How to recognise it
The leaves yellow between the veins (inter-veinal).
What causes it
- Iron deficiency – General inter-veinal yellowing with young leaves worst affected. The unaffected veins stand out as dark green against the yellowed tissue.
- Manganese deficiency – General inter-veinal yellowing with older leaves worst affected. Patches of dead tissue may appear among the yellowed areas. On some plants (such as potatos) a young leaf can pale and all leaves may roll upwards. Peas, and to a lesser extent beans, can also suffer from marsh spot, brown circular spots seen within the seed when the two cotyledons are separated.
- Magnesium deficiency – Inter-veinal yellowing (sometimes at the centre of the leaf) and red tints developing between the veins, giving a marbled effect. The veins remain green. In the case of red-pigmented plants (eg beetroot) the colouring may only be red. The symptoms occur on the older leaves first and late in the season. On apples severe premature defoliation may occur.
In ericaceous plants (such as rhododendron) iron or manganese deficiency can be a sign of growing them in soil which is too alkaline. On the reverse, magnesium deficiency often occurs on acid, sandy soils.
A particularly high level of iron within the soil can cause a manganese deficiency and vice versa.
Plants fed with a high potash feed to promote flowering (eg tomatoes) become more susceptible to a magnesium deficiency.
If only the lower leaves are affected this could be due to poor drainage rather than a nutrient deficiency.
Why it’s a problem
It’s natural for the odd leaf to show chlorosis, but if most or all of the foliage is yellowed this suggests a serious nutrient deficiency.
With magnesium deficiency the affected leaves may fall early and, when it affects apples, the yield can be reduced. However the main problem is really the appearance of the plant.
With iron deficiency plants will lose vigour and in extreme cases can fail to flower or fruit and may die.
Plants need magnesium, iron and manganese to form chlorophyll (the green pigment used in photosynthesis) and for several other functions. Iron is fairly immobile in the plants, which is why the younger leaves are affected first (they aren’t able to draw sufficient iron supplies from the rest of the plant as they develop). Magnesium and manganese are both fairly mobile, so the younger leaves draw the nutrients from other parts, leading to the chlorosis affecting the older leaves first.
Where you are likely to find it
Pretty much any plant can suffer from nutrient deficiency induced chlorosis.
Ericaceous plants (eg rhodendrons, skimmia, azaleas and camellias) are most susceptible to iron and manganese deficiencies. It can be a particular problem if they are grown in soils overlying chalk or limestone.
Some fruit trees and soft fruits (especially strawberries and raspberries) are also vulnerable to iron or manganese deficiencies.
A wide range of plants, including beetroot, brassicas, parsnips, peas, beans, spinach can also be affected by manganese deficiencies.
Magnesium deficiencies are common on light, acid, sandy soils where the magnesium is easily leached, so the effects are worse in wet weather. They are particularly noticeable on apples, tomatoes, some brassicas, annual bedding plants, lettuces and potatoes.
How to prevent it
With ericaceous plants, ensure that they are planted in the right type of soil (ie acidic soil) and watered with rain water (not tap water). They may survive in neutral or even slightly alkaline soil if planted with enough peat and regularly provided with an appropriate feed, but you need to consider whether it’s really worth all the hassle!
Ensure that you regularly monitor the health of your plants to ensure you can react to any nutrient problems efficiently.
How to get rid of it
Apply a fertiliser which supplies the missing nutrient. In the case of an iron deficiency compounds known as chelates or sequestrenes are available. For a manganese shortage feed with a solution of manganese sulphate at a rate of 1.5g per litre of water for every 2m2. If any liming of the soil is carried out, reduce it or cease it altogether if an iron or manganese deficiency is identified.
A magnesium deficiency can be treated with the application of magnesium limestone.
Ensure that the plant is generally well looked after to aid its recovery.
Is it good for anything?!
Other useful information
Other nutrient deficiencies can also cause a more general (ie not inter-veinal) leaf chlorosis.