Excerpt From The Course
TURF DISEASES
Although there are a variety of conditions such as lack of water, poor nutrition, and waterlogging which can cause the most common symptom on lawns – discoloured turf, it can also be caused by a number of diseases and so the cause is worth investigating.
Fungi on Turf
Let us firstly recap on what we already know about fungi. Fungi are a primitive form of plant life which, unlike green plants (such as grasses), are unable to produce their own food through photosynthesis. This means that fungi must obtain their food from other life forms (plants or animals – living or dead). Some types of fungi are in fact of benefit to us, living on dead organic material and helping decomposition. Other fungi however attack living organisms, feeding from and causing deterioration to the life form it attacks.
Most fungi are made up of a body comprised of filaments which grow hyphae. Together, groups of filaments are called mycelium. When the mycelium establishes sufficiently and has the right conditions, it will produce fruiting bodies (e.g. the umbrella which we eat of a mushroom – this is the mushroom fruiting body which has grown up from a mass of hyphae growing in organic matter in the soil). The fruiting bodies of fungi can vary greatly in shape and size. On maturation, one fruiting body will release many (sometimes thousands) spores (i.e. the equivalent of seeds in flowering plants). These spores are microscopic and move in the air, soil, water etc. They can lie dormant sometimes for years, until the conditions are suitable for growth. Under the right conditions, the spores will grow to produce a new mycelium.
When a plant leaf, stem, root, flower, or fruit is affected by fungi, hyphae grow into the body of the living plant feeding off its tissue and (depending on the severity of the type of fungus) causes anything from a slight ill effect through to death of part of the plant, or whole plant.
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 dense, or in wet spots. Overwatering is a significant cause of damping off. Reduced watering as well as application of a fungicide (e.g. Zineb) are the best techniques for control.
Red Thread
This is caused by the fungus, Corticum fusiform, usually in the autumn or late summer. it is more noticeable following rainfall or morning dews and is visible as pinkish red patches. Close inspection reveals horn shaped red fungal growths attached to grass blades and stalks sometimes sticking them together since they become gelatinous with moisture. Often damage is minimal, being more unsightly than anything else, and the fungus disappears after several weeks. If there is a severe outbreak then the fungus may remain in drier weather. It often takes hold in soils low in nitrogen and with poor aeration. Aerating the soil and removing thatch therefore helps, as does feeding with a nitrogenous fertiliser. Fungicides containing benomyl, thiophanate-methyl or carbendazim are also beneficial.
Brown Patch
This appears as light yellowing or browning of grass blades in irregular patches. The areas will increase in size if unchecked and can result in the death of grass and subsequent invasion by mosses. Lack of aeration, poor drainage, and warm weather are contributors to the infection. High applications of nitrogen fertilisers in summer make grass more susceptible to attack.
If fertilising you are better to apply a little, more frequently, to reduce likelihood of brown patch.
Hollow tine aeration will help control brown patch. Chemical control can be achieved with Captan, PMA or Thimer.
Fairy Rings
These appear as a ring of toadstools or puffballs (small round white balls) growing in a circle. The mycelium of these fungi can penetrate soil to a depth of 8 inches in a mass of white fibres. This fibrous growth throughout the soil can have a waterproofing effect. Since water does not penetrate, 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 (this means killing the turf and starting afresh).
Dollar Spot
Small pale green or yellow spots 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. Overwatering, 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 is achieved with Benlate or Daconil. You should be sure that Benlate is only from a freshly opened packet since this chemical deteriorates once exposed to air.
Rust
Rust appears as orange, brown or black streaks on leaf blades of grass. Rust is more commonly a problem on greens, particularly in autumn. Severely infected grass can die.
Some fungicidal sprays may help, however the best control is achieved by removing all grass clippings from the area of the turf and by maintaining a program of regular fertilising and deep watering.
Susan Stephenson