Fight against mildew

What is downy mildew? Downy mildew is a disease caused by fungi belonging to different genera (Peronospora, Plasmopara, Bremia, Phytophtora, etc.). It causes the appearance of pale green to brown spots that gradually spread. The tissues eventually dry out. These brown lesions then affect the leaf petioles and then the stems. Entire branches can be affected. Plants affected by downy mildew very early on can produce deformed fruit with brown mottling. Downy mildew is one of the most common vegetable garden diseases and is the nightmare of amateur and professional gardeners alike. Under what conditions does downy mildew develop? Symptoms appear in late spring and summer and progress rapidly in humid weather. In France, climatic conditions are particularly favorable for its development! Heavy rainfall and temperatures above 16°C encourage the appearance of the pathogens responsible for downy mildew. The fungal filaments grow inside the tissues and emit suckers inside the cells. The disease is spread by spores produced on the underside of the leaf and form a white down. They are spread mainly by rain and wind, sometimes over long distances. Some spores are able to survive for several years in the soil and re-affect the host plant if it is planted in the same location. Which plants are mainly affected by downy mildew? Vines, lettuce, peas, onions, shallots, chives, sunflowers, artichokes, cabbages, tomatoes, potatoes and many plants belonging to the Solanaceae family (tobacco, etc.). How to fight downy mildew? Resistant species! Less susceptible varieties exist, particularly for lettuce, onions, etc. However, be aware that fungi are constantly evolving! These varieties do not guarantee the absence of infection, they can be contaminated by new strains of fungi. Space the plants Sow or plant at a good distance to promote air circulation and regularly ventilate the shelters. Some advise spacing the plants 1 meter apart because the fungus will develop less easily. Diversity! Varieties all react differently to mildew attacks. A vegetable garden with many varieties will be more resistant to diseases. Destroy infected leaves quickly and gradually to avoid contamination. Inspect the garden and burn any part of the plant affected by mildew. In this way, you will limit the quantity of infectious spores spread by fungi contaminating the plants the following season. Avoid humid places The conditions would be ideal for the development of fungi. Shelter the tomatoes to limit humidity on the foliage and the spread of spores by rain. In greenhouses, high humidity conditions will be conducive to the development of the disease. When conditions permit, open doors and encourage air movement. Do not water the foliage for the same reasons. Remove leaves that touch the ground because this area is generally humid, especially at night. The goal is to keep the foliage airy and dry, because fungal spores cannot develop on dry surfaces. Limit plant pruning. Wounds caused by pruning plants are entry points for pathogens. We generally remove suckers from tomatoes, eggplants, etc. Remove only small ones; the wound will heal more quickly. Avoid watering in the evening. This would lead to high humidity levels that would persist throughout the night. Watering in the morning is preferable to allow the leaves to dry quickly. Rotate. Do not replant the same species of plants that were affected by mildew the previous year in the same place. This will prevent contamination by spores remaining in the soil. Stimulate plant defenses Use nettle, horsetail, comfrey, or fern manures to stimulate plant defenses and fight mildew. You can also bury a few handfuls of nettle at the base of the plants when planting. Copper Copper-based products such as Bordeaux mixture are the most widely used and perhaps the most effective. However, they may contain certain compounds that are toxic in the long term to the soil and its inhabitants, which are so beneficial to plants. Limit their use as much as possible by only spraying when the first symptoms appear. Pay attention to weather conditions when applying and only treat when the weather is dry. Baking soda Bordeaux mixture can be replaced by baking soda. Prepare a solution of 1 L of water, 1 teaspoon of baking soda, 1 tablespoon of oil or black soap. Apply as a preventative measure and as soon as the first spots appear.