Post-Application Irrigation: Critical for Root Disease Control

— Written By NC State Extension
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Many soilborne pathogens infect the crowns, stolons, rhizomes, and roots of turfgrass plants often causing detrimental outbreaks of disease. A few examples of common crown/root diseases include Pythium root rot, summer patch, take-all root rot and spring dead spot. Proper cultural practices such as topdressing, aerification, and the use of fans to maintain airflow are great methods to reduce disease; however, fungicide applications are also commonly needed to supplement cultural practices in order to provide acceptable disease control. Most fungicides have a high affinity for soils and organic matter (i.e. thatch layer), so they are bound easily making movement to the crown and roots of a turfgrass plant (where soilborne pathogens often infect) difficult.

Fungicide Properties

fungicide properties table

Koc (above) is a measure of the tendency of a chemical to bind to soils, corrected for soil organic carbon content. For comparison, the herbicide paraquat has a Koc of 15,473-51,856 (V. High) and the herbicide dicamba (salt) has a Koc of 2.00 (V. Low). Most of these listed fungicides fall into the Moderate-V.High Koc range.

There are many ways to mitigate this issue: use wetting agents and applying irrigation after application of the fungicide. These methods are helpful because they increase the likelihood of the fungicide to reach the target site of the crown or roots where the pathogen is located. Below is data demonstrating the positive effect of post-application irrigation after applications of propiconazole for summer patch control in creeping bentgrass:

turf quality bar chart

root length bar chart

Irrigation Amount

irrigation amount impact on roots

It is apparent that post-application irrigation is beneficial when controlling soilborne pathogens. So, how does post-application irrigation, as well as the addition of a wetting agent, affect fungicide movement? It helps push the fungicide further down the plant canopy and through the soil column to the target site of the pathogen.

bar chart

bar chart

From these data, as well as feedback from various turfgrass managers, it is evident that inclusion of a wetting agent and post-application irrigation increases the effectiveness of fungicides when applied to control soilborne pathogens.

Wendell Hutchens

This article was written by Wendell Hutchens. He is a masters student in the Department of Entomology & Plant Pathology at NC State University under the direction of Dr. Jim Kerns and Dr. Travis Gannon.