Bacterial Wilt of Annual Bluegrass
Bacterial diseases of turfgrasses appear occasionally on golf greens. Turf is predisposed to bacterial disease by various stresses including intensive mowing and grooming, heat and/or drought stress, and high traffic. The increased incidence of the disease in recent years is associated with intensive management practices to increase green speed such as ultra-low mowing heights, low nitrogen fertility, and aggressive grooming practices. Outbreaks are typically seen on only the most intensively managed turf, often shortly after preparation for summer tournaments.
Research in the past decade has revealed that Xanthomonas translucens pv. poae causes bacterial wilt in Poa annua, while Acidovorax avenae subsp. avenae causes etiolation and decline in Agrostis. Symptoms of bacterial disease are similar in both Poa and Agrostis. The disease tends to develop first in places where turf stress is highest, such as pocketed or shaded areas, high or low areas, periphery or clean-up areas, and wherever drainage is impeded. Symptoms first appear as small, yellow spots. Thinning of turf occurs, especially in high traffic areas. Etiolation (elongation and yellowing of foliage) is a notable symptom. Wilt, yellowing, collapse, and death may occur. Turf decline occurs when daytime temperatures reach the mid-80s and humidity is high. The putting surface may become speckled with numerous pits and, in severe cases spots will coalesce, creating a general blight. Bacterial streaming from infected leaves is observed under the microscope. Other diseases may occur simultaneously.
The bacteria are spread by moving water and by mowers which create wounds and allow bacteria entry into the plants. Contaminated mowers can spread bacteria to uninfected greens. Seed transmission is not suspected.
- Mowing turf only when it is dry may slow the progression of the disease.
- Increase mowing height and reduce mowing frequency to every other day.
- If possible, when the disease is limited to one or a few greens, a dedicated mower (preferably light-weight, walk behind mower with solid rollers) for these greens should be used to prevent disease spread.
- Grooming, aerification, and topdressing should be avoided when the disease is active.
- Provide adequate nutrients. Avoid ammonium sulfate fertilizers, which are associated with increased etiolation.
- Use fans to alleviate heat stress.
- Redirect foot traffic away from affected areas as much as possible.
There are no bactericides labeled for the management of this disease. Studies have shown that application of plant growth regulators (PGRs) may alleviate or exacerbate symptoms: effects are highly variable and dependent on several factors including host, active ingredient, concentration, and environmental conditions.