UNL CropWatch Aug 6, 2010: Defending New Winter Wheat and Alfalfa Fields from Grasshoppers

UNL CropWatch Aug 6, 2010: Defending New Winter Wheat and Alfalfa Fields from Grasshoppers

August 10, 2010

Even with early spring rains reducing some grasshopper numbers this summer, late season grasshopper activity has been high in many parts of Nebraska, especially the Panhandle, a University of Nebraska-Lincoln entomologist says.

With wheat harvest finishing up, many wheat growers soon will start to get ready for winter wheat planting, said Jeff Bradshaw, UNL Extension entomologist.

However, it's important to remember that grasshoppers can make emerging wheat seedlings their next meal.

"The risk increases the closer we get to fall and more grasshoppers are adults," Bradshaw said. Some growers may want to plant earlier this year because last year wheat crops were damaged by October snow storms. However, the problem with earlier planting, in addition to wheat streak mosaic, is the seedlings also are more susceptible to grasshoppers.

The same goes for alfalfa. August is an excellent time to plant alfalfa if conditions are wet. However, it is important to watch out for grasshoppers, said Bruce Anderson, UNL Extension hay and forage specialist.

Although grasshopper populations decline through the late summer and fall, they can remain significant enough to cause damage until the first hard freeze.

Growers should monitor grasshopper densities and use a seed treatment on wheat, Bradshaw said.

To save money, growers can plant a 60-foot border in their fields with the treated wheat, and the other without to create an insecticide-treated border.

Densities in the range of 11 to 20 grasshoppers per square yard is enough to cause significant loss in winter wheat.

When it comes to alfalfa, if growers find more than two or three grasshoppers per square yard in the field to be planted or more than 10 grasshoppers per square yard in field margins, treatment with insecticides probably will help, Anderson said.

Other options to help reduce the risk and/or manage grasshopper problems in winter wheat include:

  • Avoid early planting in areas of high grasshopper activity. Planting higher risk fields near the end of the optimum planting window will reduce the time period that a field will need to be protected from grasshoppers in the fall.
     
  • Increase the seeding density of wheat in field margins. This may compensate for partial stand loss and allow for a reasonable stand after grasshopper damage has run its course.
     
  • Neonicotinoid seed treatments can provide protection from emergence, and treatment can easily be limited to treating only the field margins to reduce costs. These treatments will be effective for moderate grasshopper densities, but they will likely not hold up under severe grasshopper pressure. These seed treatments are only available through a certified seed treater so advanced planning is necessary when ordering seed. Also, to be effective the highest registered rate of product must be applied to the seed.
     
  • Several foliar insecticides can be used to treat wheat for grasshopper control; however, treatment of the emerging wheat crop will result in little residual activity of the product because of the restricted leaf area for insecticide deposition.

Other options to help reduce the risk and/or manage grasshopper populations in alfalfa include:

  • Treat field margins before new alfalfa seedlings begin to emerge to head off potential invasions. If the surrounding area is a non-crop area, the best treatments to control adult grasshoppers would be Warrior (or other lambda-cyhalothrin products) and Asana (or other esfenvalerate products.) If the area surrounding the field is pasture, the best products would be Warrior or Mustang MAX. Warrior is the only product that can be used in non-crop areas, pasture, alfalfa or wheat.
     
  • Several other insecticides also help control grasshoppers in field margins as well as in the seeded field itself. Pyrethroids like Baythroid, Warrior and Mustang are labeled for grasshopper control on alfalfa.

"Whenever using any insecticides, be especially careful to avoid injuring bee and other important pollinating insects," Anderson said. "Time of day when spraying, using less toxic insecticides and avoiding areas with blooming plants are some precautions to take to protect bees."

With all insecticides, be sure to carefully read and follow all label directions.

For more information, visit the UNL Department of Entomology's Grasshoppers of Nebraska website at http://entomology.unl.edu/grasshoppers/.

Sandi Alswager Karstens
IANR News Service