Grasshoppers are abundant this year, and have been a particular concern in winter wheat. Below is basic information on grasshoppers. Management recommendations for winter wheat are at the bottom of the page.
Species in MT: More than 100 different grasshopper species occur in Montana; about 24 can damage rangeland and crops. Clear-winged (Camnula pellucida) (image 1), two-striped (Melanoplus bivittatus) (image 2), and migratory (Melanoplus sangunipes) grasshoppers are often especially abundant. Numbers increase during hot dry periods in rangeland and other grassy areas, from where they can invade and damage many different crops. The USDA lab in Sidney Montana maintains a webpage with extensive grasshopper information: http://www.sidney.ars.usda.gov/grasshopper/.
Appearance: Depending on the species, grasshoppers come in a variety of sizes and colors. Mature adults can range from ¾ to 2 inches in length. The juveniles resemble the adults in shape, but can differ widely from adults of the same species in color. Grasshoppers develop through five juvenile instars (stages) before reaching adulthood (image 3), and only the adults have fully formed wings for flying. On juveniles, the developing wing buds increase in size with each instar, and this feature is often used to time insecticidal sprays.
Geographic range: Grasshoppers are found across the US and globally, mostly in hot arid regions. In Montana the highest populations are typically found in the central and eastern regions.
Host range: Most grasshoppers prefer to eat grasses, and some species are more common on rangeland. However, most will feed opportunistically on a wide range of plants including forbs. Later in the summer when grasses are dry or have been consumed, these grasshoppers will move to, and feed on, almost any available green vegetation. Juvenile grasshoppers can migrate on land and adults can fly long distances.
Damage: Grasshoppers have chewing mouthparts and damage rangeland and crops by consuming the foliage. At high populations they can strip a field bare. As the season progresses and grasshoppers get larger, damage can become more severe. Crop damage is often first observed along the field margin as grasshoppers migrate from surrounding grassy areas. In some cases they may cause yield damage more directly, by clipping off wheat heads or by preferentially feeding on developing pulse crop flowers.
Life cycle: Grasshoppers mate and the females deposit egg pods (8-30 eggs in a pod) in the soil. The eggs overwinter, usually hatching during May – July depending on the species. The juveniles develop through five instar stages over 30 to 40 days, and are wingless. Adults live for 40-60 days and they are winged and capable of flying (with a few species exceptions). While most overwinter in the egg stage, a few species overwinter as nymphs. In the spring these are commonly mistaken as “unusually large grasshoppers”, but these species do not cause economic damage. The adults of smaller species are often mistaken as a late hatch but can be identified as adults because they have fully formed wings. Hot dry spring seasons favor grasshopper survival while cool wet springs cause juvenile mortality. Large region-wide outbreaks typically last 2-4 years and collapse as natural diseases build up in the population. Mortality of overwintering eggs due to cold temperature is usually not significant.
Management: Most methods for managing grasshoppers rely on insecticide applications based on scouting, and thresholds are crop-specific. Biological and cultural control options are generally not highly effective. Scouting for grasshoppers can begin at the end of May and may continue throughout the summer. Early in the season grasshoppers are small, less mobile and more difficult to see. Populations may first aggregate on south facing slopes that are warmer. Later in the season they are very mobile and may appear suddenly in high numbers.
Grasshopper numbers can be estimated using the square foot method: the number of grasshoppers in a one square foot area is estimated visually and randomly repeated 18 times while walking a transect. Grasshoppers are less active earlier in the morning and easier to count. The total number of grasshoppers is tallied and divided by 18 to give the average number per square foot. Alternatively, four 180- degree sweeps with a 15-inch diameter sweep net is considered equivalent to the number of grasshoppers per square yard.
Management in Winter Wheat: Emerging winter wheat can be particularly vulnerable to damage. Adult grasshoppers are more difficult to control and can fly into emerging winter wheat fields from surrounding grassy areas. Treatment thresholds for emerging winter wheat are lower. Border treatments applied as insecticidal sprays or seed treatments are the main recommendation for protecting emerging winter wheat. Typically, spraying 150 feet beyond the edge of the crop or 1-2 passes with treated seed around the perimeter of the field is a sufficient border. For adults, the higher end of the label rate is recommended. When applying border sprays, timing is important. Border sprays beyond the edge of the crop need to be applied just before the wheat emerges; if it’s applied too early there may not be enough residual, and if it’s applied too late damage may have already occurred. Systemic seed treatments eliminate the timing concern, but systemic insecticides require feeding to be active, though damage should be slowed considerably. See insecticides listed on the High Plains IPM Guide: https://wiki.bugwood.org/HPIPM:Crops