Grasshopper Biology and Management (continued)

E-272 (Revised), February 1997

Cultural Control Methods
Chemical Control
Descriptions of Economically Important Grasshoppers
Necessary Precautions in Controlling Grasshoppers

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Cultural Control Methods

Cultural control methods for grasshoppers are procedures which are variations of normal production operations and are usually the least expensive control options. Modifying the environment through use of cultural control methods that take advantage of vulnerable times in the grasshoppers' life cycle can reduce or eliminate populations.

Unlike chemical control, cultural control methods must be used ahead of grasshopper damage to be effective. Cultural control methods usually associated with grasshoppers include early seeding of crops, crop rotation, tillage, trap strips and early harvest. Cultural control methods can also be used in conjunction with chemicals to increase the efficiency of both types of control.

Early seeding

Fields that are to be cropped and have a high potential for grasshopper damage should be seeded as early as agronomically and environmentally possible. Established, vigorously growing plants can tolerate more injury than younger plants. This may not be an effective option with late season crops such as soybeans, dry beans, corn, sunflower and safflower, because an early seeding date for these crops may mean they would still be small when the grasshopper hatch is beginning.

Early seeding of early crops like small grains and canola may not prevent crop injury, but it will reduce the amount of economic damage and allow the producer a longer lead time for insecticide application. In addition, early seeded crops will mature earlier and the risk of late season migration of adult grasshoppers into these fields should be lessened, thus reducing late season crop damage and egg laying.

Crop rotation

Crops should not be planted in fields with severe egg infestations. In general, a field cropped to a small grain the previous year and maintained free of green plant material after harvest will not be severely infested with grasshopper eggs. If the field was planted to a late season crop such as soybeans, dry beans, sunflower, corn, safflower, or flax, it may have attracted grasshoppers prior to harvest and could have an extremely high egg population.

Tillage

Late summer tillage of summer fallow fields discourages females from depositing eggs in the fields. Similarly, tillage immediately after harvest of early season crops will discourage females from laying eggs in these fields.

There is little value in using tillage to destroy grasshopper eggs directly. Deep tillage will bury many eggs, preventing hatching nymphs from emerging, but this is no longer a common practice. Surface tillage causes some reduction in subsequent nymphal population but rarely significantly reduces nymphal populations in fields with threatening egg levels. Soil erosion and reduced moisture conservation must be weighed against any small benefits from tillage operations.

Soil tillage can be an effective cultural practice in fields that are to be summer fallowed and contain high egg populations. First nymphal stage grasshoppers cannot be sustained on dead plant material and cannot move long distances (often less than a yard from their hatching location) to find food sources. Therefore, if all the green vegetation has been eliminated before the eggs hatch, the young grasshoppers will starve. For this control strategy to be effective, tillage must have been completed with enough time to cause the plant material to be killed before the hatch.

If a no-till or reduced tillage system is being used in the cropping system, herbicides may provide adequate control. The effectiveness of the herbicides will depend on environmental conditions, and best results should be obtained if the herbicide is applied two weeks before egg hatch to ensure all green vegetation is killed.

Trap strips

If grasshoppers hatch before the tillage operation, control will be reduced. Grasshoppers that have reached the second nymphal stage are usually mobile enough to reach adjacent crops. Under these situations, trap strips may be used to concentrate grasshoppers in a relatively small area, making an insecticide application more efficient and more economical.

To prepare the trap strips, destroy plants with tillage in a 10 yard wide strip around the outside of the field. Leave an unworked green strip of at least 10 yards before resuming cultivation (Figure 6). Repeat the process as often as necessary to produce additional strips. All green vegetation must be eliminated between the trap strips if they are to be effective. Once tillage removes the green vegetation in the strips grasshoppers will move into the weedy strips; however, the strip must contain enough green vegetation to hold the grasshoppers for several days. To ensure the strips contain enough green vegetation, small grains can be sown within the strips several weeks before the tillage operation.

Figure 6. An example of trap sites used to concentrate grasshoppers in a fallow field.

Migration of small grasshoppers to the green strips may take several days. After the migration is complete, infested strips and about 10 yards of the adjacent crop should be treated with an insecticide.

Early harvest

If grasshoppers are migrating into crops that are close to harvest, growers should consider harvesting the crop early if it has reached physiological maturity. The economic advantage may favor early harvest when compared to the cost of an insecticide.

Chemical Control

Grasshoppers are more easily and economically controlled while they are in the nymphal stage and still within hatching sites (roadsides, fence rows, etc.). There are a number of advantages in treating grasshoppers early:

1. fewer acres will have to be treated and less insecticide is necessary to obtain control, thus reducing cost;
2. grasshoppers are killed before they have had the opportunity to cause significant crop loss;
3. smaller grasshoppers are more susceptible to pesticides than larger hoppers;
4. early treatment before grasshoppers reach maturity prevents egg deposition, which may help reduce the potential grasshopper threat for the following crop year.

Descriptions of Economically Important Grasshoppers

There are five species of grasshoppers that pose a significant threat to crops in the Northern Plains.

Clearwinged grasshopper
Camnula pellucida

Identification
Adults are of medium size (� inch long), yellow to brown, and have mottled forewings and transparent hindwings. The forewings have light stripes that converge near the middle when the grasshopper is resting.

Nymphs are cream, tan and black.

Economic Importance
This grasshopper feeds primarily on grasses. It can be a severe pest of small grains. It is most destructive early in the season. It prefers to feed on wheat, barley, western wheatgrass, and reed canarygrass. Hatching nymphs disperse quickly. Invasion of fields of young small grains at hatching results in extensive crop damage.

