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How to manage the threat of rapid blight and anthracnose on Poa annua putting greens

By Dean Mosdell, Ph.D., technical services manager, Syngenta

Rapid blight (Labyrinthula terestris) is a turfgrass disease that can affect Poa annua, Poa trivialis and perennial ryegrass species. Although its origin is unknown, it most closely resembles a pathogen of marine grasses. This explains why disease severity is correlated with saline irrigation water and soil salinity. Cultural practices, such as salinity management and using tolerant species in winter overseeding, are important for rapid blight management.

A limited number of fungicides effectively suppress rapid blight’s severity. Fungicides in the QoI class and mancozeb were once the only options for superintendents. Although resistance has not been detected, continuous applications of a single mode of action fungicide can cause a shift in pathogen sensitivity, not only in Labyrinthula, but in other pathogens, like anthracnose present in the thatch/soil during application. Managers of Poa annua greens in California need to implement a preventive fungicide program to not only control rapid blight, but other key diseases such as anthracnose and summer patch.

Anthracnose (Colletotrichum cereale) is the one of the most destructive diseases of Poa annua putting greens across the country. Anthracnose is most severe on stressed turf, but can be found on greens from the spring through the fall. A preventive fungicide program, combined with cultural practices, can help manage severity of anthracnose.

Velista® fungicide is a systemic fungicide in the SDHI (FRAC code 7) class with a label and 2(ee) additions in various states that include rapid blight and other turf diseases, like anthracnose, summer patch and fairy ring. In combination or rotation with Secure® Action™ fungicide, a multi-site contact fungicide, this strategy controls several turf diseases for a robust greens fungicide program, and also includes Daconil® Action™ and Appear® II fungicide to support a resistance management strategy.

In a University of California, Riverside trial, Velista and Secure were applied to a Poa annua putting green with a history of rapid blight and anthracnose incidence. Applications were made on a 14-day interval from June-September and ratings for presence of disease and turf quality were recorded. Velista and a tank mixture of Velista and Secure showed outstanding rapid blight and anthracnose control in September and early October. Secure applied alone effectively suppressed these diseases (see graph below). The image below compares the Velista treated plot versus the untreated at the trial’s conclusion in 2014. 

California, 2014-2015.​​​​​​​ Rapid blight and anthracnose trial. Plots were aerified to encourage rapid blight.

California, 2014-2015. Fungicides applied on 14-day intervals starting in early summer. % disease rated 7 and 14 days after last application.

A greenhouse trial at Clemson University in 2015 shows the benefits of tank-mixing Secure with Velista or Heritage® fungicide (or with Heritage® Action™ fungicide) for control of rapid blight on perennial ryegrass. For added convenience, Multipaks containing combinations of different Syngenta products can be viewed at GreenCastOnline.com.

To learn how to prevent rapid blight and other key turf diseases as part of an agronomic program, visit www.GreenCastOnline.com/Programs

All photos are either the property of Syngenta or are used with permission.

©2020 Syngenta. Important: Always read and follow label instructions. Some products may not be registered for sale or use in all states or counties and/or may have state-specific use requirements. Please check with your local extension service to ensure registration and proper use. Action™, Appear®, Daconil®, GreenCast®, Heritage®, Velista® and the Syngenta logo are trademarks of a Syngenta Group Company. Secure® is a trademark of Ishihara Sangyo Kaisha, LTD. All other trademarks are property of their respective owners.