How to recognise & prevent diseases in the garden
In summer, heat and humidity favour the spread of diseases in the vegetable garden, the orchard, and the ornamental garden. The best way to fight diseases is to prevent them, so it is important to anticipate them by offering the best growing conditions to plants, but also to know how to diagnose them to better target treatments.
Prevention is better than cure
Diseases that are rampant in the garden in summer, such as powdery mildew, grey mould, or mildew, are caused by micro-fungi. Simple preventive actions will limit the damage, because once declared, these diseases are difficult to control.
• A suffering plant is more sensitive to diseases and parasites. Hydric stress, an unsuitable substrate, too narrow plantings, or even a deficiency or excess of nutrients can all make plants more fragile. Check the growing conditions to correct the deficient parameters.
• Plant resistant varieties such as tomatoes, peppers or melons that are not susceptible to the most common diseases.
• The micro-fungi that cause cryptogamic diseases need humidity to develop. Water at the foot of the plants and not on the foliage.
• Mulch the base of cucurbits, tomatoes, and strawberries to protect them from soil and water splashes because diseases can lie dormant in the soil.
• Use plant purines to prevent diseases and parasites. Garlic decoctions and horsetail purees are the most effective in preventing cryptogamic diseases. Nettle purine can be used to strengthen the plants.
• Cut and burn the affected parts, remembering to disinfect the blades of the pruning shears between each plant so as not to propagate the diseases.
• Never leave diseased leaves or fruits to rot on the ground.
• In the orchard, eliminate all diseased fruits and do not let the fruits mummify on the tree because they are real reservoirs of diseases.
Recognise the main diseases to better target treatments
• Powdery mildew: white felting and discrete filaments. The disease develops when the weather is humid, and temperatures rise. Very present on melons, zucchinis, cucumbers, roses, and strawberry plants.
• Mildew: brown spots on foliage and sometimes a light whitish felt on the back. The disease spreads to the flowers and fruits making the harvest impossible. Very present on tomato and potato.
• Grey mould (botrytis): a grey felting develops on the fruits, the flowers wilt, the leaves show brown spots, the stems dry up. Quite common on strawberries, small red fruits, tomatoes, roses.
• Moniliasis: lives in mummified or rotting fruit on the ground, but also in wounds. Beige spots in concentric circles of white or light brown dots develop on the fruits which soften and rot. This disease concerns the orchard.
• Rust: circular orange spots on the leaves with pustules on the reverse side. This disease is common on roses, hollyhocks, pelargonium, but also on potatoes or beans.
• Marssonina (black spot disease): black spots with a yellow halo on the foliage which eventually falls off. Very frequent pathology on roses.