Another Day, Another Dollar (Spot)
Dollar spot is one of the most common turfgrass diseases and is particularly problematic on close-mown turf. On golf courses in the United States, more money is spent managing dollar spot than any other turfgrass disease.
The fungal pathogen that causes dollar spot is called Sclerotinia homoeocarpa. It only infects the leaf blades, so infected turf can recover, but healing can take a considerable amount of time. The disease creates a sunken area of turf that can range in size from a quarter to a silver dollar-sized patch — thus, the name dollar spot.
The dollar spot pathogen is ever-prevalent in nature and naturally exists in organic material such as thatch. It begins to grow and infect susceptible grasses in the spring when nighttime air temperatures exceed 50℉. The disease becomes symptomatic once daytime air temperatures reach the 60-90℉ range. It also requires extended periods of leaf wetness, primarily in the form of dew, to become symptomatic. Under these conditions, a heavy, white, cottony, mycelium is visible on infected lesions in early mornings. Disease activity lessens once daytime high air temperatures consistently exceed 90℉.
Sunken patches on putting greens are unacceptable because they affect ball roll, so it’s especially important to control dollar spot on greens. Fairways, tees, and rough areas are also susceptible, but control on these areas isn’t as critical with regard to playability. Most of the time, breakout of the disease in these areas is more of an aesthetic problem. If left unchecked, though, it can create a problem with sunken turf and therefore ball lie.
Dollar spot incidence is more prevalent on nitrogen-deficient or underfed turf, so turf of this nature is slower to recover from its damage. Consider the following methods for dollar spot control:
- Plant dollar spot-resistant cultivars.
- Maintain adequate fertility, specifically Nitrogen.
- Irrigate between midnight and 6 a.m. to minimize leaf wetness.
- Remove leaf wetness in the mornings via mowing, dragging, or whipping turf areas.
- Control thatch with regular verticutting and core aerification in conjunction with frequent topdressing.
- Implement an aggressive preventative fungicide program. Begin in early spring and maintain the applications on a regimented basis through fall. Be sure to rotate chemistries to avoid the development of resistant varieties.