University of Idaho - I Banner
A student works at a computer

VandalStar

U of I's web-based retention and advising tool provides an efficient way to guide and support students on their road to graduation. Login to VandalStar.

Grasshoppers

Ranchers and farmers in Valley County partner with the Idaho Department of Agriculture to fight grasshoppers.

Grasshoppers are voracious feeders, eating about one-half of their body weight in green forage per day. Grasshoppers affect the available forage that ranching depends on.

In some areas, there have been more than eight grasshoppers per square yard. At that point only chemical controls are effective.

At densities of 30 grasshoppers per square yard, they will eat all the green forage available. At higher levels, they may eat shrubs, woody material and even paint on buildings.

The Department of Agriculture is using a Reduced Agent and Area treatment. The insecticide is reduced from the strength on the label. Untreated swaths are alternated with treated swaths.

The pesticide used is malathion. This common insecticide has been registered for use in the United States since 1956. It is widely used in mosquito control to contain West Nile virus.

The aerial spraying needs to be carefully controlled, since malathion also kills bees and other beneficial insects, some fish and other aquatic life.

Malathion is moderately toxic to other fish and birds. It is considered low in toxicity to mammals and humans.

Grasshopper populations build and decline in cycles. However, when the weather is favorable, the populations will build higher.

If natural enemies can’t control the populations, they will explode to much higher than normal levels.

When warm, dry autumns follow hot, dry summers, the grasshopper populations grow. The long, warm autumns allow a long time for the adults to breed and lay eggs.

It has been thought that long and cold winters will kill the eggs, but Valley County has a protective snow blanket that saves the eggs from much damage.

Camnula pellucida (scudder), known as the clear winged grasshopper, concerns us most. This species is considered early hatching. It will start to show up as tiny (4-6mm) black grasshoppers on warm sandy roads, driveways and ditch banks around the third or fourth week in May.

When you first see them, you will likely see hundreds or thousands. They are coming out of the hatching beds and moving to find food and shelter.

Since the eggs can be laid for several weeks in the late summer and fall, you may see tiny black insects for several weeks. If the weather is favorable, the first hatch will reach adult stage in 40 days.

The window of opportunity for control is fairly narrow for each hatch, but with several hatches spread out, more than one treatment may be needed.

If the grasshoppers are flying, they are adults and you have waited too long to control them. The first adults will appear in Valley County around the fourth week of June, depending on the weather.

Normal populations are always present in Valley County. In a normal year, you may notice a few grasshoppers, but not enough to cause concern.

Grasshoppers lay eggs in pods each fall. The eggs mature to a point and then must overwinter. They finish developing in the spring when the weather warms.

After hatching, the young nymphs move quickly from the hatching beds in search of food.

In our area, sandy roads, ditch banks, thick layers of meadow grass, weedy areas and dung all make ideal egg laying habitat.

Even though grasshoppers only produce one generation per year, they lay eggs over a period of time. This makes for a long grasshopper season—especially since it takes 40–60 days for grasshoppers to reach the adult stage.

In general, the populations decrease when the weather turns cold and a killing frost occurs.

Rain early in the fall seems to help the population decline.

If the fall stays warm and dry, the population will remain until the adults breed and eventually die.

First, reduce the desirable habitat so that the grasshoppers want to live elsewhere. Grasshoppers like tall weeds and grass that give them a food source and protection.

Grasshoppers like a nice green food source close to areas that are dry to allow them to gather for mating and egg laying.

Be prepared to apply pesticides if there are too many grasshoppers. Some biological controls are available, but they may be too slow when you want the insects gone.

Many different pesticides control grasshoppers. Some pesticides act faster than others, and some pesticides are easier to use than others.

The control you choose depends on your management objective. Controlling grasshoppers on livestock range will have a different approach than controlling grasshoppers around the yard.

Any time a pesticide is used, the label directions must be followed exactly. Any pesticide, if misused, can be harmful. If unsure, always check with the pesticide dealer.

First, the responsible approach is that we can live with some insects. It would not be cost effective to kill all insects.

For protecting range and cropland, make certain that it is a pest species. Not all grasshoppers will damage crops and range.

Next, the population level must be high enough that the money spent on control is offset by return in saved crop or range. Of course, also consider what the population may do next year if it is not controlled this year.

If you use pesticides, grasshoppers must be controlled in the early to mid nymph stages. Once grasshoppers are adults (wings present), the damage is done; you are only hedging your bets by killing some females before they can mate and lay eggs.

Eight grasshoppers per square yard is considered the economic threshold for pest species. When the population reaches this level, some controls should be considered immediately.

For pesticide recommendations around the home or for crops and rangeland, consult with a dealer or crop advisor. Always read and follow label directions for pesticides and check for any restrictions for grazing or harvest.

Dimilin is a new product registered only for range, pasture and other non-crop areas. It is a chitin inhibitor that interrupts the exoskeleton forming during molting. The new exoskeleton does not harden and the grasshopper dies from injury and exposure.

The product is safe for mammals, birds and bees. Dimilin works much longer than other chemicals. This helps control young grasshoppers not yet hatched when it was applied.

Dimilin does take from several days to as much as two weeks to kill the grasshoppers. They must first eat the product and then go through a molt. (Applying this product after the grasshoppers mature is ineffective.)

When pesticides are not used, the percentage of population controlled is going to be less than if they are used. This is not necessarily bad, but when grasshopper levels reach above infestation levels of eight per square yard, non-chemical controls have not proven to be very effective.

The options are limited. During the depression, farmers used turkeys, ducks and chickens to help control grasshoppers. This would obviously take a lot of birds.

Some commercial products contain a protozoan named Nosema locustae. This protozoan infects the grasshoppers and eventually kills them. It is most effective with young grasshoppers, since adults can survive it.

Around the yard and home, keeping the area well watered, especially in the evening, may have some effect in keeping grasshoppers away. You can also cover gardens and landscape plants to protect them from grasshoppers.

University of Idaho Extension

Physical Address:
Mill Street Building
501 Kelly's Parkway
Cascade, ID 83611

Mailing Address:
PO Box 510
Cascade, ID 83611

Phone: 208-382-7190

Email: valley@uidaho.edu

Web: uidaho.edu/valley

Our People Directions from Google Maps

UI Extension, Valley County