How the weather can change things. The weather patterns over the last several weeks have made many of changes in our landscape.

From the freezing temperatures that froze the soil, and likely brought death to some plants, to the high 60 degree week that has weeds and lawns showing signs of life — the weather has been unpredictable. Many of us are ready to start working once we see something new growing on the yard this time of the year, but chances are all you find are winter weeds.

It is still too early for our spring lawns to begin the spring transition despite warm January days. Here are two questions about dealing with winter weeds.

Q: What is a preemergence herbicide?

A: It is still a little early to be answering this question but we have been receiving it so here we go. It is best to be proactive and attempt to stop most weeds before they take over or become competitive with our desired turf species.

There are two main classifications of herbicides; preemergence and postemergence herbicides.

Preemergence herbicides are applied to the turf before weed germination occurs. For summer annuals, preemergence herbicides should be applied from early to mid March. If you do not spray a preemergence herbicide you can still control most weeds with a postemergence herbicide.

Postemergence herbicides, like the name suggests, are sprayed on after the weeds have emerged. Many of these products will recommend you use a surfactant with it. Surfactants increase the surface tension of spray droplets causing them to spread more on the leaf surface, and help dissolve the waxy layer on the leaf to enhance herbicide movement into the vascular system of the plant.

When possible I would recommend a preemergence herbicide to reduce the weeds problems, but if you miss that opportunity wait for the weeds to emerge then spray with a postemergence herbicide.

There are over a dozen preemergence herbicides MSU recommends so contact us or go online if you would like more details.

Q: Can I put out a preemergence herbicide now?

A: Statewide soil temperatures ranged from about 55 degree F near the Gulf to about 45 degree F in the far north delta last week.

While there is still some debate about the proper time to apply a preemerge herbicide for control of crabgrass and warm season weeds, most agree that the millions of seeds in the soil will start to germinate when soil temperatures approach 60 degrees.

Vegetable gardeners using one of the trifluralin products for weed control should be aware of local soil temperatures. An easy way to test this is to stick a thermometer in the ground at the depth you are going to plant. Very few things grow well below 50 F and almost everything grows well above 70 F.

Right now in the Miss-Lou if your yard has weeds taking over you need a postmergence herbicide which in many cases can be used as a preemergence herbicide as well. The herbicides do differ depending on what type of home lawn you have and the weeds you are targeting.

Therefore, knowledge is the key. If you need help deciding if you should spray, call our office for more information, and always carefully read all labels before using lawn care products.

David Carter is the director of the Adams County Extension Service. He can be reached at 601-445-8201.