By now if you have tomatoes in your garden, I’m sure you have been seeing leaves that have started to turn yellow and develop spots. These are symptoms of any one of three fungal diseases that infect tomato plants in our area; Early Blight, Late Blight and Septoria Leaf Spot. They are often referred to by many gardeners as just “Tomato Blight”.
Early Blight spots usually form concentric rings as the spots get bigger. Late Blight Spots have less distinctive borders and often look watery, while Septoria Spots appear smaller and separated.
Blight on my tomato plant, can you guess which one it might be?
Early Blight and Septoria are the most common and show up very frequently in tomatoes, so much so that many gardeners accept this as a normal part of tomato growing. Late Blight is a much more serious infection.
Late Blight and Early Blight will infect the fruit as well as the leaves while Septoria will cause reduced yields and damage from sun scald due to lack of leaves available for photosynthesis and to protect the fruit from the direct rays of the sun. Late Blight can be particularly damaging as it can kill an entire garden full of tomatoes in 10 days if the weather conditions are right
The treatment is about the same for all three diseases: spraying the plants with a fungicide. The treatment will not “cure” the disease but will help keep the symptoms from progressing further. Be aware that you need to be vigilant in applying your fungicides if you decide to spray. Rotation of your planting from year to year helps somewhat if you have the space to do so. Dead and dying plants should be removed and bagged up and be sent to the landfill along with your regular trash to avoid spreading the diseases.
Michigan State University has a good Fact Sheet that discuses these diseases in more detail.
These Blights will also infect Potatoes which belong to the same plant family as tomatoes.
Bob