Seeding Areas Where Preemergents were Used
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Seeding areas where preemergence herbicide was applied this spring
A fairly typical question now is, "Can I seed an area where preemergence herbicide was applied earlier this spring?" The answer is a very simple "No." These herbicides are active in the soil for up to 120 days and their nature is to be absorbed into the root of a germinating weed (or turfgrass seedling) killing the very young plant. Most preemergence herbicides (other than Tenacity, Tupersan, or products containing siduron) cannot distinguish between germinating crabgrass or turfgrass seedlings, so you'll have to wait until July or August to consider seeding. Activated charcoal could be used to absorb the herbicide and allow for improved germination in emergency situations, but this product is very cumbersome to use. Alternately, you could remove an inch or more of soil (which should remove the herbicide), bring in new soil and then resod or reseed. Even with activated charcoal or removing soil, you would end up with somewhat compromised seedlings or sod having to survive a typical Indiana summer, and that rarely ends well. Your best bet is to wait until August and seed then.
Zac Reicher, Professor/Turfgrass Extension Specialist