April's Ag Advice by April Borders Grasshoppers have always been a major concern for farmers and ranchers and it is looking like this year will be no different.
We are starting to see little hoppers, between 1/8 and 1/4 inch, appearing in the road ditches. Once the weather starts to get warmer we are likely to see grasshopper numbers explode.
Because of our cool, wet spring weather we usually see grasshopper numbers suppressed but this is not a typical year so far. So far they are staying in the road ditches, along the field borders and in pastures.
Egg hatch for grasshoppers normally starts around mid-May to June 1. Hatching usually lasts for about a six-week period and then slows during the late summer months. The eggs hatch into "mini" grasshoppers called nymphs and the nymphs generally require about 45 days to develop into the adults.
Grasshoppers will shed their skin (exoskeleton) as they develop and mature. Shedding will happen five times before grasshoppers reach the adult stage. Each stage is referred to as an instar. Nymphs start feeding immediately after hatching and usually feed on the same plants as adults.
The primary injury caused by grasshoppers is defoliation, as they consume and clip foliage as they feed. Grasshoppers can also cause direct crop losses. Early hatches can threaten establishment of spring planted crops.
If grasshoppers mature early, they can move into corn fields, enter the whorl and destroy the developing tassel. In alfalfa, their primary damage is defoliation but under high levels of infestation they may feed on stems and crowns, causing severe damage. Small grains can be seriously damaged as grasshoppers can clip the stems, causing entire heads to fall to the ground.
The best way to monitor grasshopper populations is by scouting field margins and road ditches, etc. Grasshopper density can be estimated by walking through an area while sweeping in a half circle (180 degrees) through the vegetation. Make about 40 sweeps per location in at least three different areas. Figure the number of grasshoppers collected in the 40 sweeps. Divide that number by 10 and this will give you an estimate of the grasshopper density per square foot. If a sweep net is not available, do a visual count to estimate grasshopper populations.
Treatment is considered when grasshopper populations reach threatening levels or an economic threshold. The following control thresholds are suggested for South Dakota.
Rights of way � Should be treated when levels reach 50 nymphs per square yard. Treat before 5 percent reach the adult stage.
CRP, wastelands, grassy ravines � Treat when 35-45 nymphs or 20-40 adults are present per square yard and pose a threat to neighboring cropland or pasture.
Fields crops � Treat when 15-20 nymphs or eight adults are present per square yard. This assessment should also be based on growing conditions, stage of crop and grasshopper numbers.
Grasshoppers are easiest to control before they become adults. The ideal time to control is when the grasshoppers are in the third or fourth instar stage. The larger the grasshoppers, the more damage they do and the harder they are to control. It is also best to treat them before they start moving into croplands and causing damage.
Grasshoppers can be controlled by using sprays or baits. Read the label thoroughly before applying any insecticide.
and follow safety instructions and precautions. Also when spraying, especially in areas bordering croplands, be sure you carefully read and follow label restrictions for grazing.
Several chemicals are labeled for use for grasshopper control. An Extension publication FS905 Grasshopper and Bean Leaf Beetle: Economic Thresholds in Soybeans is available at the Extension Office. For more information call 677-7111.