Take-all Patch Disease
General view of take-all patch disease.
This is a fungal disease common on bentgrass turf, especially on newly established areas.
The fungus responsible for this disease is Gaeumannomyces graminis var. avenae (formerly Ophiobolus graminis). There are three varieties (var.) of G. graminis, namely var. avenae, var. graminis and var. tritici. The latter two, although very similar to the one that causes take-all patch on turfgrasses, cause root diseases in cereals and other grasses.
This soil-borne fungus is favoured by rootzones with high pH, although the fungus may become active in acidic rootzones if the pH level increases by only a small amount. It is therefore not so important what the pH of the rootzone is, but how it is allowed to change through maintenance practice. Both topdressing materials and irrigation water are common reasons for an increase in rootzone pH and both should be checked regularly on turfgrass areas prone to this disease. Take-all patch disease will spread in damp rootzones and therefore maintaining adequate surface drainage is important to control spread of the disease.
All bentgrasses can be affected by this disease, but the fungus is also capable of also attacking other turfgrasses. Over recent years, I have seen an increasing number of Poa annua swards with take-all patch infections.
The fungus will start to grow along the roots of the host plants during the spring when rootzone temperatures start to increase. It will eventually enter the plants roots and colonise the root tissues, reducing the movement of water and nutrients through the affected plant. Symptoms of disease will start to show as the turf comes under stress during the summer and autumn months.
Initial signs of disease show as patches (a few centimetres) which increase in size up to about 0.5m dia. Plants initially take on a bronze colour but as the disease progresses and the root system is gradually reduced, the plants become straw coloured and die, being easily removed from the turf. At the base of the stems and around the crown, dark brown flask-shaped structures about 1mm long can be found. These are the reproductive structures of the fungus from which the spores will be released.
The fungus responsible for this disease can actively reduce the amount of manganese (Mn) available to the plant. Since Mn is used by the plant in producing chemicals with which to defend itself from soil-borne infections, reduction in its availability to the plant by the fungus leaves the plant more susceptible to infection.
Generally this disease remains active for 3 to 5 years, during which time antagonistic fungi and bacteria build up in the rootzone and out-compete the fungus that causes this disease. Once the levels of these organisms become 'balanced', the disease goes in to what we call take-all decline.