April 24, 2013

NYS IPM Weekly Field Crops Pest Report, April 25, 2013

 

 

In this issue:

  1. View from the Field
  2. Snow Mold in Small Grains
  3. Early Season Diseases: Evaluating Winter Wheat!
  4. Alfalfa Weevil Growing Degree Days
  5. Clipboard Checklist

 

View from the Field

There have been changes to the NYS Weekly Field Crops Pest Report this year. The web version of the pest report will have a new look this summer. We have gone from a static webpage to a Cornell University CCE blog site. You can subscribe to this blog by entering your email in the space provided on the right side of the screen. You then will get an email notice each time there is a new report posted. Also new this year is that Weekly Field Crops Pest Report notices and pest alerts will also be posted on Facebook  and Twitter. We will continue to mail the report to the Cornell Field Crops list serves.

I have been evaluating triticale varieties for snow mold this spring at the Cornell Research Farm at Valatie, NY. This winter was a good one to test the level of resistance in each variety. There was a substantial amount of snow mold in the test plots this spring. If you are planting winter triticale it is important to select a variety that has resistance to this disease.

Snow Mold in Triticale

Snow Mold in Triticale

For more information on snow mold see the article below.

Keith Waldron reports finding winter cutworm near Geneva, NY. Winter cutworm (Noctua pronuba) sometimes called snow cutworm has a wide array of host plants.   They will feed on alfalfa, grass hay and small grains. Winter cutworm also feeds on: beets, cabbage, carrot, grape, grasses, lettuce, potato, strawberry, Swiss chard, strawberries, tomato ornamental plants and weeds. They are very cold resistant and can survive the winter as a larvae. The adult form of this species is called yellow underwing moth.  For pictures and more information view Diagnostic Services: Insects and Arthropods.

Dr. Gary Bergstrom is reporting that mosaic symptoms of Soilborne Wheat Mosaic Virus are showing up on susceptible varieties of winter wheat in Tompkins/Seneca County.

Mike Stanyard in Western NY has observed powdery mildew in winter wheat.  See more on powdery mildew and management strategies in the following article.

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Snow Mold in Small Grains

Ken Wise, NYS IPM

Pink snow mold (Fusarium nivale) and speckled snow mold (Typhula species) are the two main fungi that cause this disease. Pink snow mold is by far more common than speckled snow mold. Fusarium infects and survives on living plants as conidia or mycelium. Typhula over-winters as sclerotia in plant debris or soil. When the spores of speckled snow mold or pink snow mold germinate they infect the leaves of the plant. The older leaves that touch the soil surface under the snow canopy are first infected. The crowns may or may not become infected. Fungi under the canopy of snow will continue to develop eventually producing conidia or sclerotia. The disease is most aggressive at temperatures that are slightly above freezing.

Results of Snow Mold on Plants

Results of Snow Mold on Plants

Many times snow mold occurs in patches in the field after the snow melts. You will observe a fungal mass on the leaves that appears pinkish, whitish or gray. Many times the leaves will have brown-black fungal bodies which are called sclerotia. The leaves could be partly or entirely killed. If snow mold infects the crown it will kill the plant. If the crown is not infected most likely new leaves will grow back and the plant should produce grain.

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Early Season Diseases: Evaluating Winter Wheat!

Ken Wise, NYS IPM

Spring is the time to look for certain foliar diseases you may encounter on your winter wheat. These are powdery mildew, Stagonospora nodorum blotch, and wheat rusts. You normally start to see this in late April or May. It is best to get out and scout your fields now! Here is what you will want to look for:

Powdery mildew

Powdery mildew forms a white to gray, fungal coating on the above-ground parts of the wheat plant. Lower leaves are usually the most severely infected because of the high humidity in the lower canopy. As disease lesions age small black fruiting bodies (cleistothecia) develop with in white infected areas. Powdery mildew is favored by wet and humid days with moderate temperatures of 600 F or above. Powdery mildew is disseminated by airborne spores.

Powdery mildew

Powdery mildew

Stagonospora Nodorum Blotch

Symptoms usually appear within two or three weeks of head emergence. Leaf lesions begin as very dark brown flecks or spots, sometimes with a yellow halo. These small irregular lesions expand into oval light brown lesions with dark brown centers. On wheat heads the lesions begin as either grayish or brownish spots on the chaff, usually on the upper third of the glume. As lesions enlarge, they become dark brown and the centers turn grayish-white in color as tiny brown or black dots (pycnidia) develop within them. Splashing rain or thunderstorms can move spores from field surface to the plant.  Wheat seed can be infected from spores when it is harvested. This disease may also be in the wheat residue on the surface of the field.

