Grass Diseases

There are somewhere in the neighbourhood of 100 different diseases that affect turf grasses. Just like human illnesses, each turf disease has a specific prescription for its cure and prevention.

Some diseases can be suppressed by the application of nitrogen fertilizer, whereas others are encouraged by more nitrogen. Other diseases are suppressed by high soil pH, and others are encouraged by low pH.

A long list of other turf management practices can be used to control disease, but the most effective prescription is specific for each disease.


Turf grass diseases are very difficult to identify. Grass plants are very small and most diseases are caused many microorganisms that can’t be seen without a microscope.

However, with some basic knowledge and a lot of practice, you can vastly improve your diagnostic skills.

By learning how to diagnose just a few common diseases, the greenkeeper will be able to diagnose most of the disease problems that encountered during the season.

Diseases may produce spots, circles, patches or rings. Some diseases produce an irregular or non-patterned symptom across the turf.

Generally, the best plant symptoms can be observed along the border between healthy and diseased turf. The plants in severely affected areas that are already dead are not very useful for diagnosis of turf grass diseases.

The symptoms that may be observed on individual plants include:

  • Leaf spots, sometimes known as leaf spotis
  • Foliar lesions
  • Stem lesions
  • Foliar blight
  • Foliar dieback
  • Crown rot
  • Root rot

Leaf Spot

Leaf spot shows as a round or oval area on the leaf with a distinct border, which is usually a different colour than the centre of the spot.

Foliar Lesion

A foliar lesion is irregular in shape and is typically larger than a leaf spot, but still has a distinct border that is usually a different colour.

Stem Lesion

A stem lesion is very similar to a foliar lesion, but is present on the stem or leaf sheath of the grass plant rather than on the leaves.

Crown Rot

Crown rot is observed as a dark and rotten area at the base of the turf grass plant.

Root Rot

Root rot produce a visibly dark and rotten root system, and also a noticeable reduction in root depth in affected areas. Crown rots and root rots often occur together and may also include rotting of stolons and rhizomes if present.

The visible signs are the evidence of the presence of a pathogen. Most turf grass diseases are caused by fungi, and even though fungi are microscopic organisms, some produce larger structures at certain times in their life cycle that can be seen with the naked eye.

Please see the Fungi page for all the information you need to know!