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Pythium spp. cause many diseases of turfgrass roots and/or foliage including Pythium blight, root dysfunction, and damping-off. Cool-season grasses are most commonly damaged by pythium blight in hot, humid conditions including high night time temperatures with high humidity and in poorly drained areas. Potassium phosphite (KH₂PO₃) is an alkaline salt of phosphonic acid and has been shown in previous research trials to suppress pythium blight and improve plant health by upregulating plant defense mechanisms including antioxidants and phytoalexins. This study was conducted in Virginia Beach, VA on a two year old stand of ‘Southern Belle Overseeding Blend’ perennial ryegrass. Treatments were applied on 7 Jul and reapplied every 14 days through 2 Sept. The objective of this study was to evaluate the effectiveness of phosphite-based products in alleviating summer heat stress and control of pythium blight on a perennial ryegrass fairway and applied preventatively. Pythium blight severity was very low due to environmental conditions. At the end of July, significant differences in quality were observed with Heritage TL and PK Plus (6 fl. oz./M) being greater than the untreated control. The % pythium infection data was not meaningful because of mixed disease infection at the site of Pythium and Rhizoctonia zeae. The results suggest a confounding effect of another pathogen, Rhizocotonia zeae which limits the meaningfulness of this study. The low disease severity from the Heritage TL treatments, the performance of the standard Pythium fungicides, and isolation of samples from the diseased area leads to the conclusion that this was a mixed infection of Pythium and Rhizoctonia zeae. Clearys 3336 Plus (thiophanate methyl) is not effective at controlling R. zeae whereas the Heritage TL (azoxystrobin) would, confirming the possibility of a mixed infection.

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Pythium_HamptonRoadsHorvath2008.pdf		63 Kb