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Effect of post-application irrigation and the usage of soil surfactants on fungicide movement and efficacy

Wendell Hutchens: North Carolina State University

<div>Soilborne plant pathogens are challenging to control in turfgrass systems due to the low solubility of many fungicides and their high affinity to bind to organic matter. The most effective approach to deliver fungicides into the root system is through the use of soil surfactants, high application volumes, and post-application irrigation. The effect of post-application irrigation on fungicide movement in soil has not been well characterized. A laboratory experiment was conducted to determine how various post-application irrigation amounts (0, 0.3175, 0.635, 1.27, and 2.54 cm) both with and without the use of the soil surfactant polyoxyalkylene polymers (25.47 L ha<sup>-1</sup>) affect movement of the fungicide myclobutanil. A growth chamber experiment was also conducted to determine the influence of post-application irrigation amounts on efficacy of propiconazole for managing summer patch disease of ‘Penn A-4’ creeping bentgrass caused by <em>Magnaporthe poae</em>. In the laboratory experiment, regardless of irrigation treatment, at least 76.5% of the recovered fungicide remained in the top 5.08 cm of soil when applied without a soil surfactant. The only treatments to have significant (>5%) fungicide residues below 5.08 cm were 1.27 and 2.54 cm of irrigation. Post-application irrigation of 2.54 cm coupled with the soil surfactant resulted in the greatest fungicide movement. In the growth chamber experiment, post-application irrigation with 0.635 cm of water resulted in increased turf quality and root length compared to the other three treatments. These data support the importance of post-application irrigation when applying fungicides in turfgrass systems to control soilborne pathogens.</div>