Pre-emergent control for winter weeds by Bill Hayes

For those of us who battle summer weeds in the lawn and garden from March through September, you would think that we would get a break from October to February. Well, that’s just not going to happen in an area where temperatures can go into the 70’s in any winter month. Warm to moderate winters mean that a whole new crop of weeds will move into our lawn and garden areas.

The garden is usually a little easier to control because of several mulch choices. Mulch will help prevent weeds from germinating by blocking the necessary sunlight required to germinate. The lawn is a different story and vigorous weeds may be the only green thing visible on a brown lawn. So, how do we combat the green guys and who are they anyway?

Typical winter annual weeds in this area include common chickweed, annual bluegrass or poa annua, wild garlic and onion, several thistles, wild mustard, Shepherd’s Purse, Carolina Geranium, henbit, black medic and many more. There are additional weeds categorized as “perennials” that will also appear. Remember that pre-emergence herbicides prevent annual weeds but not perennial weeds. Perennial weeds mainly come back vegetatively while annual weeds come back strictly from seed. Many perennial weeds require multiple applications of selective post-emergence weed killers, spot applications of Roundup, or will require hand digging. Now that we know who they are, how do we prevent them from making a mess in our lawns?

Preventing the weed seeds from germinating is the key. Part of the problem is that all seeds don’t germinate at the same time. That means that we have to get our pre-emergent herbicide into the ground in a timely basis. September 15th is an easy date to remember and offers the best timing for a fall application. It also means that a second application around December 1st may be necessary to catch the late germinators. Contrary to popular belief, pre-emergent weed killers don’t destroy weeds and their seeds. They simply stop them from growing. Some seeds are known to last fifty years, so if the herbicide isn’t applied each year, the weed will grow.

There are many pre-emergent products available. Some of the more common are benefin (Balan, Crabgrass Preventer, etc.), pendimethalin (Halts, Lesco Pre-M Plus), dithiopyr (Dimension, StaGreen Crab Ex, Crabgrass Preventer, Vigoro Crabgrass Preventer and prodiamine,(Barricade). Read the label carefully before applying since manufacturers often vary in their application requirements.

Most pre-emergent herbicides require water to get them into the “kill” area. Try to time your application with a normal rainfall but water the product in by hose with at least