Could Fungus be Causing the Brown Patches on my Lawn?

Patchy lawns can be attributed to a number of causes – but could fungus be the real problem?

So your lawn still has those brown patches in what should be a uniform green and you have examined all the options. The soil is good, it’s raining incessantly so water isn’t the problem, and the rain would have neutralised urine, so you can’t blame the dog. But patches of brown have appeared in the otherwise lush green lawn and you need to find out why.

The likelihood is a fungus – either Brown Patch, Dollar Spot, or Pythium Blight.  

Brown Patch

Although Brown Patch tends to be a Summer disease, in favourable climatic conditions it may also occur in Spring and Autumn. All species of warm or cool-season turfgrasses are susceptible and the disease spreads rapidly.

How to Recognise the Disease

Brown Patch is caused by a fungus called Rhizoctonia. Depending on the cultivar of the grass and the climatic conditions, it may present in varying ways. Typically, it appears at first in lawns, as circular areas of dead grass measuring between 12 cm and 3 m in diameter. A dark, narrow border, more visible in the morning, can be seen around the area of dead grass. Leaf lesions develop on wide-bladed grass species showing a light brown center with dark brown to black margins.

Typical Conditions for the Appearance of the Disease

Brown Patch favours temperatures of more than 30°C during the day and over 15°C at night. In warm-season grasses, the disease may still arise in certain spring and autumn conditions, such as several days of rain or humidity. It is more prevalent when the turf is cut back harder than the optimum for the species of grass.

Management of the Turf

  • Increase the cut of your lawn.
  • Water only in the early morning.
  • If necessary, improve drainage to the area.
  • As a general rule use medium to low amounts of nitrogen on your lawn, moderate amounts of phosphorous, and moderate to high amounts of potash.
  • Avoid nitrogen if Brown Patch is active.
  • Increase sunlight to the area by thinning tree branches.
  • Reduce any thatching from the grass.
  • Apply a recommended fungicide to the blighted areas.

Dollar Spot


Dollar spot causes indented circular patches of around 5 cm in diameter on low mown grass and larger patches on higher mown turf.  As such, golf course conditions are more prone to Dollar Spot than the average lawn.

If you examine the leaves more closely you may be able to see small lesions that sometimes extend the full length of the leaf. These turn from light green to yellow with a reddish-brown border. In some instances, the fungus produces small cottony strings from the diseased leaf blades. Ultimately, if not treated, the coin-like patches are likely to merge leaving bald areas on the lawn. Both warm and cool-season turf is susceptible to Dollar spot.

Conditions favouring Dollar Spot

Dry soil conditions lacking in nitrogen may produce Dollar Spot. The weather conditions that favour the outbreak of the disease are periods of high humidity and temperatures of between 15°C to 30°C. It thrives on warm days with cool nights and heavy dew falls. The fungus can be spread from one area to another by foot traffic, water and mowers etc.

Turf management

  • Apply an appropriate level of nitrogen, particularly during spring and early summer.
  • Mow your lawn grass at regularly.
  • Reduce thatching.
  • Water the grass deeply and infrequently to encourage deep rooting.
  • Spray your entire lawn with a recommended fungicide and repeat application within 7 to 14 days for it to clear completely.

Pythium Blight

All turfgrass species are known to be susceptible to blight. It is one of those diseases that may appear suddenly during hot, humid weather. While Pythium Blight shows certain similarities to Dollar Spot and Brown Patch and other fungi, Pythium Blight often requires distinct methods of management.

Pythium blight appears suddenly during hot, humid weather. Initially, greasy brown spots of between 2 – 5cm appear in the grass and quickly increase in size. The infected grass forms a growth of white, aerial mycelium – also known as cottony blight – which looks rather like candyfloss. It is most evident when the infected leaves are wet after a night of rain or heavy dew.  These blighted areas coalesce forming irregular areas of dead turf.

Conditions favourable to Pythium Blight

Pythium Blight occurs in areas that experience more than 10 hours a day of rain for several consecutive days with night temperatures of over 20°C. It favours sodden conditions in places with poor drainage and limited air circulation. Lush turf under nitrogen fertilisation is particularly susceptible to this disease.

Turf management

  • When signs of the cottony-blight is evident avoid mowing while conditions are wet to minimise spreading the disease.
  • Reduce any thatching.
  • Improve soil drainage.
  • During periods of hot weather, avoid nitrogen application.
  • Minimise the amount of shade and, where possible, increase air-circulation to improve the drying time of the turf.
  • Water your lawn early in the day and aim to water deeply and as infrequently as conditions will allow.
  • Spray with a recommended fungicide.

Bearing in mind the conditions that may encourage the growth of fungi, do a once a week walkabout of your turf and enjoy a fungi-free lawn this summer.


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