Dollar Spot Fungus: Identification, Causes and Control

Identifying dollar spot fungus in grass

The name describes the symptom on a putting green: sunken, coin-sized spots of bleached turf. On taller lawn grass the spots are larger and often merge into irregular straw-colored patches that can be mistaken for drought, dog damage or other diseases. Look for these signs.

• Patch size and color. Round to irregular tan or white patches, 1 to 3 inches on golf turf, 2 to 6 inches on lawns.
• Leaf lesions. Tan bands spanning the width of the blade with a distinct reddish-brown border, often pinched into an hourglass shape on wide-bladed grasses. This is the most reliable field diagnostic.
• Mycelium. In morning dew, infected areas show fine, white, cobweb-like growth that disappears as the turf dries. Pythium also produces mycelium, so confirm with the leaf lesions.
• Pattern. A scattered, shotgun pattern rather than one expanding ring, often first in low-fertility areas and along mower tracks.

Pythium is the one to rule out quickly, because it moves fast and kills turf; the pythium blight guide covers how to tell them apart.

What causes dollar spot

Dollar spot is caused by fungi in the genus Clarireedia, formerly Sclerotinia homoeocarpa before a 2018 revision. The fungus survives in thatch and spreads by mycelium growing leaf to leaf and by clippings moved on mowers and shoes. Several conditions favor it, most within the turf manager’s control.

• Low nitrogen. The strongest driver. Nitrogen-deficient turf cannot outgrow leaf infections; dollar spot is often called a disease of hungry turf.
• Extended leaf wetness. The fungus needs water on the leaf for many hours. Lingering dew, evening irrigation, fog and poor air circulation all extend that window.
• Temperature. Strongest with days of about 60 to 85°F and warm, humid nights: spring and fall in the South, early summer through fall in the North.
• Dry soil with a wet canopy. Light, frequent irrigation produces exactly this combination.
• Thatch. A thick thatch layer harbors the fungus and holds moisture at the crown.
• Susceptible cultivars. Bentgrass, annual bluegrass, hybrid bermuda, zoysia, Kentucky bluegrass, fescues and ryegrass are all affected, with wide differences between cultivars.

Dollar spot in bermuda grass

Bermuda grass dollar spot is a particular headache on Southern fields and fairways. Hybrid bermudas such as Tifway 419 are susceptible, and the disease flares in two windows: spring, as the grass greens up low on nitrogen, and fall, as growth slows and nights cool. In peak summer, well-fertilized bermuda usually outgrows it.

On a bermuda field it shows as straw-colored patches a few inches across, worst where turf was scalped in spring or thinned by traffic. Management is mostly about timing nitrogen, with a steady supply through green-up and a late-season feeding, plus a preventive fungicide in the spring and fall windows on high-visibility surfaces.

How bermuda compares with the other warm-season options on disease, shade and wear is covered in the St. Augustine vs zoysia guide.

Controlling dollar spot in a lawn or field

Cultural control does most of the work; fungicides are for high-value turf when pressure exceeds what culture handles.

1. Fertilize adequatelyKeep the turf growing steadily through the dollar spot season. On lawns this often means a light application when symptoms appear; on fields, frequent small feedings.
2. Water deeply and earlyWet the root zone, then wait for early wilt before watering again. Irrigate between about 4 and 8 a.m. so leaves dry with the sun.
3. Remove dewOn fields and greens, dragging a hose or an early mow shortens the wetness period by hours and measurably reduces dollar spot.
4. Manage thatch and airflowKeep thatch under half an inch and prune vegetation that blocks morning sun and air movement.
5. Mow correctlySharp blades, the upper end of the recommended height, and no mowing of wet turf, which spreads mycelium.
6. Choose resistant cultivarsWhen renovating, pick cultivars rated for resistance in your region’s extension trials.
7. Use fungicides when warrantedDMI, SDHI, benzimidazole and dicarboximide classes are effective. Rotate classes, because resistance has developed in heavily treated turf, and follow the label.

Pro tip: if a lawn gets dollar spot in the same spots every year, test the soil there. Low nitrogen, compaction and a high spot that dries first are the usual culprits.

Disease pressure and surface reliability

Dollar spot is manageable, but managing it is ongoing. A grass field in a humid climate needs a nitrogen program, irrigation discipline, dew removal, aeration and often a fungicide rotation to stay ahead of this one disease, and it is one of several the field faces each season. Each task is a point of failure when staff, water or weather does not cooperate.

For most lawns that variability is tolerable. For a field that has to be uniform and playable on a schedule, it is a real reliability problem, and it is part of why heavily used facilities consider synthetic surfaces for their most important fields. If disease and dormancy are making a field unreliable, it is worth talking with experienced crews about professional turf installation and what a well-built synthetic surface would mean for that site.