Campbell Vaughn: Weed control may seem beyond control

Weeds, weeds and more weeds. Spring has sprung and so has a bumper crop of weeds in our landscape. I teach classes on weed control and even I have them in abundance.

 

What caused this tsunami of weeds? Let’s just call it the perfect storm. Warm weather mixed with adequate moisture and a lack of freezing weather would be the biggest factors.

Cool-season weeds like dandelions, henbit and the dreaded annual bluegrass (Poa annua) germinate in the fall, survive the winter and actively grow in the spring. Since we didn’t have winter this year, these cool-weather weeds are loving life.

What can we do to help? I would first suggest going back in time and putting out a pre-emergence. Early October would have been the best time to apply, making sure it got watered in within a few days. Since time machines aren’t readily available, let’s focus on the weeds that are there now.

Weeds can indicate soil, site and cultural practices that need to be changed. For example, ground ivy is often found in shady areas where shade-intolerant turfgrass has begun to thin out and decline. Bluegrass thrives under adverse growing conditions such as wet or shady areas, compacted soil or in turf that receives close, frequent mowing. Many weeds, such as broadleaf plantain, prostrate knotweed and prostrate spurge, will readily grow in compacted soil where turfgrass will not grow. Spurge will adapt to droughty soils. Nutsedge prefers wet soils. Chickweed and crabgrass are commonly found in lawns that are mowed too short.

Soil fertility can also affect the types of weeds in your lawn. Plantain, lespedeza, clover and common speedwell are found in lawns grown with infrequent applications of nitrogen fertilizer. Annual bluegrass and chickweed are found in lawns with high levels of nitrogen. The presence of Red sorrel can be an indication of acidic, infertile soil. There are so many things to consider.

First thing to do is get your soil right. The pH needs to be correct. Do a soil sample and then add lime as needed. Don’t water grass during the winter. We overwater in Augusta something terrible. The grass is mostly dormant so it doesn’t need water. Fertilize at the proper time — DO NOT fertilize turf until late April. Mow at the proper height, especially if you have weeds now. It will keep these weeds from heading out and therefore reproducing.

If your soil is super compact, plan to aerate after these warm-season grasses are completely green. The exception to the rule on core aeration is not to do it to St. Augustine and Centipede grasses, which tend to get too beat up. Top-dress with good organic material. White play sand isn’t good organic material because it doesn’t hold moisture or nutrients. If the dirt is fine-textured and black-looking, then it probably has good organic material.

Now that the things to do and not to do are established, let’s focus on removing the weeds that are there now. Most of what we’re seeing now are broadleaf weeds. If you can’t hand-pull them, there are numerous selective postemergent herbicides available. A selective herbicide can be sprayed over a range of plants and it will kill only what it is labeled to kill. In other words, it kills the weeds and not the grass.

Postemergence herbicides are applied directly to visible weeds, those that have emerged and are actively growing at the time of treatment. Herbicides are not sold as pure chemicals but formulated with solvents, emulsifiers and other additives to improve the storage life, application ease and handling characteristics of the active ingredient. Lawn herbicides are available in easy-to-mix liquid formulations, dry formulas that dissolve in water, wettable powders that don’t dissolve but mix well in water and granules that can be broadcast with a drop or rotary spreader.

Which ones work best? It depends on the lawn. The biggest thing to know for weed control is what type of grass you have. Many products that work great on weeds in Bermuda and Zoysia grasses can’t be used on Centipede and St Augustine turf, so always read the label.

My quick and easy go-to postemergence herbicides for St Augustine and Centipede is atrazine. Atrazine works well on most broadleaf weed and even kills bluegrass. Another good thing about atrazine is that it can act as a preemergence as well. Atrazine is sold as Image with Atrazine for St Augustine and Centipede or Hi-Yield Atrazine.

On Bermuda and Zoysia grasses, try using a three-way product of 2,4-D + MCPP + dicamba. This broadleaf weed control is found in products like Bayer Advanced Southern Lawn Weed Killer, Fertilome Weed Out, Spectrum Lawn Weed Killer and Spectracide Weed Stop. Make sure to follow the label on any of these products. With the weeds as prevalent as they are now, multiple applications may be necessary.

Reach Campbell Vaughn, the agriculture and natural resources cooperative extension agent for Richmond County, at augusta@uga.edu.

 

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