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Symptoms and Signs

Infections occur on the coffee leaves.The first observable symptoms are small, pale yellow spots on the upper surfaces of the leaves (Figure 3). As these spots gradually increase in diameter, masses of orange urediniospores (= uredospores) appear on the undersurfaces (Figure 4). The fungus sporulates through the stomata rather than breaking through the epidermis as most rusts do, so it does not form the pustules typical of many rusts (Figure 5). The powdery lesions on the undersides of the leaves can be orange-yellow to red-orange in color, and there is considerable variation from one region to another.


Figure 3	Figure 4	Figure 5

While the lesions can develop anywhere on the leaf, they tend to be concentrated around the margins, where dew and rain droplets collect (Figure 6). The centers of the spots eventually dry and turn brown, while the margins of the lesions continue to expand and produce urediniospores. Early in the season, the first lesions usually appear on the lowermost leaves, and the infection slowly progresses upward in the tree. The infected leaves drop prematurely, leaving long expanses of twigs devoid of leaves (Figure 7).


Figure 6	Figure 7

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