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July 28, 2010

Small grains:

Wheat scab (Fusarium head blight) risk has increased in the last few days because of recent rains.  For susceptible varieties scab risk has been moderate to high in most of the area over the past few days.  The exception to this is in western Williams county and most of McKenzie county.  These areas ave had low scab risk for all varieties.

For up to date information please go to the NDAWN website (Applications, Wheat, Disease Forecaster) and select the closest location and stage of wheat development (flowering is the best timing for scab control).  Please refer to the 2010 North Dakota Field Crop Fungicide Guide for scab fungicides. 

Ergot was observed in wheat fields in McHenry, Renville, and Mountrail counties.  The percentage of the fields affected ranged from 2-6%.  Ergot contains an alkaloid that is toxic to humans and animals.  Livestock that eat ergot contaminated grain may have convulsions, hyperthermia, loss of milk, and gangrene.  Ergot can be managed by using high quality seed and rotating to a non-cereal crop.  For more information on ergot, please see http://www.ag.ndsu.edu/pubs/plantsci/crops/pp551w.htm.

Loose smut has been observed in a number of fields in the area.  A wheat field in Burke County had 8% of the field infected with loose smut.

We have continued to find symptoms of wheat streak mosaic virus (wsmv) in the area.  A spring wheat field in southwest McHenry County that was in the boot stage had a significant wsmv infection.  Planting date is a significant factor in the severity of this disease.  Late planted spring wheat and early planted winter wheat are at higher risk for severe wsmv infections.

Field Peas and Lentils:

Pea aphids were found at levels approximately 5-fold above the economic threshold in a late planted pea field in northern McLean County.  The best timing for pea aphids is when approximately 50% of the peas are at early pod.  Late pod applications are less effective and may not be economical.

Field peas in Sheridan County were severely infected with powdery mildew.  Powdery mildew is common in warm humid weather.  The green pea varieties Majoret, Cruiser, and CDC Striker were severely affected, whereas, the yellow pea varieties DS Admiral, CDC Golden, and Agassiz were relatively unaffected.  Quadris and Headline fungicides have efficacy against powdery mildew and are most economical when severe infections occur during early pod development.

A lentil field in southern McHenry County was infected with white mold.  Crop rotation to non-broadleaf hosts, use of tolerant varieties (e.g., Pennell), and fungicides can be used to manage white mold.

Sunflowers:

Most of the fields in the area are in the R1 to R3 stage.  The R5.1 stage (start of bloom) is a good insecticide timing especially for red sunflower seed weevil and banded sunflower moth, two of the most damaging insect pests of sunflower in our area.  Wild sunflowers are in the R5.1 to R6 stage in the area and are a good prelude to what insect pests will be a problem in the area.  We have been finding a number of red sunflower seed weevils and Lygus bugs on wild and cultivated sunflowers and are catching significant numbers of banded sunflower moths in our traps.

The “mystery bug” was in fact a ragweed plant bug, Chlamydatus associatus.  According to information from Manitoba, it is typically not an economic pest.  Thanks to Pat Beauzay and Jan Knodel for help with identification.

Regional_Pest_Updates_07.28

Caption: Ragweed plant bug on sunflower (John Gavloski, MAFRI)

Downy mildew has been found in sunflower fields in Renville and McHenry Counties.  Foliar fungicides are not effective against this disease.

Soybeans:

Soybean aphids continue to be low or absent in fields in the area.  Green cloverworms have been found feeding on soybean leaves.  Cloverworms and other leaf feeding Lepidoptera have a threshold of 20% leaf loss at bloom, 15% at pod fill and 30% post-pod fill to harvest.  For more information on leaf feeding caterpillars in soybeans see the August 16, 2007 issue of the Crop and Pest Report (issue 14).

 

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