Preemergent herbicides

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Preemergent herbicides prevent the germination of seeds by inhibiting a key enzyme. Preemergent herbicides are used to prevent crabgrass from appearing in the summer by application during the spring.

[edit] Preemergent herbicides

Pendulum, used for control of crabgrass in turf. Its active ingredient is pendimethalin.
Surflan, used for control of crabgrass in turf. Its active ingredient is oryzalin.

[edit] Crabgrass

Preemergent herbicides must be applied at a critical time. If they are applied to the soil too early they get washed too deep into the soil by rainwater. If they are applied too late the key enzyme inhibited is no longer active. The rule of thumb is to apply when the local forsythia blooms are wilting. These herbicides can be formulated into slow release pellets that can be applied earlier in the year and still be releasing seed germination inhibitor at the critical time.