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Unfortunately, the apple orchard, like other fruit orchards, suffers from pests, which, by the way, are many. These are such well-known diseases as rot, powdery mildew, cytosporosis. The most dangerous fungal disease is scab on an apple tree, how to deal with which, this article will tell.
What does a scab look like?
Scab on an apple tree is easy to identify by its characteristic external features: first, olive-green spots appear on the leaves, blackening and cracking over time. The disease affects almost the entire tree: leaves, fruits, ovaries, petioles.
The fungus also affects young shoots, for which this can be a difficult test – often a diseased plant dies. The bark of diseased seedlings is covered with swellings, which burst after a while, and the bark itself cracks and peels off.
Prerequisites for development and distribution
The development and spread of the disease is facilitated by a wet, rainy spring, as well as thickening of the crowns of trees in the garden. The greatest danger of infection of trees occurs during the flowering period of the apple tree – the end of May, when the weather is humid and warm.
The causative agent of scab is the fungus Venturia unequal (Venturia inaequalis), and the fungus spreads with the help of its asexual form, Fusicladium (Fusicladium dendriticum). In early spring, spores of the fungus, thanks to drops of water, fall on the foliage of the apple tree, where they attach to the surface with the help of the mucous membrane and germinate.
Stages of the disease
The first signs of the disease are visible to the naked eye 2-3 weeks after the opening of the kidneys. Olive spots appear on the leaves, where asexual spores develop. The next stage of distribution: young branches and fruits are affected, on which dark areas of damaged tissue are formed, under which the pulp of the fruit is destroyed.
Due to the fact that the fungus does not disrupt the process of photosynthesis in the leaves of the plant, the tree continues to grow and develop, contributing to the spread of the disease. Leaves affected by scab fall off prematurely, fruits shrivel.
In the third stage, coprotrophic, the fungus passes with the onset of autumn, when the leaves fall. The fungus overwinters in fallen leaves, infected fruits and tree bark. In the spring, spores ripen again in the formed bags and the apple tree undergoes a new infection.
Prevention
Autumn
Proper and timely care of your garden will become the basis of prevention and will help prevent the appearance and development of such a disease as scab on an apple tree, the treatment of which is a rather lengthy and laborious process. Prophylactic work aimed at preventing diseases should be started in the fall. As soon as the crop is harvested, immediately proceed to remove the dried fruit. Trim dried branches, clean, where necessary, the trunks to a healthy tissue and do not forget to whiten them. Collect all the foliage that has fallen in one place, and then take it out or burn it.
Spray the crown of the apple tree with a 5% solution of copper sulphate.
Spring
Disease prevention can be started in early spring, but only until the buds open.. At this time, it is recommended to carry out the first spraying of the apple tree with Bordeaux liquid 1%. If there is a need, then the second spraying is carried out immediately after the flowering process, again with Bordeaux liquid or solutions of cineb, captan, cuprosan.
15 days after flowering, the third spraying is carried out. If Bordeaux liquid is used for it, then you need to make sure in advance that the leaves will not get burned. To do this, conduct an experiment – select a couple of branches and spray only them. In the event that, after treatment, necrotic spots do not appear on the leaves, and a pattern in the form of a grid does not appear on the fruits, the concentration of the solution is normal and the entire tree can be sprayed.
It is advisable to use immunostimulating biological products, such as potassium humate or Fitosporin M biofungicide, in processing before the onset of scab (second half of May). . This will reduce the number of chemical treatments in the future.
In the event that the lesion is massive, then during the season it will be necessary to carry out at least 4 treatments, and in especially severe cases, all 6 times.
It is also advised to spray the tree in the green cone stage with a preparation such as Raek. For preventive spraying in the spring, “Skor” and “Vektra” are also used. For repeated spraying of both young ovaries and in the fall after harvesting, Zircon is used.
Treatment
If the preventive methods did not bring the expected results and turned out to be ineffective, then to combat the fungus, they resort to chemical preparations – fungicides. But before applying, you need to familiarize yourself with their features.
Application of fungicides
Many of these drugs are available under different brand names. And, despite the fact that they have different names, but the active substance is the same. Therefore, when choosing a fungicide, pay attention to the active substance. If this is not done, then there is a high probability that you will constantly use the same drug and over time the parasite will develop resistance to it. Therefore, it is important not to constantly use a fungicide with the same active ingredient to fight infection during one season.
In suburban garden plots, drugs belonging to hazard classes 3 and 4 are used. They do not accumulate in fruits and are not dangerous for human skin, as they do not penetrate the skin. In no case do not use chemicals on your plots that are used to control pests in horticultural farms – such drugs are mostly dangerous to humans.
Fungicides copper sulfate and Bordeaux liquid should be sprayed more abundantly, to the state of large raindrops. Such spraying is also called “blue spraying” because the tree acquires a blue color after the procedure.
It is necessary to carry out processing in the morning or in the evening. The main thing is that the weather should be calm. Since we use pesticides, it is necessary to use personal protective equipment (gloves, masks, goggles).
Spraying after rain is considered the most effective.
Video “Processing apple trees with fungicides against scab”
This video will show you how to treat scab-infested apple trees with fungicides.
Basic chemicals
Substances that contain hay bacillus are considered less dangerous. It actively suppresses the pathogen fungus. For small farms, Gamair is used, its 10 tablets should be dissolved in 10 liters of cold water. Spraying is carried out up to 3 times per season.
The drug “Horus” is effective even at low temperatures of + 3- + 10 degrees. The spraying procedure is recommended to be carried out 2 times. Before bud break and after flowering. Its distinctive feature is that it is not washed off during the rain.
“Fitolavin” belongs to the group of streptothricin antibiotics. To prepare a solution, 20 ml of this drug is dissolved in 10 liters of water. They carry out 4 treatments per season, at intervals of 15 days.
“Strobe”. The drug is active not only against scab, but also useful in the fight against soot fungus, powdery mildew. To prepare the solution, you need to dilute 10 ml of this substance in 2 liters of water. It is necessary to carry out at least 3 sprayings per season.
Treatment with mineral fertilizers
It is believed that mineral fertilizers “work” no worse than chemistry in the fight against scab. In addition, they are also foliar top dressing. For treatment, highly concentrated solutions of 10% ammonium nitrate, 10% ammonium sulfate, 15% potassium salt, 15% potassium nitrate are used.
These fertilizers can also be used for prevention, only at lower concentrations.
Scab on an apple tree is a dangerous enemy of our garden, but with proper care, and above all thanks to autumn preventive work, in most cases you can save your garden from infection.