Bean rust is a fungal disease affecting leaves, pods and stems of snap beans (=green beans, French beans) and common beans. This disease can reduce yields up to 30%. The symptoms are rust-coloured spots within yellowed areas. The spots first appear as small brown dots containing a brown powder, which are spores of the disease. Later, spots become larger and spores turn black. The disease can cause leaves to fall off, and pods getting deep dark pits.
Bean rust occurs mostly in wet weather. It is easily spread by wind from one plant to another. This fungal disease only infects bean plants and no other crops. It can survive from one season to the next on crop remains.
Bean rust can be controlled by using a combination of management practices:
- Use clean bean seeds originating from non-diseased plants or from certified seed dealers. Using clean seeds prevents spreading of rust disease.
- Plant varieties such as Kabanima, Uyole 98, Ilomba, Lyamungu 90 or Selian 97, that are resistant or tolerant to the disease.
- Pick affected leaves as soon as symptoms are seen to reduce disease spread. Do not openly carry leaves around, as this spreads the disease.
- Do not walk through your field during wet weather to prevent the spread of the disease from one plant to another.
- Remove the crop remains from the field and bury them to reduce the spread and the over-season survival of the disease.
- Deep plough to about 45cm to encourage rotting of the plant remains and reduce the amount of fungal disease carried over to the next bean season.
- Plant beans towards the end of the rainy season and not at the beginning, because bean rust requires cool wet conditions for mass infections.
- Fungicides are most effective when used preventively or in the very early stages of the disease. You may use products containing mancozeb which is less toxic than other products (WHO toxicity class U: unlikely hazard). You may use copper oxychloride, or tebuconazol, but these fungicides are toxic to you and consumers (class II: moderately hazardous). Always wear protective clothing during sprays. Always read product labels. Spray maximally twice per season, and stop spraying 35 days before harvest. Nobody should enter sprayed fields during 3 days. If disease symptoms are found on most of the bean plants, spraying is too late.
When using a pesticide, always wear protective clothing and follow the instructions on the product label, such as dosage, timing of application, and pre-harvest interval.