| | Grasshopper numbers vary from year to year. When grasshopper numbers are low, damage is minimal. When numbers are high, damage can be significant and producers should consider management options. Grasshoppers can eat 30 to 100 mg of plant material (dry weight) each day and although forage losses are seldom estimated, even a moderate infestation of 10 grasshoppers/mē can consume up to 60% of available forage, depending on the condition of the forage stand.
Over 85 species of grasshoppers are found in Alberta but fortunately not all are considered pests. A grasshopper is not a pest if it has colored wings, makes a sound or is large early in the season (late May, early June). Problem species all over-winter as eggs and hatch in late May to early June. Only four species are considered of economic importance in Alberta: the migratory grasshopper, the clear-winged grasshopper, the two-striped grasshopper and Packard's grasshopper. The migratory grasshopper is the most common species, found throughout Alberta. It is a mixed feeder consuming both grasses and broadleaf crops. The two-striped grasshopper is more common in southern Alberta. It is also a mixed feeder, but prefers lush crops. It is often a problem in irrigated alfalfa fields. The clear-winged grasshopper is more common in Saskatchewan and consequently more commonly found along the eastern side of Alberta. It has a preference for grasses, especially wheatgrass. Packard's grasshopper is the least common species in Alberta, although numbers have been increasing in recent years. It prefers to lay its eggs in sandy soils, which probably limits its distribution. It has a preference for broadleaf crops. It is important to note that if food is scarce, all four species will eat anything green, so don't be surprised to see any of these species in any crop.
A number of insecticides are registered for controlling grasshoppers in pastures and hayfields. Insecticides can be applied as sprays or baits and both can be equally effective if used as directed. If control is needed, insecticides are most effective when applied while the grasshoppers are still in the early nymph stages. Grasshoppers go through five to six nymphal stages before reaching adulthood. The most serious economic damage from grasshoppers occurs while the insects are in the third to fifth nymphal stages. Control measures should be taken during or preferably prior to that to prevent economic damage to the crop. As the hoppers approach adulthood, chemical control becomes increasingly difficult and higher rates are necessary. Read labels thoroughly before using any insecticide and observe safety and grazing restrictions. For a complete and up-to-date listing of registered insecticides and rates consult Alberta Agriculture, Food and Rural Development's "Blue Book", Agdex 606-1: Crop Protection 2004.
An innovative grasshopper control strategy was recently developed by researchers at the University of Wyoming. It is known as Reduced Agent/Area Treatment or RAAT and is designed to reduce the amount of insecticide used and the area treated. Insecticide is applied at reduced rates in 30 m passes alternating with 30 m untreated passes. Higher rates and greater coverage may be necessary to control later instars or adults. This innovative strategy is successful because grasshoppers move from untreated to treated areas and pathogens and predators are preserved in the untreated areas. In a study done in southeastern Wyoming, a RAAT treatment was essentially indistinguishable from a standard blanket treatment with both treatments resulting in 80% to 90% grasshopper mortality. Cost however, was substantially reduced. It is important to note, however, that reduced rates of insecticides are not registered in Alberta.
Remember that not all grasshoppers are pests. Scout your pastures and hayfields often, beginning in late May and use appropriate control strategies to manage the hoppers while they are still in the early nymph stages. Less insecticide will be needed and better control will be obtained in these early stages. Also, because eggs are laid in field margins, roadside ditches and along fence or tree lines and nymphs move into the field from these areas, one or two spray passes around the field may be all that is needed if scouting is done early enough. Consider using rotational grazing to keep numbers down and if spraying, consider strip spraying to preserve grasshopper pathogens and predators.
Paul Laflamme, P.Ag. , Provincial Integrated Pest Management Specialist, AAF, Grande Prairie |
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