Fruit and Vegetables

Lemon tree with diseased leaves

Question: lemon tree with diseased leaves

Hi, my lemon tree that had been producing fruit in the industry for a few months until last winter has all its leaves shriveled and with a kind of black and white powder on it ... how can I fix it? A massive pruning of the branches could be useful? Thanks

Answer: lemon tree with diseased leaves

Dear Giuseppe,
the white powder, present on your lemon, could be oidium, which develops when the night is very cool and the days definitely rainy or humid; it is a fungal disease that blatantly spoils the foliage; it is treated by treating the plant with sulfur-based products (only if it is not in bloom), which dry the water that remains on the leaves and kill the spores of the fungi that have attacked them.
If in addition to hatred there is also a black powder, it could be smokings; also in this case it is a fungal disease, which usually develops on honeydew produced by insects, such as cochineals or aphids. So, if your plant develops fumaggini, the wrinkled leaves are also hosting insects, which must be eradicated to eliminate even the fumaggine.
It is probably the climate that is not helping you, given that spring was very cold and rainy; I believe that a good treatment based on sulfur, and the climate that is becoming decidedly warmer and drier, will help you a lot in the care of your lemon. If you also see insects on the foliage, you can try chasing them using an insecticide based on pyrethrum, or nettle; or you can draw them away from the plant by using the special adhesive traps, which are based on the fact that some insects love the yellow or white color, and therefore approach the trap, remaining trapped.

Diseases of the lemon

The lemon diseases which can be found more frequently are mainly powdery mildew, as seen before, cochineal, root rot (especially in pots), dry disease but also viruses and bacteria.
Powdery mildew affects lemon leaves and proliferates in a very important way in hot and humid seasons, in which it finds the ideal conditions for its proliferation. Powdery mildew is a fungus that appears powdery on the upper side of the leaves creating a whitish powdery patina that is difficult to eradicate in particularly rainy seasons. Usually copper is used to combat powdery mildew which must be sprayed in aqueous solution on the leaves.
Another disease that attacks lemons, especially those that are brought to the greenhouse during the winter period, is the cochineal, an insect with a very particular shape that sticks to the leaves and pierces them to feed on the sap of the plants. Cochineal is not very dangerous unless it is a very strong infestation. In any case, it is a parasite that is eliminated by spraying the white oil on the foliage of the lemons. White oil is a mineral oil that creates a patina on the leaves and suffocates the coccingilia. It should not be administered in the hottest months of the year unless it is a special white oil for the summer, as creating a patina on the leaves, when temperatures rise, can create a boiling effect on the leaves, not allowing a adequate perspiration in the hottest months.
Still talking about diseases related to the winter shelter of lemons in greenhouses, another parasite that attacks these plants quite frequently are aphids. Aphids are sap-sucking insects that pierce the leaves and extract the sap from them, a sap that is largely secreted later by the insects themselves through the honeydew, a sugary substance that is deposited on the underlying leaves. This honeydew may, after a while, favor the arrival of another disease, the fumaggine, a fungus that feeds on honeydew and covers the leaf with characteristic black spots, preventing photosynthesis and favoring the start of a process of leaf necrosis.

Lemon tree with diseased leaves: How to treat sick lemons

After having examined all the main ones lemon diseases describing the symptomatology and possible treatments for each of them, it is also useful to give an overview of the intervention modalities to be adopted in case of infestation.
Accurately identifying the parasite that is attacking our lemon is in fact of fundamental importance, just as it is very important to know the methods of intervention for its eradication. First of all, after discovering the disease that has affected our plant, it is important to go to an authorized sales center to buy the necessary products or contact a person authorized to use pesticides if it is necessary to use products of this type.
The products should be sprayed on days that are not too hot and not too windy. The wind can indeed disperse most of the product used, as well as the heat. Very important is the respect of the right dosages that are legally reported on the products: an excess of active principle inside your solution will not bring improvements to your intervention.