Late Blight is a potentially serious potato and tomato disease and is caused by a fungus. It is particularly dangerous in cold and humid climates and has effects on all parts of the plant. The young lesions on the leaves are small and look like a dark water stain. If a plant is infected, these leaf spots will rapidly expand and white mold will appear at the edges of the infected area. This is usually on the underside of the leaves. Within 14 days of the start of infection, the plant will begin to brown and the leaves and stem will shrink.
The fruit of the tomato plant will develop a glossy, dark olive green lesion that will cover a large area of the fruit. The fungal spores of this disease are spread by both rain and wind. Daytime temperatures in the high 70s Fahrenheit and high humidity are ideal conditions for this disease.
There are preventative measures that can be taken to control this disease in your garden. By keeping the foliage of the plants dry, avoid environmental irrigation and locate the garden to obtain the maximum amount of morning sun. Keep the plants separate when planting separately, so there is plenty of room to improve the air flow between and around the plants. Destroy all plants that have been infected with the disease, do not compost them.
Keeping your garden soil healthy is the key to having a successful organic garden. Adding a lot of organic matter to the soil’s food web will provide the necessary fuel for microorganisms in your garden soil to create a healthy and nutrient-rich soil structure for the benefit of the crops you are growing.
by John Yazo