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How to cure thescab of apple, pear, medlarand other fruit and ornamental plants.
Scab, what is it
Therescabit is a disease caused by various fungi. It is among the most serious diseases that can attack crops ofApple treeis However. It also attacks medlar, strawberry tree, olive tree and many other fruit plants. Its development is not limited to the fruit field, these fungi can also be devastating for ornamental plants such as roses and photinie.
The agents that cause this plant disease are pathogenic fungi that belong to the order of the Ascomycetes. These are different species that attack different crops.
Thereapple scab it is caused by the fungusVenturia inaequalis. Therepear scabit is caused by the fungus Venturia pyrine. Regardless of the species, howevertreat scabseveral interventions with fungicides will be necessary. THEnatural remedies, although always recommended, this time may not be enough. THEtreatmentsthat we will indicate to you are of two types, allowed in organic farming or conventional.
Apple and pear scab, symptoms
Recognizing apple scab is very simple. Symptoms are typical of this disease and occur on all aerial parts of the plant.
On the leaves you will notice discolored spots that gradually become darker and take on a velvety appearance. These dark spots on the leaves of the apple tree only spread the disease.
When the scab is in an advanced state, the dark spots, at first only on the upper part of the leaves, also appear on the underside of the leaf.
Even theappleshave clear symptoms. On the apples there are roundish brown-olive spots. The spots on the apples grow slowly. When this fungal disease attacks plants with early fruit, it can also cause deformation of the apples. When the disease attacks in a late phase (when the apples are already well developed) it can cause superficial mottling, cracks, russeting, ... The symptoms are similar even when we talk about pear scab.
Compared to the apple tree, in thepear scabattacks on younger twigs are more frequent. By attacking the younger twigs, the fungus becomes difficult to get rid of. Even if you will apparently think you have eliminated it, the fungus will remain dormant in the youngest twigs of the plant and then manifest itself in subsequent seasons.
Scab of the rose
If you have noticed black spots on the leaves of roses and are looking for effective remedies, know that you will most likely have to deal with the rose scab fungus. For all natural remedies we refer you to the in-depth study dedicated to this flower:black spots on the leaves of roses.
How to eliminate and treat scab
Below we indicate thecarenecessary for thetreatment of scab of apple, pear, medlarand all the pome fruit (strawberry tree or rowan, common medlar or Japanese medlar, azerole, quince ...).
Treatments allowed in organic farming
The cupric products are indicated for the defense againstscab. On the market you can find: copper hydroxide, copper oxychloride, Bordeaux mixture, tribasic copper sulphate ... The action of the copper ion is preventive and therefore should be used early.
They must be applied before the rains or immediately after (within 24-36 hours from the beginning of the rain). These treatments are recommended to prevent fungal spores, already present on plants, from germinating and penetrating into the tissues.
Sulfur, especially in liquid formulation, is effective against scab. It can be used alone or in combination with cupric compounds. If you use sulfur-based products, wait at least 15 days before continuing with white oil-based treatments.
Interventions with calcium polysulphide are effective against cochineal and have recently been used, with the same timing, also to prevent and counteract the attacks of scab fungi.
Potassium bicarbonate acts as a fungicide that prevents or limits the germination of spores and the development of hyphae (i.e. the spreading organs of fungi spores). I recommend using it in combination with sulfur-based products.
Where to buy products to eliminate scab? At specialized garden centers or taking advantage of online sales. On Amazon it is easy to find cupric fungicides, liquid sulfur, potassium bicarbonate and the other specific fungicides mentioned. To get an idea of the prices, I refer you to the page dedicated toliquid sulfur on Amazon.
Treatments with conventional products
In the non-organic method, the scab is treated with products such as fenbuconazole, difencolazole and dithianon. Diaton is a very powerful but also very persistent fungicide, so be careful when using it.
In the photo above, two apples affected by scab. In the central photo, a leaf tissue seen under a scanning electron microscope. The image highlights the reproductive components of the pathogenic fungi that cause scab.
The disease cycle of scab
Scab, caused by the fungus Venturia inaequalis (anamorph Spilocaea pomi), can be quite serious when the weather becomes rainy and cool in spring. The fungal spores are produced in early spring on dead and fallen apple leaves, when the buds begin to develop. These spores are sprayed by rain and blown by the wind to land on developing plant tissue and thus start the cycle of infection.
After the appearance of spots on the newly formed leaves, more spores are produced which spread the infection to other parts of the tree. Also in this case, rainy weather greatly favors the spread of spores and infection during the secondary phase of spore production. The mushroom therefore overwinters on fallen leaves.
How to manage scab
There are a few things a non-expert farmer / gardener could do in order to manage scab and, perhaps, help prevent it effectively.
For example, it's a good habit collect and dispose of fallen leaves in autumn. This will help reduce the inoculum that can cause disease the following spring. To obtain the maximum production of high quality fruit, a spraying program is usually necessary with particular attention at the beginning of the season.
Applications must be done in rose, bloom, petal fall and 10 - 14 days after petal fall. Different products can be used for the treatment of apple scab, and a sharing with an expert gardener will certainly indicate which ones are most suitable for your specific case, thus allowing you to better face this potential danger for your crop.
Much for example will depend on the type of plant. For ornamental plants, a fungicidal product can be used to suppress the pathological element, or a fungicide containing chlorothalonil or propiconazole.
In the home orchard, you can use a generally based on copper, calcareous sulfur or sulfur. However, it is a good idea to ask for specific clarifications, because some of these products should not be applied at certain stages of plant growth.
Many people also prefer to purchase and use some multipurpose spray mixtures that can also help control other parasites, in addition to the subject of our current study.
Our suggestion, in addition to the one - already summarized - of asking for expert advice from a professional, is to make sure that any pesticide formulation you purchase is registered for its intended use. Therefore, follow the instructions on the label of all the products used and avoid the use of insecticides during flowering so that the bees are not harmed.
Also note that sulfur can damage some apple varieties (MacIntosh, Golden Delicious, Jonathan, and others). Additionally, some chemicals that can be purchased online may not be legal here in Italy, or may not comply with the recommended safety precautions. Therefore, it is always advisable to avoid the use of do-it-yourself procedures and, instead, proceed to a complete sharing with an expert.
If plans are also underway to plant more apple trees, consider planting apple scab-resistant cultivars, such as Enterprise, Goldrush, Liberty, Jonafree, Macfree, Prima, Pristine, Redfree, and Sir Prize.
You may also be interested in our related article on fruit plant diseases and our article on pear blight.