One of the worst weed problems during the summer is crabgrass. It can be bad any year, but it's worse when we have a rainy spring like we had this year.

Crabgrass is in the genus Digitaria, and there are six species. Three are generally the problem weeds, and they include large crabgrass, southern crabgrass, and smooth or small crabgrass. All crabgrasses have similar growth habits and flowering structures, but species are separated by the minor differences in the flower structures and leaf pubescence.

There are several characteristics that make crabgrass unwanted. First, all crabgrasses are annuals, which gives them a chance to thrive and invade when turf grass dies back in fall and winter.

In the flower garden, the ungainly texture of crabgrass doesn't fit into the landscape theme, and in the vegetable garden, its quick-growing characteristics allow it to out-compete desirable vegetables, causing considerable yield reductions.

Crabgrass basically germinates the entire growing season. It is one of the first weeds to germinate in the spring (or even late winter), when the soil temperature gets to 55 degrees.

It's also a prolific seed producer. One plant can produce 150,000 seeds in a season.

As with most plants, there are a few redeeming characteristics, even in crabgrass. Apparently, the seeds can be toasted and ground for flour, used to make porridge and fermented to make beer.

Prevention is the best answer to crabgrass. Pre-emergent herbicides such as benefin (Balan, Crabgrass Preventer), pendimethalin (Halts), atrazine, dithiopyr (Dimension, Turf & Ornamental Weed and Grass Stopper), trifluralin (Preen, Treflan) and oryzalin (Surflan) applied in late winter or early spring prevent crabgrass seeds from germinating..

Several years ago, many new herbicides, such as clethodim (Envoy), sethoxydim (Poast, Vantage, Post Emergence Grass Killer), fenoxaprop (Acclaim Extra), and fluazifop (Fusilade, Over the Top, Green Light Bermudagrass Killer, etc.) came on the market, providing better postemergence control of crabgrass. Envoy, Acclaim Extra and Fusilade are packaged for landscapers while the rest are available to homeowners.

If you have a Bermuda or zoysia lawn, the best herbicides for postemergence crabgrass control are MSMA or CAMA. They also work on bahiagrass. You cannot use these two herbicides on centipede or St. Augustine.

In a centipede lawn, the best herbicide is sethoxydim. This can be used only on centipede. It also works well in controlling bahiagrass.

If you have St. Augustine, you are pretty much out of luck when it comes to post-emergent control. You can try atrazine or Image, but you can expect poor results. The only thing to hope for that your St. Augustine can out-compete the crabgrass.

Pre-emergence control is vital to a St. Augustine lawn. Of course you can always pull it up by hand, but if there is a lot it, that is not very practical.

For existing crabgrass control in ornamental and flower beds, you can use sethoxydim, or fluazifop. You can spray right over the top of the flowers and it won't hurt them. As a matter of fact, you can kill almost any unwanted grass in your flowers without hurting them.

In established ornamental plantings, mulches alone or in combination with landscape fabrics can provide an excellent control for crabgrass and other annual weeds.

Sid Mullis is the director of the University of Georgia Extension Service Office for Richmond County. Call him at (706) 821-2349, or send e-mail to smullis@uga.edu.