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July 14, 2010

Small grains:

Wheat scab (Fusarium head blight) has been observed in commercial fields and at the North Central research extension center.  Although most scouted fields in the area have had low levels of scab, a wheat field in the Kenmare area had 12% incidence with one-third of the kernels damaged by scab on infected heads.  The risk for scab infections ranged from low risk in the Minot, Watford City, and Williston areas, moderate risk in susceptible and /or very susceptible varieties in the Bowbells, Crosby, Mohall, Plaza, and Rugby areas, and high risk in the susceptible/very susceptible varieties in the Berthold and Bottineau areas.   There was low risk for scab infection in the moderately resistant varieties across the region from July 10th through the 13th.  For more 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. 

Loose smut has been observed in a number of wheat and barley fields.  Loose smut is a seed borne disease that can be managed using quality seed and fungicide seed treatments. 

Symptoms of the wheat streak mosaic virus have been observed in a number of spring wheat fields in Bottineau, McHenry, McLean, and Ward counties.  With new infections or on younger leaves, the mosaic pattern is the predominant symptom on leaves.  On older leaves or older infections, the thin green streaking is the most common symptom (see figure below).    

Wheat stem maggot damage has been observed in some fields in the area.  Most of the fields were at or below one percent damage.  The characteristic white heads that pull easily from the stem are caused by wheat stem maggot.  If greater than one percent of the heads were lost from wheat stem maggot a $2/acre insecticide application would bring the producer extra return with a yield of 50 bushels/acre and $4.00 wheat.  Research conducted by Eric Eriksmoen at Hettinger showed the greatest yield in a wheat stem maggot infested field when insecticides were applied at the 5-leaf and jointing stages.      

Field Peas and Lentils:

Pea aphid populations have recently increased dramatically to above threshold numbers.  Our sweep net samples averaged 40 aphids per sweep compared to a threshold of 12 aphids per sweep.  Research from Manitoba has shown a 10% yield loss at 20 aphids per sweep.  The best timing for pea aphids is when approximately 50% of the peas are at early pod.   Pea aphids also feed on alfalfa and can move into field peas at especially high rates after alfalfa is cut.  Lygus bug numbers have been low on field peas but above threshold on lentils. 

Sunflowers:

The number of banded and Arthur’s sunflower moths have increased to more than 100 in our traps in western Bottineau County.  Trap catches are not reliable for determining when insecticides should be applied.  Egg counts or examining individual plants for adult moths will help producers determine if an insecticide is warranted.  For more information see NDSU publication E-823 (http://www.ag.ndsu.edu/pubs/plantsci/pests/e823.pdf).

 

(Figure Caption) Wheat streak mosaic virus symptoms on wheat.  The leaf at the top has the mosaic pattern more characteristic of a recent infection on younger leaves.  The leaf at the bottom has the streaking pattern more characteristic of an older infection (photo by D. Waldstein). 

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