What's bugging you? April 27, 2016
By Jim Leser
Published Thursday, April 28, 2016 7:57 am
I recently was given a question pertaining to early season grasshopper control. So where do all the little grasshoppers come from this time of year? They come from egg pods that were laid in soil the previous late summer or fall. These eggs are not laid just anywhere. Grasshoppers prefer to lay their eggs in undisturbed areas such as ditch banks, roadsides, fencerows, pasture areas and alfalfa fields. Cultivated gardens don't seem to be a common site for egg laying. Eggs are laid in the upper 2 inches of soil.
When soil temperatures warm in spring, grasshopper eggs hatch and the young nymphs begin to feed on nearby plants. Nymphs readily move to new locations when food supplies become scarce. Most species molt five to six times before becoming adults and usually have only one generation a year. Adult grasshoppers are usually winged and can live two to three months. They die out when food becomes scarce or when the weather becomes too cold.
Grasshopper population sizes vary from year to year, and severe outbreaks normally occur only every five to 10 years. Some outbreaks last two or three years but most only a single year. If favorable conditions -- such as warm, moist springs that produce a lot of food in uncultivated areas -- persist for several years, populations may build to high levels.
Most grasshoppers are general feeders, but they prefer tender young green plants. Grasshoppers have chewing mouth parts that can remove large sections of leaves and flowers, sometimes devouring entire plants. Garden damage is usually limited to a few weeks in the summer immediately after range weeds dry up. However, during major outbreaks, grasshoppers will feed on almost any green plant, and damage may occur over a considerably longer period.
The key to grasshopper control is to get them when they are small. The larger nymphs and adults are much more difficult to control and winged adults can easily move to your yard from a distant source.
During years when huge numbers of grasshoppers are on the move, there is almost nothing you can do to protect plants once the invasion has reached your garden. The best strategy in agricultural and rangeland areas during major migrations is to treat the grasshoppers with an insecticide early in the season when they are still young nymphs living in uncultivated areas. Usually gardeners don't have control over these areas, so management options are few. Gardeners can apply a bait containing carbaryl (Sevin) around the borders of their garden before grasshoppers arrive. These bait mixtures typically contain bran, molasses and the insecticide. Commercial bait preparations are often difficult to find. Many farmers will mix up their own bait. Insecticides have only a few days of residual activity against grasshoppers, and because baits lose their effectiveness after rain or irrigation, they will need to be reapplied if migrations continue.
Commercial baits containing the protozoan Nosema locustae can be used to kill nymphs of migrating grasshoppers in uncultivated breeding areas early in the season. Unfortunately, Nosema baits are very slow-acting and only affect nymphs of certain grasshopper species, so this management technique may or may not work for you.
Once grasshoppers have invaded the garden, insecticides won't be very effective and must be reapplied every few days as long as the invasion continues. Carbaryl and pyrethroid insecticides such as permethrin and cyfluthrin are commonly used as sprays for grasshopper control. They are very toxic to bees and natural enemies of grasshoppers. Reserve the use of insecticides for serious situations where they may provide a significant level of control. Insecticide treatments do not need to completely cover the area since grasshoppers are mobile. Consider spraying a band between your yard or garden and the areas grasshoppers are moving from. This is most effective against wingless nymphs.
For those of you in more rural areas, chickens may be the best bet yet for hopper control. When a flock (rafter) of wild turkeys is in my area, I don't have grasshopper problems.
Jim Leser retired to Cedaredge in 2007 after a career with Texas A&M University Extension in entomology. He is a member of the Cedaredge Tree Board and a Colorado Master Gardener.