Application of Preemergence Herbicides to Lawns in 2017

Crabgrass is a common weed in many lawns.  Crabgrass is an annual, warm-season grass.  Germination of crabgrass seeds usually begins about mid-April in southern Iowa, early May in northern parts of the state.  Crabgrass seeds continue to germinate over several weeks from spring into summer. 

The best way to prevent crabgrass infestations in lawns is to maintain a thick, healthy lawn through proper mowing, irrigation, and fertilization.  Crabgrass has a difficult time germinating and surviving in thick turf.  Gardeners who have had crabgrass problems in recent years will need to apply a preemergence herbicide in spring. 

A key to the successful control of crabgrass in lawns is the correct timing of the preemergence herbicide application.  A preemergence herbicide must be applied before the crabgrass seeds germinate.  If the material is applied too early, crabgrass seeds that germinate late in the season will not be controlled.  If applied too late, some crabgrass seeds will have already germinated.  Preemergence herbicides should normally be applied in early to mid-April in southern Iowa, mid-April to May 1 in central Iowa, and late April to early May in the northern portion of the state. 

Longtime residents of Iowa realize that this state's weather is rarely "normal."  This has been true for the last few weeks.  The warmer than normal weather in February and early March has prompted the emergence of spring-flowering bulbs.  Lawns have also begun to green up earlier than normal.  The unseasonably warm weather has prompted questions as to when to apply preemergence herbicides to lawns.  If the weather over the next few weeks remains warmer than normal, apply the preemergence herbicide early in the normal time period.  If you are still uncertain as to when to apply the preemergence herbicide, Mother Nature provides some helpful clues.  Crabgrass seed germination usually begins with the end of the forsythia bloom season or when redbud trees reach full bloom.


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