The Homeowners Column

The Homeowners Column

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Water grass. What is it?

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Sandra Mason
State Master Gardener Coordinator
slmason@illinois.edu

You say "water grass". I say "what is it?" Take a poll at a coffee shop and wildly different descriptions for "water grass" will emerge. Numerous grassy weed species are called "water grass". It may not seem like a big deal but proper identification is key to controlling grassy weeds in lawns.

First, the best way to prevent weeds from invading your lawn is through proper lawn care practices which encourage a dense stand of vigorous grass. Weeds get a clear invitation anytime lawns have bare areas due to poor growing conditions or improper management practices.

For example, lawns mowed higher (over 2 inches) tend to have fewer problems with annual grasses such as crabgrass. Closely mowed lawns tend to open, allowing weed invasions. Light, frequent watering also favors crabgrass. It often invades areas seeded in late spring since bare soil, frequent watering, and onset of hot weather is ideal for crabgrass growth. Ideally new lawns should be seeded in fall with April as a second option.

The most common grasses called "water grass" include quackgrass, tall fescue, nimblewill and crabgrass. A grey-green colored grass with white fleshy rhizomes is likely quackgrass. Lucky you, quackgrass is one of the most difficult weeds to control in lawns and flowerbeds. Tall fescue can also appear as a weed in Kentucky bluegrass lawns. It is a clump grass with a wide leaf blade that often grows faster than bluegrass. This weed tall fescue is the pasture type and not the more desirable turf-type tall fescues. Quackgrass and tall fescue are both cool season perennial grasses so they start to green early in spring at the same time as Kentucky bluegrass.

A warm season grassy weed is nimblewill. Its fine-bladed, light green leaves do not green until warm weather, usually in late April to May. Nimblewill is most noticeable as a straw colored patch in green lawns in spring.

Quackgrass, tall fescue and nimblewill are perennials which mean the same plant comes back every year, bringing its family of seedlings or rhizomes with it. There aren't any selective herbicides available to home gardeners to kill these perennial weeds and not kill your desirable grass.

Conventional crabgrass controls will not control these perennial grasses. You have three options with perennial grassy weeds: 1) either thoroughly dig it out; 2) spot treat it with a non-selective herbicide such as glyphosate sold as Round Up™ or Kleen Up™ then after the weed is dead or removed, the area should be reseeded or resodded or 3) live with it and only look at your lawn through your car windshield.

Crabgrass is an annual and must come back every year from seed. Crabgrass germinates when soil temperatures are greater than 55 to 60 degrees F for 7-10 consecutive days, and continues until soils reach 95 degrees F. Other annual grasses germinate later as soils warm. If you see a big clump of grass with long leaf blades in early spring then it is not crabgrass.

If an herbicide is desired to control crabgrass, preemergence herbicides should be applied in our area by mid to late April. Timing of application is very important since preemergence herbicides must be applied before crabgrass germinates.

Do not use preemergence control if you plan on also reseeding the lawn this spring. Only one preemergence herbicide, siduron (Tupersan™) is labeled for application to newly seeded areas. All others have a waiting period. Be sure to read, understand and follow all pesticide label directions.

For more information check out the University of Illinois Extension Lawn Talk website http://extension.illinois.edu/lawntalk/ Or if all else fails just say, "at least it's green".

All about Composting - Join me on Tuesday, April 19 at 7 p.m. as I discuss the ins and outs of composting at UI Extension office at 801 N. Country Fair Drive, Champaign, IL.

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