Washington State University Extension

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written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA

One of the most common lawn problems brought into our local WSU Extension Master Gardener Plant Clinic is creeping bentgrass. Lawn owners note that patches of this grass seem to die or turn brown in the middle of summer but then come back again in the fall. The owners also note that when they pull on patches of the grass, it comes up much like a carpet or a loose piece of sod. We like to see samples of the grass to confirm its identification, but the offending grass is usually creeping bentgrass.

Creeping bentgrass is a low-growing, perennial cool-season grass that spreads out horizontally via above ground stems (stolons). These stolons can root where ever they touch the ground, resulting in circular patches of grass that stick out like sore thumbs in the typical Kentucky bluegrass lawn. That’s because the bentgrass has a finer texture and a blue green color that makes the spots obvious, especially when the bentgrass goes dormant and brown during the heat of summer. Walking on large areas of creeping bentgrass feels like you’re walking on a soft carpet. That’s no doubt why another common name for creeping bentgrass is ‘carpet bentgrass.’

Creeping bentgrass is an invasive grass that often shows up in older lawns, especially ones that are watered and fertilized heavily and mowed too short. You might wonder how creeping bentgrass first invades a lawn. Bentgrass can get started via seed in irrigation water or even as a contaminant in the original lawn grass seed. Because creeping bentgrass also reproduces via pieces of the stolons, it can be spread by mowers and other lawn equipment used on bentgrass infested lawns.

When it comes to control of bentgrass Jenny Glass, WSU Plant Diagnostician, notes that ‘there are no “magic bullet” herbicides available for removing one unwanted grass species from the desired types without hurting the wanted turf.’ Because creeping bentgrass has very shallow roots, one approach is to cut small patches out of the lawn using a spading shovel, digging down one to two inches to remove the both the grass and roots. The resulting hole is filled with clean soil and reseeded with grass that matches the rest of the lawn. However, one is seldom able to remove all pieces of bentgrass with digging and it will eventually return in that spot.

The other alternative is treating the bentgrass patches with glyphosate. Glyphosate, the active ingredient in Roundup and other non-selective grass herbicides, kills perennial grasses including the desirable lawn grass. When trying to kill a patch of creeping bentgrass in a lawn with a glyphosate product, the patch as well as an area six inches beyond the patch should be treated. The effective time for treatment is when the grass is green and actively growing in spring or fall, not when it’s brown and dormant in mid-summer. Once the grass in the treated area is dead, rake it out and reseed the spot.

If a creeping bentgrass infestation involves large areas of lawn, not just a few patches, you will need to renovate the entire lawn by killing all the grass and starting over… or you may decide to just live with it.

As with many yard and garden problems, your best defense against a bentgrass infestation is keeping the lawn in a healthy condition with deep, infrequent irrigation, proper fertilization, and mowing the lawn regularly at a height of 2.5 inches.

Need help with a lawn or garden problem? Call the WSU Extension Master Gardener Plant Clinic at 736-2726 Monday through Friday from 9 to 12 and 1 to 4. You can also stop by their table at the Pasco Farmer’s Market on Saturday mornings.

Published: 5/11/2012 2:19 PM


written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

This year, one of the major problems I’ve seen in area lawns is creeping bentgrass (Agrostis palustris). We’ve talked about this weed before, but as a refresher… bentgrass is a grass that’s desirable only on golf course greens and fairways. It’s considered a weedy problem when it shows up in area home lawns. Creeping bentgrass is undesirable because it develops excessive thatch and it’s very prone to winter disease problems. It also tends to turn brown when stressed by drought and heat during the hot summer months.

As you might guess, the name “creeping” is also what makes creeping bentgrass a problem. Once it shows up in a lawn it spreads by stolons and takes over. It has a tendency to lie down and form light green puffy patches when mowed at regular mowing heights.

Creeping bentgrass is a common problem, especially in older lawns. However, because it’s green and has a fine texture, many homeowners don’t notice that they have a bentgrass problem until it turns brown and dies due to excessive thatch or drought. The brown patches are easily pulled up.

You can’t really “manage” or “control” a creeping bentgrass invasion. There are no herbicides that can be applied that will kill out the bentgrass and leave the good lawn grasses. You have three choices… you can learn to live with the bentgrass, you can renovate your lawn, or you can start all over again “from the ground up”.

Renovation involves correcting lawn problems without removing all of the sod and starting over. When creeping bentgrass has extensively invaded a lawn, total renovation is a viable option that can be taken to restore a lawn to attractiveness. Renovation is also a potential solution when other weedy grasses, such as Bermuda grass, have taken over your lawn.

The first step in renovation is getting rid of the “bad” perennial weedy grasses in the lawn.. This includes coarse grasses (such as velvetgrass, tall fescue, orchardgrass, or non-turf-type perennial ryegrasses) and creeping perennial grasses (such as bentgrass and Bermuda grass). To get rid of these grasses all lawn vegetation is killed with the application of glyphosate (a.k.a. Roundup). Apply the glyphosate in mid-spring or late summer. With the persistent creeping perennial grasses, like creeping bentgrass, it will probably take more than one application to kill all their rhizomes. If you don’t take the time to completely destroy these hard-to-kill grasses, your renovation may look good initially… but it will quickly become reinfested.

After you’re sure you’ve killed the offending weedy grasses in your lawn, you have a choice of removing the dead sod and starting all over again including tilling the soil… or you can follow steps 1–6 for total renovation suggested by the WSU Extension turfgrass specialists .

