How to Treat Helminthosporium Leaf Spot

Helminthosporium is a fungal disease that impacts all turf grass species. It is caused by a group of complex fungi, which all cause similar symptoms when they infect grass leaves.

Warm season turfgrasses, specifically Kikuyu, are primarily affected by Bipolaris spp. and Exserohilum spp. Couch, Bent, Fescue, and Ryegrass are susceptible to disease outbreaks caused by Drechslera spp.

Helminthosporium Leaf Spot symptoms can vary depending on the grass variety and fungi involved. In Kikuyu, symptoms appear as pinhead-sized brown to purple spots that appear on the leaves. In Couch grass, the disease appears as white or black blotching of the turfgrass surface. These blotches are irregular in shape and can range from 20mm to 600mm in diameter. Inspection of the leaves and stems shows lesions which are purple to black in colour.

Grass blades affected with Helminthosporium Leaf Spot will eventually die and wither. Severe infestations result in turf thinning, and eventual death.

Helminthosponum thrives in conditions when leaves remain wet for an extended period of time, such as during evening irrigation, on cloudy days, or when air movement is limited. It can grow in most temperatures but progresses more quickly in hot weather.

Stressful conditions such as heat, drought and excessive traffic, along with the use of nitrogen fertilisers, can create an ideal environment for the development of the disease.

As soon as wet weather ends, disease pressure usually declines, so Helminthosporium rarely requires fungicide treatment in backyard lawns.

Maintaining grass health through nutritional balance is important in the control of Helminthosporium disease. During prolonged wet periods, avoid excess nitrogen and apply a slow-release potassium source in autumn and spring to reduce disease incidence.

Mow your lawn at the recommended height for the variety and time of year. After mowing, get rid of grass clippings to avoid an accumulation of organic debris on the lawn’s surface.

Helminthosporium disease is often found in areas prone to water logging. You should address any areas of poor drainage through a program of regular aeration and dethatching to improve the circulation of air and uptake of nutrition.

Reduce periods of leaf wetness by avoiding excessive watering. Plan to water your lawn in the morning, rather than late in the day, and irrigate deeply and infrequently to promote strong roots.

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If you live in a warm, humid climate, your lawn may be susceptible to fungal diseases, such as Helminthosporium Leaf Spot. The best way to avoid infection is to keep your lawn in good health, by maintaining a healthy balance of nutrition and addressing issues such as thatch and poor drainage with annual aeration.

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