CAUSES OF DISEASE
Any factor causing a lowering of growth and loss of colour:-
Organisms that attack living plants and cause disease are pathogens, and generally for turf culture purposes it can be assumed that, fungi are the main agents responsible for causing diseases. Other alternative agents include:- bacteria, virus, mycoplasma and there can also be nutritional deficiency diseases.
Fungal diseases of turf are not caused independently and although the fungi may be present, the disease only breaks out when conditions are suitable. It is the interaction between the fungi, grass and the environment that causes the disease. A good example is the interaction between mild, damp autumn weather, lush grass and the development of fusarium.
2. TURF DISEASES
The following are the main diseases found on turf grass in the U.K.:-
Fusarium patch disease
Ophiobolus or take-all disease
These are diseases such as damping off, or post-emergence damping off, and occur mostly in early spring or late autumn when the soil is cold and wet.
Ensure thebed is well drained; avoid at too high a seeding rate, and also avoid too early or late in the year.
Fusarium patch disease (Microdochium nivale)
This disease is very common on all types of turf, and it is probably the most damaging disease, particularly of fine turf in the U.K.
The disease most commonly occurs during mild, humid conditions in the spring and autumn. It is accentuated by high levels of nitrogen, alkaline soil conditions, presence ofmeadow grass and when clippings are returned.
At first, small orange-brown spots appear which, under humid conditions, spread rapidly and kill off patches of grass. The diseased grass is often wet and slimy. The disease can also be active and spread under snow.
Cultural controls can do much to avoid this disease, e.g.:-
Moisture control –, spiking, switching -which will help humid surface conditions.
Avoid alkaline conditions.
Reduction ofmeadow grass.
Removal of clippings and thatch control.
Corticium disease (Laetisaria fuciformis)
Commonly known as red thread and attacks mainly red fescue (and also perennial rye grass in areas of low fertility).
Symptoms are bleached patches of damaged grass, which are often tinged pink with red needles visible under wet conditions. The damage is mainly superficial and total death of grass is rare.
Adequate fertiliser application, especially of summer nitrogen, and selection of cultivars which are disease resistant are recommended.
Dollar spot (Sclerotinia homeocarpa)
Attacks red fescue, particularly from sea marsh turf. Outbreaks generally occur in the summer and autumn where fertility is low. The particles of dead grass formed are small, very distinct and circular, usually about 50 mm (2 inch) in diameter, and give the area a spotty appearance. The individual spots are usually dry, bleached white, or straw coloured.
The disease can be prevented by choice of resistant cultivars of fescue and the avoidance of sea-washed turf.
Ophiobolus or Take all disease (Gaeumannomyces graminis)
This disease affects Agrostis Spp. being most active in late summer and autumn and favoured by wetness and alkalinity, especially after liming.
Rings of yellow or orange grass appear as a result of fungal attack on the. The centres of the diseased patches tend to become colonised by resistant grasses.
Careful control of surface moisture and surface pH is important. If liming is to be carried out in the autumn, a spring fertiliser application should be given to re-acidify the surface.
This is the name given to bands (usually in arcs and circles) of dark green turf or crops of toadstools caused by soil inhabiting fungi.
Three types are common:
Type 1 – Marasmius oreades – (fairy toadstools)
The most damaging one, producing two dark green rings of stimulated grass with a bare zone between. No method of preventing the rings establishing in turf is known. Chemical control is recommended by the STRI.
Type 2 – Aaaricus campestris – (mushroom fungi)
This produces rings of stimulated grass with no actual damage to the grass. Control is similar as for Type 1.
Type 3 – Hvarophorous spp.
Produces toadstools or puffballs. warranted.
Control is rarely
An integrated control technique for fairy rings
Lift the affected turf from the ring, including 300 mm on either side. Trench dig the central 300 mm wide area where the rings were, and remove the soil. Thoroughly treat the remaining soil and trench with formaldehyde. Replace with fresh earth from elsewhere – (or formalin – treat the extracted earth very thoroughly). Cover for three days. Uncover, check for the smell of the remnants of the formalin treatment and wait for these to clear before re-turfing.
Apply Benodanil or Oxycarboxin fungicides to the centre and surrounds of the ring area. (One of the causes of the bare earth ring brought about by Marasimus is the drought effect achieved by the waterproof layer of Mycelium of the fungi present close to the soil surface: a wetting agent will assist with the penetration through this layer.)
Treat the trench with formaldehyde – 2 litres per 100 litres water at up to 50 litres per square metre.
Carry out the treatment ideally in the spring or autumn.
These are superficial fungi that can occur at any time of the year, and are usually confined to the fibre layer of turf. The fungi appears to break down the fibre, producing sunken areas with darker green or yellow coloration.
Prevention is best attempted by reducing accumulations of thatch.
Melting out (Drechslera poae)
This affects smooth stalked meadow grass, especially if mown very close. Individual plants usually have brown or purplespots, followed by an overall browning or disappearance of the species. Selection of resistant species is recommended as the best method of control.