Rust is a general term which refers to a large family of fungi that attack plants.
Leaves are affected most commonly, but rust can also be found on stems, flowers and fruits.
The spore pustules produced by rusts vary in colour, according to the rust species and the type of spore that it is producing.
Some rusts have complex life-cycles, involving two different host plants and up to five types of spores.
Rust diseases are favored by 4-8 hours of low light intensity, warm temperatures and moisture/ humidity, dew or rain, followed by 8-16 hours of high light intensity, high temperatures and slow drying of leaf surfaces.
Host
A wide range of plants is attacked by Rust diseases.
These include;
- Legumes, e.g. beans, cowpeas
- Ornamentals, e.g. roses
- Cereals, e.g. wheat, maize
- Coffee
- Sugarcane
Disease Cycle
All rusts are obligate, meaning that they need a living host to complete their life cycle.
They produce spores when conditions are favourable, which are blown by wind or by water splashing back up onto the foliage of healthy plants, where they initiate infection.
Symptoms start appearing within 1-2weeks of initial infection, and the earlier the infection time, the greater the potential for yield reduction.
Some rusts spend their entire life on one plant and produce just one or two types of spore. Others need two, often completely unrelated plants in order to complete their life-cycle, and can produce up to five different spore types.
Rust fungi can also be categorized by their life cycle.
Signs & Symptoms of Infection
Rust is most often found on mature plants where symptoms appear primarily on the surfaces of lower leaves.
- The pustules are found most commonly on the lower leaf surface and produce huge numbers of microscopic spores
- Usually leaf distortion and defoliation occur.
- Pustules can be orange, yellow, brown, black or white. Some are rusty brown in colour.
- Severely affected leaves often turn yellow and fall prematurely.
- Pustules sometimes form on leaf stalks (petioles), stems and, rarely, on flowers and fruit
- Heavy infection reduces the vigour of the plant. In extreme cases the plant dies.
Control
In order to prevent losses attributed to rust diseases, proper control and/or management strategies should be employed. These methods are as follow;
Chemical method
This entails the use of fungicides.
The following fungicides are recommended for use against rust diseases
- MILESTONE 250EC 10ml/20l
- DEFACTO 500EC 20ml/20l
- DOMAIN 250EC 10ml/20l
- RANSOM 600WP 15g/20l
- DUCASSE 250EW 20ml/20l
- EXEMPO CURVE 250SC 15ml/20l
- BRADLEY 500SC 10ml/20l
- EXPLORER 3SL 10ml/20l
- JUPITER 125SC 15ml/20l
- MILLIONAIRE 690WDG 40g/20l
- MONUMENT 400EC 40ml/20l
- PROVIDENCE 400WP 50g/20l
- SPARROW 500EC 15ml/20l
- TOMAHAWK 250EC 10ml/20l
- TRINITY GOLD 425WP 50g/20l
- ABSOLUTE 375SC 10ml/20l
- COLONIZER 440WP 50g/20l
Note
- Whenever conducting any foliar spray, it is highly advisable to mix the fungicide with INTEGRA 3ml/20l, which improved the efficacy of the fungicide by acting as a sticker, spreader and penetrant.
- Timely application of fungicides is very crucial for effective control
- Alternating different fungicides throughout a plant’s season prevents the fungus from developing resistance over any of the fungicides.
Non-chemical methods
- Use rust-resistant plant varieties.
- Crop rotations with non-host crops
- Maintenance of field sanitation/hygiene
- Pick off and destroy infected leaves
- Drip irrigation and soaker hoses can be used to help keep leaves dry.
- Use a slow-release, fertilizer on crops and avoid excess nitrogen.
- Prune or stake plants to improve air circulation. Make sure to disinfect your pruning tools.
- Proper weed control
- Use a thick layer of mulch or organic compost to cover the soil after you have raked and cleaned it well. Mulch will prevent the disease spores from splashing back up onto the leaves.
- Burn infected plants after the growing season. Do not compost.
