The Diseases

Cavity spot of carrots

Light leaf spot of brussels sprouts

Potato blight

Phytophthora infestans causing late blight of potato. Left and middle: fairly healthy and 10 days later devastated potato field; right close up of blight lesions with fungal spores. Caused a social disaster in Ireland in 1840s and still one of the hardest diseases to control.

Frosty pod and black pod of cocoa

Frosty pod is currently the most serious disease of cocoa in the Americas. Should it escape to West Africa, the main producer of cocoa, it would be catastrophic. Photo courtesy of CABI. hi-res image Black pod of cocoa caused by a species of Phytophthora can cause total loss of pods. It has spread across West Africa and requires combined cultural and chemical control. Photo courtesy of CABI. hi-res image

Rice blast


Rice is a major food crop for more than one third of the world and Magnaporthe blast of rice is recognised as one of the main threats to world food supplies.

Cassava mosaic virus

Left: Effects of cassava mosaic virus in Uganda. Note distorted leaves and virtually no yield. These farmers were desperate following almost complete crop failure. Right: In a non-affected area in Togo - how the starch-filled roots should appear. Cassava is not well known in N Europe but is the fourth most important staple in the tropics feeding around 600 million people.