Tech Notes Issue 12
Weather conditions Favorable for Microdochium patch
Winter weather conditions are favorable for Microdochium patch in southern Australian States and up through New South Wales. Temperatures in the range of 0 to 7 C along with extended periods of wetness are ideal for disease development. Wintergrass (Poa annua) is especially susceptible under these conditions. The classic symptoms are circular pink colored patches that can reach a diameter of 25 cm. However, during periods of extended wetness or rain, the spores can spread along water flow (drainage) patterns. The result is a streaking symptom that is sometimes confused with cool temperature pythium.
Spring Dead Spot is a Serious Disease of Couchgrass through the Winter
Spring dead spot is a common disease of both common couchgrass (Cynodon dactylon) and the hybrids (C. dactylon x C. transvalensis). The pathogens associated with the disease in the southern hemisphere are Ophiosphaerella narmari and Ophiosphaerella korrea. Symptoms appear as circular white to bleached out patches varying in size up to 1 meter in diameter. Symptoms often appear in early spring when couchgrass begins to break dormancy. However, symptoms can appear from late autumn through winter during periods of cool wet weather. Symptoms can persist well into the summer even when couchgrass is actively growing.
The pathogens associated with spring dead spot attack the root system of couchgrass during the winter months when soil temperatures range from 12 to 14 C. A sign of this disease is the production of brown runner hyphae on the outside of the roots.
To reduced the severity or likelihood of spring dead spot fertilize with moderate rates of nitrogen, correct any potassium deficiencies (ammonium sulfate along with potassium over time appears to reduce the severity of the disease), and raise the mowing height slightly. Raising the height appears to be only effective with reducing the severity of the disease on the hybrids.
Fungicide control of spring dead spot is challenging. Generally, applications should be timed during the autumn when the pathogen is actively infecting the root system.
Photograph: Spring dead spot symptoms still visible during summer
