Is Root Rot on Your Radar?

— Written By NC State Extension
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– By Daniel Freund, M.S. student

For those who manage golf course putting greens, Pythium root rot should be on your radar as this disease favors prolonged wet conditions. The causal agents of Pythium root rot are classified as oomycetes that can move and reproduce in the presence of water. Symptomology consists of irregular patterns of orange and yellow hues. Root density and depth is greatly reduced in affected areas, hence the name root rot. Individual plants appear dark and greasy on the crowns, roots, rhizomes and/or stolons. Disease will often be most severe in areas with poor drainage or accumulation of thatch and organic matter. Therefore, it is vital to regularly implement cultural practices such as aerification, vertical mowing, as well as topdressing. Regarding chemical management of Pythium root rot, it is important to time fungicide applications in a preventative manner. When weather forecasts are predicting consecutive days of rainfall, fire up the sprayer and apply appropriate fungicides before the rain. May 15th is a great date to target your first preventative fungicide application. Segway (cyazofamid) is an extremely efficacious product for managing Pythium root rot. Applications at the low rate (0.45 fl oz/1000ft2) over 14-21 day intervals proved as effective as applying the high rate (0.9 fl oz/1000ft2).

Pythium root rot chart image

Pythium root rot developed naturally in July. Disease severity was greatest in the non-treated controls on 28 Aug reaching 18%. Only Segway and Union treatments suppressed Pythium root rot curatively when compared to the non-treated control.

Keep in mind that the annual maximum application amount for Segway cannot be greater than 2.7 fl oz/1000ft2. A new product coming to market this year is Union by PBI Gordon. It is a combination of cyazofamid and azoxystrobin. This fungicide has proven efficacious in field trials and was developed to manage Pythium diseases as well as brown patch, summer patch, and other turf diseases.

In order to get the most out of your fungicide, it is crucial to deliver the active ingredient to the target site in the first few inches of soil where the pathogen can be found. This can be a challenge in turfgrass systems due to the dense foliar canopy and thatch layer. A single application of Segway was applied independently to research plots on a creeping bentgrass putting green. Plots received an irrigation amount of either (1/8”) or (1/4”) applied either immediately (0h) or 6 hours (6h) after the fungicide application. Cup cutter cores were harvested at 0, 1, 5 and 7 days after fungicide treatment and were sectioned into remaining above ground vegetation (RAV; verdure/thatch), 0-1”, 1-2”, and 2-3” subsections. Core subsections were subjected to residue analysis using high-performance liquid chromatography and data was presented as a percent of applied.

applied irrigation chart image

Irrigation applied immediately significantly enhanced cyazofamid movement through the RAV down into the 0-1” region at 0 and 1 days after treatment. Although not statistically significant, irrigating with 1/4” resulted in greater cyazofamid at deeper depths when compared to 1/8” post application irrigation. When applying fungicides targeting root diseases, it is important for practitioners to immediately water-in their chemical application before the fungicide has time to dry and bind onto plant canopy surfaces.

– This post was written by Daniel Freund, an M.S. student advised by Dr. Travis Gannon and Dr. Jim Kerns.

Daniel Freund