Keep on grasshopper alert | TSLN.com

Keep on grasshopper alert

Roger Gates

Rangeland Extension Specialist, SD State University West River Ag Center

Adult grasshopper surveys conducted last fall by USDA’s Animal and Plant Health Inspection Service (APHIS) indicated the potential for high grasshopper populations during the 2010 growing season in western South Dakota and neighboring states [see map]. Recent cool and wet weather may be beneficial by both delaying and interrupting hatching and development. However, the risk is large enough that grassland managers should be alert to the potential and management alternatives.

One approach that may limit grasshopper development is to manage pastures to minimize bare ground and maximize shading. North Dakota research demonstrated that pastures that were grazed rotationally had less bare ground, more shading and lower grasshopper populations resulted. If grasshopper emergence and development becomes excessive, routine management approaches may be insufficient to protect pasture feed resources.

Appropriate questions might include, “how much will grasshoppers consume, what control options are available, and under what conditions is control appropriate?” Research indicates that at a density of one grasshopper per square yard, their activity results in disappearance of nearly one-half pound of forage per day. At a density of 15 grasshoppers per square yard, the effect will be removal of over 200 pounds per acre per month. Grasshopper densities can be estimated by selecting a representative plot of known size counting the number of grasshoppers that leap or fly as the plot is walked. A sweep net may also be used, but are useful to provide a more qualitative “high or low” population estimate.

If a serious outbreak occurs, insecticide application becomes the primary remedy. Insecticides available for grasshopper control on rangeland include carbaryl (Sevin), diflubenzuron (Dimilin), malathion (Fyfanon, Malathion 5EC), and lambda-cyhalothrin (Warrior). Application costs are estimated to range from $2 to $10 per acre for material and application. Some cost share may be available from USDA (up to 100 percent on federal lands, 50 percent on state lands and 33 percent on private lands as federal budgets allow).

When the infestation level is determined, rational decisions about insecticide application become primarily financial. The other factors are the anticipated forage loss, the value of the loss and the actual application cost. The table at left estimates the value of forage lost based on grasshopper population density and the value of an Animal Unit Month of forage (approximately 800 pounds). An alternative manner to view the table is what “out of pocket” cost could be paid per acre to apply insecticide control. For example, if grasshopper density is estimated at eight per square yard and you value an AUM at $28 (or that would be the cost to replace lost forage), you would break even by paying $3.86 per acre for control.

As this growing season proceeds, ranchers should keep a close eye on emerging or developing grasshoppers. Helpful contacts include your local extension office who can contact state specialists. In addition the South Dakota Department of Agriculture (605-773-5425) or the USDA-APHIS-PPQ office in Pierre (605-224-1713), can provide information or direct you to resources about grasshopper control and availability of control cost assistance.

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Like a number of organisms that are normal components of the ecosystem, grasshoppers generally exert minimal disturbance. But careful management may infrequently require some level of control as a means to securing intended uses of the rangeland.

As always, enjoy the miracle of new and emerging life that spring affords and make careful observation of all the life forms on the landscape your normal practice.

Adult grasshopper surveys conducted last fall by USDA’s Animal and Plant Health Inspection Service (APHIS) indicated the potential for high grasshopper populations during the 2010 growing season in western South Dakota and neighboring states [see map]. Recent cool and wet weather may be beneficial by both delaying and interrupting hatching and development. However, the risk is large enough that grassland managers should be alert to the potential and management alternatives.

One approach that may limit grasshopper development is to manage pastures to minimize bare ground and maximize shading. North Dakota research demonstrated that pastures that were grazed rotationally had less bare ground, more shading and lower grasshopper populations resulted. If grasshopper emergence and development becomes excessive, routine management approaches may be insufficient to protect pasture feed resources.

Appropriate questions might include, “how much will grasshoppers consume, what control options are available, and under what conditions is control appropriate?” Research indicates that at a density of one grasshopper per square yard, their activity results in disappearance of nearly one-half pound of forage per day. At a density of 15 grasshoppers per square yard, the effect will be removal of over 200 pounds per acre per month. Grasshopper densities can be estimated by selecting a representative plot of known size counting the number of grasshoppers that leap or fly as the plot is walked. A sweep net may also be used, but are useful to provide a more qualitative “high or low” population estimate.

If a serious outbreak occurs, insecticide application becomes the primary remedy. Insecticides available for grasshopper control on rangeland include carbaryl (Sevin), diflubenzuron (Dimilin), malathion (Fyfanon, Malathion 5EC), and lambda-cyhalothrin (Warrior). Application costs are estimated to range from $2 to $10 per acre for material and application. Some cost share may be available from USDA (up to 100 percent on federal lands, 50 percent on state lands and 33 percent on private lands as federal budgets allow).

When the infestation level is determined, rational decisions about insecticide application become primarily financial. The other factors are the anticipated forage loss, the value of the loss and the actual application cost. The table at left estimates the value of forage lost based on grasshopper population density and the value of an Animal Unit Month of forage (approximately 800 pounds). An alternative manner to view the table is what “out of pocket” cost could be paid per acre to apply insecticide control. For example, if grasshopper density is estimated at eight per square yard and you value an AUM at $28 (or that would be the cost to replace lost forage), you would break even by paying $3.86 per acre for control.

As this growing season proceeds, ranchers should keep a close eye on emerging or developing grasshoppers. Helpful contacts include your local extension office who can contact state specialists. In addition the South Dakota Department of Agriculture (605-773-5425) or the USDA-APHIS-PPQ office in Pierre (605-224-1713), can provide information or direct you to resources about grasshopper control and availability of control cost assistance.

Like a number of organisms that are normal components of the ecosystem, grasshoppers generally exert minimal disturbance. But careful management may infrequently require some level of control as a means to securing intended uses of the rangeland.

As always, enjoy the miracle of new and emerging life that spring affords and make careful observation of all the life forms on the landscape your normal practice.

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