Olive tree diseases: yellow leaf

The olive tree with yellow leaves is sick

The olive tree is a fruit tree that does not usually have serious problems: it may be attacked by a mealybug, or it may be very thirsty as a result of a drought that is lasting too long, but it really is not a tree that requires much care. However, in the event that its health weakens, one of the first symptoms that we will see is the yellowing of the leaves.

Being quite fragile and vulnerable, the foliage of a plant is usually the first part of its body to change: it changes color, loses firmness, and in some cases even folds. That's why we want you to know what are the diseases of the olive tree whose main symptom is yellow leaves so that you can take the necessary measures so that new damage does not appear.

Pests

Prays oleae is a pest that causes yellow spots

Image - Wikimedia / Giancarlo Dessì

Although it is not a plant that is usually affected by pests, on certain occasions we can see that it has some. These are insects that usually they are very active in summer, and resting or hibernating during winter. I say "generally" because it may be the case that a winter is especially warm, and of course, this stimulates some.

The pests that cause olive leaves to turn yellow are the following:

  • Borer: specifically, the Phoeotribus scarabaeoides. This is a beetle that, in its larval phase, feeds on the inside of the branches and the trunk of the tree. This causes the olive tree to weaken and its leaves to turn yellow until they finally fall off. Unfortunately, there is no curative treatment, but there is a preventive one: the remains of pruning must be eliminated, as well as those branches that are brittle.
  • olive moth (Prays oleae): it is an insect that goes through three phases of development: the phyllophagous, which is when it feeds on the leaves and tender stems; the antófaga, which is when it feeds on the flowers; and finally the carpófaga, which is when it destroys the fruits. To avoid this, treatments with specific insecticides must be carried out. Learn More.

Diseases

Xylella is a bacterial disease

Image – Wikimedia/Sjor

As far as diseases are concerned, these can be caused by fungi, viruses or bacteria. Many of the pathogenic species use an insect as a vector; that is, as soon as it bites a leaf, flower or fruit, the microorganism passes into the interior of the plant through the animal's mouthparts. Therefore, in all cases it will not be enough to treat the disease itself, but the insect that transmits it will also have to be controlled.

But which ones make leaves turn yellow?

  • I repeat: it is a disease transmitted by the fungus Spilocaea oleagina which causes the appearance of spots on the leaves that are first yellow and then brown. It is one of the most damaging, since it greatly weakens the tree, and as a consequence, it reduces its production. It should be treated with fungicides such as this, but it is best to keep the plant well cared for, and even make sure that the variety that you want to buy is resistant to the repilo.
  • Xylella fastidiosa: it is a relatively new disease in Spain, since it was detected in 2016. It is caused by a bacterium (X. fastidiosa) which is native to northern California (United States). Its vectors are those insects that feed on the wood of plants. And the symptoms it produces are the progressive yellowing of the leaves and the weakening of the tree. Unfortunately, there is no curative treatment, but if the olive tree is not thirsty, and if it is paid regularly, the risk of being affected by this bacterium can be reduced. Learn More.

Other problems

Olive trees are a resistant tree

Image - Wikimedia / Burkhard Mücke

Although as we have seen there are pests and diseases that cause yellowing of olive leaves, sometimes the cause can be, for example, in excess or lack of water, or even in the soil. Let's talk about it:

Excess or lack of water

Our protagonist is an evergreen fruit tree native to the Mediterranean. In this region, the summers are very hot (they can reach 41-42ºC in some points, and have several nights with lows above 20ºC), and the winters are mild (except in the highest peaks, where there can be frosts of up to the -12ºC, it is normal that it does not drop below 7ºC.In fact, at low altitudes it is rare for it to drop below -2ºC). Y If we talk about the rains, they are very scarce: between 250 and 700mm of precipitation per year on average, although they can exceed 1000mm.

The olive tree, therefore, is able to live with little water. Moreover, in Mallorca, where I live, they are grown without any problem in areas where they do not exceed 300mm of annual rainfall. And I can assure you that the harvest is good. Therefore, it is very important that we take this into account, as it does not need as much water as other fruit trees.

Moreover, if it is planted in the ground, it will suffice to water it if we see that the drought has lasted several weeks and it is very hot. Of course, we will also have to do it if it is in a pot, since it is normal for the soil to dry out very quickly.

What are the symptoms of excess or lack of water in the olive tree? The yellow leaves. In the first case we will see that the first to change color will be the oldest, and in the second the youngest. To recover our tree, we will have to suspend irrigation if we see that we are watering too much and also treat it with fungicide so that the fungi do not harm it; and on the contrary we will have to water it more often if it is drying out.

Land

Although it is a fruit tree that grows in poor soils, do not make the mistake of planting it in one that is very heavy and compact. And it is that, it can tolerate a punctual flood, but if its roots are always flooded, it will not take long for them to die. For this reason, before planting it in the orchard or garden, you have to see if it has good drainage, because if the soil does not absorb water quickly, then it will not be good for the olive tree.

But this has a pretty easy solution: it simply involves digging a large hole, 1 x 1 meter, and filling it with a mixture of black peat and perlite in equal parts.

As you have seen, the olive tree can have yellow leaves for different reasons.


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