Kelly Nichols, Agriculture Agent Associate
University of Maryland Extension, Frederick County
kellyn@umd.edu
Perennial weeds like pokeweed, hemp dogbane, and horsenettle can flourish in no-till corn and soybean fields. Without tillage to break up the roots, perennial weeds can continue to regrow every year. Here are a few tips on how to control perennial weeds in your fields.
Use a residual herbicide to prevent seedlings from germinating later in the summer. Those later-emerging seedlings may still have time to become established enough to survive the winter and re-grow the following spring.
Apply post-emergent herbicides at the proper time. About the time that the perennial weeds are producing flower buds and blooms (approximately mid-summer), they begin to send food reserves down to the roots. Since things are moving in a downwards direction in the plant, the herbicide is more easily taken down to the roots, which will provide better control. A late post-emergent application is more possible in soybeans, which are a shorter-statured plant. One benefit from the wet spring and late-planted fields is that the corn is shorter than normal at this time of year, making a late post-emergent herbicide application possible in corn as well.
Rotate the field into other crops. In an alfalfa field, perennial weeds will not be able to withstand the frequent mowing. It depletes the food reserves in the root, weakens the plant, and reduces the chance for winter survival. Small grains that are harvested for grain will compete with the perennial weeds trying to grow in the spring and summer. An herbicide application could follow the harvest to control any late-summer weed emergence.
The Mid-Atlantic Field Crop Weed Management Guide provides herbicide recommendations and information for agronomic crops. To purchase a pdf or hard copy, visit the Penn State Extension website. To view a low-resolution pdf for free, visit the University of Delaware Extension website
