in Field Crops Fact Sheet No. 5.535 Series|Crops by F.B. Peairs* Grasshoppers are one of the most are concentrated in a small area. They can Quick Facts important insect pests in Colorado. They therefore be controlled with low rates of follow a roughly 22-year cycle in Colorado. applied to a relatively few acres. • Grasshoppers often appear The last major outbreak was in the late 1970s Once they reach the field margins, they first in weedy areas of and early 1980s. Some problems occur even may be larger and require higher roadsides, fence rows, in years of low numbers. Although they rates for good control, al­though the acreages irrigation ditches and other are most important on rangeland, they also involved will still be small. After they spread noncrop areas. attack field crops, often with economic losses throughout a field, high insecticide rates to the farmer. An exception is sorghum, applied to larger acreages are required to • After these food plants are which usually is not fed upon once it has protect the crop. gone, the leave in reached about 10 inches in height. Table 1 gives information useful in search of other food, often Grasshoppers lay eggs in undisturbed deciding if a grass­hopper population is an irrigated crop or newly areas, usually in late summer and early enough of a threat to a crop to justify emerged winter wheat. fall. Small nymphs or “hoppers” hatch the spending money on an insecticide treatment. following spring. Winged adults appear five to Modify these general guidelines according • Control grasshoppers in the six weeks after hatch. Eggs of a few Colorado to species, crop conditions, and weedy areas with low rates of species hatch in late summer and pass the crop value. For example, use lower counts insecticides. Once they reach winter as nymphs. Winged adults of these for a valuable crop such as pinto beans and field margins, they may be species usually appear early in the following higher counts for a lower value crop such larger and require higher rates summer, often causing undue alarm about as proso millet. Walk through the field and of insecticides for control. unusually early grasshopper activity. Some of count the grasshoppers that jump or move these early-season species are important on within a square foot area. Take 18 counts • Two options are available rangeland, but none are considered a threat to per field and then divide the total by two to to farmers once it has been field crops. Most field crop damage is caused get grasshoppers per square yard. Consider determined that crops are by the differential, redlegged, two-striped treatments when the average count reaches threatened: poison baits, and and migratory grasshoppers, all species that the threatening level. foliar or soil insecticides. follow the typical grasshopper life cycle. Two options are available to farmers once it has been decided that crops are threatened: poison baits and foliar or soil insecticides. Control of Grasshoppers The usual pattern of grasshopper damage in field crops is for early development to Poison Baits occur in weedy areas of roadsides, fence rows, The main advantage to poison baits is that irrigation ditches and other noncrop areas. As they can be applied to crops or weedy areas these food plants are eaten or dry down, the in which the plants are too small for good grasshoppers leave in search of other food, insecticide spray coverage, such as newly-cut often an irrigated crop or newly-emerged alfalfa or weeds that have dried or been eaten winter wheat. Here they first feed in the field down. Under other conditions, insecticide margins and then, conditions permitting, sprays are cheaper and more effective. spread throughout the field. Carbaryl insecticide-impregnated Grasshoppers become more difficult bran bait is available as a 2 or 5 percent and expensive to control as this pattern formulation. The keys to success are uniform ©Colorado State University develops. Grass­hop­pers in the weedy areas distribution of bait and reapplication if the Extension. 6/98. Revised 10/14. bait is no longer attractive to grasshoppers. www.ext.colostate.edu Attractiveness of the bait is reduced * Colorado State University Extension entomologist substantially by moisture (rain or heavy dew). and professor, bioagricultural sciences and management. 10/2014 Table 1. Treatment guidelines based on number of grasshoppers (nymphs and adults) per square yard for crops other than winter wheat. The following website provide a large Grasshopper Field amount of information on the biology, Population Field Margin Treatment necessary? identification and management of Non-economic 0-2 5-10 No grasshoppers in the West. Light 3-7 11-20 Questionable, depends on size, species, type of crop www.sidney.ars.usda.gov/ Moderate 8-14 20-40 Probably grasshopper/ Abundant 15+ 41+ Yes

Table 2. Spring treatment guidelines for immature and adult grasshoppers in winter wheat (modified from University of Minnesota information). Nymphs/yd2 Adults/yd2 Ratinga Adjacent Crop Treat? Adjacent Crop Treat Light 25-35 15-25 No 10-20 3-7 Yes, if there is potential for for head clipping.

Threatening 50-75 30-45 Depends on 21-40 8-14 Yes, if there is prices, crop potential condition for head clipping.

Severe 100+ 60+ Yes, monitor 41+ 15+ Yes, consider wider for retreatment border treatments and monitor for treatment. aThis is a general rating used in all crops.

Table 3. Fall treatment guidelines for adult grasshoppers in winter wheat (modified from University of Minnesota information). Adults/yd2 Ratinga Adjacent Crop Treat Medium 10-20 3-7 Yes

Threatening 21-40 8-14 Yes, consider wider border treatments

Severe 41+ 15+ Yes, use wider border treatments and monitor for retreatment. aThis is a general rating used in all crops.

Nosema locustae, a disease organism Winter Wheat that attacks many grasshopper species, is Grasshoppers pose a significant threat also available in bait form. This disease to emerging winter wheat because the can reduce grasshopper populations over plants are small and the grasshoppers are a period of several years, but Nosema baits adults. Light to moderate infestations, will not protect a crop during the same as defined in Table 3, can cause stand growing season in which it is applied. reductions in field margins. Treatments Nosema baits may be effective when applied can be limited to field borders. Spring early in the season against small nymphs, infestations have the potential to clip heads, but there are no data showing their as summarized in Table 2. effectiveness in protecting field crops. Options for controlling low to moderate infestations include foliar insecticides Foliar Insecticides applied just prior to crop emergence or seed treatments.(See the High Plains Foliar insecticides are the treatment Integrated Pest Management Guide (www. of choice in most situations. TheHigh highplainsipm.org), for details. Be sure Plains Integrated Pest Management to read, understand and follow all label Guide, www.highplainsimp.org, lists the instructions. If grasshopper infestations are insecticides currently approved for control high, consider doubling the seeding rate for of grasshoppers on Colorado field crops the outer one or two passes. and noncrop areas that serve as infestation Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating. sources. These registrations are subject CSU Extension programs are available to all without to change, so check the current label. Be discrimination. No endorsement of products mentioned sure to follow all label instruc­tions and is intended nor is criticism implied of products not mentioned. precautions.