Grasshoppers in vegetable gardens and small acreage farms
Order: Orthoptera
Family: Acrididae
Description
Grasshoppers have chewing mouthparts and are medium to large insects closely related to crickets and katydids. The exact size and coloration depend on the species, but adults typically measure 1-7 cm (0.4-2.8 inches) long and are a combination of brown, grey, or green. Some species also have brightly colored wings and different markings. Grasshoppers can fly short distances and have enlarged hind legs for jumping. The nymphs resemble adults but are smaller and lack developed wings. In Colorado, pestiferous grasshopper species include the differential grasshopper (Melanoplus differentialis), migratory grasshopper (Melanoplus sanguinipes), twostriped grasshopper (Melanoplus bivittatus), redlegged grasshopper (Melanoplus femurrubrum), and clearwinged grasshopper (Camnula pellucida). Of these, the differential, twostriped, and redlegged grasshoppers are most likely to injure vegetables. The exact appearance depends on the species.
Differential grasshopper
At 5 cm (2 inches) long, this is a large grasshopper species. Adults usually have yellow bodies with black chevron markings on the hind legs. Instars of differential grasshopper nymphs are identified by the presence of spots, stripes, and varying shades and patterns of color from light tan, yellow, green, and black. However, some individuals are completely black through their development. The egg pods of this species are curved and about 3.8 cm (1.5 inches) long.
Twostriped grasshopper
Adults of this species measure up to 3.8 cm (1.6 inch) long. They have two light yellow stripes running parallel on top of the head and thorax. At high densities, adults can have slimmer bodies and long wings which makes them more adapted to flight. Like the differential grasshopper, nymphs vary in color and size, depending on the instar. The egg pods of the twostriped grasshopper are curved and 3.8 cm (1.5 inches) long.
Redlegged grasshopper
Adults of the redlegged grasshopper measure up to 2.5 cm (1 inch) long and have bright red segments on the hind legs and a bright yellow underside. Although rare, some individuals have yellow-green or blue segments on the hind legs. These grasshoppers have a pointed spur located between the base of the forelegs and can fly up to 40 feet when disturbed. They tend to fly fast and evenly about a yard above vegetation. Nymphs are different combinations of yellow and black markings and typically do not develop a red segment on the hind leg until reaching adulthood. The egg pods of this species are curved and measure up to 2.5 cm (1 inch) long.
For images of each grasshopper, consult the webpage on grasshoppers in hemp.
Feeding injury due to grasshoppers. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Grasshoppers on drybeans grown in field. Image credit: Howard F. Schwartz, Colorado State University, Bugwood.org
Grasshopper on pumpkin stem. Image credit: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
Common bean injured by grasshopper feeding. Image credit: Howard F. Schwartz, Colorado State University, Bugwood.org
Mating pair of differential grasshoppers on an injured host. Over 100 species of grasshoppers occur in Colorado and their populations fluctuate from year to year. They may cause serious damage to vegetable gardens during outbreaks, usually associated with periods of drought. Image credit: David Cappaert, Bugwood.org
Common bean with severe defoliation due to grasshopper feeding. Image credit: Howard F. Schwartz, Colorado State University, Bugwood.org
Quick Facts
- There are over 100 grasshopper species in Colorado, but only several are considered pests.
- Grasshoppers can eat a wide range of plants, especially when food is scarce. Preferred vegetables include lettuce, spinach, carrots, beans, sweet corn, onions, and Brassica spp. such as kale and turnips. Grasshoppers tend to avoid squash, peas, and tomatoes (leaves, not fruit).
- Grasshoppers are difficult pests to control because they are highly mobile. During periods when local outbreaks are developing, control usually involves using perimeter sprays or baits, which tend to have limited efficacy
- All grasshoppers lay eggs in soil as pods. Each egg pod contains multiple eggs. Eggs are often consumed by larvae of blister beetles.
- Grasshoppers are closely related to crickets and katydids.
- Grasshoppers are difficult pests to control because they are highly mobile. During periods when local outbreaks are developing, control usually involves using sprays or baits.
Life history and habits
All grasshoppers develop through three life stages and lay their eggs in soil as tight clustered pods. Eggs are laid in pods in different substrates and each pod can contain well over 100 eggs, depending on the species of grasshopper. The differential grasshopper lays egg pods among plant roots in the sod land and rank weeds adjacent to corn fields, while the twostriped grasshopper prefers ovipositing in sod. The redlegged grasshopper lays egg pods in south-facing ditch banks and the borders of crops with compact drift soil. The timing of egg hatch depends on soil temperature, for most species this occurs in mid to late spring. At egg hatch the tiny first stage nymphs move to the surface and seek tender foliage on which to feed. The first few days are critical to survival, and adverse weather or absence of suitable foods can cause high mortality. Surviving grasshoppers continue to develop over the next several weeks, usually molting through five or six stages, before ultimately reaching the adult form.
The most important factors in grasshopper populations are weather-related, particularly around the time of egg hatch. For example, cold, wet weather is very destructive to newly hatched grasshoppers.
