TurfMD: The rise of fungicide- resistant bluegrass
Early spring is like Christmas time in lawn and landscape stores across the country. Strolling through these stores, you’ll see a plethora of products designed to give you that green dense lawn or a new landscape. The products are brightly packaged and displayed to target and attract buyers. The essential products used in lawn care like fertilizers, insecticides, herbicides and combinations of these products are prominently displayed on the shelves and in bags organized across the floor.
Walking between the organized stacks of products is like walking through a maze; a different product at each turn.
Increasingly encroaching through these stacks and on the shelves are lawn disease products. Although not considered a major treatment or application like fertilizers, herbicides or insecticides, fungicides are gaining prominence.
Disease control is not part of the vast majority of lawn care programs. It has been an extra treatment at a premium cost for the most part. A significant advancement in Kentucky bluegrass lawn maintenance was the development of melting-out- or leaf spot-resistant cultivars in 1947.
That first Kentucky bluegrass cultivar was known as ‘Merion’. It was selected from Merion Golf Club in Ardmore, Pa., in the mid-1930s from a small patch just off the 17th tee, by the golf course superintendent at the time, Joe Valentine.
Merion led to the classification of improved Kentucky bluegrass cultivars. These improved cultivars were resistant to the springtime disease melting-out or leaf spot (caused by the pathogens Bipolaris and Drechslera spp.) Cultivars susceptible to these diseases fell into the ‘common’ Kentucky bluegrass cultivars. Examples of common cultivars were ‘Park’ and ‘Kenblue.’
Since then, the Kentucky bluegrass cultivars have been further categorized, but the two major categories have improved and become standard. With improved cultivars, the need for controlling leaf spotting with fungicides was limited.
With leaf spot being the major disease and controlled through resistant cultivars, the remaining diseases were considered minor problems. Minor diseases were controlled through cultural practices like mowing, fertilization and irrigation. Additionally, making a fungicide treatment for a lawn disease was prohibitively costly at the time; for the most part, fungicides just a decade or more ago were branded or on patent. This meant that for the end user or homeowner, these products were costly and, for the most part, needed to be applied by a trained or licensed pro.
In the last 20 years or so, we have seen an increase in what used to be considered minor diseases besides melting-out and leaf spot infecting lawns. Diseases like dollar spot, red thread and brown patch are becoming more common lawn problems.
A number of fungicides have come off patent in the last decade or two and are produced as generics. This has resulted in reduced price and availability for the active ingredient.
When I was walking through the lawn and landscape store, I was struck by the number of different products described as providing control to a broad spectrum of diseases. Under the banner of broad spectrum or systemic control of diseases was a range of active ingredients in the various products. The fungicides ranged from thiophanate-methyl in one product to propiconazole in a second and, finally, azoxystrobin in the last.
Of the fungicides mentioned, the benzimidazoles (ex, thiophanate-methyl) and QoIs (azoxystrobin) are considered the highest risk to develop resistance due to single-gene resistance mechanisms, with demethylation inhibitors like propiconazole less likely for rapid resistance development when used repeatedly.
It strikes me that as fungicides become widely available for use for the general population, resistance will become an issue, affecting some of these fungicides through potential indiscriminate use.
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<p>The post TurfMD: The rise of fungicide- resistant bluegrass first appeared on Golfdom.</p>