During spring green-up, lawns may reveal many variations in color, growth rate, and leaf width. This variation can be due to some of the following reasons:
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Species and cultivars: Perennial ryegrass is always the first of the desired cool-season grasses to green-up, followed by tall fescue and eventually Kentucky bluegrass (Fig. 1). Even within a species, different cultivars may green-up faster or have inherently darker green color. Recommendation: wait a few days to weks for everything to green up normally.
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Weed species:
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Warm-season grasses in cool-season grasses are the most obvious brown to tan turf in otherwise green turf. Zoysiagrass creates fairly dense patches (Fig. 2), while nimblewill creates very thin patches (Fig 3). Recommendation: Little can be done short of multiple glyphosate applications to control zoysia, and encouraging it to spread may be the best idea. Nimblewill can be controlled with glyphosate for homeowners, but professionals may be able to obtain Syngenta’s Tenacity for experimentation this year or buy it for sure by next year (see the earlier Turf Tip at http://www.agry.purdue.edu/turf/tips/2009/03202009_tenacity.html)
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Annual and rough bluegrass are light green whereas more desired turf species, such as Kentucky bluegrass, are darker green (Fig. 4). Creeping bentgrass is more bluish green (Fig. 5) than the desired Kentucky bluegrass, perennial ryegrass, or tall fescue. Annual and roughstalk bluegrass green-up in early spring, while Kentucky bluegrass is slower to green-up. Recommendation: Nothing can be done until summer or fall. Annual bluegrass can be controlled with summer drought followed by preemergence applied before Labor Day. Rough bluegrass can be control by two to three applications of Certainty, though perennial ryegrass may be damaged slightly by Certainty. Multiple glyphosate applications or Tenacity will control creeping bentgrass.
- ‘Kentucky 31’ tall fescue, orchard grass, or winter annuals like downy brome will have wide leaf blades, a lighter color, and grow much faster than the rest of the lawn (Fig 5). Recommendation: Frequent mowing will help mask the differential growth rate. Tall fescue can be dug out, controlled selectively with Corsair or Certainty, or controlled non-selectively with one application of glyphosate. Orchardgrass can be dug out or controlled non-selectively with one application of glyphosate. Downy brome can be dug out, controlled non-selectively with one application of glyphosate, or allowed to die naturally with the summer heat.
Identification of all of the mentioned grasses is difficult for even the seasoned professionals. More identification help is available at our turfgrass identification web page at: http://www.agry.purdue.edu/turf/tool/index.html
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