Dollar spot solutions

Overview

The problem

Dollar spot, caused by Sclerotinia homoeocarpa, is a widespread and very destructive turfgrass disease that can be observed throughout the year in Australia. Dollar spot is known to attack most turfgrass species including wintergrass, bentgrasses, fescues, Kentucky bluegrass, perennial ryegrass, zoysia, couch and buffalo.

What to look for

Dollar spot is favoured by air temperatures ranging from 16 to 32°C (optimum 21–27°C) with extended periods of high humidity (>85 per cent at night). The disease tends to be most severe under the following conditions: warm days, cool nights, infrequent rain but long dew periods, daily ground fogs that extend leaf wetness periods, and low nitrogen fertility. When the fungus is active and leaf surfaces remain wet, a fine, white, cobwebby mycelium covers the infection centres or diseased patches during early morning hours.

Symptoms of dollar spot can vary based on the turfgrass species and height of cut. Under close mowing heights, as with intensively maintained bentgrass or wintergrass, the disease appears as small circular straw-coloured spots of blighted turf about the size of a 50 cent coin. On coarser textured turf maintained under higher mowing practices, such as Kentucky bluegrass or perennial ryegrass, the blighted areas are considerably larger, straw-coloured patches 7.5–15 cm in diameter.

Affected patches frequently coalesce and involve large areas of turf. Grass blades generally die back from the tip with distinct hourglass-shaped lesions that are straw-coloured or bleached white. Hourglass bands may not appear on warm-season grasses.

The solution

Implementing proper cultural practices is crucial to reducing disease severity. Management tactics include: maintaining adequate nitrogen when dollar spot is active, making light frequent nitrogen applications, avoiding drought stress, limiting irrigation towards dusk, removing dew by mowing, poling or rolling, aerifying to reduce compaction and thatch, and removing trees or adding fans to increase air circulation.

Fungicides are also important to manage dollar spot. Since dollar spot is a foliar disease, select spray nozzles and spray volumes that provide good coverage to maximise fungicide activity. Bayfidan and Dedicate are ideal for early season dollar spot control. Routine fungicide applications are commonly needed when air temperatures are 21–32°C; Chipco GT and Interface®Stressgard are especially helpful in hot weather since they are non-DMIs and can be used without risk of negative plant growth effects. Extended periods of temperatures above 32°C may significantly slow dollar spot development.

Dollar spot resistance to certain classes of fungicides can be significant. Preventive applications and rotating fungicide classes, including the use of multi-site fungicides, is important for reducing the risk of resistance. Non-DMIs like Chipco GT and Interface Stressgard will control DMI-resistant dollar spot.

Technical Information

(L and C) Symptoms of dollar spot on a creeping bentgrass and a wintergrass green. (R) Active mycelial growth on Kentucky bluegrass.
Photos: Dr Derek Settle and Dr Rob Golembiewski, Bayer CropScience. Mr Dan Dinelli, North Shore Country Club.

SOLUTION1 RATE
APPLICATION INTERVAL
Dedicate® 3 L/ha 14–21 days for curative control
21–28 days for preventative control
Chipco® GT 10 L/ha 14 days for curative control
Monthly for preventative control
Interface® Stressgard 12.5 L/ha 14 days for curative control
Monthly for preventative control
Bayfidan®
3–6L/ha Low rate on a monthly program for preventative control
High rate as required for curative control
Reserve® Stressgard
130–200 mL/100m2
in 20–60 L water
 

1. Always read and follow label instructions carefully.

Research data

2011, 2004 Bayer research, Jyri Kaapro