TURF PLAGUES

You've read the headlines: “Gray leaf spot runs rampant over perennial ryegrass;” “Dead spot puts a strangle hold on bentgrass;” “Rough bluegrass, annual bluegrass and perennial ryegrass hit by Chytrid.”

So where did these diseases come from? I remember the days when no one had heard of summer patch, anthracnose, yellow tuft and spring dead spot. Does this mean that these diseases just suddenly appeared? Or had they been around plaguing turf without anybody knowing it? Are there diseases affecting turf right now that we diagnose as something else? I posed these questions to a couple of noted turfgrass pathologists and this is what they told me:

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DR. ERIC NELSON, CORNELL UNIVERSITY

“Actually both scenarios may apply. In some cases, the diseases may have been occurring in turf for a long time but hadn't reached the severity that would sound an alarm. There are many minor problems that we see on turfgrasses all the time that never warrant diagnosis or a control measure. In other cases, the disease may never have been a problem because the grass genotype used in the past was not susceptible, or perhaps the fungicides used at the time never provided the appropriate selection for the pathogen. The grasses, fungicides and stresses we have on turf today are quite different from those a number of years ago. As we introduce new germplasm, management chemicals and practices, new things pop up.”

DR. PETER DERNOEDEN, UNIVERSITY OF MARYLAND

“Most new diseases/pathogens have been around and did not express themselves for imperfectly understood reasons. Summer patch, anthracnose and other diseases did not express themselves until management practices became more intense. In the case of summer patch, improved KBG cultivars turned out to be more susceptible than the common types. GLS probably first developed in annual and perennial ryegrass forages in the Deep South. This was reported in the early 1970s. It just took time for the pathogen to move north, build inoculum and find good eating in the predominately perennial ryegrass fairways of the Mid-Atlantic. I suppose something similar is happening with the Chytrid. Dead spot, however, may have been introduced. It is likely that most pathogens always have been here and something in the growing environment changed to give them a more competitive opportunity.”

Nature has a way of balancing things. As with the Dutch boy who tries to plug the holes in the dike — sometimes plugging holes creates new holes. The more we improve turfgrasses and management practices, the more new problems we see. Guess that's what keeps us all in business. With the disease season lying just ahead, this issue focuses on combating plant diseases.

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