Light colored spots taking over lawn

Asked March 25, 2017, 9:31 PM EDT

I replanted my front lawn almost 2 years ago with rye grass and since then it has developed sections of lighter colored grass that seem to be spreading, is this a type of "weed" or what. Is there anything I can do to stop/reverse this? Any information is much appreciated. Thank you, Gary

Multnomah County Oregon lawns and turf

1 Response

Hello Gary,

It looks like Rough bluegrass from your photos. The reality of growing lawns in the Pacific Northwest is that it is impossible to grow a clean stand of perennial ryegrass for any length of time because the soil seed bank contains many other grasses.

The most common contaminants are annual bluegrass, which flowers aggressively in the spring (you probably have some of this grass as well), bentgrass, Rough bluegrass, and velvet grass (Holcus lanatus).

The first couple of years the contaminants look the worst because they are light colored spots in an otherwise dark lawn. Over time, the lighter patches coalesce and the lawn looks better, albeit not as dark.

If you want a high quality lawn, the key is to focus on regular mowing (1 1/2 - 2") with a sharp blade, regular fertilizing (May, June, early September, and November) and consistent watering in the summer. In April and May, you may have to mow two times per week because the grass can grow so fast. It is also helpful to return clippings. Edging your lawn really adds that manicured look as well.

There are chemicals available (some require licensed pesticide applicators) but they require repeated applications every year and they are still only marginally effective.

Just to put it in perspective, every golf course in the Pacific Northwest has converted to annual bluegrass (and other grasses) in spite of the fact that they were planted with perennial ryegrass and bentgrass. And most of them spent a lot of time and money trying to stop the conversion.

Be patient, it will look better over time.