Grey Leaf Spot
Caused by: Pyricularia grisea
The symptoms of grey leaf spot vary depending on the grass cultivar. On St. Augustinegrass, grey leaf spot first appears as small, brown spots on the leaves and stems. The spots quickly enlarge to approximately 0.5 cm in length and become bluish-grey in colour and oval or elongated in shape. The mature lesions are tan to grey in colour and have depressed centers with irregular margins that are purple to brown in colour. On Perennial Ryegrass and tall Fescue, symptoms first appear as small, water-soaked lesions that turn brown. Lesions may have a yellow halo. The leaf tips will have a twisted or fishhook shape.
Conditions favouring Disease
Grey Leaf Spot favours temperatures between 26°C to 32°C. It is also found in areas with high nitrogen levels and that are stressed by various factors,
including drought and soil compaction. This disease is most severe during extended hot and humid periods.
Integrated Turf Management
Avoid medium to high nitrogen levels during mid-Summer.
Irrigate turf deeply and as infrequently as possible to avoid water stress.
Allow water to remain on leaves for only a short period of time.
Reduce thatch by vertical cutting.
When possible, plant turfgrass that is resistant to grey leaf spot.
Avoid using herbicides or plant growth regulators when the disease is active.
Apply penetrant fungicides on a preventive basis.
Heritage has a label recommendation for Grey Leaf Spot in South Africa.