Hatching
This is an early hatching grasshopper. Development of the egg resumes in the spring once the soil temperature reaches 55�F. After accumulating 150 degree days, the eggs are ready to hatch. Emergence begins when soil temperature reaches 80�F and air temperature is 65�F. Nymphs emerge in the morning, especially after a shower the previous evening.

Twostriped grasshopper
Melanoplus bivittatus

Identification
It is one of the two largest Melanoplus spp. (Differential grasshopper is the other). Adults are brown or green with two light yellow or cream stripes running from the front of the head to the wing tips. The yellow on the hind femur has a conspicuous black dorsal band. Adults are 1-1/4 to 1-7/8 inches long.

Nymphs can be identified by their spots, stripes, and color patterns. The head may be tan or green with dark spots. There is a light colored horizontal stripe on the segment behind the head. The femur of the large hind leg has a solid black stripe.

Economic Importance
This species is a major crop pest, causing damage to small grains, alfalfa, and corn. A population of 10 adults per square yard in a corn field will defoliate the crop. They feed on many kinds of plants. Although grasses and cereals are eaten, they also feed on many forbs (e.g., mustards, legumes, composites). This species develops better on a mixed diet.

Hatching
This species hatches early. It is one of the first to appear in the spring. Hatching begins eight to 10 days before the migratory grasshopper. Hatching may last for four to six weeks. Flushes of hatching often occur after rain and warm temperatures.

Migratory grasshopper
Melanoplus sanguinipes

Identification
Adults are brown to gray; body length at maturity is 7/8 to 1 1/8 inch. Hind tibia are red or pale blue.

Nymphs are tan or gray, occasionally light green. They have eyes with many light colored spots and with a narrow brown bar across the middle; there is a narrow pale yellow crescent below the eye.

Economic Importance
They feed on grasses and forbs and can be a serious pest of either field crops or rangeland. They feed on wheat, barley, oats, alfalfa, clover, corn, and vegetables. they also attack vines, bushes, and trees, feeding on foliage, fruit, and bark. Small grains are very vulnerable. Early hatching nymphs may destroy seedlings. Defoliation throughout the growing season can reduce yield and quality. Defoliated plants are vulnerable to head clipping.

Hatching
They are an early hatching grasshopper. Hatching is first observed along south facing slopes in field and range sites where there is little vegetative cover and soils are sandy. Where soil conditions are uniform, hatching may be completed in three weeks. When habitat includes clay soils and shade from vegetative cover, hatching may extend over a six week period.

Differential grasshopper
Melanoplus differentialis

Identification
Adults are yellow, greenish or grayish yellow with black markings, especially chevrons on the outer side of femur. They are 1-1/8 to 1-3/4 inches long.

Nymphs are recognized by their spots, stripes, and colors. The eyes have light tan spots. A pale yellow, horizontal stripe begins behind the head on the first segment; a black stripe is visible in the center of the hind femur.

Economic Importance
They are a severe pest of crops including small grains, corn, alfalfa, soybeans, some vegetables, and fruit trees. They feed on both grasses and forbs. They usually consume more forbs than grasses and do well when feeding on single plant species such as sunflower, soybean, and wheat.

Hatching
Eggs begin to hatch in late spring, about three weeks after the two-striped grasshopper. They hatch during a two-week period.

RedLegged grasshopper
Melanoplus femurrubrum

Identification
Adults are slightly under 1 inch long. The general color is brownish-red. The hind tibia are usually pinkish-red with black spines.

Nymphs are brightly marked with yellow and black. The eyes are brown to burgundy with light tan spots; the head has a dark band in center with a light yellow band on each side.

Economic Importance
This grasshopper is a crop pest, damaging alfalfa, clover, soybeans, corn, and small grains. Large numbers may develop in pastures, damaging forage grasses. Mixed diets provide the best nutrition levels.

Hatching
Eggs begin to hatch three weeks after the eggs of the twostriped grasshopper. Hatching may occur over a six week period. Prolonged hatch is due to the female placing eggs throughout the habitat, subjecting the eggs to a range of moisture and temperature conditions.

Necessary Precautions in Controlling Grasshoppers

Farmers and ranchers have a number of effective insecticides available for controlling grasshoppers.

Check the chart and make your insecticidal selection to fit your farm or operation before purchasing grasshopper insecticides. The laws and regulations pertaining to the proper and safe use of all pesticides are well established and no one can afford to use the wrong kind of insecticide.

• Always follow the dosage recommended on the label.
• Always comply with the preharvest intervals required for each grasshopper insecticide. A preharvest interval is the time interval (in days) between the last application and harvest or grazing. This information is given in the following charts under the column "Restrictions on Use."
• Never spray a crop in bloom unless it is absolutely necessary. If spraying a crop in bloom (or any other crop) is necessary, spray when there will be minimal honeybee activity, preferably during the evening hours. During most summer evenings, honeybees leave fields by 8:00 p.m. and do not return until 8:00 a.m. or later the following day. Evening spraying also allows the insecticide to dry on the crop before bee activity resumes the next morning.
• Read the label — it is a tool. Learn how to use it.

References

Kemp, W. P. and B. Dennis. 1991. Towards a general model of rangeland grasshopper (Orthoptera: Acrididae) phenology in the steppe region of Montana. Env. Entomol. 20: 1504-1515.

Pfadt, R. E. 1994. Field guide to common western grasshoppers. Wyoming Agric. Exp. Sta. Bulletin 912.

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[ Life Cycle ] [ Damage ] [ Natural Enemies ]
[ Estimating Grasshopper Infestations ] [ Monitoring Hatch Population Development ]
[ Planning Mangement Programs ]
[Insecticidal Control Recommendations]

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E-272 (Revised), February 1997