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Horticulture and Home Pest News
Horticulture & Home Pest News is filled with articles on current horticulture, plant care, pest management, and common household pests written by Iowa State University Extension specialists in the Departments of Entomology, Horticulture and Plant Pathology.

Application of Preemergence Herbicides to Lawns in 2014

This article was published originally on 4/11/2014

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 especially true in the last few months.  The colder than normal weather in February and March has delayed the greening up of lawns, the emergence of spring-flowering bulbs, and the leafing out of trees and shrubs.  The long, cold winter has prompted questions as to when to apply preemergence herbicides.  In 2014, we are recommending the following application dates; April 12 to April 27 in southern Iowa, April 19 to May 4 in central Iowa, and April 26 to May 11 in the northern portion of the state. 
 
It's important to remember that crabgrass is a warm-season grass.  Crabgrass seeds don't germinate in the first warm days of spring.