Injury
Grasshoppers have chewing mouthparts and can defoliate entire plants. Food habits vary between species of grasshoppers. Some species primarily feed on grasses or sedges, while others prefer broadleaved plants. Most grasshoppers prefer younger, tender foliage. A variety of vegetables are susceptible to grasshopper feeding, including but not restricted to carrots (Daucus carota), onions (Allium cepa), beans (Phaseolus vulgaris), lettuce (Lactuca sativa), and green leafy vegetables such as spinach (Spinacia oleracea) or Brassica spp. such as turnips, kale, collards, mustard, and turnips. In addition to the consumption of plant tissue, which can significantly reduce yields, the quality of harvested produce can be reduced due to contamination with grasshopper excrement and insect parts.
Grasshoppers can also be significant pests of field crops and rangeland in years when their populations are extremely high. Surveys of grasshoppers can be very useful in anticipating problems and informing decisions related to management. The number of grasshoppers present in late summer and early fall can be a good indicator of problems in the subsequent year. Predicting outbreaks is complex, and the USDA ARS in Montana has excellent resources including a prediction model updated each year.
Management:
Biological control
Preserving natural enemies is an important component of integrated pest management, and there are many natural enemies of this pest. Some species of blister beetles develop on grasshopper egg pods. Adult robber flies are common predators of grasshoppers during summer and other flies develop as internal parasites of grasshoppers. Many birds, notably horned larks and kestrels, feed heavily on grasshoppers. Grasshoppers are also frequently eaten by coyotes.
In addition to predators, grasshoppers are also susceptible to certain pathogens. A fungus (Entomophthora grylli) infects grasshoppers causing them to move upwards and cling to plants shortly before they kill the insect host. Stiff, dead grasshoppers found stuck to a grass stem or twig indicate infection with this disease. Another entomopathogenic fungus, Beauveria bassiana, is commercially available and marketed for grasshopper control. A nematode (Mermis nigriscens) also occasionally attacks and develops in grasshoppers. Fungi and nematodes are favored by moisture. Lastly, Nosema locustae (Canning) is a commercially available protozoan that can infect grasshoppers through baiting, however there are certain criteria that will increase the efficacy of N. locustae. Only young grasshoppers are susceptible, and it cannot be used effectively after adult migrations have occurred. Often it is most effective in long-term grasshopper management when combined with other controls. The baits are also perishable and should be stored in the refrigerator before use. More information on N. locustae can be found in the Utah State University factsheet. For more information on grasshopper management through baiting, see the chemical control section below.
Cultural control
In gardens and small plantings, grasshoppers can be handpicked and squashed. The installation of protective covers can prevent feeding injury, although grasshoppers can chew through certain materials. For this reason, it is recommended that metal window screening be used instead of cloth or plastic. One strategy that can mitigate grasshopper densities during migrations is to keep an attractive green border of tall grass or lush green plants around the perimeter of the garden. This will trap the insects and divert them from vegetables or flowers. Mowing these areas should be avoided since the remaining grasshoppers will migrate to nearby vegetable plants.
Chemical control
Treatments should be directed at young grasshoppers and vegetation near breeding sites. This often occurs in May at lower altitudes and June at higher altitudes. Insecticide treatments do not need to completely cover the area since grasshoppers are mobile. Garden plants can also be sprayed as a last resort, but it is important to note that the grasshoppers need to feed on plants to acquire the toxin, which means that grasshoppers may continue feeding on plants after the insecticide application. When large numbers of grasshoppers are invading the area, repeat applications will be necessary at 3–4-day intervals.
Another protocol for chemical management of grasshoppers involves the use of baits. To be successful, baits and sprays need to be applied during developmental stages and concentrated at sites where egg laying occurs. The ability of baits to control grasshoppers declines as they develop and migrate. Alternately, certain baits can be broadcast. Bait formulations are made by mixing the insecticide with bran or another carrier and must be re-applied after rain.
CSU Extension Fact Sheet
Download or view the CSU Extension’s PDF fact sheet for your reference.
References
Amarasekare, K., and J. Edelson. 2004. Effect of Temperature on Efficacy of Insecticides to Differential Grasshopper (Orthoptera: Acrididae). Journal of Economic Entomology. 97(5): 1595-1602. Available here.
Evans, E. 2008. Grasshoppers. Utah State University – Extension. Available here.
Flint, M. 2013. Grasshoppers. University of California – Department of Agriculture and Natural Resources. Available here.
MDC. (n.d.). Differential Grasshopper. Missouri Department of Conservation. Available here.
Royer, T., and E. Rebek. 2017. Grasshopper Control in Gardens and Landscapes. Oklahoma State University – Extension. Available here.
USDA. 1994. Differential Grasshopper: Melanopulus differentialis. United States Department of Agriculture – Agricultural Research Service. Available here.
USDA. 1994. Redlegged Grasshopper: Melanoplus femurrubrum. United States Department of Agriculture – Agricultural Research Service. Available here.
USDA. 1994. Twostriped Grasshopper: Melanoplus bivittatus. United States Department of Agriculture – Agricultural Research Service. Available here.
Zuehlke, S. (n.d.). Pest Profile: Redlegged Grasshopper. University of Nebraska – Lincoln. Available here.