Your best approach for crabgrass control is preemergent herbicide applied early next spring. After the crabgrass is well established, your control options in turf are few and don't work that well. Crabgrass begins to germinate when 50 to 75 Growing Degree Days (GDD) have accumulated (here in Ohio that is when Forsythia begins to bloom). Crabgrass germination peaks at 175 to 200 GDD. Here, in Ohio, excellent control is achieved when a weed and feed product is applied to the turf when the forsythia just beginning to bloom.
This is a U of Mn publication that may help. http://www.extension.umn.edu/distribution/horticulture/dg1137.html
You can contact your local (right in your backyard) office of Minnesota Cooperative Extension here:
UM Ext Blue Earth Cnty
204 S 5th St Ste 310
PO Box 8608
Mankato, MN 56002-8608
(507) 304-4325 (phone)
(507) 304-4059 (fax)email@example.com
The following is a newspaper article I prepared for publication this spring:
Master Gardener News Herald Article
May 2, 2010
Spring Got Here Early by Bill Hudson
Spring arrived early, almost two weeks early, at my house. Caught flat-footed, my application of weed-and-feed was later than optimum, so I am expecting to see an increase in the amount of crabgrass I will have to deal with this summer.
This leads to a question that is important for understanding crabgrass, a very troublesome weed in home turfgrass, and its effective control. If the calendar is not a reliable determinant of when to apply crabgrass control herbicides, what can be used to effectively predict the timing of this application?
For years, the calendar has been used to recommend windows of time for application of various products used in lawncare and other horticultural activities. While very useful, the calendar does not control the environment nearly as well as it controls us. For comparison, in 2008, my first mowing was April 14, in 2009; my first mowing was April 17. This year, April 4 was the first mowing, fully 10 and 13 days prior to the previous two years.
As for the application of the weed-and-feed, I made timely applications in 2008 and 2009 on April 18. This year I was late when I made the application on April 6. In all three years the calendar would say that my applications were timely. Why would I say that I was late this year? Because I was not paying close attention to landscape plants that signal particular events. Specifically, forsythia was in glorious bloom when I applied the weed-and-feed and 99 Growing Degree Days (GDD) had accumulated by the time I made application.
What is a GDD and why look at the forsythia bloom? GDD is a measure of accumulated heat units determined by mathematical calculations based upon temperature. The basis for the calculation is not important, for this discussion, however, the number of GDD is. As for the forsythia, bloom begins when a specific number of GDD have accumulated. Together, a specific action by specific plants are related to specific GDD and is called a phenological calendar.
What this all means is that crabgrass begins active germination between 50 and 75 GDD and reaches peak germination between 100 and 200 GDD. Early blooming (Northern Lights) forsythia begins to bloom at 55 GDD and reaches full bloom at 94 GDD. The day I applied the weed-and-feed, 99 GDD had accumulated. Although I had beat the peak germination, by very little, I still needed a good rain to water the chemical into the soil to be effective. Bottom line, I was late and cannot expect excellent control because the already germinated crabgrass will not be controlled, only the crabgrass germinating in the presence of herbicide in the soil will be controlled.
Spend some time surfing the Ohio Agricultural Research Development Center (OARDC) Growing Degree Days and Phenology for Ohio website at http://www.oardc.ohio-state.edu/gdd
to learn more about this very useful tool.
For those asking themselves, does he really know the dates he mows his lawn and applies different products to it? Yes, I do. Spreadsheets are marvelous tools. And, no, you don’t want to know how many times I mow my lawn each year.
Interested in scheduling a speaker or learning more? Call the Lake County office of Ohio State University Extension at 440-350-2582 or stop by our office at 99 E. Erie St., Painesville, Ohio 44077-3907, to arrange the schedule. More information is available at http://ohioline.osu.edu/lines/lawns.html