Spray pattern of herbicide injury in rice
Originally published May 14, 2017
These three photographs show herbicide injury related to application problems. The variety is CL161 which has excellent herbicide tolerance. The field had been sprayed with a mixture of Newpath, Permit, and Grasp plus a crop oil. From an undetermined cause the herbicide application was uneven with some areas getting too much herbicide resulting in the pattern shown in the top photo. The bottom left picture is of plants in the affected area. The bottom right photograph compares the root systems of affect plants on the left and “normal” plants on the right. Clearly there is reduction in root mass. This is NOT root pruning. The affected roots are not short and stubby, there are just less of them and those present are not as long as the unaffected. True root pruning results in damage to the root tips where growth occurs. The consequence is a short, stubby root or a root obviously missing the root tip. The first type of pruning can happen when herbicides containing pendimethalin (Prowl, Stealth) contact the root. The second type of purning usually is the result of insect feeding as in the case of rice water weevils or disease such as root rots or hydrogen sulfide toxicity. Twenty or thirty years ago most herbicides had a 2X measure of safety built into them, but today’s herbicides do not. It was already a pretty hot mixture and overlapping the pattern caused injury.
Close up view of herbicide injury to several rice plants
A comparison of injured roots (left) and normal roots (right) of rice
The LSU AgCenter and the LSU College of Agriculture