Tomato blight, also known sometimes as potato blight, is a fungal disease which is caused by wet, damp conditions and mainly affects tomato plants growing outdoors.
However, greenhouses that are poorly aerated can also be a cause of blight because of high humidity and condensation.
If it has been wet in your area for a prolonged period, and you are growing tomatoes outside, it is possible that your plants have, or could soon have blight.
The combination of wet leaves and high humidity over a prolonged period is almost curtain to cause tomato blight. As a fungal infection, it can easily spread from plant to plant and on fingers too, so it’s best not to touch plant leaves and run the risk of contaminating healthy plants.
It is common to have a touch of fungal infection on one or two lower leaves when growing outdoors if you live in an area that gets a lot of rain. Remove the infected leaves and leaf branches, and keep the base of plants free from decaying leaves. Good air circulation at soil level helps keep plants healthy.
Tomato Blight Treatment
However, if blight has affected a number of leaves it is time to spray with Dithane 945 or apply Bordeaux Mixture. This may stop the disease spreading, and more importantly infecting other plants, but there is no cure for blight, it is only possible to stop it getting worse.
Treatment for tomato blight may be different depending on country regulations regarding the use of chemicals for garden use, but just ask at your garden center for a systemic fungicide.