Summer Disease Management on Poa annua/Bentgrass Greens with New Fungicide Products

Diseases,

Summary: In replicated field trials conducted on a poa/bentgrass putting green, fungicides were tested for efficacy and phytotoxicity against a variety of summer diseases. Key results include:

• An unseasonably cool summer produced unusual disease patterns, with Rhizoctonia causing the most significant damage to turf, and anthracnose causing only limited damage. Summer patch was observed, but caused insignificant damage to turf.
• Symptoms caused by Rhizoctonia spp. were well controlled by several of the products tested, including BAS 500, BAS 505, Heritage and Eagle. A rotation of Banner (2.0 oz/1000 sq ft) followed by monthly applications of Compass at the high rate (0.4 oz/1000 sq ft) also provided excellent control.
• It is possible that the high application volumes used in the study (3.5 gallons/1000 square feet), in combination with the fact that irrigation immediately followed fungicide applications may have interfered with the activity of Compass, whose mode of action is mesostemic, rather than systemic.
• A rotation of Banner (3 bi-weekly applications in May/June) followed by high rates of Compass (2 monthly applications) performed significantly better against Rhizoctonia than season-long monthly applications of Compass at the same rate. It is likely that early season treatments with Banner helped to decrease the disease inoculum levels, allowing the Compass to perform better later in the season.
• Good control of Rhizoctonia lasted up to 6.5 weeks for BAS 500, BAS 505, Heritage and Eagle.
• Anthracnose, caused by Colletotrichum graminicola was well controlled by almost all of the treatments tested, with the exception of the low rate of BAS 505 (0.15 oz/1000 sq ft).
• No phytotoxicity was observed for the majority of products. However, BAS 505 produced moderate levels of phytotoxicity on most rating dates, with the higher rate (0.25 oz/1000 square feet) producing higher levels of damage than the lower rate (0.15 oz/1000 square feet). The observed damage was primarily to Poa annua. As a result, a gradual increase in bentgrass was observed in plots sprayed with BAS 505, particularly in the plots treated with the high rate. This type of gradual suppression of Poa annua may have commercial value to superintendents attempting to maintain pure bentgrass stands.

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Principal Investigators: Wendy Gelernter, Ph.D. and Larry J. Stowell, Ph.D.

Cooperator: John Martinez, SCGA Member’s Club

Sponsors: BASF, Novartis, Rohm and Haas, Zeneca