I’ve been growing tomatos in my raised garden bed in the last 3 years and haven’t noticed this before. I start tomato seedlings indoors and transplant them out after hardening. Seedlings looked great but within a few weeks of planting the stem of the tomatoes at the base near the soil line become cinched and turn brown but the rest of the plant is green. Some plants topple over very early though still young and don’t need support. What could be causing this?
Hi, and thank you for writing for info regarding your suffering tomatoes. From the image attached, and your report that the body of the plants are green, it would seem that the issue likely lies at the soil level. There are several fungal diseases that can thrive on tomato plants, including Early blight (Alternaria Solani), Alternaria stem canker (Alternaria alternata), and Southern blight (Sclerotium rolfsii).
The latter, Southern blight, shows symptoms of dark brown lesions at the soil level, as with your plants. Noted that you took good care to harden-off your seedlings before setting outdoors. But it is possible even setting out was too early — weather-wise — considering Toronto’s lengthy rainy spring this year. An excess of water during the early growing stage, could have made your plants more susceptible to a disease.
You also mention this is the 3rd year you have grown tomatoes in your particular raised bed. And so it is possible that this year’s tomatoes have been infected from a prior-year fungal soil issue. Remember, too, that blights that infect tomatoes are also shared by potatoes. Potatoes are family members with tomatoes, and are susceptible to the same diseases, and insect problems. So perhaps your raised garden bed has been isolating one of a possible number of fungi.
For your further reading: Southern Blight of Tomato and Pepper is described very clearly HERE.
Hopefully you’ll now be better able to identify your plants issues for this gardening season.