Helminthosporium Disease
Causal Agent
Bipolaris spp., Drechslera spp. and Exserohilum spp.
What is Helminthosporium disease?
Helminthosporium Disease is a complex of turfgrass diseases previously known as Helminthosporium leaf, crown and root disease.
What are the Symptoms of Helminthosporium disease?
Although the fungal symptoms of the Helminthosporium diseases are quite characteristic, the symptoms can vary greatly with each pathogen or host. General symptoms include:
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Initial symptoms are small lesions on leaf blades.
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Leaf tissues turn yellow around these lesions.
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Severely infected leaves may die and appear light tan to straw-coloured.
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On Couch, white or black blotching of the turfgrass surface appears. The blotches are irregular in shape and range from 2-6cm in diameter. The leaves and stems show lesions that are purple-black in colour.
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Young seedlings may be killed by the disease, but mature plants will usually overcome the damage during favourable growing periods.
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Typically, on cool season grasses and Kikuyu symptoms appear as very small (pinhead size), solid brown to purple coloured lesions or spots.
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Severely infected leaves will eventually wither and dry to a light tan colour.
What causes Helminthosporium Disease in Turfgrass?
Helminthosporium Disease can be caused by Dreschlera spp., Bipolaris spp. or Exserohilum spp..
Dreschlera spp. is capable of surviving unfavourable conditions as conidia (thick cell walled resting spores) or dormant mycelium. These conidia are spread predominantly by wind, rain or machinery and when conditions become ideal, the conidia germinate and infect plant tissue.
Bipolaris spp. and Exserohilum spp. survive adverse conditions by surviving in infected plant material and debris. When rainfall occurs, these fungi sporulate profusely and eventually gain entry to further plant tissue.
When does Helminthosporium Disease occur?
In general, conditions that are favourable for Helminthosporium disease include:
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Temperatures between 3°C and 30°C.
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10+ hrs a day of leaf wetness for several consecutive days. Leaf moisture is required for infection.
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Poor air movement (high humidity in the micro-climate).
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Excessive nitrogen fertiliser.
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Any stress situation such as drought, herbicide injury or heavy traffic can increase the severity of the disease.
What can I do to manage or control Helminthosporium Disease?
Management practices that can help control or reduce instances of helminthosporium disease include:
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Maintain healthy turf through proper fertilisation. Pay particular attention to potassium and nitrogen levels.
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Irrigate infrequently and deeply but avoid late afternoon or evening irrigations. Do not allow the turf to become extremely dry during warm weather.
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Increase air movement and improve turf drainage.
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Avoid herbicide applications during critical periods of disease activity.
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Disperse traffic in high-traffic areas.
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Mow turf at the recommended height for turf species.
