Before you get too alarmed, our gardens have not gotten blight. Unfortunately, my Mom’s tomatoes have and I realized that I didn’t know that much about blight other than you should remove the leaves and fruits infected by it.
Tomato blight can affect the entire plant from stem to leaves to the fruit. This is caused by a fungus called Alternaria solani which over winters in the soil. Apparently blight can be difficult to diagnose because it can look like several other diseases that affect tomatoes. Early detection can be done through observation. Dark circles that are brown to black and 1/4 to 1/2 inch in diameter will form on the stems and leaves on the lower portions of the plant. The leaves will then yellow and drop.
The photograph above is from http://www.veggiegardener.com and shows the characteristic dark brown circles and the leaves turning yellow prior to dropping.
Blight typically occurs when the weather has been overly humid and especially after heavy rainfall. After doing this research, it made me paranoid and I investigated all of our tomato plants. While some leaves look a little iffy, they don’t look like they are infected. Here are some photographs below to show you what I mean:
The leaves do not have the characteristic spots, but are a little bit brown and yellow. I think this is simply due to the extreme heat we have been having (95+) and little water. We do have the drip system set up and that helps with the watering. I cannot do anything about the hot sun, but try to keep the plants well watered.
Treatment seems to be relatively straight forward. If you notice early blight in your tomato plants, infected leaves should be removed immediately. A copper spray can be used once a week and and after a heavy rainfall. This can be sprayed until dripping on the leaves. If that doesn’t seem to work, a fungicide can be used as treatment, but this needs to be done early on as blight can become resistant to fungicides.
This all sounds great (and pretty easy if you spot it early on) but how can you prevent blight from even occurring? One of the best things that you can do is rotate your crops. This means that every year you should plant different vegetables or fruits in each garden. When the same plant is located in the same garden year after year, certain molds, bacteria, or fungus can live in the soil and continue to attack the same plants.
Another great idea is to grow your tomatoes in a raised garden bed. This promotes bettter drainage and can help reduce the spread of disease, particularly when contained within one garden. While all plants need water, it is best to water tomatoes at the soil rather than splashing the entire plant with water. Wet leaves close together can promote disease since air does not flow well and the leaves remain wetter for longer. On this same line of thinking, try to plant your tomato plants a couple feet apart. This helps to prevent not only the spread of disease, but air flow to help dry out the plants. Staking tomatoes will also help promote circulation.
Ideally, prevention is the mode of action for tomato blight. Good luck to everyone growing tomatoes!