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Protea Diseases


Proteas are prone to a large variety of diseases, most of them inconsequential in nature, but a bane to gardeners who have only a few plants. Sterilization is essential: wash spades and equipment used for seed beds or for mulching with a strong fungicide before using near proteas. Knives, shears, and secateurs should be regularly sterilized using a strong disinfectant (clean off before use!). Soil can be sterilized in large quantities with methyl bromide or steam. Home growers could oven bake soil (covered with foil) at 80C for 30 minutes. Protea Atlas Logo

Damping off Diseases

These are fungal (Colletotrichium or Rhizoctonia) diseases which result in sudden, large-scale deaths. The fungus lives on the soil surface and attacks seedlings at ground level, killing cells in the stem and hence the plant.

Damping off is enhanced by:

  1. Re-using seeding soil without re-sterilizing
  2. Too high a density of seedlings
  3. Too damp a soil
  4. Poor ventilation and
  5. Too high or too low temperatures.

Treatment

  1. Sterilize beds after sowing with a strong fungicide or use new, sterile soil and briefly sterilize seeds using a mild bleach solution
  2. Sow seed at a lower density
  3. Improve the drainage, or water less frequently taking care not to wet leaves - alternatively water during the early morning only so that plants don't remain wet overnight
  4. Ensure adequate ventilation to help keep plants dry
  5. Place beds in full sunlight, with ground heating to stimulate growth if conditions cool down too much at night.

Phytophthora cinnamoni (Root rot fungus)

This is a soil-borne fungus which results in root decay of both young and adult plants. It is spread in water, and occurs in all rivers throughout the country. It cannot spread fast in acidic soils, but proliferates in disturbed soils. Different species vary in their susceptability to Phytophthora. In resistant species the symptoms are stunted growth due to root death and branch die back, whereas susceptable species wilt and die overnight, usually under hot weather conditions (when the plant suddenly needs to make use of the roots that the fungus has killed). If detected early enough, a severe pruning (remove 50-80% of leaves) may occasionally allow plants to recover.

Treatment

  1. Fumigate potting and seeding soils (steam, methyl bromide) and sterilize all equipment (spades and containers) before use
  2. Keep soil, seed trays and potted seedlings well drained and clear of standing water
  3. Burn dead plants
  4. Avoid planting susceptable species in poorly drained soils
  5. Never disturb the soil around established plants - rather sow other plants in the bed: do not allow soil to remain bare of plants for too long
  6. Alternate susceptable and resistant plants in beds and do not plant too densely
  7. Graft susceptable strains onto resistant rootstocks.
  8. Before replanting where a plant has died, preferably with a resistant species, apply undiluted fungicide into the planting hole, and water well. If water is suspected of containing spores, store it for few days, as the spores which spread the disease have a short life-span.
  9. A variety of diseases and arthropods attack Proteaceae leaves and stems. As a rule simply prune off diseased material if it is causing die-back (sterilize equipment before and after) and burn, and treat as you would any other garden plant. Otherwise accept blackened leaves as part of life.

Shoot blight, canker and die-back

Leaf lesions, stem cankers and premature death of flowerheads, usually found in pincushions, are due to Drechslera (a fungus). Cankers, lesions on stems and shoots, and leaf blight in Protea are due to Colletotrichium (a fungus), which also causes dieback in seedlings. When the above fungi have disfigured shoots, Botryosphaeria fungi may become established and further weaken infected plants.

Treatment

  1. Avoid susceptable species or cultivars
  2. Sterilize seeds
  3. Prune and burn dead infected branches and
  4. Spray or dust infected areas with fungicides.

Leaf speck, blotch and spot diseases

These are caused by fungi which live superficially on the leaves and, although they spoil the appearence of leaves, they seldom require treatment. The treatment described above for other fungal diseases will usually be effective.


Scab

Scab is caused by an Elsinoe fungus. Symptoms are similar to citrus scab and include: corky lesions on the leaves, shoots and flowering branches, resulting in twisting and distortion of the stem and reduced flowering. Infection usually occurs when wet weather coincides with a growth flush, and is enhanced by overhead irrigation.

Treatment

  1. Avoid susceptable species or cultivars
  2. Avoid overhead irrigation
  3. Plant in areas with good air circulation and
  4. Spray or dust with a contact or systemic fungicide.

Witches Broom

Witches broom occurs on a variety of Proteaceae species and is associated with the Eriphyoid mite Aceria proteae. The symptoms are a fine proliferation of small leaves and stems, often with a redder tint than normal leaves, usually leading, after a few years, to the death of the stem. Seedlings are killed and growth and flower production is lowered in adult plants.

Treatment

  1. Prune off and burn all proliferating material.
  2. Spray or dust adjacent material with a systemic pesticide.

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