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Downy mildew and its life cycle
Downy mildew is a disease caused by a family of fungi of American origin. It affects both plants for agricultural use indiscriminately, reducing the production of the crop, and for ornamental use, ruining them aesthetically. In spring, in the initial phase of its life cycle, the fungus settles on the leaves of the plant where it begins to absorb nutrients and grow. Subsequently the fungus starts to reproduce and spread on the remaining aerial parts of the plant such as flowers, buds and buds. The fungus causes necrosis and death of plant tissues until the affected part falls. During this phase the fungus, which remains attached to the dead parts of the plant, begins the production of oospores. Downy mildew uses oospores to survive during the winter, to then reactivate the following spring and begin a new cycle.
Symptoms caused by mildew
The symptoms caused by downy mildew are specific based on the type of plant but generally have common diagnostic traits. At the beginning the downy mildew attack can be identified by identifying the presence of round translucent spots on the upper page of the leaves while in the lower part we can observe the formation of white-grayish mold. As the disease progresses, the translucent spots tend to grow larger and become first yellow, then brown, and the leaf margins begin to curl up until the leaf falls. The defoliation is one of the first damages caused by the downy mildew that causes the weakening of the plant and therefore a lower production of flowers and subsequently of fruits. If the disease is not treated promptly, it can also lead to the fall of the flowers and the rotting with subsequent death of the fruits.
Causes of downy mildew
The ideal climate for the formation and spread of downy mildew is a high humidity (80%) and an average temperature of about 15 ° C. For this reason the beginning of spring is the best time for the development of the fungus. Moisture is fundamental for spore germination and rooting of the fungus on the leaves, in fact in arid or dry areas the development of this pathogen is rare or even absent. A cause that can increase the likelihood and speed of diffusion of blight is the presence of trauma or injury to plant tissues that make it more vulnerable to attack. Very practical for predicting an attack is the three ten rule, which states that when the shoot length is at least 10 cm, the rainfall is at least 10 mm and the minimum temperature is 10 ° C, the probability of an attack from downy mildew is maximum.
Downy mildew: Remedies and Prevention
The best way to combat downy mildew, in order to minimize damage, is with prevention. The first thing to do is to avoid creating the conditions suitable for the germination of fungal spores. The ground below the plants must be kept clean of dead vegetable residues and check that there is good drainage in order to avoid dangerous water stagnation. There are also fungicides that can be used in a preventive way to prevent the development of blight. Generally they are products based on copper that act by contact, to be used before the favorable climatic conditions are present for the development of blight. In the case of plants already attacked by the fungus, systemic fungicides can be adopted which are absorbed directly by the fungus. The frequency and doses of the treatments change according to the type of cultivation and the period in which it is carried out.