Advice from the Help Desk of the
UC Master Gardeners Program of Contra Costa

Client:  This weed is growing in my lawn. Could you please tell me what it is and how do I eradicate and/or prevent it?

MGCC Help Desk:  Thank you for bringing the weed sample from your lawn for identification and recommendations on its elimination and control.

We have been able to identify this sample as Annual Bluegrass (Poa annua), a very common lawn weed in coastal areas of California. This annual weed looks similar to regular lawn grass for a short while. It also looks a little like Kentucky bluegrass, except it has a lighter shade of green, shallower roots, and develops a short seed head early in the season. It dies off when the weather gets hot, leaving big empty patches in your lawn

Annual bluegrass loves damp, shady areas. You can reduce favorable conditions for this weed by watering deeply and infrequently. The weed's shallow roots will not be able to reach down to where the moisture is. Annual Bluegrass will also invade lawns where the soil has become compacted. You can reduce lawn compaction by aerating during non-sprouting periods. This will allow water to settle deeper in the soil away from the shallow-rooted weeds.

Annual Bluegrass Leaf Tip

Annual Bluegrass typically grows in dense, low clumps, 3 to 12 inches (8–30 cm) tall. To reduce its ability to survive in your lawn, mow your grass high, preferably between 3-4 inches to shade out the weed. Lawns with taller grass tend to have fewer Annual Bluegrass problems. Mowing high will also reduce the opportunity for flowering. Annual bluegrass reproduces by seed and can have many generations in a single season if left to flower and set seed.

For more information on this weed and its control, please see the UC Davis publication, How to Manage Pests in Gardens and Landscapes - Annual Bluegrass at http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7464.html.

Please let us know if you have any additional questions

Help Desk of the UC Master Gardener Program of Contra Costa County (VLT)

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Note: The  UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions.  Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA  94523. We can also be reached via telephone:  (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog  (http://ucanr.edu/blogs/CCMGBlog/). 

Help for the Home Gardener from the CCMG Help Desk

Client has a problem with "brown spots" in the lawn:

The lawn in question is in Orinda and is 1000 sq ft. The lawn has brown patches which pull up without the roots attached. After contacting a lawn care company, the client was sent lawn care information assuming that the problem was white grubs.  The client would like help sorting out the problem.

CCMG Help Desk's Response:
We took a quick look at the materials that you received from the lawn care/pest control company. They are good resources, but don't really answer your primary question as to the source of the problems you are experiencing. We concur that you need to do more investigation to confirm a diagnosis rather than just assuming that the cause is white grubs.

Here is a link to a UC website that discusses the management of Masked Chafer Beetles and White Larval Grubs: http://www.ipm.ucdavis.edu/TOOLS/TURF/PESTS/inchaf.html. As you'll see when you visit the website, UC recommends that you dig around the roots of the turf in a damaged area in late fall through spring to look for the grubs. The website has good photos of what you are looking for. If you do locate the grubs, one of UC's recommendations for managing the problem is to apply beneficial nematodes.

This UC website describes the life cycle of the masked chafer beetle/white grubs: http://www.ipm.ucdavis.edu/TOOLS/TURF/PESTS/inchaflife.html As you'll see on the site, according to UC, the adults emerge from the ground and lay eggs in late spring and early summer. With this timing, the white grub larvae would be emerging during the summer months. UC recommends that for white grubs, nematodes should be applied in the late summer or early fall when more mature larvae are present and active. A second application about 2 weeks after the first will enhance control.

If you do not locate any white grubs, you may want to investigate further to see if other lawn insects are present. This UC website has information about how you can investigate to determine if other lawn insects are present: 
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7476.html. In particular, take a look at Table 2 which tells you whether you should use a drench test or dig in the area looking for signs of the insects. If you click on the blue highlighted names of the insects, you'll link to sites which have photos of what you are looking for.

If you decide to do a drench test, here's UC's website telling you how to do the test: http://www.ipm.ucdavis.edu/TOOLS/TURF/PESTS/indrench.hrml. We did some quick research and learned that the amount of dish soap that you use for the drench test should not harm the turf. 

If you locate and identify other types of lawn insects, you can again consult the UC Pest Note websites for guidance on managing them. In some cases, beneficial nematodes can be used. However, as you may have noticed on the UC webpage discussing nematodes, for most lawn pests (other that the white grubs), nematodes are most effective when applied in late spring and early summer. The UC Pest Note also discusses other pesticides that can be used to manage lawn pests if the timing is not suitable for using nematodes.

Finally, even with this information in hand, if you believe conducting these types of diagnoses isn't your forte, you could use this information to hire a consultant and/or pest control/lawn care company. CCMG can't make recommendations, but there are numerous sources in the telephone book and/or on the web. UC also provides some guidance in this area as well in the Pest Note “Hiring a Pest Control Company” (http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74125.html)


CCMG Help Desk

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Editor's Note: The Contra Costa Master Gardener Help Desk is available year-round to answer your gardening questions.  Except for a few holidays, we're open every week, Monday through Thursday from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA  94523. 

We can also be reached via telephone:  (925) 646-6586, email: ccmg@ucanr.edu, and we are on the web at http://ccmg.ucanr.edu/