My tomato plant has yellow leaves

by Stephanie Chase
(Peoria, IL, USA)

This is my first garden. I planted both cucumbers and Brandywine tomatoes. The cucumbers have already started dying. The leaves turned yellow then brown and died. Now my tomatoes are having the same issue. The leaves at the base of the plant are yellow and the edges are turning brown and curling. The plant is producing a lot of fruit still and they look good though still green. The stem also turns yellow once the leaves turn brown. I have examined the leaves carefully but see no dark spots or bug circles. I thought I was over-watering so I lessened my watering. That did not help so I then watered more. Nothing. It has been very, very hot. Temperatures in the upper 90s to 100s. Humidity has also been very high. The plants are in direct sunlight all day til about 7 PM then shade. I have attached pictures of two of the branches and a picture of the tomato plant.

Q. Welcome to the world of gardening. We're glad you're part of our growing family!

It has been a tough season for many gardeners so you're not alone. Congrats on getting much fruit. Also, your plants look strong (apart from the yellowed leaves, of course) so you're doing something right!

There are several reasons why your tomato plant's leave could be turning yellow, then brown, then falling off. You've been smart to check things carefully, ruling out over-watering, under-watering, and pests, but there are still a few possibilities:

• Heat. Let's face it, those temperatures are brutal. Sometimes it's just too hot for too long. That kind of weather is stressful for tomato plants. Tomatoes flourish when temperatures are in the mid-80s. Right now, they're just trying to survive. You can't change the weather. But it's helpful to know that it may not be something you're doing or not doing.
  
• Sun. Can you give them any shade in midday? You can use shade cloth in different weights and sizes or even try a shade cloth kit.
  
• Blight. Plants may still be victims of Septoria leaf spot. This disease is often confused with early blight. But Septoria doesn't show itself with concentric rings that are characteristic to early blight. You can even compare Septoria with late blight. Your leaves look brownish/grayish, which is consistent with late blight. Either way, the treatment is the same: treat organically with a biofungicide like Serenade or with another fungicide like Daconil or Mancozeb.
  
• Wilt. Both verticillium wilt and fusarium wilt exhibit yellowed leaves. Fusarium often just affects one side of the plant. Verticillium encircles the plant.
  

Good luck and happy gardening!
Your friends at Tomato Dirt