The almond tree is a tree of Asian origin that has been widely cultivated throughout the Mediterranean region for centuries; in fact, many of us who live in lands bathed by that sea, have so many specimens throughout our lives, that we consider it to be a "tree that is very much ours." Of course, especially dry and hot summers cause their leaves to fall earlier than they should. But it also has another problem that is much more serious if possible: the ocher stain.
From the first moment you can see that something is happening to it: the leaves, previously green, now begin to have spots that turn yellow and then brownish; and in the end they dry up completely and fall, leaving the tree without foliage. That's why, it is very important to know everything about the ocher spot of the almond tree, since this way we will have the possibility of recovering it.
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What is the ocher spot of the almond tree?
It is a disease caused by asmycete fungi of the species Polystigma fulvum (before Polystigma ochraceum). Although the symptoms are very visible, they do not usually appear until a month after the infection, so it is advisable to be vigilant, especially if there are almond trees with this problem in our area.
These symptoms are the appearance of brown-yellow spots on the leaves, which eventually end up brown and fall to the ground. What happens is that the microorganisms will remain there, in the soil, during the winter, where they will develop to infect new almond trees.
When do the first symptoms appear?
A tree that has been infected will start to show symptoms in spring, this being the season in which the fungus is much more active. These spots can measure up to a centimeter in diameter, which overlap each other as they increase in size.
Later, when the disease is very advanced, they develop reproductive structures in order to create new spores. In this way, the Polystigma fulvum can continue to expand.
What conditions does the fungus need to develop?
You need above all this: high air humidity and heat. That is why it is so common in the Mediterranean region, because in summer temperatures exceed 30ºC, and the humidity of the air is very high (above 50%) which makes every morning humid, with dew. .
Thus, although during those months it does not usually rain at all, the fungus can develop normally, thus harming the almond trees in the area.
Are there varieties of almond trees that are resistant to ocher spot?
It is not that it is more resistant, but it is more tolerant. I'm talking about the variety Bellona. This is a late-flowering variety, developed in Aragón (Spain) in the late 1980s. Unlike other varieties, this one begins to flower at the end of February, and not in January, so the ripening of the almond is not delayed. complete until mid/late summer.
By contrast, the Tono, Vairo or Guara varieties are very sensitive, to the point that they can be left without any leaves after infection.
Which is the treatment?
Since symptoms take time to appear, the best we can do is prevent infection. And that goes through remove all the leaves that have fallen to the ground, since this reduces the risk of fungi damaging the tree.
It is also convenient carry out treatments with insecticides whose active ingredient is Boscalida, after flowering, and after an episode of heavy rain.
Can an almond tree be prevented from having ocher spot disease?
Not at all, but in addition to carrying out the preventive treatments that we have mentioned above, it is important to keep the tree well cared for. In other words, if we know that during the summer it has a hard time due to lack of water, we can help it if we water it from time to time (2-3 times a week) until the rains come and the weather cools down.
Likewise, it will be highly advisable to pay it in spring and summer with natural fertilizers, suitable for organic farming, such as guano (not mixed with fertilizers), compost, seaweed fertilizer, mulch, manure,... or any other of organic origin.
As well it is extremely important not to prune it, or to do it only at the end of winter. We will use previously disinfected tools, and we will seal the wounds with healing paste. In addition, when pruning, we must avoid cutting thick branches, as these take longer to heal, and apart from that, the only thing that is achieved is that the tree does not look pretty.
I always say that the pruning that is best done is the one that cannot be seen, and that is how it is. We have to respect the plant that we are pruning, and eliminate or cut those branches that are necessary, neither more nor less. You have to choose to do small pruning every year or every few years, than a drastic pruning one year.
Almond ocher spot is a very common disease, but it can be treated.