Scab is a fungal disease that attacks fruit trees. It must be taken seriously because the damage it causes is considerable, especially since there is no no curative treatment which eliminates it 100%. It is therefore very important that the gardener knows how prevent scab so that its apple and pear trees have every chance of being spared. Let’s take stock of this disease caused by pathogenic fungi and see how to protect your fruit trees.
Scab: a serious fungal disease
The scab is a fungal disease very problematic for apple and pear growers because it is by far the main disease affecting these fruit trees. She can quickly contaminate an entire orchard at the end of vegetative rest, when the buds are covered with fluff (down), swell then open, revealing young leaves or flowers. It is the period of bud burst. Without intervention during this phase, the disease grows, the wind spreading the spores widely in the surrounding area.
When scab is rife, stems, twigs, leaves and fruit bear lesions and are dotted with black spots. Many apples or pears rot on the tree, others only begin to show signs of contamination during storage, ie well after harvest. Even if they remain edible (just remove the affected parts before consuming these fruits), they are generally deformed and therefore difficult to sell. Furthermore, yields go down considerably because scab also affects apple and pear blossoms.
The parasitic fungi responsible for scab are Uneven adventures in the apple tree and Venturia pyrina at the pear tree. This fungal disease is favored by thehumidity and the risks increase further when the heat gets involved. You should also know that fruit trees injured by pruning, for example, are particularly sensitive to scab, but it also attacks healthy subjects.
Scab: treatment and prevention
Scab-causing fungi can overwinter on the ground in the layer of dead leaves from fruit trees. This is enough so that at the beginning of spring their ascospores contaminate apple trees, pear trees and even plum trees elsewhere. A serious problem that can however be avoided if one adopts good habits.
Raking leaves
In autumn, it is necessary to rake the fallen leaves of the apple tree, and more widely of all the fruit trees then burn them immediately to eliminate any pathogenic fungi and protect your orchard against the risk of scab. These leaves that litter the ground should not be incorporated into the compost. If the leaves have been left on the ground throughout the winter, it is necessary from the beginning of spring to pass the mower or the brushcutter. This greatly promotes their decomposition.
Another solution is to spread lime on the dead leaves, which has the effect of increasing their Hydrogen potential (pH) and consequently of degrading the bacteria and pathogenic fungi that they are likely to harbor. When the inoculum rate is high, lime is a solution that should not be neglected, but we can also carry out Bordeaux mixture sprays on the areas surrounding the fruit trees (lawn, paths, etc.).
Pick up fruit
Apples, pears and other fruit that have fallen to the ground must be picked up as they are foyer de contamination.
Add compost
Compost should be placed at the foot of the fruit trees duringfall.
Use healing putty
After pruning apple and pear trees, as is also recommended for all other trees, it is necessary to put a healing mastic on the famous pruning wounds because they are a real open door to diseases.
Carry out two preventive treatments
To prevent apple and pear scab, the gardener should to anticipate by applying a first fungicide treatment in autumnwhen all the leaves of the fruit trees have fallen, and a second in spring, at the time of bud break. The best solution is to spray with Bordeaux mixture. In case of recurrent rains, it is advisable to renew this preventive treatment up to three times between March and April.
Other antifungal treatments based on sulfur or copper authorized in organic farming can be used against scab. You can also buy antifungals made from natural substances in garden centers which therefore have no negative impact on the environment.
Synthetic treatments have been used. The systemic fungicides or fungicides unisite such as IDMs, triazoles are penetrating products with the advantage of protecting the organs of fruit trees over the long term and this includes the organs that form after the application of the treatment. As to antifungal treatments of contact or fungicides multisites, they can be mineral (with potassium bicarbonate, copper or sulphur). They constitute a protection against the scab but only for all the organs already formed. However, to spare the environment, the law now prohibits the use of some of them.
Keep a light hand on the products
It is essential to adopt different preventive measures against apple or pear scab so as not to abuse treatment products.
We know that when the weather conditions are inclement, the fight can be more complicated due to the leaching of the antifungals by the rains because it is necessary to continue despite everything to treat when the infection is substantial, by spraying fruit trees between showers, rather than waiting, without doing anything, for the return of good weather. Especially since the rains contribute to the dissemination of spores of pathogenic fungi.
Moreover, in the event of high winds, it is quite problematic to carry out spraying only on the targeted trees. It is therefore necessary to choose a more favorable moment. Hence the importance of anticipating by applying the preventive control measures that we have previously reviewed.
Protecting your apple and pear trees against the risk of scab requires perseverance because prevention is better than cure, especially since at present, we do not have no treatment capable of completely eradicating scab fruit trees. The inexperienced gardener has every interest in approach a professional for’get valuable advice if he wants to treat his trees affected by this cryptogamic disease, especially since certain products should not be applied when the fruit trees already show spots or lesions because this makes the pathogenic fungi more resistant.