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Pale stains that appear on the foliage and then burn : we often look for a disease when actually it is only a mistake by the gardener. Luckily it is not very difficult to cure.
The symptoms
Suddenly, part of the plant’s foliage discolours. Quickly afterwards, this discoloration gives way to a browning, as the leaves’ tissues wither. It is mainly the larger leaves and the ones most exposed to the sun that are affected. The plant’s leaves situated on the side opposite to the sun and the very young ones are not affected. This symptom can be observed in two cases only: on a plant that we have just moved (such as the potted plants that we bring outside in the spring) or after a severe pruning on neighbouring plants.
Lifecycle The burn caused by excess sun can be seen quickly but not immediately. Depending on the plant physiology, the burn can develop on the same day or latter. Plants, which have pale and thin foliage, show signs of burns after the first day of excessive sun. The plants with thicker and darker leaves, such as Camellias and Rhododendrons, will only show damage after several weeks. As the plants have a certain capacity to adapt, young foliage still forming does not suffer from it. Therefore, sunburn is a transitory problem.
How to fight it
When the burns are present, it is best not to touch the affected leaves. To remove them could threaten and provoke a burning of the leaves underneath, which where previously protected. Place a protection on the plant and adapt it progressively to the light, for example covering it with a net, which you take off little by little. You can also carry out a pruning of the plant to force it to grow new leaves, which will be more resistant than the ones that have burnt.
How to avoid it
When you bring a plant outside, do not put it straight away in the sun. Place it in the shade to start with, bring it closer to the sunlight progresively, in two to three weeks. Before pruning a plant, ensure that the neighbouring plants will not be brutally exposed to excessive sun light. If pruning is absolutely necessary, place a shading net on the most vulnerable plants.
Good to know
Plants with golden foliage are sensitive to excessive sun light. This vulnerability can be explained by the fact that they have less chlorophyll than the other plants. Therefore, their foliage can burn when they are exposed to full sunlight. This is the case when they are planted in the wrong site or after the pruning of a neighbouring plant, which was protecting them from direct sunrays. This phenomenon can be also found with shade loving plants that are suddenly exposed to sunlight, whereas they were previously protected from it. - Photos (1)
Sunburn
Sunburn
Author: Jean-Michel Groult
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