T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Leaf spots

Leaf spots are round blemishes found on the leaves of many species of plants, mostly caused by parasitic fungi or bacteria. Positive identification usually requires laboratory diagnosis.

A typical spot is "zonal", meaning it has a definite edge and often has a darker border. When lots of spots are present, they can grow together and become a blight or a blotch. Fungal spots are usually round or free-form in shape. A leaf spot disease causes the leaves to become disfigured but tree growth is not usually affected. However, heavy infestations may cause premature leaf drop or affect photosynthesis. The spots will vary in size and colour depending on the plant, the organism involved and the stage of development. Spots are most often brownish, but may be tan or black. Concentric rings or a dark margin around the spot may be present. Over time the spots may combine to enlarge and form blotches. Spots or blotches that are angular and located around the veins are generally referred to as anthracnose. Leaves may yellow and drop prematurely.

An especially harmful version of this disease is called anthracnose which attacks many tree species including dogwood and sycamore.