Mid-Spring Weed Control Reminders

By Dave Gardner, Ph.D.

Hopefully you got your preemergence herbicide out in time.  March 2025 was the 8th warmest on record (monthly average 48.03° in Columbus, normal is 41°) which caused Magnolias, cherries and forsythia to bloom about 1-2 weeks earlier than normal.  It also caused turfgrass weed pressure to be a bit earlier than normal. Nonetheless, it will be time to switch to broadleaf weed control soon, if you haven’t already.

There are a seemingly endless number of combination herbicides for broadleaf weed control.  Generally, if your weed pressure is light and does not include a lot of difficult to control weeds you can choose a less expensive option that will typically include 2,4-D, MCPP and dicamba.  Products that include triclopyr and either clopyralid or fluroxypyr instead of MCPP may cost a little more but also tend to be more active.  For difficult weed control situations, you should invest in a 4-way herbicide that includes a protox inhibitor (carfentrazone, sulfentrazone, or pyraflufen ethyl).  While this is rarely an issue when using combination herbicides, you should check the label to make sure all the target weeds you treat are controlled by the product.  Use this guide for assistance.

Due to the record drought last year, there was a lot of thinning turf and therefore a lot more winter annual weed pressure this spring compared to years past.  These can be very difficult to control postemergence, even with our best herbicides.  One of the problems with controlling winter annuals is that when they are most visible in March/April it’s tempting to use a postemergence herbicide to control.  Amine formulations of herbicides (and even esters) can be less active during this time.  Use either a combination herbicide with an ester or  Florasulam is a good choice to consider because it is more active in cool weather and quite effective on winter annuals (as well as dandelion and white clover).  You can usually get better control in late April to May, but by this time the weeds have gone to seed and are beginning to decline naturally.  It’s best to keep these areas mowed to reduce seedhead infestation and to map them out so that you can consider either 1) the application of a preemergence herbicide in late August or 2) a postemergence herbicide application in late October.  Either of these timings tend to be more effective.

We know that there is buckhorn plantain in Ohio that is resistant to most of the broadleaf herbicides we use on turf.  If you apply a product and you get great control of all but one weed that you used to get good control of then it’s time to suspect a resistant population.  When you suspect weed resistance you should retreat about ½ of the area with the same herbicide (to rule out a problem with the first application) and the other half with a herbicide that has a different mode of action.  The Buckeye Turf Team can assist with confirmation of resistance and alternate herbicide selection when needed.

Both are ephemerals meaning the foliage will die back in late spring.  But they are very noticeable in April to early May.  Either sulfentrazone or 2,4-D or products that combine the two actives tend to give best control. As with winter annuals, keep these mowed close to try to reduce their vigor.

Dave Gardner, Ph.D. is a Professor in the Department of Horticulture and Crop Science at The Ohio State University.