Will the cold temperatures increase grasshopper egg mortality? The answer for 2021 is probably not. In Canada, few grasshoppers hatched following a winter with temperatures at negative 22 degrees Fahrenheit (Riegert, 1967). However, Canada had little snow cover during the time period when mortality occurred. Snow cover generally reduces the impact of cold temperatures on below-ground overwintering insects.
How long does a seed treatment like Gaucho remain effective on grasshoppers? Insecticide seed treatment usually last about 21 days and will work for young grasshopper nymphs if they move into the field edges. Grasshoppers will typically stay in ditches where grasses are tall and move out when the grass is mowed or hayed (Janet Knodel, NDSU Entomologist).
What would be a good step by step management order if grasshoppers continue to exceed economic threshold levels?
Step 1: Seed treatment on outside borders (minimum of 150 feet).
Step 2: Spray grass borders and neighboring rangeland at beginning of egg hatch (Reduced Agent and Area Treatment Strategies (RAATS) using Dimilin insect growth regulator)
Step 3: Use Dimilin on field borders (a minimum of 150 feet).
Step 4: Spray contact insecticides if populations exceed economic threshold. Be sure to rotate groups.
How long is Dimilin affective? Dimilin has a residue of 30 days. The most important point is that it is applied early when you see young nymph grasshoppers (<1/2 inch) since it is an IGR (Insect Growth Regulator) and disrupts the molting process as the nymphs grow (Janet Knodel, NDSU Entomologist).
Is it true that oats and peas are less preferred by grasshoppers? Yes, oats, peas and chickpeas are the three crops that are most tolerant of grasshoppers. Lentils are very susceptible to adult grasshoppers because they can clip the pods. The action
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threshold is only 2 grasshoppers per square yard in flowering to pod stages.
Why would chickpeas be tolerant of grasshoppers? Chickpea stems, leaves and seedpods are covered with small hairlike glandular structures that secret malic and oxalic acids, which deter insect pests. Researchers have observed that some grasshopper species are reluctant to feed on chickpea (NDSU Extension).
References:
Riegert PW (1967) Association of subzero temperatures, snow cover, and winter mortality of grasshopper eggs in Saskatchewan. The Canadian Entomologist 99: 1000-1003.
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