University of Idaho Extension, Valley County U-Idaho Extension Image Map
 
grasshopper1A number of ranchers and farmers in Valley County have partnered with the Idaho Department of  Agriculture to fight an outbreak of grasshoppers.  Grasshoppers are voracious feeders, eating approximately one-half of their body weight in green forage per day. Infestation in some areas had reached levels of greater then 8 grasshoppers/yd2 at which point non-chemical controls are considered ineffective. In comparison: at densities of 30 per square yard, grasshoppers will consume all the green forage available and at higher densities shrubs, woody material, and even paint on buildings may be consumed. Since ranching ultimately depends on availability of forage (grass), the concern is understandable.
 
The Department of Agriculture has elected to use a Reduced Agent and Area treatment in which the rate of insecticide is reduced from levels recommended by the label and untreated swaths are alternated with treated swaths (consult the USDA website for more information on this method). The pesticide used is Malathion. Malathion is a common insecticide that has been registered for use in the United States since 1956, and is widely used in mosquito control to contain West Nile virus. The aerial spraying needs to be carefully controlled, however, since malathion is equally effective in killing bees and other beneficial insects, some fish, and other aquatic life. Malathion is moderately toxic to other fish and birds, and is considered low in toxicity to mammals and humans (see fact sheet on Malathion from Oregon State University).
 
The below information on grasshopper infestations and effective treatments in Valley County was compiled by Steve Heinz, University of Idaho Extension.

Grasshopper FAQ’s

Grasshopper populations build and decline in cycles. However, when the weather conditions are favorable, the populations will build to higher than normal levels, and if natural enemies can’t control the populations, they will explode to much higher than normal levels. When we have several hot, dry summers followed by warm, dry autumns, the grasshopper populations do well. 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 keeps the eggs from much damage.

From where do the grasshoppers come?

Normal populations are always present in Valley County. On a normal year, you may notice a few grasshoppers around, but not enough to cause concern. Certainly, you may even have to hunt to find enough for a fishing trip. Grasshoppers lay eggs in pods each fall. The eggs mature to a point and then must over winter before completing development in the spring when the weather warms. In the spring, 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.

When will grasshopper numbers decrease this year?

Even though the grasshoppers only produce one generation per year, they lay eggs over a period of time which makes for a long grasshopper season – especially since it takes 40-60 days for grasshoppers to reach the adult stage. In general, the populations will decrease when the weather turns cold and a killing frost occurs. A 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.

How can I reduce the numbers of grasshoppers around my place?

To begin with, reducing the amount of desirable habitat so that the grasshoppers want to live somewhere else can help.  Grasshoppers like areas of tall weeds and grass that give them a food source and protection. Keep in mind that grasshoppers like areas where they can get a nice green food source close to areas that are dry and allow them to congregate for mating and egg laying. You should be prepared to apply pesticides if you decide there are just too many grasshoppers. There are some biological controls available, but they are just too slow to make a difference when you want the insects gone quickly.

What are my options if I don’t want to use pesticides?

You must first realize that when pesticides are not used, 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 8/yd2, 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. Commercial products of various names contain a protozoan named Nosema locustae. This protozoan infects the grasshoppers and kills them eventually. It is most effective with young grasshoppers and 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 exclude the grasshoppers from them.

Are pesticides truly effective?

Yes. Many different pesticides can control grasshoppers. Some pesticides are faster acting than others and some pesticides are easier to use than others. The method of 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.

When should pesticides be used?

First, the responsible approach is that we can live with some insects. We do not want to kill all insects and it would not be cost effective to try. For producers protecting range and cropland, first make certain that the species you are trying to control is a pest species. Not all grasshoppers will damage crops and range. Next, the population level must be high enough so that the money spent on control is offset by return in saved crop or range. Of course, you may want to give some consideration to what the population may do next year if it is not controlled this year. If you decide to use pesticides, grasshoppers must be controlled in the early to mid nymph stages. Once grasshoppers reach adults (wings present) the damage is done and you are really only hedging your bets by killing some females before they can mate and lay eggs. Eight grasshoppers per square yard are 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.

What is Dimilin 2L that has been used before in valley County?

Dimilin is a new product that is registered only for range, pasture, and other non-crop areas. It is a chitin inhibitor that causes an interruption in the exoskeleton formation of the grasshopper during molting. The new exoskeleton does not harden and the grasshopper will die from injury and exposure. The product is safe for mammals, birds, and bees. A major advantage is that it has a many day residual that allows it to work much longer than other chemicals. This will help control young grasshoppers not yet hatched when it was applied. It 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. (Note that applying this product after the grasshoppers mature will be ineffective).

When should I expect to see grasshoppers in Valley County?

Our main species of concern is Camnula pellucida (Scudder) commonly called the clear winged grasshopper. 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 forth week in May. Most likely when you first see them, you will see hundreds if not thousands. They are coming 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 these tiny black insects for several weeks. If the weather conditions are 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, control may need to take place more than once. 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.

 July 30, 2013