Rough bluegrass (Poa trivialis L.) is a yellowish-green grass with soft leaf blades which are glossy beneath and have a narrow boat-shaped tip. It spreads by stolons and forms dense, thick patches. The leaf blades are upright at first, but tend to lay down and mat as the patches become older. Because the root system is shallow, the patches are easily pulled up in tufts or clumps.
Rough bluegrass is capable of forming a reasonable turf under certain limited environmental conditions and careful management. It is fine-textured turfgrass developing a high shoot density under cool, moist conditions. It is capable of withstanding a considerable amount of shade if sufficient moisture is present. It is one of the most winter hardy turfgrasses with very good low temperature tolerance. The major weaknesses of rough bluegrass include poor wear, drought and high temperature tolerance. In home lawns in Southern Ontario, it is considered to be one of the top three most serious grassy weeds. It is sometimes included in a seed mixture with Kentucky bluegrass because of its shade tolerance. However, due to its tendency to produce bright yellow-green patches, it does not blend well with Kentucky bluegrass (Figure 1). It responds vigorously to fertilizer and irrigation, and under conditions where water is supplied too frequently, it becomes intolerably aggressive and smothers out the Kentucky bluegrass. During July and August patches of rough bluegrass wilt and brown-out markedly unless careful attention is paid to its water requirements (Figure 2).
Figure 1. A management program providing too much fertilizer and water promoted the infestation of the Kentucky bluegrass lawn by the bright yellow-green, aggressive rough bluegrass.
Figure 2. Rough bluegrass turns brown under high summer temperatures.
Figure 3. The rake tines catch the horizontal stolons of the Rough bluegrass and pull them out with limited disturbance to the Kentucky bluegrass.
Since rough bluegrass has limited use as a turfgrass only a limited number of improved cultivars have been developed which are more tolerant of high temperature stress and turf diseases and have an improved dark green colour. Refer to OMAFRA Publication 384, Turfgrass Management Recommendations for information on available cultivars. Rough bluegrass is not recommended for home lawn use. However, it competes well in cool moist areas where cutting heights are as low as 1 to 2 cm. It grows well in wet meadows, and particularly well in light-shaded areas which are moist, such as under weeping willows, along stream banks, and in other moist or poorly-drained areas that are not subject to drought. While recommended for wet shade situations, it seldom provides a good lawn if the area is dry.
Where rough bluegrass has invaded a Kentucky bluegrass home lawn, it is usually desirable to remove it from the sward. The following practices have provided some control:
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