Herbicides Photosynthesis Inhibitors
Leaves develop interveinal chlorosis or mottling, turning the tissue between veins yellow. During later stages, the leaf margins become yellow while the leaf veins remain green. Gradually, leaves dry up and may drop within two to five days, giving them a 'paper bag'-like appearance.
The symptoms depend on the product used, dosage and time of application. The damage is caused by group C herbicides, such as atrazine, bromoxynil, diuron, and fluometuron. Due to their rapid and harmful effect on leaves, they are often qualified as 'bleachers'. They block photosynthesis and destroy the green pigments contained in the cells, discolouring them. Older leaves are more affected than younger leaves. Symptoms develop most rapidly in full sunlight. Problems with development of resistance are common in several types of weeds (grasses, mustard, stinging nettle and wild radish, for example).
There are no biological control solutions for the damage. Prevention and good farming practices are the keys to avoiding harm in the first place.
Always consider an integrated approach with preventive measures and biological treatments, if available. Before planning a herbicide spray, be sure that you know the type of weed you are dealing with (basically broadleaf weeds vs grasses) and choose the best. Carefully select the herbicide, by reading the label carefully and following dosage instructions, as indicated.