Sunflower XIV-8

Grasshoppers

Frank B. Peairs

Grasshopper.

Field Biology and Identification

There are many different species of grasshoppers, with some having a greater pest potential than others. Correctly identifying a species is important because: (1) species vary in their biotic potential and in their capacity for causing damage; (2) depending on their food habits, species may be either pests or beneficials; (3) certain species of pest grasshoppers are highly migratory and often pose a serious threat to distant crops; (4) species vary in their seasonal cycle (period of hatching, development, and reproduction) which in turn affects the timing of control treatments; (5) because current chemical and biological methods of controlling grasshoppers are more sophisticated, their effective use requires greater knowledge of the pests' life histories and habits; and (6) as environmental impacts of control are more finely evaluated, identification of species is important in the selection of management strategies.

Most grasshoppers overwinter as eggs in the form of a pod laid in the soil. These elongate shaped pods may contain from 20 to 120 eggs each. Eggs hatch into nymphs in late May and June, maturing in two to three months. By August most nymphs are adults. Grasshoppers feed during the day and rest during the afternoon and night on vegetation.

Plant Response and Damage

Grasshoppers chew on leaves and flowers. Large infestations will defoliate and even kill plants.

Management Approaches

The usual pattern of grasshopper infestation is for egg-laying to be concentrated in dry, undisturbed areas, especially in weedy areas of roadsides, fence rows, irrigation ditches, and other noncrop areas. As the local vegetation is consumed the young grasshoppers begin to leave in search of other food, often a nearby crop. They feed in the field margins and then, conditions permitting, spread throughout the field. Grasshoppers will become more difficult and more expensive to control as this pattern develops. Before entering field margins they can be controlled with low rates of insecticides applied to a relatively few acres. Once they enter the field, they may be larger in size and require higher insecticide rates.

An additional advantage to early control of grasshoppers is that such measures have an effect on the next year's population. If grasshoppers in an area are reduced to less than one per square yard before they have a chance to lay eggs, it will be several years before they again reach levels high enough to threaten crops.

Table XIV - 3 gives information useful in deciding if a grasshopper population is enough of a threat to a crop to justify spending money on an insecticide treatment. An infestation of eight per sq yd is considered to be of economic importance.

Table XIV - 3. Damage potential of grasshoppers to field crops.

Grasshoppers per square yard

Classification

Treatment Decision

Field Margin

Field

Not economic

Usually not

1 - 10

0 - 2

Light

Perhaps, depending on grasshopper size and species and crop stage and value

11 - 20

3 - 7

Moderate

Usually

21 - 40

8 - 14

Heavy

Yes

>40

>14

Product list for Grasshoppers
Pesticide	Product/Acre (Fl oz. or oz. product)	Preharvest Interval, remarks
Asana XL^R^,1	5.8 - 9.6	28 days. Do not feed forage or fodder tolivestock. Extremely Hazardous to Bees!
Baythroid XL^R^,1	2.0 ? 2.8	30 days. Extremely Hazardous to Bees!
carbaryl¹^,2	See labels	60 days. 30 days to graze or forage. Extremely Hazardous to Bees!
chlorpyrifos 4E^R1,2	16 - 24	42 days. Do not graze. Up to 2 lb preplant. Up to 4.5 lb total AI/yr. Extremely Hazardous to Bees!
Furadan 4F^R	4 - 16	28 days. Apply only before bloom. Extremely Hazardous to Bees!
Delta Gold^R^,1	1.0 ? 1.5	21 days to harvest. Do not apply more than 0.045 lb ai/acre/crop.? Do not graze or feed treated forage to livestock. Extremely Hazardous to Bees!
lambda cyhalothrin^R1,2	2.56 ? 3.84	45 days. Do not exceed 0.12 lb total AI/yr. Extremely Hazardous to Bees!
Proaxis^R^,1	2.56 ? 3.84	45 days. Do not exceed 0.06 lb total AI/yr. Extremely Hazardous to Bees!
^RRestricted use pesticide. ¹Labeled for chemigation. ²Generic active ingredient, may be additional formulations.
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.

Categories: Sunflower, Insects, Grasshoppers

Date: 5/17/2007