Get a Grasp on Grasshoppers to Protect Your Crops
The American grasshopper, Schistocerca americana (Drury), occasionally causes serious damage to crops and ornamentals and can be a nuisance when numerous. Adults invade fields during the day and roost in trees and shrubs at night. The short-winged nymphs are less mobile and normally remain in the fields.
In North America, the grasshopper is found east of the Great Plains and is common throughout Florida.
Adults bear fully developed wings with large, dark brown spots on a lighter background. Color gradually changes from a pinkish- or reddish-brown to more of a yellowish-brown hue as the grasshopper reaches sexual maturity. Nymphs vary in color. At higher population densities, the latter instars will be more yellow, orange, and black; at low densities, nymphs are mostly green.
The American grasshopper can injure a variety of crops including citrus, corn, cotton, peanuts, sugarcane, tobacco, and vegetables. Numerous grasshoppers can cause significant damage. High populations commonly follow an increase in favored foods such as weedy grasses. This can result from weather that favors weed growth such as mild winters and increased rainfall, or decreased livestock grazing.
Active last instar nymphs and young adults cause the most damage. Initially, damage from grasshopper feeding tends to be concentrated along field margins.
Survival and Spread
Females deposit their eggs in the soil about an inch below the surface. The egg cluster generally consists of 60 to 80 eggs secured together by a glue-like substance. Females may lay three egg pods. The nymphs hatch in three to four weeks. Nymphs undergo five or six instars before reaching adulthood.
The American grasshopper has two generations per year and is present throughout the year in Florida. It overwinters in the adult stage, unlike most grasshoppers, which pass the winter in the egg stage. Principal hatching periods are from February to May, and again from August to September.
Grasshopper densities may be estimated using two methods. The first is a physical count of the number of grasshoppers to obtain an estimate of number per unit of area. The second is to use a sweep net. When the numbers of late instar nymphs or adults exceed about 15 per square yard, there is potential for damage.
Biological controls only affect them on a small scale. Some flies are known to parasitize grasshoppers. Blister beetle and bee fly larvae will consume grasshopper eggs.
Grasshoppers fall prey to several birds; Cattle egrets consume large numbers.
The entomophagous fungus, Entomophaga grylli, may be locally effective in controlling grasshopper populations under favorable conditions.
Weeds can encourage high populations of grasshoppers. Disking and plowing are good ways to destroy grasshopper eggs and kill small nymphs. A continuous weed suppression program can help reduce numbers. Applying insecticide before maturity makes it easier to kill the nymphs.
Consult UF/IFAS recommendations of currently labeled insecticides for grasshopper control in sweet corn and other vegetables in Florida.