Grasshoppers are moving out of their young nymph stages and are starting to cause more damage in sunflower fields. South Dakota has seen the most grasshopper damage so far, but there are still pockets in other areas such as North Dakota where growers are opting to spray borders. With the 10 day forecast looking hot and dry you will want to keep an eye on your fields.
Grasshopper damage in sunflowers can be very apparent due to their ability to defoliate large portions of sunflower leaves. Decisions to spray should include the number of grasshoppers present in the field and level of defoliation. Sunflowers can compensate for up to 25% defoliation.
Grasshoppers will typically start at field margins that border weedy patches or matured small grains. It’s important to recognize insect levels at field margins vs the inside of the field. Scouting can be done by visually estimating how many are seen in one square yard.
Threshold:
30-45 nymphs or 8-14 adults
25% defoliation
Watchouts:
– If grasshoppers are seed feeding on the heads, you are likely above threshold
– When reducing adult populations use the highest labeled rate
SDSU Pest Management Guides on labeled insecticides can be found here:
https://extension.sdstate.edu/south-dakota-pest-management-guides
Sources:
Compendium of Sunflower Diseases and Pests, APS Press, 2016
https://extension.sdstate.edu/watch-sunflowers-grasshopper-defoliation-and-flower-feeding
