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NY Weekly Field Crop Pest Report, 2005

August 19, 2005 Volume 4 Number 18

1. View from the Field

2. Dry Conditions - Pest Impacts?

3. Winter wheat, Aphids and Yellow Dwarf

4. White Mold in Soybeans

5. Soybean Rust Update

6. Soybean Aphid Management Decisions?

7. Growing Degree Days in NYS

8. Clipboard Checklist

9. Contact Information

View from the field

Western NYS

Julie Stavisky

Reports are in from many areas of the Finger Lakes and Western regions of NY that soybean aphid numbers are dropping. Many factors are contributing: humid conditions encouraged outbreaks of fungal pathogens, lady beetle populations have continued to increase, or control with insecticides has been successful. Now is the time to start watching fields for winged aphids. As soybean pods fill and plants dry down, aphids with wings will head for “greener pastures” - or in the case of soybean aphids, buckthorn plants as an overwintering host. From the TAg team fields in Orleans County, Nancy Glazier (NWNY Team) observed that every field scouted has a lot of downy mildew. As the pale spots of affected tissue darken and die, it can look like other leaf spot diseases.

Corn rootworm adults are still abundant in fields where silking was late in areas. Potato leafhopper adults and nymphs continue to be sparse in most alfalfa fields.

Dry Conditions - Pest Impacts?

Keith Waldron, NYS IPM

Wilting, curled and discolored leaves, stunted plants, parched soil - all signs of drought stress. Dry conditions are the norm in many areas of the state this week and rain dances have had spotty success at best. Drought impacts harvest timing decisions, yield and crop quality. What effects might these dry conditions have on our common field crop pests?

For row crops with poor weed control, yield and quality impacts are an issue. Potential for herbicide carryover may be another concern.

For fields where root or vascular injuries are (or have been) present, dry conditions add to plant stress and make a bad situation more obvious. As a general rule of thumb, sucking insects and those that bore into plants, and diseases that damage roots and vascular systems, have a greater impact during dry periods. Corn rootworm, clover root curculio, and alfalfa snout beetle larval damage, vascular diseases like Verticillium wilt, root rots like Phytopthora (previously damaged plants) and crown diseases like Fusarium crown rot are some problems that can become more evident under dry conditions. Tunneling by stalk boring insects like European corn borer (ECB) may show greater impacts and worse if combined with a stalk rot like anthracnose. On the flip side for ECB ­ dry conditions cause high mortality to ECB eggs and newly hatched larvae.

Dry conditions affect the balance of biocontrol provided by beneficial fungal pathogens like Pandora and Entomophthora spp, that help control common field crop arthropod pests. Reducing efficacy of these biological control agents can increase risk of some pests like spider mites, potato leafhopper, and aphids.

Dry conditions can interact with other stresses and pest problems. High populations of potato leafhopper (PLH), a sucking insect, for example, have been shown to interact with water stress to produce even greater plant damage. Remember to HALVE PLH thresholds for fields under drought stress…

Stalk rots of corn may be another issue for fields under drought stress, particularly for those fields that had good pollination. Gary Bergstrom described the situation as a “source / sink” issue. Plants are working hard to send photosynthates to the developing kernels. Under dry conditions, that decrease production of photosynthates, kernels win over stalks as the place plants send their manufactured food to. As this happens stalks lose out and become weakened and at risk for stalk rots such as Diplodia, Anthracnose and Fusarium.

On the plus side, many field crop diseases can be less common or severe during extended dry conditions. Diseases like anthracnose leaf blight (corn), spring black stem (alfalfa), and Septoria brown spot (soybean) are favored by overcast skies, frequent showers, and moderate to high relative humidity. These types of diseases require moisture and periods of wet leaves for fungal spore germination and host infection. Rainy conditions can be important for movement of disease inoculum. Locally, storms can splash fungal spores and bacteria from one plant to another, like eyespot of corn, and physically move disease organisms, such as Phytopthora root rot, through the field. “Globally” storm weather patterns are an important means of transporting some diseases across great distances (rusts of corn, wheat, soybean). Other good news? Lowered levels of infected crops this season could translate to lowered overwintering inoculum and potentially reduced risk to infect crops next season. Remember the disease triangle? Presence of a susceptible host, virulent pathogen, and favorable weather conditions. The actual incidence and severity of foliar diseases next season will still depend to a large extent on the weather patterns that develop.

