Get Your Preemergence Herbicides Down Now!

3/19/2012

By Dr. David S. Gardner

As everyone in the Midwest, Northeast, indeed most of the eastern United States has probably noticed, it's unusually warm right now.

How warm is it? If the forecast holds up, by the end of this week (Friday March 23), the monthly mean temperature in Columbus, OH (where I'm writing this), will be 53.5 degrees. This is the normal monthly mean for April. Also, Columbus will have had at least nine days in the 70's this March, two days at or just above 80 degrees. This is similar to what central Ohio experienced in April 2011.

In addition, if one looks out the window in central Ohio they will see not only forsythia in full bloom (our indicator plant that tells us it's time to put down preemergence herbicide) but also cherry trees and Bradford pears.  Cherry trees normally do not bloom in central Ohio until the third week of April.

Soil temperatures in Columbus this morning (March 19) are 57 F. Theoretically, the soil will be warm enough this week for crabgrass to germinate. I say theoretically because we've not seen crabgrass in Columbus in March before - and this just as Kentucky bluegrass is barely out of dormancy.

All of the other phenological indicators are out of alignment, too. No model shows forsythia, cherries and magnolias in bloom simultaneously. But, importantly, soil temperatures will be warm enough this week for crabgrass to germinate. Of course, there's always a chance that a late frost will knock out some of the early germinating crabgrass.

Even so (and this is the take-home message): Get your preemergence out as soon as possible. 

Remember, even if you see some crabgrass, new plants will continue to germinate up until the first part of July, so at least the preemergence herbicide can prevent subsequent germination. Don't rely just on a post product on these sites.

Consider using products that offers both pre- and postemergence control.  Dimension is a great choice, as is Echelon or Cavalcade PQ.  If you decide to use Echelon or Cavalcade PQ, I would wait until crabgrass is 1-4 leaf (which looks to be sometime in mid-late April this year). That way the quinclorac will take out the early crabgrass, plus you won't have to be as concerned with premature breakdown of the preemergence herbicide.

If you have the materials on hand, you can also combine prodiamine with Tenacity herbicide and this will give both pre- and postemergence crabgrass control.

All of the above advice could be rendered unnecessary if we have a turn in the weather to more normal or below normal temperatures.  However, there is nothing from the National Weather Service Climate Prediction Center (which has been remarkably accurate the past several years) to suggest that this current trend of above normal temperatures is going to end anytime soon. Plan your spring as though everything is 3-4 weeks ahead of last year.

About the author: Dr. David Gardner is Associate Professor, Horticulture & Crop Science, at The Ohio State University and technical advisor to TURF magazine.