Stagonospora Nodorum Blotch

Stagonospora Nodorum Blotch

Leaf Rust

Rust lesions are small, circular, and vivid orange in color. They may occur on stems, but are most common on the upper surface of leaves. Leaf rust can develop very rapidly so it should be treated as soon as possible.  Leaf rust is favored by warm and humid weather with thunderstorms in June. Leaf rust is disseminated on winds which carry the airborne spores great distances. Temperatures between 600 and 800 F are optimal for disease development.  For photo of leaf rust on wheat please see: Iowa State University Image Gallery: Leaf Pustules on Wheat.

Monitoring the fields

Scout and assess upper three leaves for symptoms and signs of these three diseases in early to mid-May through June, before flag leaf emergence.  If disease (any amount) is observed on approximately 50 percent of main tillers that averaged across the field, a fungicide should be considered now.

Table 1: Management Options

Management Practice

Powdery Mildew

Stagonospora Nodorum Blotch

Leaf Rust

Certified Seed

2

Timely Planting

2

Fungicide Seed Treatment

1

3

Host Plant Resistance

2

Rotation

2

1

Fungicide Application

1

2

2

Control Measures and Their Effectiveness (1=high to 3=slight)

Source: Purdue University Field Crops IPM Handbook

If a field is over threshold for one of these three foliar diseases the next step is to go through an analysis of whether a fungicide application is an economic option. Please follow the steps listed below to determine if a field might need an application of fungicide.

Guidelines for Wheat Fungicide Decisions

(Taken from Cornell Guide for Integrated Field Crop Management)

Does the crop have a reasonable yield potential?

Assess the crop in early May (stem elongation stages) for adequate stand (density of approximately 30 strong stems per foot of row for 7-inch rows on good soils) and plant vigor. If the stand is sparse or plants are not vigorous or show widespread symptoms, fungicide application should not be considered further.

____ Yes    ___ No

Have foliar diseases been observed before flag (last) leaf emergence?

Assess upper three leaves for symptoms and signs of powdery mildew, leaf spots, or leaf rust in early to mid-May, before flag leaf emergence. If disease (any amount) is observed on approximately 50 percent of main tillers, averaged across the field, a spray should be considered now. This threshold is exceeded in less than 50 percent of location/year situations in New York, so there is a significant risk of making an unnecessary fungicide application.

____ Yes   ___ No

Have foliar diseases been observed during head emergence?

Assess upper two leaves for foliar diseases in late May to early June; if disease (any amount) is observed on approximately 50 percent of main tillers, a spray should be considered now. Fungicide applications made after early June may control some diseases but are unlikely to produce significant yield benefits.

___ Yes  ___ No

Are climatic predictions conducive for further disease development?

Powdery mildew development is reduced dramatically once the average daily temperature rises above 70˚F; this disease often disappears by June. Severe leaf spot development is favored by extended periods of wet weather; it may be insignificant if dry weather persists in May and June. Listen for regional advisories on the threat from leaf rust; rust inoculum often builds up in areas to the south and west of New York and is deposited here by thunderstorms in June or July. In addition to disease observations, use long-range local weather forecasts in making your spray decision.

What is your short to medium term weather conditions?

Have I selected fungicides appropriate for the disease spectrum and have I read the label carefully?

Be sure that the materials you spray will be effective against the range of diseases found in your field; e.g., some products effective against powdery mildew are ineffective against leaf spots or vice versa. Check in the Cornell University Guide for Integrated Crop Management.

Is the spray decision consistent with my perception of risk?

A simple formula for evaluating the relative economics of a fungicide spray is: Relative Profit = (Grain Yield Increase x Grain Price) – (Cost of Fungicide + Application Costs). If ground spray rigs are used, the yield lost to wheel traffic should also be factored in. Each of these variables influences the relative economics of fungicide application as illustrated in Table 5.7.3. of the Cornell University Guide for Integrated Crop Management.

