One of the most common diseases of apple trees is Apple scab. sooner or later Apple scab will appear in your orchard, even if there is only one apple tree. Apple scab is not considered a fatal disease, it does not destroy the tree directly, but it affects it indirectly – reducing its immunity, winter hardiness, and resistance to pests and diseases.
In addition, Apple scab causes the fruit to completely lose its marketable appearance; you can certainly eat them and use them for processing, but they will not be stored and are impossible to buy for people in the market.
Apple scab on apple trees happens by accident, but it’s not feasible to get rid of it all at once, but it is possible to do it. Today let’s talk about what kind of disease it is, the rules to prevent it, and the means to combat Apple scab.
WHAT IS AN APPLE SCAB?
Apple scabs on trees can be detected by everyone: spots (on leaves, fruits), which have a yellowish-green color in their initial stages of development, later turn black and often become fissures that can be seen immediately.
The causative fungus of Apple scab is a marsupial fungus, Venturia inaequalis, which usually affects the leaves, but also the ovary and, of course, the fruit. The fungus is most active in wet years and during seasonal periods when there is heavy rain, fog, or prolonged wet weather.
Usually, the Apple scab fungus appears on bark and branches in early spring, where it attaches to branches through the mucous membrane and immediately begins to develop, sometimes quite actively.
The first visible signs of fungal emergence can usually be observed during the flowering of apple trees, which usually occurs in May. Usually, heavy rains combined with warm weather will help the fungus to grow.
Apple scab fungus spores spread quite actively with water, wind, animals, and people, and if they land on the leaves, they begin to develop very rapidly, literally penetrating deep into the leaf tissue. The vital activity of the fungus causes spots to appear on the leaves and then – just through, round holes.
The development of Apple scab is more active in the summer when abundant dew and rain combined with high temperatures above 32° F promote its development. Apple scab develops most actively at temperatures of 71° F (22-25° C). Developing during the season, Apple scab forms fungal spores near fall, and they simply overwinter perfectly in the soil and shoots, “hiding” in the leaf litter. The vital activity of the fungus disrupts photosynthesis, but is usually not critical, so the tree does not die, but the fungus is actively spreading.
Often, leaves affected by Apple scab do not shed until a few days before expiration, and the fruit may not shed at all, but often their shape changes to irregular, with wrinkles and cracks (instead of spots) and a reduction in fruit weight.
The overwintered fungus is activated again with the arrival of spring and the whole cycle of its development is repeated. Therefore, it is impossible to prevent and get rid of Apple scab on the plots only with treatments, the whole necessary combination of measures is important here.
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PREVENTING THE EMERGENCE OF APPLE SCAB
In general, preventive treatment of Apple scab should not be started in the spring, but in the fall to prevent the fungus from surviving the winter in the soil and plant residues.
In addition, it is very important to take proper care of apple trees, observing all agronomic practices, and plot cleaning, just like personal hygiene, which will help prevent the appearance of the disease, or at least reduce the risk of its occurrence.
To prevent the occurrence of Apple scab in the fall, in addition to plant treatments, all plant residues should be removed from the site and rhizomes. Leaves that have naturally shed should be collected and burned at the back of the plot.
Shoots should also be collected and burned and dried and broken shoots should be cut off. Do not allow any fruit to hang from the shoots, they must also be collected and destroyed as they can spread infection.
Try not to leave any flaking bark on the trunk, it must be gently scraped off and burned. The scraped area must be treated with copper sulfate, diluted in one tablespoon in 0.26 Gal (1 liter) of water. When a stable temperature below 32°F arrives, it is recommended to brush the trunk with lime powder (up to the first branch).
Those who only plant apple trees on plots should be reminded to follow the planting plan for these plants. Plantings should not be overgrown under any circumstances, and air must circulate freely in the garden, but if this is not done, water will not evaporate from the surface of the fruit, shoots, and leaf discs, and fungi will settle on them.
Apple trees are best planted on dwarf rootstocks, leaving 10 feet (3 meters) between plants, and for strong growth, you can safely leave 13 feet (4 meters). At first, it may seem like you are leaving a lot of space, but after ten years, you will praise yourself for the ease of moving, collecting crops, and caring for the trees in your garden, and they will thank you by giving you a large apple harvest.
Also, always make sure you use the correct dose of fertilizer and remember that neither a lack of fertilizer nor an overabundance of fertilizer is good for the plant and often has a debilitating effect on its immunity.
If we talk about preventive treatments, it is likely that some biological agents will be used. As a preventive spray before the buds open you can use 1% Bordeaux mixture and if necessary, repeat the treatment after flowering.
By the way, if an Apple scab appears in your garden every year and affects the most fruits and leaves, do not be lazy and have the soil analyzed, preferably in a specialized laboratory.
It is possible that Apple scab is rampant because your soil has a low pH, i.e., high acidity. In soils with a high pH, plants tend to be deficient in nitrogen, which means that the lack of nitrogen makes the plants less immune.
Don’t forget that you must apply nitrogen fertilizer every year (in the spring). In addition, you can apply 90-100 grams of lime per 11 square feet of soil every 5 years as a preventive measure, and if the soil is very acidic, you may have to apply a double dose of lime every year.
Breed apples for resistance to apple scab. Apple varieties with good resistance include Akane, Chehalis, Liberty, Prima, and Tydeman Red.
Therefore, to prevent Apple scab on trees, you need to: take proper care of the plants, be sure to water them, apply fertilizers, including potassium and phosphorus, remove plant residues from plots and secure bark areas, brush off flaking bark, whiten trunks, apply preventive treatments, and choose varieties resistant to Apple scab (you can learn about them in nurseries or in the National Registry or on our website (read variety descriptions on our website).