1. Adjust the mower to approximately 3/4 inch and mow the lawn thoroughly.

2. Power rake the lawn as many times as may be necessary to remove accumulated thatch. It’s best to de-thatch in opposite directions. Thoroughness is important.
3. When all thatch has been removed, mow the turf again at approximately 3/4 inch high.

4. Over-seed the lawn at seeding rates recommended for new lawns. One pound of available nitrogen per 1,000 square feet from complete starter fertilizers applied following seeding will hasten establishment. If the soil is extremely sandy, two applications of 1/2 pound each per 1,000 square feet should be made instead of the one 1-pound application to avoid the possibility of leaching and nutrient loss.

5. If you have some high and low spots in the lawn you may want to even them out. Before overseeding, remove the sod in and adjust these areas to the proper lawn grade for a uniformly smooth surface.

6. Provide adequate irrigation. It’s important to maintain surface moisture for germination of the newly applied seed and then to maintain a moderately moist soil for the growth of the new grass.

The WSU specialists note that ninety percent of turfgrass renovations are not successful as far as changing turfgrass species… due to the fact the areas are usually sprayed once, overseeded, and expected to be totally converted to a new species. When not done properly, the site will look good to begin with, but will eventually return to the conditions existing before renovation.

If your lawn looks terrible and needs the drastic step of total renovation or the even more severe action of starting over, be sure that you’ve killed out those pesky perennial grasses. I have only seen successful renovation achieved by killing out the entire lawn at this time of year (late summer), waiting, and then retreating any weed growth that appears again the next year after the weather warms up. Only after you’re sure that the grasses that ruined your lawn are dead and gone, should you proceed. Otherwise, why go to all that trouble and hard work?

Heads Up Lawn Care Notes: Fall is the most important time to fertilize your lawn. Fertilize now in early September and again in late October or early November.

If you’re planting grass seed at this time of year to fill in some bare spots or even starting a new lawn, you should get the grass up and growing well before severe frost and cold weather settles into the region. So, plant grass seed by the middle of September. Take note that you will need to water for about six weeks to keep the soil moist for the germinating seed and young grass plants. Will you have water available for that long?

Published: 9/11/2004 2:17 PM


written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

After a very long stretch of hot weather, weedy grasses and a few other problems are sticking out like… sore thumbs in many local home lawns. Here are some first aid tips for two of those lawn “injuries.”

Creeping Bentgrass: Creeping bentgrass grass forms dense puffy patches in home lawns. At this time of year those patches turn brownish. That’s because creeping bentgrass is a cool season grass that’s native to parts of Europe and Asia. It grows best in areas with cool, humid summers. During midsummer in our area, it tends to turn brown with heat and drought stress.

If soft puffy brown patches in your lawn aren’t enough to make you consider creeping bentgrass undesirable, both it’s different texture and color make it stick out “like a sore thumb.” Before it turns brown in summer heat, it’s a very soft, fine–textured grass with a blue-green color. It has vigorous shallow roots and spreads by means of creeping above-ground stems (called stolons). In our region of Washington, it forms very dense patches and forces out the desirable turfgrasses planted in a lawn. Lawn owners often note that these patches are like a carpet that can be lifted and peeled back.

Creeping bentgrass is not a recommended turfgrass in eastern Washington. It’s considered a weed. It may be a weed in our lawns, but creeping bentgrass is intentionally planted on golf course putting greens throughout the United States. That’s because it forms a dense smooth turf, especially when mowed at very low heights of less than one-half inch. It creates a great surface for putting. However, when invading home lawns that are mowed at much higher heights, bentgrass very quickly develops dense patches and excessive thatch.

A bandage and a little attention won’t take care of a creeping bentgrass problem. There is no selective herbicide that can be applied to the lawn that will kill the bentgrass and not harm the desirable turf. It takes an intensive, long term approach. First the offending grass must be killed by treating the patches with glyphosate (the active ingredient in Roundup and other similar products). The grass in the patches should be green and actively growing when treated.

Once totally dead after treatment with glyphosate, the bentgrass should be removed and the spot raked to loosen the soil. Then new seed or sod can be planted at the appropriate time of year. Pick grass seed or sod that matches the surrounding turfgrass.

Crabgrass: It isn’t until this time of year that crabgrass becomes very obvious in home lawns. These bright green wide-leaved grasses lay down almost flat in a mowed lawn. If you have it in your lawn, you probably just started noticing it during the last few weeks. That’s because it’s a warm season annual grass that grows most vigorously during the heat of summer. This is in contrast to cool season perennial turfgrasses that slow to a stop during hot weather. Crabgrass is also starting to flower and produce prolific many-fingered seedheads.

At this time of year there aren’t any practical ways of curing a crabgrass sore thumb, short of pulling out individual plants. It’s too late to apply post-emergent herbicides that would have killed it a couple of months ago. However, you can take some steps to try to avoid crabgrass next year. The most important step is to create a dense healthy turf. Crabgrass takes advantage of weak, thin open turf. By watering, fertilizing, and mowing your lawn correctly, you will go a long way in preventing a crabgrass infestation next year.

Crucial at this time of year is fertilization. During the cooler fall months, cool-season turfgrasses grow sideways. Fertilize your lawn in early September and again in early November. This stimulates sidewards growth and improves turf density. A dense turf shades out crabgrass and prevents it growth. Other sound turf care practices, such as watering correctly and mowing the grass at a height of two to two and one-half inches, contribute to turf density and help prevent crabgrass too.

If your crabgrass infestation is severe, you’ll want to take these steps to improve your lawn density, but you’ll also want to apply a pre-emergent herbicide next spring to prevent this year’s seeds from germinating and growing next year.

Next time, we’ll talk about intervention for a few other lawn injuries.

Published: 8/18/2007 2:13 PM



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