Preemergent herbicides used for controlling crabgrass and other annual weedy plants must be watered into the soil to be effective (Fig. 10.15). As noted earlier, they affect the seed as it begins to germinate, but before the plant emerges from the ground.
Figure 10.15. Water following preemergent herbicide application.
Depending on the soil type, ¼ to ½ inch of moisture should be applied following application of these products. This not only puts the product where it will be the most effective, but moves the material into the surface soil so it will be much less likely to be carried away in runoff.
For all weed control products, ALWAYS follow label directions for how soon after application the product will remain bound to the foliage even if rainfall or irrigation occurs. In some recent products this time period can be as little as two hours. Again, the product label will be your guide in this matter.
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