MAJOR LAWN DISEASES Diseases are often difficult to diagnose, since different infections can appear together. Some diseases can establish themselves even before seeds and seedlings sprout (pre-emergent diseases), leading to the development of an uneven, patchy lawn. Damage due to post-emergent diseases can manifest in the form of yellowing, followed by complete disintegration of the infected plants. Fineleaved species of Festuca and Agrostis are most severely affected. The pre- and post-emergent diseases are caused by a number of fungi, particularly Fusarium and Pythium. Typhula incarnata Grey snow mould SYMPTOMS Dying off of plants in spring after snow cover melts; pale pink mycelium. The hard, round, pinhead-size sclerotia of the fungus can be found on pallid leaves close to the ground. Damp and temperatures of +6°C are optimal conditions for the spread of the fungus. Lolium is especially prone; Festuca rubra is less endangered. TREATMENT Balanced fertilising; sanding, aeration after the snow melts in spring. Drechslera spp. (Helminthosporium) Leaf blight SYMPTOMS Small brown, oval spots can be seen first on the leaves, later on the leaf sheaths; the centres of the spots later turn white. This can affect Poa pratensis in particular at low temperatures and high humidity levels. Other Poa species can sometimes also be susceptible. TREATMENT Preventively sow resistant varieties. Treatment by chemical means not currently possible. Marasmius – Fairy rings The fungus spreads out in a circle from a single point under the grass. In advanced stages, a ring-shaped dead zone develops, which is marked on both sides by particularly strongly growing grass. The dead zones are caused by a mycelium that prevents the grass roots from absorbing water. The decomposition of organic substances in the soil releases nitrogen that promotes growth on either side of the dead zone. Fairy rings appear particularly in light, sandy, rather infertile soils. TREATMENT Balanced fertilising as well as intensive aeration of the soil can go some way to combating the fairy ring. Soil replacement can also help. Sclerotinia homoeocarpa Dollar spot SYMPTOMS Individual yellowish spots of 10 to 15 mm in diameter that can grow to 50 mm, become yellow-brown and may have a fine, white mycelium between the leaf sheaths. Agrostis and Festuca on fine lawns are particularly susceptible. Warm, damp weather promotes spread. TREATMENT Good soil aeration; drainage, removal of thatching; avoiding nitrogen fertilising in late autumn. Optimal conditions and good-quality seed prevents germination diseases. Microdochium nivale (Gerlachia, Fusarium) Snow mould SYMPTOMS Starting as early as autumn, but mainly after snow cover has melted, plants are beset with white-grey or reddish mycelium coating; small, round patches in the lawn, which under favourable conditions can grow to 300 mm in diameter and merge with each other. Susceptible are mainly Lolium perenne, Agrostis and Poa on sports fields and golfing greens. TREATMENT Strengthening the grass plants with lime, which reinforces the cell walls; no nitrogen fertiliser too late in the autumn; avoid standing wetness; scarify and aerate; avoid stressing the grass in winter. Preventive chemical treatments possible on fine ornamental lawns and hard-wearing grass in areas prone to snow mould. 67 SERVICE
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