Fungus in Lawns mostly occur when humidity is high. Generally they are not common in residential lawns. Fine leafed lawns which are mown low and have high nutrition demands to combat the low mowing, such as bowling greens, are the most susceptible. Occasionally, however, they will show up in domestic situations if the conditions are favourable. Below are two of the most common in Perth.
Dollar Spot (Leaf Disease)
Dollar spot is small straw coloured roundish patches, about the size of a dollar coin in turf that is mowed tightly, however the patches can be as big as 15cm in turf that is mowed higher. Dollar Spot can be identified by a web like substance (mycelium) that shows up in the early morning dew.
You see it most often from Spring through to Autumn, when temps are higher, but there is still moisture in the mornings (humidity).
Dollar Spot often occurs in a lawn that is low in nitrogen and potassium, or a lawn that has a lot of thatch build up. It is most common in couch type lawns that are prone to developing a thatch layer. Vertimowing (Dethatching) will help remove this thatch layer. This is recommended yearly for this type of lawn and you can find a reputable contractor on the LMCA website (Lawn Mowing Contractors Assoc). You should also mow your lawn at around 10mm and preferably with a cylinder type mower such as contractors use. This will help to control thatch build up and keep the leaf short, helping to eliminate the conditions that are preferable for fungus to thrive.
Watering in the evenings can cause excess moisture to sit in the thatch layer overnight, so in a lawn prone to fungus, watering in the mornings is recommended, especially in humid conditions.
To kill of the fungus, apply a fertiliser which has a fairly high nitrogen content. This should be done every 6 to 8 weeks all year round. Fertiliser in Perth should be applied regularly and lightly, due to our sandy soils. Cut back any trees that might be giving your turf too much shade and water in the mornings. If necessary vertimow your lawn you can apply a fungicide such as Mancozeb +. Try not to walk on the affected area and wash your mower after use. Contractors or licensed herbicide sprayers can use products such as Bayfidan and Rovral GT.
Spring Dead Spot (Root Disease)
The first symptoms of Spring Dead Spot show up in Spring and are circular, bleached dead patches. The patches can also be visible in Autumn and Winter. They can be a few cm to over 1 metre in diameter and can reappear in the same spot for a number of years. The leaf dies off, however it is actually the roots that are attacked.
It is most common in intensely managed couch grass. This pathogen prefers cool temperatures and moist soil. It takes control when the soil temps are lower and the grass is dormant. This is why it shows up after the winter in spring, when the fungus restricts the growth of the turf coming back from dormancy and the turf is darker in colour. Low cut playing fields such as bowling greens and tees are the most effected as they are generally weaker with less leaf growth.
Spring Dead Spot does not like the hotter weather, so the turf can compete with it and the spots will become less active.
The management practices are the same as for Spring Dead Spot, except cease the application of Nitrogen 6 weeks prior to dormancy (mid April – May), however the fungicide is best applied in February March. Products recommended for a licensed Professional are Chipco GT.