Johnsongrass – Weed ID Wednesday

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Johnsongrass is easily spotted in pastures and hayfields because it grows in bunches that tend to be taller than the forages present. It is a warm-season perennial and can be drought tolerant. Johnsongrass can be grazed and often has good nutritional value, but has to be managed for it’s times of stress.

When in times of stress, which tend to be drought or early frosts in our area, johnsongrass can be poisonous to livestock because of levels of prussic acid and nitrates. Prussic acid will dissipate from cut hay by the time it dries enough to be baled, but nitrates will not. Hay with stressed johnsongrass present needs to be tested to determine its safety before feeding.

In pastures, johnsongrass will likely be grazed down fairly quickly. If rotational grazing is used on your farm, be aware if upcoming paddocks have johnsongrass and if the weather could be stressful for it. Plan to either wait to move paddocks and/or graze where there’s no johnsongrass present. Note that small tender plants are more likely to be toxic than larger mature ones. This is important to consider if the paddock has been previously grazed and is working back up into the rotation during weather stress.

If interested in chemical control, using a Weed Wiper or WIC applicator is a great tool. Since johnsongrass tends to be significantly taller than our forages, this makes for a great time to use the WIC. Our Soil & Water office rents a WIC applicator out and can be contacted at 336-342-8260.

Johnsongrass stalk Hand holding Johnsongrass
Overhead view of Johnsongrass