Grasshopper survey and pest control explained
South Dakota is home to approximately 70 different species of grasshoppers. Not good news for the state's crop and forage producers, explained Anitha Chirumamilla, SDSU Extension entomology field specialist.
"Grasshoppers are one of the most difficult and challenging insect pests in western South Dakota. They feed on a wide variety of plants and have the potential to cause severe destruction when huge numbers coincide with drought conditions," Chirumamilla said. "Of the 70, 10 species are considered pests of field as well as forage crops."
To estimate population levels and determine the need for suppression programs, annual grasshopper surveys are conducted by the USDA's Animal and Plant Health Inspection Service (APHIS), over thousands of acres of range and forest lands.
Populations of grasshoppers that trigger the need for a suppression program are normally on a case-by-case basis said Bruce Helbig with USDA, explained Chirumamilla. "Suppression programs are carried out based on the threat of potential damage and severe destruction of forage for livestock and wildlife, reduction of wildlife habitat, soil erosion and the threat of crop damage and yield loss resulting from migrating grasshoppers."
The goal of APHIS suppression programs, Chirumamilla said is to reduce grasshopper populations to acceptable levels in order to protect rangeland ecosystems and/or cropland adjacent to rangeland.
How the survey works
APHIS conducts their surveys each spring starting mid-May by counting nymphs, and continues to the end of August with the survey of adult grasshoppers.
Sampling for nymphal populations is carried out using sweep nets and making 40 sweeps at each site (one per township). The density of grasshopper nymphs per square yard is calculated using the formula: Total number of nymphs from 40 sweeps divided by 10.
The adult grasshopper survey utilizes a visual count. Grasshoppers are counted at 18 one-square foot sites, and the total number for the 18 sites is divided by two for the number per square yard.
Although the annual surveys are intended to estimate the population levels in the current year, Chirumamilla said they also enable us to forecast future population levels and identify risk zones for the following spring and summer.
"The predictions will be based on adult grasshopper numbers that have the potential to reproduce and lay their eggs in the soil prior to the winter. Climatic conditions that prevail after survey and into the following spring are also taken into account," Chirumamilla said.
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