Grey Leaf Spot of Turf
Tiny brown spots appear on the stems and leaves and rapidly enlarge into round or rectangular spots along the axis and may extend almost across the width of the leaf. They turn tan to bluish grey with age with brown to purple edges and often have yellowing surrounding these edges. The centre of the spot may be covered with grey mycelia. The leaves may appear scorched in severe infestations and look like drought stress. In some plants it may affect the stem below the seed head causing “rotten neck” and loss of seed production.
It is an ascomycete or sac fungus. These fungi produce spores, called conidiophores and conidia, which are dispersed by the wind and splashing rain. These spores can overwinter on seeds and stubble and infect new growth in the following year. Spores produced in the diseased plant can further spread the infection during the season.
Magnaporthe grisea is the sexual or perfect form of the fungus and it is not seen in the field but is referred to in the literature.
Species Affected:Buffalo Grass (Stenotaphrum secundatum)
Perennial Ryegrass (Lolium perenne)
Rice (Oryza sativa)
Biology:The disease is worst during warm humid weather with temperatures between 25 and 300C. Infection is most likely after long periods of rain or high humidity with little wind and warm nights (18-23°C). These conditions favour spore germination and formation.
Drought, excessive nitrogen and soil compaction appear to predispose the turf to and outbreak of the disease.
It is often more common on newly established lawns that have had high nitrogen applications.
Life Cycle:Origin and History:
Significance:It is most important pathogen of rice on a world scale.
Management and Control:Avoid high nitrogen applications during summer.
Apply more water at reduced frequencies and avoid watering in humid conditions or at night when the leaves will remain wet for extended periods.
Reduce compaction and thatch.
Plant resistant varieties.
Avoid herbicide and growth regulator applications on diseased areas.
Destroy diseased crop residue.
Flooding rice reduces the disease.
Benomyl was used in the past for control and two new fungicides, pyroquilon and tricyclazole appear to be effective.
Related and Similar Species:References:
Collated by HerbiGuide. Phone 08 98444064 or www.HerbiGuide.com.au for more information.