Cercospora Leaf Spot
Found worldwide. Most damaging in tropical and
sub-tropical regions where warm, wet conditions prevail
Circular spots appear with a light gray center and a
reddish-brown margin, growing up to 1 cm in diameter.
Spots later become tan with a dark ring and a yellowish
halo around the ring, resulting in a “frog-eye” appearance.
Under conditions of high humidity, and using a good
high magnification hand lens, thin, needle-like spores
may be seen in the center of the spots arising from
small black fungal tissue. The affected centers of lesions
dry and often drop out as they age. When numerous
spots occur on the foliage, the leaves turn yellow and
may drop or wilt. Defoliation is often serious, exposing
fruits to sun scald.
Spots also develop on stems and petioles but they
are oblong rather than circular. Fruit are not infected.
Conditions for Disease Development
The fungus survives in or on seed, and as tiny black
fungal tissue known as stromata in old affected leaves
in the soil. Spores will survive in infected debris for at
least one season.
Foliar infection occurs by direct penetration of the
leaf. The fungus spores require water for germination
How to Identify Cercospora Leaf Spot
Circular tan spots with dark rings and yellow halos.
Centers of spots are light gray with black spores
Numerous spots create
Written by Ray Cerkauskas, Visiting Scientist from Agriculture and Agri-Food Canada. Edited by Tom Kalb. Photos by Lowell L. Black
and B.H. Chew. Published by AVRDC – The World Vegetable Center; P.O. Box 42, Shanhua; Taiwan 741; ROC
tel: (886-6) 583-7801; fax: (886-6) 583-0009; email: firstname.lastname@example.org; www: www.avrdc.org
and penetration of the host; however, heavy dew appears
to be sufficient for infection. The disease is most severe
during periods of warm temperatures; for example, 20–
25°C during the day and excessive moisture (either from
rain or overhead irrigation). Fungal growth is limited if the