Any excess of nutrients can create an undesirable effect on plants as it decreases the plant’s growth and quality.
Excesss nitrogen symptoms — An excess of nitrogen causes rapid growth with reduced flowering and fruit formation. The plants look overly green, and may have thin stems. The soft new foliage becomes attractive to pests and susceptible to diseases.
Excess phosphorus symptoms — Most Australian soils are deficient in phosphorus and native plants have become very efficient in extracting this nutrient. Fertilising natives with a general fertiliser is not recommended as those fertilisers contain phosphorus. Symptoms of toxicity include lack of growth, apparent iron deficiency (yellowing between the veins of youngest leaves), red colours starting in oldest leaves, drop of oldest leaves, tip death in the worst cases, and a susceptibility to root rot fungi such as phytophthora.
A guide to nutrient deficiency symptoms
Deficiency showing on older leaves — symptoms affecting the whole leaf:
- Nitrogen — Yellowing of older leaves, usually at the base of the plant.
- Phosphorus — Reddish purple and drying of tips on young leaves.
Deficiency showing on older leaves — symptoms affecting only parts of the leaf:
- Potassium — Edges of older leaves look scorched; yellowing between the veins; dead spots.
- Magnesium — Mottling, yellowing parts, sometimes reddened; dead spots.
Deficiency showing on younger leaves with distorted terminal buds:
- Calcium — Young leaves become hooked, then begin to die back from the tips and edges.
- Boron — Young leaves become pale at the base; other leaves appear twisted.
- Zinc — Yellowing between veins; dead spots become large.
Dead spots on young leaves:
- Manganese — Small dead spots appear in areas that have yellowed but veins remain green.
Pale colouring in leaves:
- Iron — New leaves become pale and in some cases white, but veins remain green.
- Sulphur — New leaves, including their veins, become pale yellow, but older leaves remain green. Veins become chlorotic.
The Department of Agriculture and Food, Western Australia (DAFWA) is on the lookout for animal and plant pests, diseases and weeds that could pose a threat to agriculture and the environment.
Please read the sending specimens for identification web article before sending, or bringing in, samples to the Pest and Disease Information Service, 3 Baron-Hay Court, South Perth, 6151, WA.