Agronomy Bulletin 105
GRASSHOPPER DAMAGE
Watch for outbreaks when temperatures rise.
SITUATION
Grasshopper population levels are highest during hot, dry summers. Active scouting and
applying appropriate crop management practices can help guard your crop from damage.
FACTORS TO CONSIDER
• Temperature
• Identifying damage
• Crop rotation
• Insecticides
• Insect biology
ACTION PLAN
1
2
Understand the life cycle of a grasshopper. The economically significant
species of grasshoppers overwinter in egg pods below the soil surface. Eggs are deposited
in pods from August through October. Depending on the species, a female may produce
up to 25 pods, each containing up to 100 eggs. Most grasshopper eggs hatch from late
May through early July, with only one generation produced each year. Young grasshoppers
(nymphs) resemble small adults without wings.
Proactively scout for grasshoppers. Scouting should begin in May.
Grasshopper infestations have the greatest impact in field crops when the weather is
hot and dry. They often first appear in weedy areas of roadsides, fencerows and irrigation
ditches. After those plants are eaten or dried down, grasshoppers migrate in search of new
food sources, such as irrigated crops or newly emerged winter wheat. Grasshoppers begin
feeding on food sources in field margins and then multiply throughout the field.
3
Identify damage. Grasshopper injury is most often associated with rangeland, corn,
small grains and vegetable crops. However, during heavy infestations, they will attack trees,
shrubs, flowers, lawn grasses and other types of vegetation. Grasshoppers have chewing
mouthparts, and their feeding destroys the plants.
4
Consider control options. Begin by estimating the number of grasshoppers per
square yard, surveying several sites within a field to ensure a representative estimate of the
infestation level. Refer to Table 1 from Colorado State University to determine the need for
treatment. Depending on individual situations, including the value of the crop, treatment
may be necessary when populations reach or exceed 40 nymphs per square yard.
5
Take action with insecticides. Depending upon the infestation level of the
grasshoppers, their size and other considerations, field margins can be treated effectively
with low rates of an appropriate insecticide. Larger-sized grasshoppers can require higher
rates. For control of grasshoppers, consider Cobalt® Advanced insecticide. As always,
growers, consultants and applicators should understand and follow all label directions.
Actively scout for grasshoppers to prevent crop
yield loss.
Summary
Uncontrolled grasshoppers can reduce
yield in row crops during hot, dry
summers. Work with your Mycogen Seeds
customer agronomist or trusted
agronomic adviser to assess infestations
and determine the appropriate course
of action to prevent damage.
Resources:
NDSU Grasshopper Biology and Management, Grasshopper
Biology and Management
Colorado State University Extension, Grasshoppers in Field Crops
www.mycogen.com ®Trademark of The Dow Chemical Company
(“Dow”) or an affiliated company of Dow. Cobalt Advanced is
a federally Restricted Use Pesticide. Cobalt Advanced is not
registered for sale or use in all states. Contact your state pesticide
regulatory agency to determine if a product is registered for
sale or use in your state. Always read and follow label directions.
©2013 Mycogen Seeds. Mycogen Seeds is an affiliate of
Dow AgroSciences LLC.
S47-137-103 (07/13) BR 010-13320 MYCOGENL3006 GH