Last week, I wrote about some of the winter weeds that are present in our lawns now.
It might seem strange with the cold weather we have had to be thinking about controlling weeds that we will have this summer. But the best way to control our summer weeds is to start early and use pre-emergent herbicides to kill the weed seeds as they germinate. This is especially true of the grassy weeds such as crabgrass and goosegrass.
Grassy weeds are very similar to the lawn grasses that we are trying to grow, and there are few herbicides that will control these weeds without hurting the lawn grass. So the best way to reduce the weeds is to have a thick, healthy turf that reduces the amount of sunlight that reaches the soil surface.
The most common grassy weed in lawns is crabgrass. There are five or six types of crabgrass that will grow in our area. There is tropical crabgrass, smooth crabgrass, India crabgrass, large crabgrass, southern crabgrass and blanket crabgrass.
Crabgrass will grow in any soil type and under any condition. It is one of the earliest summer weeds to start growing in the spring and will germinate and grow until frost kills it. Crabgrass will start producing seeds in mid-summer and will produce seed until frost. These seeds will lay dormant until the soil temperature at a 4-inch depth reaches 55 degrees. Usually, this is around the first two weeks of March. This past Tuesday, the soil temperature was 56 degrees in Dearing.
The University of Georgia College of Agriculture and Environmental Sciences has weather stations around the state, including two stations close to our area. The first is at Strom Thurmond Dam, and the second is at McCorkle's Nursery in Dearing. The sites can be viewed at www.georgiaweather.net, with current weather conditions and historical weather data.
The other grass that is common is goosegrass, which is an annual grass that grows in areas that see heavy traffic. These heavy traffic areas are usually compacted and will hold moisture. Also, goosegrass likes shallow, frequent irrigation schedules. So, the amount of goosegrass can be reduced with lawn aeration and changing watering practices.
Lawns should be watered deeply and less often. Goosegrass seeds will start germinating when the soil temperature at 4 inches reaches 60 degrees.
Pre-emergent herbicides are one of the best ways to control these grasses. There are a number of products available. Most pre-emergent herbicides available to homeowners come in a granular form that is easy to apply.
For these herbicides to work best, they need to be watered in. The chemicals in them are not activated until water is applied. Read the label for each product for rates and how to use the product. The rate on the label is the amount needed to give good control.
I have heard many times that putting out more herbicides than what is called for on the label will do a better job of controlling the weeds. This is not true. It will not give better results and it could injure the grass. Also, make sure the herbicide gets on the grass and not in flower beds and on hard surfaces such as driveways.
For those planning on reseeding lawns, do not use a pre-emergent herbicide this spring. The herbicide will kill the grass seeds as they germinate.
When looking for a herbicide, look at the chemical name on the label. Many of these herbicides can be found in more than one brand name. Some of the easily found herbicides are pendimethalin, which is found in Scotts Halts; prodiamine, which is found in StaGreen Crabgrass Preventer; dithiopyr, which is found in StaGreen Crabex; benefin plus trifluralin, which can be found in Hi-Yield Crabgrass Preventer and Team; and benefin plus oryzalin, which is found in Green Light Amaze.
These are herbicide-only products. This early in the season, it is not recommend to use a weed-and-feed product because it is too early to fertilize turfgrass.
To apply these products, put on all of the herbicide with one application. However, research at the University of Georgia has shown putting out half of the herbicide now and the other half six to eight weeks later will provide better and longer control of the weeds.
With the soil temperature above 55 degrees, it is not too late to put out pre-emergent herbicide. Normally, we will get more cold weather and frost. The frost should kill any crabgrass or goosegrass that has germinated.
Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at firstname.lastname@example.org.
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