Treatment After Harvest
Johnsongrass in winter wheat should be treated in wheat stubble after wheat harvest. Allow established rhizome Johnsongrass to grow back after wheat harvest to a height of at least 18 inches or the boot to heading stage of growth and spray with one quart or 41% Glyphosate in 4-10 gallons of water per acre. Use 1.5-2 quarts of 41% Glyphosate per acre if using more than 10 gallons of water per acre.
Controlled Droplet Application (CDA) will deliver the lower water rates at a more uniform coverage for better Johnsongrass control. Allow at least 14 days after treatment before tillage or burning of stubble.
Two or three years of these treatments may be necessary to kill all of the rhizomes in the soil if heavily infested. Seedling Johnsongrass can be controlled by tillage in the stubble while the seedlings are small to keep them from forming rhizomes.
Johnsongrass seeds may last for up to 10 years in the soil on the property and seedlings should be controlled for those 10 years and not allowed to produce seed to rid the property of Johnsongrass.