Effect of Various Irrigation Amounts on Fungicide Movement and Efficacy.

Soilborne plant pathogens are difficult 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 ways to move fungicides into the root system is through the use of soil surfactants, high spray volumes, and post-application irrigation. The effect of post-application irrigation on the movement of fungicides has not been well characterized. Experiment 1 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^-1) affected myclobutanil movement. In support of the research above, a growth chamber experiment (Experiment 2) was conducted to determine the influence of post-application irrigation amounts on efficacy of propiconazole for summer patch (Magnaporthe poae) of ‘Penn A-4’ creeping bentgrass. In Experiment 1, 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 average significant (>5%) fungicide residues below 5.08 cm were 1.27 and 2.54 cm of irrigation. The most fungicide movement in Experiment 1 was with 2.54 cm of irrigation coupled with the soil surfactant. This combination allowed for up to 5.7% of the myclobutanil to reach a 10.16-12.7 cm depth. The other treatments reached marginally deeper depths in conjunction with a soil surfactant compared to the treatments without the soil surfactant. Experiment 2 resulted in increased turf quality and root length with the 0.635 cm irrigation amount compared to the other three treatments. These data display the importance of post-application irrigation when applying fungicides in turfgrass systems to control soilborne pathogens.