Causal organism: Fungus
Asian soybean rust; Soybean rust (Phakopsora pachyrhizi, P. meibomiae)
Bean rust (Uromyces appendeculatus)
Coffee rust (Hemileia vastatrix , H. coffeicola)
Common rust; Corn rust (Puccinia sorghi)
Beans, Allium, corn, sorghum, rice, banana, coffee, and a wide range of agricultural crops
Affected plant stages
Affected plant parts
Stems, leaves, petioles, and pods
Asian soybean rust, Soybean rust, Bean rust
The initial symptom is a yellow mosaic
discoloration on the undersides of the lower leaves on the onset or during the flowering stage. The small lesions gradually increase in size and become tan or brown in color. The lesions are slightly raised and consist of small pustules, with a small hole on top where the spores emerge. The pustules become plentiful and eventually coalesce to form larger pustules that break open, releasing masses of spores. During pod formation, the disease spreads rapidly to the middle and upper parts of the plant. Lesions are found on petioles, pods, and stems but are most abundant on leaves.
The first symptom is small and pale-yellow spots on the upper surfaces of the leaves. As the spots increase in size, masses of orange spores appear on the undersurfaces. The fungus reproduces through the stomata rather than breaking through the epidermis as most rusts do. It does not form pustules which is a typical rust symptom. The powdery lesions on the undersides of the leaves can be orange-yellow to red-orange in color, but colors vary from one region to another. While the lesions can develop anywhere on the leaf, they tend to be concentrated around the margins, where dew and rain droplets collect. The centers of the spots eventually dry and turn brown, while the margins of the lesions continue to expand and produce spores. The first lesions usually appear on the lowermost leaves and the infection slowly progresses upwards. The infected leaves drop prematurely, leaving long expanses of twigs devoid of leaves. The petioles, young twigs, and occasionally green coffee berries are also infected (CABI, 2000).
Common rust, Corn rust
The initial symptoms
are yellow spots on leaf surfaces. The spots develop into oval to elongate reddish-brown powdery and elevated lesions that contain a powdery mass of orange to reddish-brown spores (pustules
) on the upper and lower leaf surfaces. The pustules are generally small, less than 0.6 cm, and are surrounded by the leaf epidermal layer which appears as a whitish covering. The spores became brownish-black when they mature. Damage is most abundant on the leaves but may appear on any above ground portion of the plant.
Conditions that favor development
- Frequent rains, drizzle, or dew with cool temperature and high humidity
- Poor quality seeds used for sowing
- Poor field sanitation
Prevention and control
- Select only diseased-free seeds for planting.
- If there was a heavy infestation of rust on your farm during the previous crop, practice crop rotation by planting a different crop in the next cropping season.
- Control weeds to facilitate air circulation and rapid drying of the plants' canopy.
- Prune coffee plants properly. Pruning improves air circulation and promotes rapid drying of the foliage, thereby reducing the rust damage. Ask for assistance from your local agriculturist office.
- Aloe leaf extract
- Papaya leaf extract