Fungi are the main cause of infectious diseases in turf grasses. These are small microscopic organisms, ranging from 0.5um to 100um in diameter, that lack chlorophyll, are non-green plants that do not produce true seeds and whose bodies lack true roots, stems and leaves.
The body of a fungus is a very simple structure. It is either made up of a single cell or a series of cells (multi cellular) arranged linearly into tube-like strands. These individual strands or filaments are known as hyphae. These hyphae have well developed walls, cytoplasm, nuclei and reproductive systems, which is typical of plant cells. They contain their genetic material inside the nucleus. The hyphae of most fungi are divided into cells by cross walls (referred to as septae). Some species of fungi, such as members of the genus PYTHIUM and PHYTOPHTHORA do not have septae and these are referred to as non-septate. A mass often develops and this is known as mycelium.
Fungal Diseases
Mycelium
Mycelium is a cottony or spider-web-like mass of fungal growth that certain fungi produce when the turf is wet or humidity is high.
Spore Masses
Mycelium is a cottony or spider-web-like mass of fungal growth that certain fungi produce when the turf is wet or humidity is high.
Sporophores
Sporophores are enclosed structures that contain fungal spores. These are often seen as small, dark specks on the diseased tissue.
Sclerotia are small, round, hard structures produced on the diseased turf or in the thatch layer by certain fungi. Sclerotia are actually survival structures that some fungi use to survive through periods of unfavourable weather conditions. Most people are familiar with mushrooms, which are the large spore-producing structures produced above-ground by Basidiomycete fungi.
Some turf grass pathogens, most notably the fairy ring fungi, produce mushrooms as a sign of their presence.
Algae
Although algae do not infect turf grasses, the blue-green algae are a significant pest problem in the turf grass industry. These organisms contain chlorophyll just like plants, but they grow by producing chains of thread-like cells similar to fungi.
Picture shows Algae (Cyanobacteria)
Algae may develop whenever thinning of the turf canopy permits sufficient air, light, and water to reach the thatch surface. Algal growth is most aggressive during the late spring, summer, and early winter when warm, humid conditions are conducive to algae growth and turf thinning. Low mowing heights, shady conditions, poor soil drainage, and frequent irrigation also encourage algal growth in the turf canopy.
Once Algae is present, the surface area must immediately be disturbed and aerated. Jik may then be sprayed onto the area at 100mm per 10l water.
When dry crust is formed this must be removed.
Dollar Spot
Symptoms
Small, circular spots 20 mm to 70 mm in diameter develop over several days on turf. The grass in the spots may be killed on the soil surface and the spots become depressed if the disease continues to develop.
Lesions on leaves are light tan and often have a dark margin at the edge when the disease is spreading.
Picture shows Mycilium for Dollar Spot (Sclerotinia homoeocarpa)
Control
Ensure that the grass is cut grass low. Adequate nitrogen fertilization and soil moisture levels will help prevent the development of Dollar Spot.
Removal of dew as early as possible will help reduce the risk of the disease developing.
Picture shows spots on green
Fairy Rings
Symptoms
Fairy rings may appear as small to large rings of very green grass, dead grass, mushrooms or puffballs with little effect on the grass or as combinations of these symptoms. The soil in the rings may become very dry and is difficult to wet during the summer and fall. Symptoms in a particular fairy ring may change throughout the year. Mushrooms or puffballs are present in the late summer and winter. These fruiting bodies may never appear, or may appear only in certain years.
Picture shows Fairy Ring – (Marasmius sp, Lepiota sp, Psalliota sp.)
Control
The removal of excess thatch and the use of management practices such as regular grooming and brushing to prevent excess thatch accumulation will help prevent fairy rings from developing in established turf.
Regular irrigation to keep the soil moist should also prevent the development or severe damage from fairy rings.
Brown Patch – Red Thread Disease
This disease occurs during spring and autumn on slow growing and nitrogen deficient turf.
Circular or irregularly shaped, small to large patches (5 – 50 cm in diameter of infected grass become water-soaked and dies rapidly. The tan colour of dead leaves may be the first symptom observed.
When the air is saturated with moisture, pink to pale red fungal growths, called red threads, may extend up to 10 mm beyond the end of the leaf tip. Pink cottony flocks of mycelium up to 10 mm in diameter may also be produced.
Control
Maintain adequate and balanced fertility, based on soil test results. Applications of nitrogen are particularly helpful in reducing disease severity, but excessive rates must be avoided.
Brown Patch – Pythium Blight
Pythium blight first appears as small, sunken, circular patches up to 300 mm in diameter during hot, humid weather.
Leaves within the patches are matted, orange or dark gray in colour, and greasy in appearance.
Gray, cottony mycelium may be seen in the infected areas when the leaves are wet or humidity is high.
The disease spreads rapidly along drainage patterns and can be tracked by equipment. This disease can spread rapidly and cause severe damage to a green very quickly when conditions are favourable for development.
Control
Avoid over-fertilization with nitrogen. Use slow release forms of nitrogen when possible.