Why Did The Crabgrass Preventer Not Work?
Sometimes people will see crabgrass in their yard even though a crabgrass preventer was put down. Crabgrass weed preventers kill the new crabgrass as it sprouts, not before they sprout. Dormant crabgrass seed will lay in the soil until the conditions are right for growth. If grass is mowed tall (3-1/2 to 4 inches) and the lawn is thick, crabgrass has a very hard time germinating in Akron Ohio. If the crabgrass preventer is active when it tries to grow, the preventer will kill it.
There are certain reasons that crabgrass preventers may not work as well as expected:
1st if the soil was disturbed after spreading by aeration, dethatching, heavy foot traffic, same pattern mowing, pulling weeds, string trimmer hitting soil or cutting to low. Crabgrass seeds will then sprout as they are exposed and the crabgrass barrier is no longer present.
2nd if there is heavy rainfalls to create flooding and soil disruption or if the spring/summer rainfall is significantly above normal, the prevention will not be as strong.
3rd if your lawn was weakened because it was mowed too short, there was drought in summer or your lawn got a fungus or insect problem that thinned the grass. When the lawn is thinned or stressed this allows natures elements to break down the barrier much faster than normal. Crabgrass can germinate if the crabgrass preventer is no longer active.