It is not uncommon for plants to suffer from a combination of deficiencies. Some visible symptoms include:
- discoloration or premature dying of leaves
- stunting of growth
- blemishes on fruits
- undeveloped root systems.
Plants can also suffer from nutrient toxicity if an excess of a nutrient is applied.
Plant disorders with similar symptoms
Check that the following symptoms are not the cause:
- a pests or a disease
- herbicide drift
- physiological conditions
- environmental conditions.
Nutrients such as nitrogen, phosphorus, potassium and magnesium are readily translocated within the plant and are referred to as “mobile”. Symptoms first appear on older leaves as the nutrients are moved to new growth. Other nutrients such as iron, zinc, calcium and boron are immobile and are not moved around the plant, with symptoms generally occurring on the growing tips. Manganese mobility is complex and depends on the species and the age of the plant and the deficiency may appear on either old or new leaves.
Factors affecting nutrient uptake
- Some soils are naturally infertile and devoid of nutrients.
- The pH should be neutral which is 7 or close to 7. When the pH of the soil is too low or high (0 indicates extreme acidity and 14 indicates extreme alkalinity) essential nutrients become unavailable. At high pH values, phosphorus, iron, copper, zinc, boron and manganese become less available.
- Soil particle size and chemistry affect the way in which water and nutrients are retained and taken up by the plant. Soils high in loam or clay have a higher water and nutrient retention compared to sandy soils where nutrients are easily leached out. Some south-west clay soils are high in iron and aluminium which bind phosphorus to the soil, making it unavailable to the plants.
- This is essential for the uptake of nutrients. Underwatering or overwatering the plants may lead to nutrient deficiencies.
- Undeveloped or insect damaged roots are ineffective in taking up nutrients.
- Extremes of temperature will inhibit nutrient uptake. For example, it is common for home gardeners to see yellow lawns or yellow citrus trees in winter.
When applying fertilisers a well balanced general purpose product containing both essential and trace elements is recommended. Trace elements are required in small amounts and should be used sparingly.
On sandy soils small amounts of fertiliser should be used frequently, to ensure a steady supply of nutrients to the plant. A time saving alternative is to use controlled release fertilisers. On heavier soils apply fertiliser in greater quantities, but less often.
Plants can also suffer from nutrient toxicity if too much of a particular nutrient is applied. Water plants before fertiliser application and ensure the fertiliser is watered in well after application, to avoid burning of the plants.
Liquid fertilisers or trace elements in a liquid form, applied to the foliage of the plant, are one of the quickest ways of solving nutrient deficiencies.
Nitrogen is a necessary element for leaf growth and blossom formation. It is an important component in chlorophyll which is essential for photosynthesis. If nitrogen is deficient, the oldest leaves appear pale and lack the lustre of healthy ones. Yellowing appears at leaf tips and will affect all the leaves. Apply fertilisers high in nitrogen such as sulphate of ammonia or blood and bone. Organic matter and manures can also be added to the soil.
Phosphorus is essential for the development of flowers, fruit and roots. It is a mobile nutrient and is moved from older leaves to the newly developing tissue. Older leaves turn a darker green followed by a purplish tint starting from the leaf margins. Leaf tips dry off. In fruit trees, flowering and fruiting may be affected. Deficiency symptoms are more prevalent during cold, wet conditions. To correct the deficiency apply solid or liquid phosphate fertilisers.
Potassium is also required for flower and fruit formation and thickening of cell walls. It is essential for the lengthening of stems. Mature leaves show a browning and drying of the upper surface and puckering on the margins. Darkening appears between the leaf veins. The stalks are thin and shortened. The fruits may fail to develop full colour, be pulpy in texture and lack flavour. To correct the deficiency apply sulphate of potash.
Magnesium is essential for photosynthesis and the formation of proteins and chlorophyll. It moves freely within the plant and is taken from the older leaves to supplement new growth. Lower leaves are first affected, yellowing from the tip downwards. Dead spots appear. Deficiencies occur on sandy acid soils and affect palms and citrus. To correct the deficiency apply magnesium sulphate (Epsom salts) or dolomite (magnesium-calcium-carbonate).
Citrus trees suffering from a zinc deficiency show yellowing between the leaf veins, rolling of the margins and smaller leaves than normal. Zinc becomes unavailable in soils which have high pH. It is not a very mobile nutrient so a foliar spray of zinc and manganese is recommended for fruit set.
A condition often referred to as lime induced chlorosis affects acid loving plants that are unable to take up iron in alkaline soils. The newer leaves become pale green, yellow and, in severe cases, white. Veins remain green. This is a common occurrence on coastal alkaline soils. To correct the deficiency reduce the pH of soil with ammonium sulphate or agriculture sulphur, and apply iron sulphate. A foliar feed with a complete liquid fertiliser will help correct this problem.
Manganese deficiency causes yellowing between the veins of new foliage. In extreme cases new palm fronds emerge withered and dead. This is referred to as frizzletop, and commonly occurs on alkaline soils. To correct the deficiency apply manganese sulphate. During summer yellowing appears on cycads as manganese is diverted from older fronds to support a flush of new growth. Yellow spots merge into a mass. A spray with the fungicide mancozeb, which contains manganese, is beneficial. This deficiency can appear on either new or older leaves.
Sulphur is a component in the formation of chlorophyll. Deficiencies result in yellow leaves and stunted growth. Sulphur can be used to lower the pH of alkaline soils. To correct the deficiency apply sulphur fertiliser such as sulphate of potash or ammonium sulphate rather than agricultural sulphur.
Symptoms are more prevalent on the fruits than on the leaves. Fruits like tomatoes, plums and olives show a blemish on the blossom end of fruit. To correct the deficiency, apply calcium nitrate early in the season.
Iron and manganese deficiency on acid preferring plants
Symptoms show yellowing between the veins, which remain dark green. This is a common condition in soil with a high pH, and particularly on citrus, roses and gardenias. To correct the deficiency add iron sulphate or iron chelate and manganese sulphate to the soil.
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.