Post-emergent herbicides for blueberries
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Several post-emergent herbicides are labeled for use in Michigan blueberries. Most can be useful as spot-treatments to control weeds in problem areas of fields. Each herbicide has different characteristics that need to be considered when making choices.
Aim, Gramoxone and Rely are burn-down materials. They kill treated plant parts, but do not move within the plant. As a result, perennial weeds are usually not killed because the chemical does not move to the roots. Rely may move slightly in plants, because it often provides a little better control of some herbaceous perennials, such as dandelion. Aim is relatively inexpensive, but does not control grasses. Rely is much more expensive, but controls broadleafs and grasses. All three herbicides kill green bark and leaves of blueberries, so take care to keep spray off blueberries.
Fusilade and Poast are selective grass killers; they have no effect on bloadleaf weeds or blueberries. Application time is critical for control. Grasses must be treated when they are 4-8 inches tall in the spring. If grass is taller, control is poor. These materials are often useful to control quackgrass or annual grasses in young plantings.
Roundup and Touchdown (glyphosate) are the most effective postemergent herbicides for blueberries, but also the most hazardous. These chemicals are absorbed by green tissues and move throughout the plant. Perennial weeds are killed because the chemical moves to below-ground plant parts. Translocation is a two-edged sword. Glyphosate applied to blueberry branches moves within the bush, and can kill large canes or whole bushes. The most effective time to treat perennial weeds is late in the summer because absorbed glyphosate tends to move down to the roots. This timing is also most hazardous for blueberries. Use extreme care to avoid contact with blueberry tissues.