Managing Anthracnose on Golf Course Putting Greens (End)

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Air circulation. The final management practice that will reduce anthracnose severity is maintaining adequate air movement throughout the putting green. Many golf courses throughout the Southeast with creeping bentgrass putting greens have installed fans at each green that run throughout the peak environmental stress periods. Continual air movement over the surface of the turf will maintain transpiration rates and reduce leaf wetness periods that lead to fungal infection. If fans are cost prohibitive, selective pruning of trees or shrubs adjacent to green surrounds will increase natural air movement. The mentioned management practices may reduce anthracnose severity, but fungicide applications must be incorporated with these practices to obtain the best control of anthracnose.

Fungicide applications. There are eight chemical classes of fungicides labeled for anthracnose control – benzimidazoles, dicarboximides, demethylation inhibitors (DMIs), nitriles, phenylpyrroles, phosphonates, polyoxins and QoIs (Murphy et al., 2008). Only three of these classes have been effective when applied alone at curative rates (benzimidazoles, DMIs and QoIs); therefore, it is imperative to initiate a preventive fungicide program for anthracnose control in April or May, depending on environmental conditions. On putting greens that exhibit annual anthracnose symptoms, these preventive fungicide applications are imperative.

As mentioned, the arsenal of fungicides capable of managing anthracnose is limited. Additionally, research over the past six years has illustrated reduced sensitivity of C. cereale to some of these fungicides, indicating that some C. cereale isolates are resistant to fungicides. Fungicide resistance to the benzimidazole, DMI and QoI class of fungicides has been identified in C. cereale populations of annual bluegrass putting greens from around the United States. A recent study completed at Mississippi State University evaluated C. cereale isolates collected from creeping bentgrass putting greens throughout Mississippi and Alabama. Approximately 90 C. cereale isolates were collected over a two-year period, and 100 percent of these isolates exhibited fungicide resistance to both azoxystrobin (QoI) and thiophanatemethyl (benzimidazole). These two fungicides have different modes of action, but small adjustments in C. cereale’s genetic makeup confirmed that these isolates were resistant to the fungicides. The results from this study were similar to other studies that identified fungicide resistance in C. cereale and other fungal pathogens studied in various parts of the United States. Anecdotal evidence of azoxystrobin resistance was obtained in a fungicide trial performed on a creeping bentgrass putting green in Arkansas (Milus et al., 2002). Fortunately, all is not lost, but this information illustrates the importance of implementing a preventive fungicide program since the chemistries identified as resistant are the three listed as curative fungicides for anthracnose.

The eight fungicide classes listed contain fungicides consisting of various topical modes of action (i.e., contacts and penetrants) that may be applied to prevent C. cereale infection. The contacts (7 to 10 days) give a shorter span of protection compared to penetrant (14 to 28 days) fungicides because they do not enter the plant. This preventive program should include a rotation of various topical and biochemical modes of action, taking care not to use fungicides within the same class in consecutive applications. In the case that environmental conditions favor fungal infection, tank-mixing may increase the efficacy of the fungicide application. Tank-mixes of fosetyl-Al + chlorothalonil, fosetyl-Al + mancozeb and propiconazole + chlorothalonil applied on 14-day intervals have resulted in good control in fungicide trials (Vincelli and Powell, 2009). Fosetyl-Al applied alone or tank-mixed has exhibited good to excellent control in many studies. It has been hypothesized that the fungicide may actually increase the health of the plant rather than affecting the fungus in a negative way, which would be a positive attribute in managing C. cereale since it infects stressed tissue. Benzimidazole, DMI and QoI fungicides should be included in the rotation, but areas concerned about potential fungicide resistance issues should tank-mix these fungicides with contact fungicides. This application would control sensitive isolates and manage resistant isolates with the contact fungicide until the subsequent application.

Table 1. Efficacy of fungicides for the control of Anthracnose diseases of turf. Adapted from Tredway et al. (2009) and Vincelli and Powell (2009).

There are cultivars of creeping bentgrass that exhibit better heat tolerance than others; therefore, they may not be affected by C. cereale as much as standard cultivars with less heat tolerance. A five year, multi-state study is currently being performed to evaluate fungicide applications and management practices to better manage anthracnose. This project also includes work being done by turfgrass breeders and geneticists to try and develop cultivars exhibiting  resistance to C. cereale infection. Keep an eye out for  further research and new cultivars that may reduce  anthracnose severity on your golf course.

Summary

  • To this point, a combination of management practices and fungicide applications is the only means to manage anthracnose.
  • Reduce turf stress by syringing, hydrojecting, promoting air circulation and raising the mowing height during summer months.
  • Skip light topdressings, aerification, deep vertical mowing (> 0.2 inch, ≥ 5 mm) and use of groomers on mowers when the summer heat stress period has begun.
  • Cultivate and fertilize turf in the spring and the fall to improve putting green health.
  • Increase summer putting green fertilization to ≥ 0.1 lb N/1,000 ft2/week to reduce anthracnose.
  • Alternate fungicide chemistries since benzimidazole, DMI and QoI fungicides are prone to resistance development among C. cereale.
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