WHY IS MY PLANT SICK?

A guide to plant symptoms, causes and possible solutions.

If a plant is not able to obtain all the nutrients it need in the right balance then its health will be affected. Like humans, unhealthy plants will be more disease prone and they will also attract more damaging insect attacks.

When a commercial hydroponics farmer discovers a sick plant amongst his crop he will send in tissue samples to a laboratory for analysis which can be expensive. Fortunately for home gardeners, a cheaper method of finding out why your plant is sick can also be derived by looking at the plants leaves, flowers and fruit for abnormal growth symptoms. These symptoms can give an indication of what nutrients are lacking or are in excess. These symptoms can also tell you what other problems the plant may be experiencing, such as insufficient light or a fungal attack.

Once you know what is the cause of a plant’s sickness might be, you can then take appropriate steps to restore the plants health.

It is also possible that physical factors may be a cause of a plants sickness and it is worthwhile considering these factors first. It may be a combination of factors. For example, untreated dam water will continuously infect plants with a fungal disease called fusarium wilt. Using limestone as a medium will increase calcium levels affecting the uptake of potassium.

Factors That May Affect The Growth Of A Plant.

  1. Wrong season or climate for growing. For example, most peas will shrivel up and die during the heat of a hot summer.
  2. Environmental factors such as poor lighting or too much shade. Adverse humidity conditions and temperatures and frosts. Poor quality or infected water supply. Excessive winds and constant rainfall. Pesticides or herbicides sprayed nearby. Poor air circulation.
  3. Growing conditions. Plants may be overcrowded. ph levels are too high or low. Poor root aeration. Nutrient concentrations are too high or low.  Medium is not suitable. Growing container is too small or badly designed causing dense bunching of roots which restricts aeration and nutrient absorption. Plant is past its prime.
  4. Pests such as snails, mites, caterpillars, aphids, grasshoppers, birds and animals etc.
  5. Diseases caused by fungus, bacteria or viruses. Disease root systems are common during periods of constant rain, high humidity and temperatures and poor air movement. Roots need to dry out more.
  6. Nutrient solution concentrations are too high or low. Nutrient solution is not balanced and there is a nutrient deficiency or excess. Irregular nutrient supply or watering.

SYMPTOMS OF NUTRIENT DEFICIENCIES OR EXCESS

NITROGEN

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Nitrogen excess results in dark green plants with abundant foliage but the flowering and fruiting are delayed. There is stunted root growth. Flower drop occurs resulting in little fruit production.

Nitrogen deficiency causes plants to be spindly with small yellowish leaves. Parts of the plant will turn purple and then the plant becomes pale and yellow esp. the older leaves. The new leaves in tomato plants point vertical. The stems are short and the leaves and fruit are small. A light red cast can also be seen on the veins and petioles. The older mature leaves gradually change from their normal characteristic green appearance to a much paler green to yellow. Similar to a phosphorus excess or a sulphur deficiency.  A  faint red shade may exist on the yellowish leaves.

The yellowing in nitrogen deficiency is uniform over the entire leaf including the veins. Nitrogen deficient plants recover immediately when nitrogen is applied as a foliar spray (leaf spray).

PHOSPHORUS

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Phosphorus excess causes leaves to be bright brown or yellow brown in colour, similar to a nitrogen deficiency. Mature leaves appear crushed. Leaves and fruit develop areas of bright dry spots. Fruit will ripen earlier. Affects the availability of copper and zinc and may cause deficiencies in these nutrients.

Phosphorus deficiencies will cause leaves to have a distinct purple tint under young leaves. Stems and petioles will have a purplish tinge. The leaves will also curl backward and wilt. Phosphorus also affects growing tips and lateral shoots causing slow plant growth resulting in small plants. The plants maturity is delayed and fruiting is poor. The roots are stunted and yellow brown. Phosphorous deficiency can occur during cold temperatures, particular during cold nights.

Phosphorus deficiency

POTASSIUM

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Potassium excess causes young leaves to turn a bright green and mature leaves become yellow. Leaf stalks become hard and brittle. Potassium is not usually absorbed by plants in excessive amounts, but high levels may also lead to deficiencies in magnesium, manganese, iron and zinc.

Potassium deficiency initially causes yellowing and burning on leaf margins (edges) of young leaves progressing to increase yellowing of leaves between the veins. The veins remain green. Older leaves will have brown mottling and will curl and crinkle. Potassium deficiency results in poor growth, small leaves, soft stems and young leaves drooping. Flowers are fewer, pale and lack brilliance. Roots develop a yellow brown colour. Plant is prone to fungus.

Fruit will ripen blotchy and boxy. A foliar spray of 2% potassium sulphate may help.

Early potassium deficiency

Late potassium deficiency

Potassium deficiency on fruit

CALCIUM

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Calcium excess reduces the absorption of potassium, magnesium and trace elements and gives the effect that there are deficiencies of these elements. Older leaves may develop spots between veins.

Calcium deficiency. A calcium deficiency will affect young tissues first. Growing tips and young leaves become stunted, turn yellow on the leaf margins at first and die. Underside of leaf turns purple and leaf curls. Root growth is stunted. Flowering fails and fruit will get brown spots first and then progress to blossom end rot (or BER Syndrome), esp. tomatoes. Hot weather accentuates this decay.

