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Grasshoppers Emerging (6/04/20)

As the field crops start to emerge, now is a good time to scout for young grasshoppers that are starting to hatch from egg pods laid in grassy ditches last year.

As the field crops start to emerge, now is a good time to scout for young grasshoppers that are starting to hatch from egg pods laid in grassy ditches last year. Nymphs are very small, about the size of a wheat kernel when they first hatch and their mobility is limited. Grasshoppers typically have 5 to 6 molts as nymphs depending on the species of grasshopper. You can tell a nymph from adult grasshopper, because a nymph has not developed wings to fly. Nymphs only have wing pads (arrow in photo), so they must crawl into fields. Blooming lilacs are often used as a general indicator of when grasshopper hatch is occurring. Yes, lilacs are blooming!

 

Grasshopper development is favored by hot and dry weather over cool and wet weather. Cool, wet weather increases disease occurrence and delays development of grasshoppers, reducing the overall population. The current forecast is for normal temperatures and below normal precipitation, so it is partially favorable for grasshopper development.

 

It’s too early to say if we will have any crop problems with grasshoppers as they move into field edges. Grasshoppers have chewing mouthparts, which create holes in leaves and cause defoliation and clipped heads or pods (later in the season when adults are common).

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Regular scouting of field edges is important because populations vary from year to year. Use a 15-inch sweep net to find small grasshopper nymphs in grassy ditches next to emerging field crops. Action thresholds are based on the number of grasshopper nymphs or adults per square yard. Since it is difficult to estimate the number of grasshoppers per square yard when population densities are high, scouts can use four 180-degree sweeps with a 15-inch sweep net, which is equivalent to the number of nymph (or adult) grasshoppers per square yard. Early detection of grasshopper nymphs is vital for effective pest management.

 

The action threshold for nymphs is:

-   50-75 per square yard in field margins

-   30-45 per square yard within the field

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Janet J. Knodel

Extension Entomologist

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