forage analysis

• Log storage locations of hays, silages.

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

• 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.

Alfalfa Seedings:

• Finish planting summer seedings before mid-August.

* 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.

Small Grains:

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

Corn:

* Monitor corn rootworm adults at silking.

* Observe corn for crop growth stage and condition, weeds, foliar diseases, vertebrate injury to ears, lodging and fertility

• Check bunkers and silos. Prepare for corn silage.

• Log storage locations of hays, silages.

Soybeans:

* Monitor for crop condition and growth stage, white mold, soybean aphids, natural enemies, foliar diseases, sudden death syndrome (Fusarium solani f. sp. glyines), brown stem rot (Phialophora gregata f.sp. sojae), 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.

- Evaluate need for face fly and stable fly control measures

Equipment:

* Provide annual maintenance to fertilizer and pesticide application equipment,

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

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