Winter Wheat, Aphids and Yellow Dwarf Virus

Ken Wise, NYS IPM

Barley yellow dwarf virus, now know as yellow dwarf virus (YDV) in wheat is a serous disease across the country. This disease is transmitted by several species of aphids that infest wheat. When infected aphids feed on the plants they infect the wheat with the virus. Winter wheat that is infected in the fall does not show symptoms. Symptoms start to appear mid-spring as yellowing of leaves. One management strategy is to plant wheat after the Hessian fly free date in your region. This can limit the number of aphids entering the fall seeded winter wheat fields. Another management option is to plant a wheat variety that is resistant to YDV.

White Mold in Soybeans

Julie Stavisky, NYS IPM

2005 has been an unlikely season for severe white mold outbreaks, but humid weather over the past several weeks did provide the conditions for disease development in some areas of New York State.

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, moist, 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 fungal mycelia colonize dead flowers and the characteristic thick white moldy covering on stems and pods develops. Interspersed with the white mold on stems are the black sclerotia. Plants may wilt and die as a result of infection. If white mold infection is late in the season, yield loss will not be as severe. Temperatures over 90 degrees will 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.

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)

File written by Adobe Photoshop® 4.0

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. 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

From: New York State Soybean Rust Information Center

2005 Asian Soybean Rust Status

Soybean rust was most recently confirmed in Hampton County, South Carolina. This is the first report from South Carolina in 2005. This is currently the most northern report of soybean rust in the U.S. To date, Alabama has reported four counties positive with soybean rust, Florida has reported eighteen counties, Georgia has reported seven counties and Mississippi has reported two counties. 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. Growth stages in New York State sentinel plots range from R5 to R6. (Last updated 8/16/05)

Soybean aphid management decisions?

Keith Waldron, NYS IPM

Soybean aphids (SBA) are still here. Populations are variable across the state but in some areas are still higher than they have been in recent years. This is consistent with other states reporting SBA issues across the country. NY soybeans are typically at or above the R5 stage.

SBA thresholds for R5 and beyond have not been determined.

Michigan State University suggests average of 1000 SBA per plant with increasing populations. If high SBA populations are determined, check the field again over the next several days. Static or decreasing SBA populations are what we’d hope for. Increasing populations are not a good sign, but watch populations of natural enemies. Some additional considerations in making management decisions: Are soybean plants stressed? Are soybean plants showing symptoms of aphid infestation (curled leaves, sooty mold, honeydew, stunted plants)? If yes, these are not good situations. Presence of winged aphids? Can be a sign the population is getting ready to leave. Are natural enemies present? If yes, they can do wonders at keeping SBA populations at bay.

Reality check ­ Some recent questions from folks in the field have added the caveat “tall” and “drilled” soybean plants. Moving spray equipment into these fields is not easy. Michigan IPM reports situations where this has led to poor insecticide coverage and the need for additional sprays. Knocking out the beneficial populations hurt these fields too and allowed a resurgence of SBA numbers. Another reality is that pre-harvest interval (PHI’s) for available insecticides is getting close. Ambush/Pounce/permethrin: 60; Warrior: 45; Lorsban and other chlorpyrifos products: 28; Mustang Max and dimethoate: 21.

For more information see: Reproductive Soybean Development Stages and Soybean Aphid Thresholds:

Growing Degree Days in NYS

March 1 - August 16, 2005

Location

Base 50 F

Batavia

1866.6

Chazy

1689.0

Clifton Park

2240.7

Geneva

1974.8

Ithaca

1835.7

Prattsburg

1753.7

Source: http://newa.nysaes.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.

• Check bunkers and silos. Prepare for corn silage.

• Check fall harvest equipment.

• Mow weeds around barn, grain storage bins, and farm buildings.

Alfalfa & Hay:

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

- HALVE PLH thresholds for fields under drought stress…..

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

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

• Record hay yields by field and quality by storage facility; take samples for forage analysis

Field Corn:

• Monitor corn rootworm adults at silking.

• Observe corn for weeds, stalk rots / lodging, and nutrient and moisture deficiencies

Soybeans:

• Monitor for soybean aphid, soybean rust, pod, stem and foliar diseases.

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:

- supplement animals on pastures with hay as needed

- Evaluate need for face fly, horn fly, and stable fly control measures

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