Good coverage of the foliage is needed. Effectiveness may be increased if two applications are made in opposite directions. Rainfall occurring too soon after an application may decrease effectiveness because the herbicide will get washed off the leaves before it can be taken up. Good control is obtained by treating perennials in the spring at the bud or regrowth stage, but sufficient foliage must be present to get a good application, and the plants must be taller than the blueberries. Additionally, fall is a time when herbicides will reach the underground parts through the natural translocation of the plant.
Perennial weeds are most susceptible to herbicides in the fall before frost.
Do not apply to grass that is stressed due to moisture, temperature, low soil fertility, or mechanical or chemical injury, or if rain is expected within one hour. Registered Herbicides Roundup was registered for use in blueberries in 1986. Wick or wiper applicators may be used to apply Roundup . A more concentrated solution should be used in a wick wiper compared to a roller applicator or on woody perennial weeds compared to herbaceous weeds. Exercise extreme care to avoid contact with blueberries or injury will result.