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Archive for Thursday, August 4, 2005

Pesky yellow nutsedge invades dormant lawns

August 4, 2005

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The stifling heat of summer has slowed the growth of our lush, green lawns. However, weed growth has kicked into overdrive.

Yellow nutsedge is a perennial "grassy" weed that has taken off and has invaded flowerbeds and lawns alike. Although it looks like a grass, it is really a sedge, a group of plants that have triangular stems and very different growth habits. Here are some tips to help keep you from going nuts when it comes to controlling this obnoxious weed:

As the name implies, yellow nutsedge is pale green to yellow in color. In the spring and early summer it grows rapidly, often sticking up above the rest of the lawn only a few days after mowing. Nutsedge grows best in moist soils that have poor drainage, but it also can be introduced into better soil conditions through contaminated topsoil or nursery stock.

The main difference between grassy weeds and nutsedge is the stem. Nutsedge leaves grow in bundles of three and grow out in three different directions, giving rise to a triangular stem. Grassy weed leaves grow two at a time and form a round stem. Likewise, nutsedge leaves bend at the midrib to form a long "V." Grassy weed leaves are usually more flat than V-shaped.

And unlike grassy weeds, hand weeding can actually increase a yellow nutsedge problem. Nutsedge produces numerous wheat kernel-sized tubers or nutlets underground, each of which can produce a new plant. Pulling a nutsedge up simply activates these dormant tubers, creating a bigger patch of weeds. For this kind of control to work, gardeners have to be watchful and persistent enough to pull up each new plant before it has time to produce yet more tubers.

The best method of control is herbicides. The safest and most effective nutsedge control is Manage. However, it is also the most costly and difficult to find. Manage is labeled for use on all Kansas turfs except buffalo grass and is available to homeowners in small packages. If an infestation is not too severe, one application should do the job.

More commonly available is a chemical called MSMA (monosodium acid methanearsonate). It is the least expensive and is the least effective. It can be found under such generic names as "crabgrass killer" or "nutsedge killer." (Check the ingredient list for MSMA.) This chemical can require repeat applications, 10 to 14 days apart, and may temporarily discolor lawn turf.

Also available is Basagran with the active ingredient bentazon. It is more effective and more expensive than MSMA, but less effective and less costly than Manage. This liquid also can require repeat applications and may temporarily discolor the lawn.

For long-term control, change the environmental conditions. Pay attention to watering practices. Overwatering can lead to nutsedge outbreaks. Likewise, as with many weeds, nutsedge is less competitive in a dense, healthy lawn than in poorer, thinner turf. In flower beds, add organic matter to increase soil drainage and add a healthy 3-inch layer of mulch to conserve moisture and keep weeds to a minimum.

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