Today it seems that we have to talk about a specific disease. Normally, in Gardenprue we are used to talking about specific pests and diseases of a crop, naming a few of them. But sometimes, given their importance, we dedicate an exclusive article to one of them. This is the case of the Sharka . Do you want to know about her? 

WHAT OR WHO CAUSES THE SHARKA OF FRUIT TREES?

Sharka is a disease and is caused specifically by a virus . As you will know within the diseases that a plant or crop can have, its origin may be due to bacteria, fungi, nematodes or viruses . The latter are very difficult to eliminate, if it can be done, of course, such as the sadness virus in the lemon tree, or since we are talking about the sharka in the fruit trees.

Returning to the topic of this virus, this microscopic infectious agent is found inside plant cells , on such a small scale that even light microscopes are not able to see them (we would have to go to electron microscopes).

THE MAIN PROBLEM, ITS DISPERSION

One of the great problems of sharka that makes it a very well-known disease in Spain, in addition to the serious symptoms it produces , is the fact that it can spread and spread to other crops very easily . It is usually transmitted when grafting or vegetative multiplication is carried out , where there is affected plant material, or some tools are not carefully sanitized. These means of transmission are controllable following guidelines of good practice in the field and the virus could be controlled in some way. But the problem is that there is another means of transmission that is much more complicated to control, aphids ( Aphis spiraecola and Aphis gossypii in southeastern Spain).. Only with the bite of the aphid (its means of feeding) an affected crop, whether for seconds or minutes, is it capable of storing the virus inside, and transmitting it when it moves to another crop. There is no latency period or anything, so in a matter of minutes several crops can be affected.

WHAT CROPS ARE AFFECTED?

In general, most stone fruit trees . Speaking specifically, fruit trees such as plums (any of them, European, Japanese, myrobolan, Brompton, chicks, etc.), apricot , peach, nectarine, almond (only as a host) and cherry trees have been affected. . This last crop, a new breed of the virus has been discovered.

WHAT HAPPENS TO MY FRUIT TREE WHEN IT IS AFFECTED BY THE SHARKA?

There are various symptoms, and as often happens, they can be very easily confused with anything, since none of us are experts (but hey, we are learning little by little). It depends mainly on the type of fruit tree affected. In the plum and apricot tree chlorotic spots appear on the leaves, generally circular, forming rings. These chlorotic spots over time become necrotic and acquire brownish tones. In the case of the fruits, there are also spots (some easily distinguishable and others not) and depressions. In the bone, in addition, deformations appear.

For example, here is an image of peach trees affected by sharka , which is not easy for inexperienced people to identify.

However, in the case of the nectarine and the M-type sharka, it is easily distinguishable. Look at the curious shapes that appear in the fruits.

HOW IS IT DIAGNOSED?

As we have discussed before, these strange spots are almost always attributed to viruses. It’s funny how when it comes to identifying a problem in a crop, when you don’t know what it is, it is usually attributed to a virus and Holy Easter. In this case, Sharka, when seen on the fruits or on the leaves, can easily be confused with any other virus. We have to check the state of the bone, where the deformations appear, to make sure that it is really sharka. Once we have seen deformations in the fruit , we have to ensure faithfully with one of the few techniques that ensure the disease, ELISA using monoclonal antibodies.

TREATMENT

It has a single highly effective treatment, uprooting the tree . As simple as that. So far there is no chemical or technique to eliminate the virus. The only existing treatments are preventive ones. Sanitize the plant material and make sure that it is virus-free, as well as the work tools , and as for the aphids, there has not been much luck in the control since the potential for transmission of the virus by this vector is very high, and it takes very little time to transmit. The best solution is to uproot the tree and avoid planting stone fruit trees in the affected area.