September 14, 2007

The abundance of grasshoppers in some areas of Nebraska has led to concerns over potential problems with establishing the winter wheat crop this fall. Grasshopper populations decline through the late summer and fall, and in fact, most grasshoppers will die off with the first hard freeze; however, that may not be soon enough for the wheat crop because much of our winter wheat will be getting established before the grasshoppers are gone.

Large numbers of grasshoppers in areas surrounding wheat fields can threaten seedlings as they emerge, especially in the field margins. Determining if a problem will develop is difficult because the standard thresholds for control of grasshoppers in cropland (seven per square yard in the field; 20 per square yard in field borders) must be lowered because the emerging winter wheat has very limited foliage and grasshoppers can easily keep the wheat clipped back completely, causing stand losses.

Grasshopper damage potential decreases as we progress into the fall, but if grasshopper densities are extreme, it is difficult to completely eliminate the damage. In areas of high grasshopper activity avoid early planting of wheat to reduce potential damage and consider increasing the seeding density to compensate for partial stand loss. This may allow for a reasonable stand after grasshopper damage has run its course.

Management

Controlling adult grasshoppers is difficult, but there are several options available for grasshopper control including: seed treatments or planting time applications to field margins or surrounding borders to protect the wheat as it emerges.

Furadan 4F is registered for use as a border treatment applied at planting under a Special Local Needs (SLN) label. The major drawback of Furadan is its safety to the applicator. Furadan should be injected through a closed system directly into the furrow through a microtube or with liquid fertilizers. This injection equipment is expensive, but will reduce safety concerns. Furadan provides effective, consistent control and does not need water for activation.

Gaucho and Cruiser seed treatments are registered for wheat. Plants are protected from emergence and treatment can be easily limited to treating only the field margins to reduce costs. These treatments will be effective for moderate grasshopper densities, but likely will not hold up under severe grasshopper pressure. The seed must be treated by a certified seed treater so planning is necessary when ordering seed.

Also see stories on: Avoid Early Planting Wheat Tips for Late Planted Wheat Wheat Production Meeting Sept. 18

Sevin bait is available in the 2 percent and the 5 percent formulation on bran. It can be applied with a bait blower or whirly-bird type spreader. Application to areas with minimal ground cover will maximize control. Even distribution of bait is critical and re-application will be needed if it rains. The main advantage of bait is that it will be present for the grasshoppers to feed on both before and during wheat emergence.

Several foliar insecticides can be used to treat wheat field margins and borders. Lorsban, Furadan, dimethoate, Mustang, Baythroid or Warrior are registered for grasshopper control on wheat, and Asana, Warrior and acephate are labeled for grasshopper control in non-crop borders. The best timing for a border application is just as wheat is emerging. Treating the emerging wheat crop can be problematic because of the restricted leaf area for insecticide deposition, and consequently, new growth will not be protected.

Grasshopper control around wheat fields can be challenging and the level of effectiveness for any control option will depend largely on the density of grasshoppers. Under very heavy pressure none of the control options will be completely effective, and the loss of some stand on the field margins may be inevitable. Borders can be replanted later in the fall. Grasshopper control in winter wheat likely will be a compromise between effective control and affordability.

Gary Hein
Extension Entomologist
Panhandle REC, Scottsbluff