Also, don’t forget to do a visual inspection of the plants, which can be done at any time of your convenience, even daily, and if the disease starts to appear, start acting immediately.
HOW TO TREAT APPLE SCAB?
However, if everything seems to be done correctly and in a timely manner, but Apple scab still becomes stronger and appears on the plant, then urgent action is necessary. Many people immediately take chemical measures and start applying fungicides, that is, preparations to combat fungal infections.
We would like to give you a piece of advice: in order for this treatment to be effective, be sure to use only fungicides that are approved for the current season and should be familiar with the list of approved medications. Then, in order for the treatment on your property to be always effective, you need to treat with fungicides of various active substances, i.e. alternate them and apply the drug to completely eliminate the disease, leaving no pockets of infection.
When using fungicides, you must be careful: wear protective equipment, do not spray fungicides in windy weather, near apiaries and reservoirs, and do not use chemicals 20-25 days before harvest.
Usually, the first treatment against Apple scab on apple trees is carried out near the end of March, and in the south, in mid-March. During this period, the weather has usually warmed steadily, but the buds have not yet expanded and unfolded. If Apple scab was rampant in the past season, this treatment can be either preventive or eradicative.
For this purpose, you can use a fungicide or, more environmentally friendly, a 1% copper sulfate solution. To prepare this dose of the solution, it is necessary to dilute 100 grams of this substance in a bucket of water and then treat the plant, covering the entire above-ground part. In addition to copper sulfate, you can also use a solution of urea (one tablespoon per 0.26 Gal of water).
Do not forget that colloidal sulfur, Bordeaux mixture, and copper sulfate can be used to control Apple scab during the same period.
The third treatment can be done immediately after flowering or, if delayed, already after harvest, in both cases if there is a lot of Apple scab. During this period, you can also use the fungicides or Bordeaux mixture mentioned above.
The main thing is, as we have already mentioned, to have time to finish the treatment 25 days before the start of the fruit harvest, and in the case of Bordeaux mixture – 15 days.
For the third treatment, you can prepare the Bordeaux mixture as follows: mix 100 grams of copper sulfate and 200 grams of caustic soda lime in a bucket of water, then get a 1% solution of Bordeaux mixture. The order of these actions is not known to everyone and there will certainly be doubts, so we will describe it in detail.
To prepare such a Bordeaux mixture, you must first add copper sulfate to a container and then pour 1.3Gal (5 liters) of water heated to room temperature. The solution is then left to stand for about 1 hour to develop homogeneity. Then in another container! Pour in the lime and very gently, preferably with a little stirring, pour in 1.3Gal (5 liters) of water.
What remains is to mix the solution, it is important to pour the alum exactly into the lime and not the other way around. It is important to pour it out so that it forms a fine stream while stirring the solution. When everything is ready, you just need to fill the sprayer with the liquid and it is ready for processing.
Do not forget that all the solutions should be kept in a plastic bucket and used on the same day, because the next day it will lose most of its useful properties.
Few people know that no chemical treatment is needed to reduce Apple scab activity until it disappears completely – just apply a mineral fertilizer. Of course, fertilizing under the roots may not solve the problem, but foliar applications must be used.
As a fertilizer to control Apple scab, you can use urea, which must be dissolved in the amount of one tablespoon per bucket of water. The first treatment with urea must be applied as soon as the signs of the disease are detected, and the second treatment must be applied one week after the first treatment.
In addition to urea, you can also use ammonium nitrate. These fertilizers work by destroying infected lesions and at the same time boosting the immunity of the plant by enriching it with nutrients.
FOLK REMEDIES AGAINST APPLE SCAB
Don’t give up on folk remedies to combat Apple scab on apple trees. They may not work as quickly as chemical agents, but they will help protect the environment and you and me.
Our ancestors used salt and horsetail infusions to control Apple scab, but it was later discovered that salt can strongly “salinize” the soil and do little more harm than Apple scab, but the horsetail fields have stopped helping altogether, and apparently the fungus has developed an immunity to it.
The good reviews from gardeners are all in favor of mustard powder. As a preventive and control measure, it is very good. The mustard powder treatment can be started at the end of May or the beginning of June. A second treatment can be given after a month or once an Apple scab is available.
To prepare a working solution based on mustard powder, dilute four tablespoons of mustard powder by hand in 0.26Gal (1 liter) of water and pour a bucket of water over this solution. Half a bar of laundry soap can be added to the bucket of solution as an adhesion agent. Gardeners have noticed that the greatest results are achieved if the treatment is done after rain when the leaf plates are wet.
Good results against Apple scab can be achieved by using manganese. Treat plants with a bright pink solution of manganese and treat in the spring before the leaves bloom. In the summer, make the solution a light pink color and treat the leaves. This treatment can be carried out up to three times with an interval of 10-15 days.
Thus, to get rid of Apple scab, you need to use folk remedies, fungicides, fertilizers, or preparations based on copper, and in order not to let the fungus “get used to” them, you need to alternate treatments, use fungicides with different active substances, or simply alternate control measures.
It is clear that it is necessary and possible to control Apple scab, but it is better not to let this fungal disease affect your plots. We have covered enough ways to prevent Apple scabs from appearing on apple trees.
If you have any questions, then ask them in the comments and we’ll be sure to answer them. We would appreciate it if you could share your experience in fighting Apple scab on your plots, and if these are variations of the traditional means of fighting it, that’s okay too.
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