Calcium deficiency will also make plants more susceptible to heat stress. In most cases the Calcium deficiency is caused is  by water stress on the plant, large variations in humidity and high levels of calcium salts.

Foliar sprays of 0.75% to 1 % calcium nitrate solution may help.

Calcium deficiency

Blossom end rot

MAGNESIUM

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Magnesium excess results in a cut and ragged appearance of mature leaves. The older leaves and fruit develop bright dry spots.

Magnesium deficiency results in leaves first turning yellow at the leaf edges, then progressively yellowing towards the centre until a green arrow shape forms. Only the youngest leaves remain green. Older leaves become mottled.  Brown dead areas form. Flowering is decreased but rarely results in yield reduction. High potassium levels can limit the uptake of magnesium and cause magnesium deficiency symptoms. In its advanced form, magnesium deficiency may superficially resemble potassium deficiency.

The deficiency is corrected by watering with a 10 % magnesium sulphate solution.

Magnesium deficiency

SULPHUR

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Sulphur excess causes small leaves and slow growth in plants. Root systems become harder and more compact.

Sulphur deficiency is not very common. Plants are stunted and young leaves turn yellow. A reddish to purple colour may form at the leaf base under the leaves. The upper leaves become stiff and curl downward. The stems, veins, and petioles turn purple. Sulphur deficiency resembles nitrogen deficiency but in sulphur deficiency the yellowing is much more uniform over the entire plant including young leaves Protein production is reduced. Root systems become larger and softer.

Sulphur deficiency

IRON

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Iron excess slows plant growth.

Iron deficiency impacts a plant quickly but is not a common problem. The symptoms are similar to a plant not exposed to light. Young plants turn almost white. The veins in older leaves first turn yellow and then the whole leaf will turn yellow and die. Blossom drop occurs and root systems may turn a yellow brown.

If the pH is too alkaline iron may become insoluble and drop out of the solution. If the pH is too low plants will uptake aluminium, restricting iron absorption. An iron deficiency may also be caused by an excess of manganese, copper or zinc

A foliar spray of 0.5% iron chelate every 3 to 4 days with restore the coloured leaves to normal. The veins in the leaves will be the first to change green.

Iron deficiency

MANGANESE

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Manganese excess causes the leaves to become bright brown or yellow brown and may affect the availability of iron. The toxic level for manganese is 500 ppm.

Manganese deficiency causes leaves to have a cut and ragged appearance. Young plants turn mottled yellow colour. As the deficiency increases, the leaves take on a grey to purplish metallic sheen and develop dark freckled and dead areas along the veins.

Plant growth is stunted. Flower buds fail to bloom. Fruit production is small and the fruit develops spots.

Foliar spray using 1 % solution of manganese sulphate is one remedy.

Manganese deficiency

BORON

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Boron excess results in the leaves having dry margins and a cut and ragged appearance. Boron is an essential plant nutrient but when it exceeds 150 ppm it becomes toxic.

Boron deficiency causes the leaf tips to yellow, then become highly coloured and defoliate. The stems become brittle. The core of the plant develops a cork like appearance and brown spots. Boron deficiency symptoms generally appear in younger plants at the propagation stage. The growing points wither and die and the growth of the plant slows down and stops. Pollen formation is poor and this results in poor fertilization of flowers. The fruit is often split and miss-shaped. Boron deficiency can lead to calcium deficiency.

Foliar spray of 0.1 to 0.25% borax is needed.

Boron deficiency in leaves

Boron deficiency in fruit

ZINC

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Zinc  excess may affect the availability of iron. Toxic level for Zinc is 300 ppm.

Zinc Deficiency causes the younger leaves to become yellow with very small leaves in the early stage of zinc deficiency.  Maturity is delayed and the stems of the plant fail to elongate resulting in rosetting of the leaves. As the deficiency progresses dead areas and pitting form on the older leaves but the main veins remain green.

Excess phosphorus may cause a zinc deficiency.

A foliar spray with 0.1 to 0.5% solution of zinc sulphate is needed.

Zinc deficiency

COPPER

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Copper excess causes chlorosis (yellowing) of the leaves and defoliation. Roots develop a black colour.

Copper deficiency causes die back. Young leaves become misshapen, curling into a tube. Leaves become pale yellow and spotted. Young tips and buds will wilt and die. Plant growth is irregular and reduced with few or no flowers. Excess phosphorus may cause a copper deficiency.

Use a foliar spray with 0.1 to 0.2% solution of copper sulphate to which 0.5% hydrated lime has been added.

Copper deficiency

MOLYBDENUM

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Molybdenum excess will turn leaves a brilliant orange at high concentrations. It causes tomato leaves to become bright yellow.

Molybdenum deficiency causes symptoms similar to nitrogen deficiency without the reddish coloration on the undersides of the leaves. Nitrates accumulate in the plant that cannot be used. An early symptom for molybdenum deficiency is a general overall yellowing. The leaves become small and yellowish. Yellowing forms between the leaf veins in older leaves. Tomato leaves turn golden yellow. The leaf margins dry out and burn. The edges of leaves curl up upward. Plants become pale.

Use a foliar spray with 0.07 to 0.1% solution of ammonium or sodium molybdate

Molybdenum deficiency