Dandelion herbicides best in fall

Q. Is fall a good time to use a pre-emergent to control dandelions?

Wayne from Boardman

A. No, fall is not a good time to control dandelions with a preemergent. In fact, preemergent products aren’t a good control option for dandelions. Dandelions can flower and produce seeds from spring into fall, which makes controlling them with a preemergent a challenge.

Dandelions are broadleaf weeds. Many people with a dandelion problem don’t realize that dandelions are a perennial weed, as is another notorious lawn weed, ground ivy. The dandelions you see blooming in the spring are not new plants that have recently germinated. They are last year’s dandelions that have overwintered. The leaves die off in winter, which is why you don’t see them, but the root and crown stay alive.

According to Michigan State University, the best time to control broadleaf weeds is the fall. In fall these plants are busily storing energy in their root systems and this makes herbicides more effective against them. If dandelions are numerous, you can apply an appropriate herbicide over the entire area according to label directions. If you have fewer dandelions you can spot spray the individual weeds. Hand digging is an option, but you need to get all of the tap root out or it could regrow. Just an inch of the root left behind can grow a new plant.

To be effective, herbicides have to be applied in the right conditions. Wearing appropriate clothing, apply the herbicide at least 24 hours before any forecasted precipitation. Herbicides work best within certain temperatures, days at least in the upper 50s and nights above 40. Don’t apply herbicides containing 2,4-D when temperatures are above 85 degrees; it can harm the turf grass. Avoid using herbicides in windy conditions, as it could drift onto landscape plants, causing damage. And remove any leaves on top of the dandelions before using the herbicide.

As always, read and follow all directions on the herbicide label. The directions describe the most effective way to use the product and how to protect both the environment and the user.

Visit http://go.osu.edu/controlinfall for more information on controlling dandelions; visit http://go.osu.edu/readlabel for more information on chemical labels.

This week’s answer was provided by David Sprague, an OSU Extension master gardener volunteer in Mahoning County, who you can meet at the Mahoning Plant and Pest Clinic. Call the office plant and pest clinic at 330-533-5538 to submit your questions. Regular clinic hours are 9 a.m. to noon Mondays and Thursdays.