Fall Seeding and K. Blue/P. Rye Mixtures

Technically the summer season lasts until September 21, but in the turf industry Labor Day weekend signifies the beginning of fall. Most turf managers welcome the fall season as grass has an opportunity to recover with the cooler air temperatures, reduced disease pressure, and increased rainfall that accompanies this time of year. The cooler soil temperatures also make the fall months an ideal time to sow seed. Soil temperatures across the state of Iowa can be viewed at: http://extension.agron.iastate.edu/NPKnowledge/soiltemphistory.html

Perennial ryegrass is often included in seed mixtures with Kentucky bluegrass because of its rapid germination. However, perennial ryegrass is much more susceptible to diseases compared to Kentucky bluegrass and monocultures of perennial ryegrass can be difficult to manage. A question that often arises this time of year involves Kentucky bluegrass/perennial ryegrass seed mixtures and how much of each species should be in the original mixture if Kentucky bluegrass is the desired species.

The University of Wisconsin and Purdue University recently conducted studies specifically designed to answer these questions. The researchers at Wisconsin used 6 seed mixtures with varying amounts of Kentucky bluegrass and perennial ryegrass (Table 1). Two years after establishing their plots, they found that a 95:5 Kentucky bluegrass:perennial ryegrass (by weight) mixture was needed in order to obtain greater than 70% Kentucky bluegrass in the stand. Seed mixtures that contained as little as 15% perennial ryegrass by weight resulted in stands of turf that were approximately 50:50 Kentucky bluegrass:perennial ryegrass. The entire report from the Wisconsin study can be viewed at: http://www.hort.wisc.edu/uwturf/pdf/athfdmix.pdf.

Purdue University is currently conducting a comparable study and thus far has found similar results (Table 2). Seed mixtures with no more than 10% perennial ryegrass (by weight) are needed to obtain turf stands primarily composed of Kentucky bluegrass. The Purdue study is also investigating the effect of seed mixture ratios and the occurrence of weeds. The results indicate that including a higher percentage of perennial ryegrass in the original seed mixture results in fewer weeds. A brief description of the Purdue trial can be viewed at: http://www.agry/purdue.edu/turf/tips/2009/08102009_grassmix.html.

The findings from each of these studies indicate that when trying to maximize the amount of Kentucky bluegrass in the final turf stand no more than 5 to 10% perennial ryegrass should be included in the original seed mixture.

Marcus Jones
Graduate Research Assistant