Relative Profit = (Grain Yield Increase _____ x Grain Price _____) – (Cost of Fungicide  _____ + Application Costs ________)

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Alfalfa Weevil and Growing Degree Days

Ken Wise, NYS IPM

It is a bit early this year to be thinking about Alfalfa Weevil… OR is it?

Calculating the alfalfa weevil growing degree days is an IPM tool to use in your alfalfa IPM program. By calculating the number of alfalfa weevil heat units you can predict the different life stages of the weevil.

Things you will have to know are the maximum and minimum temperature data from March 1 through the current day. Take the high and low temperature of each day and divide it by 2 and subtract 48 degrees F. This will give you the number of heat units for an individual day. If it is a negative number then there were no heat units that day for alfalfa weevil to develop.

(High Temperature + Low Temperature / 2) – 48 F = AW heat units.

Keep a running tally of the accumulated heat units from day to day. Compare the total GDD’s and compare this number against the expected alfalfa weevil growth stage from the following table.

 

TABLE 2: Growing degree Days for peak (50%) Occurrence of Alfalfa Weevil growth stage:

Stage or Event Accumulated growing degree days (48°F base temperature)
Eggs hatch

280

Instar 1

315

Instar 2

395

Instar 3

470

Instar 4

550

Cocooning

600

Pupa

725

Adult Emergence

815

Instead of doing all those long drawn out calculations let NEWA do it for you! NEWA is short for Network for Environment and Weather Applications. This website has a function that will calculate the alfalfa weevil heat units for your region or area of the state. This is at NEWA  Alfalfa Weevil

 

Table 3: Current Growing Degree Days in NYS

March 1 –  April 22, 2013

Location Base 48°F Base 50°F
Chazy 16 12
Geneva 45 31
Highland 69 50
Ithaca 46 31
Watertown 31 2

Source: NEWA—Growing Degree Days
It is always important to ground truth calculations with observations in the field.

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Clipboard Checklist

Keith Waldron, NYS IPM

General

*Walk fields to check tile flow, check and clear drainage outlets. Look for line breaks
*Note and record location of wet areas on field maps or aerial photo for future tiling considerations and crop decisions, check for areas of soil erosion
*Pre-plant weed evaluation, timing cultivation and/or pre-plant weed management
*Watch for early season weeds: winter annuals, chickweed, henbit, field penny cress, shepherd’s purse, giant and common ragweed, purple deadnettle, lambsquarters, redroot pigweed, velvet leaf, Pennsylvania smartweed, common sunflower, quackgrass, foxtail

Alfalfa:

*Evaluate established legume stands for winter damage (thinning stand, frost heave), determine average alfalfa stand count adjust crop plans if necessary
*Monitor for alfalfa weevil
*Monitor new seedings for Pythium blight and Phytopthora Rot Rot.
*Monitor for Alfalfa Snout Beetle (In Oswego, Jefferson, Cayuga, Wayne, Lewis, St. Lawrence, Clinton, Essex, and Franklin counties)

Small Grains:

*Monitor winter grain fields for over wintering survival, weed issues, growth stage, number of tillers
*Check stands for soilborne virus diseases, Wheat spindle streak mosaic and Soilborne wheat mosaic and powdery mildew symptoms, cereal leaf beetle, weed escapes, goose damage

Corn:

*Prepare land and plant corn as soon as conditions allow
*Pre-plant weed evaluation, timing cultivation and/or pre-plant weed management

Pastures:

*Check and mend fences as needed.
*Check crop growth
*Invasive species, plants harmful to livestock
*Review/Plan rotation system

Equipment:

*Remove / clean soil and crop debris from equipment
*Arrange for custom weed control or check your own application or cultivator equipment for repairs.
*Carry appropriate / necessary NYS DEC and EPA required documents: (pesticide applicators license, pesticide labels, MSDS sheets, etc.) with application equipment
*Calibrate:

  • planting equipment – maintain records on planting rate per field
  • manure spreaders – maintain records on amount spread per field
  • pesticide application equipment – Check nozzles, pumps, etc., recalibrate pesticide application equipment before use.

Storage:

* Check stored grain bins for temperature, moisture and signs of mold and insects. Aerate, core, transfer grain or treat as necessary
*Check forage allocation and anticipate feed program adjustments as forages from previous year are used up
*Plan where forages should be stored for optimum allocation next feeding season

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