Treatment Warm temperatures hasten the action of Round-up , because at high temperatures plant growth increases. Therefore, symptoms will occur sooner after summer applications than after fall applications. Time of Application Good control is obtained by treating perennials in the spring at the bud or regrowth stage. However, sufficient foliage must be present to get a good application, and the weeds must be taller than the blueberries. Additionally, fall is a time when herbicides will reach the under-ground parts through the natural translocation of the plant.
Perennial weeds are most susceptible to herbicides in the fall before frost.
Behavior in the Soil Roundup is strongly adsorbed onto soil particles, so leaching is very low. Microbial degradation is the major cause of breakdown of Roundup in the soil. The normal half-life, or time it takes to break down 50 percent of the herbicide, is less than 60 days. Roundup is relatively nonpersistent in the soil, and will provide no preemergence activity. Following application, clean sprayer parts by flushing tank, pump, hoses and boom with several changes of water.