Lawns look like pretty simple things; but they are far more complex than you might think. A lot occurs on below the surface; and the plants that make up a lawn can be subjected to attack from a huge range of different pests and diseases; which can cause more problems than are obvious.
Often by the time turf disease infections are noticed; it can be too late for a simple, quick solution.
If you want to optimise the quality of your turf, and minimize the effort required to control problems; it is important to learn more about what can go wrong; so you are more likely to notice problems before they develop too far.
Here are some examples of turf diseases that can arise:
Damping Off
This refers to several different types of fungus, Pythium, Phytopthora etc, which attack young seedlings causing them to rot at ground level. This disease is of significance in both the nursery industry and in turf care. In turf, damping off will show in a newly sown lawn as a reddening or bronzing of grass leaves in patches, particularly in places where grass is denser, or in wet spots. Over-watering is a significant cause of damping off. Reduced watering and the application of a fungicide, such as Zineb, are the best techniques for control.
Brown Patch
This appears as light yellowing or browning in irregular patches. The areas will increase in size if unchecked and can result in death of grass and subsequent invasion by mosses. Lack of aeration, poor drainage and warm weather are contributors to the infection. Applications of large amounts of nitrogen fertiliser during the summer will make the grass more susceptible to attack. Therefore, if fertilising you are better to apply a little fertiliser more frequently so as to reduce likelihood of brown patch. Hollow tine aeration will help control brown patch. Chemical control can also be achieved.
Fairy Rings
These appear as a ring of toadstools or puffballs, which are small round white or grey balls of fungi, growing in a circle. The mycelium of these fungi can penetrate soil to a depth of 20cm, or 8 inches, in a mass of white fibres. This fibrous growth throughout the soil can have a waterproofing effect. Water does not penetrate and the grass becomes starved for water and suffers. Aeration can assist in the short term however the only long term sure control is to fumigate the soil which means killing the turf and starting afresh.
Dollar Spot
Small pale green or yellow spots 2.5-5cm, or 1 or 2 inches, across appear at first, often with a white edge. As the disease progresses, spots may grow larger and join to form irregular patches. The disease occurs most frequently in conditions of high humidity and warm weather. Over-watering, particularly night watering in hot weather, will favour development of the fungus. Low nitrogen levels in the soil will favour development of this particular complaint. Chemical control may be achieved
Rust
This group of fungi causes rusty brown, orange or yellowish spots or stripes, normally on leaves and stems, but sometimes on flowers or fruit. These usually occur as individual spots or stripes. There are over 4000 different types of rust species. Most rusts are specialised diseases which affect only one type or group of plants, for example, carnation rusts do not affect corn and vice versa. Rust spores spread in the wind, by insects, by rain, by irrigation, and by other animals. Spores can blow into an area from long distances away. Rusts affect a wide range of plants, particularly grasses, grain crops including corn, vegetables such as beans and asparagus, pineapple, apple, coffee, carnations, and snapdragons.
Red Thread
This is also known as corticum disease and is caused by the fungus, Corticum fuciforme. It is most likely to occur following rainfall in late summer and autumn and is identifiable by pink areas of lawn. This is due to pink fungal threads attaching to the blades of grass where they become inter twined. The fungus does not usually kill the affected turf and may disappear without intervention within days or weeks of first appearing. It is most likely to emerge where soil is compacted, low in nitrogen, and drainage is poor. Severe attacks can be treated with a fungicide or top dressing containing benomyl, thiophanate-methyl, or carbendazim. It is essential to add a nitrogen fertiliser. Aeration and scarification of the lawn, as well as a sulphate of ammonia feed, will reduce the risk of occurrence.
Fusarium Patch
This is also known as snow mould as it often occurs following the melting of snow on the turf surface. Snow moulds are identifiable as circular patches of dead and dying blades of grass with a dark circle around the outside. Patches may be large in diameter and overlap. The grass becomes matted and fungal mycelia may be evident on the surface which can be white, pink or grey. Fusarium patch is a particular problem of golf courses, tees and bowling greens and is one of the most common turf diseases.
Pink snow mould tends to be more damaging to turf because it affects the crowns and roots of the turf whereas grey snow mould typically only affects the grass blades. As the grass dries out, the mycelia tend to disappear.
Cultural Control
There are a number of ways in which the turf can be prepared in order to reduce or eliminate the effects of snow mould during the winter.
Grass should be mowed right up to the point that it becomes dormant in winter
Fertilisers should not be applied within 6 weeks of winter dormancy as this will encourage fleshy susceptible growth
Dense thatch should be raked out
Leaves and other debris should be removed from the turf surface
During snowfall, snow should not be piled deeply on grass areas as this will increase thawing time
Avoid top dressing during optimal fungal growth conditions
Ensure that the turf has good drainage and sufficient air movement to avoid moist conditions. This can be achieved by removing causes of excessive shade.
Other risk factors include:
Alkaline soil
Low fertility
High humidity, combined with hot conditions and low air flow
The use of Poa annua which is highly susceptible to Fusarium patch. Fescues are more resistant to the disease.