Have you noticed yellow leaves on your tomato plants? Any time our vibrant, healthy plants begin to show stress, we naturally worry. What is the cause, and what can we do?
Yellowing tomato leaves can be caused by a variety of factors. The most common cause, characterized also by brown spots, is early blight. Thankfully, when caught early, it can be controlled.
Early Blight Causes Yellow Tomato Leaves
The official names aren’t important. What IS critical to understand is how it affects your plants.
Early blight occurs and spreads in wet and humid conditions. Since the fungus originates from the soil-level, early blight begins on leaves toward the bottom of the plant. When rain splashes on the ground, the fungal spores attach to the low-lying leaves.
I have found early blight to be particularly problematic when we experience a spring or early summer with higher rainfall amounts.
How Do You Stop Early Blight without Spraying Fungicide?
I personally do not use fungicide mainly because I can be lazy and cheap and don’t want to buy it. I also don’t want to spray my garden unnecessarily. Instead, I treat early blight via manual removal.
I simply cut off the yellowing stems. Not only are these lower leaves shaded most of the time, but I also know that by cutting these leaves off, I inhibit the pathway for the fungus to reach the rest of the plant.
Though I still have a few issues with the yellowing leaves during the season, for the most part when rains become less frequent in the summer, the tomato plants usually rebound and produce healthy red tomatoes.
5 Ways to Stop Early Blight on Tomato Plants
Clip yellow leaves and stems ASAP.
Clip stems as soon as you begin to notice the yellowing of the lower leaves with brown spots. If you let them stay on the plant, the fungus will travel from one leaf to another up the plant. By catching it early, you’ll avoid removing too many leaves and stems.
However, in particularly harsh seasons with early blight, you may find many of your stems and leaves gone if you clip them all. That’s okay. First, understand that affected leaves do not help the plant, and the fungus will travel to healthy leaves. Second, as long as you see new, healthy growth on the tomato plant, it should recover.
IMPORTANT: Do not clip the yellow tomato leaves or stems when the plant is wet. Whether because of dew or a recent rain, handling the plant when wet will only spread the fungal spores more. Instead, plan your pruning for the evening, and destroy the affected leaves. Do not compost them.
Remove Lower Tomato Leaves
Clip the lower leaves on your tomato plant, even if they’re unaffected. When the plant reaches about 18″ high, clip all stems growing on the lower 6″ of the plant. As the plant grows higher, aim for no stems on the bottom 12″ of the plant. If the leaves are allowed to touch the soil, early blight will continue to spread.
Mulch to Prevent Early Blight
Mulch thickly. Since early blight originates in the soil, inhibit its path to the plant by laying on a 4″ layer of mulch around the tomato plant.
Personally, I’ve had the best success in preventing early blight when I’ve used hay as a mulch under my tomatoes. But since a recent application of hay mulch poisoned my tomatoes, I’ve gone back to mulching with wood chips. Here are four options for mulch I’ve used in my garden, including the benefits and drawbacks of each.
Stay Vigilant, Watching for More Yellowing of Leaves
Continue checking for yellowing over the next few weeks, especially after a rain. I’ve never had early blight go away even after the most prodigious of pruning the yellow leaves. What likely happens is the fungal spores already have traveled to healthy leaves and it takes a few days or more for the leaves to show symptoms.
In particularly rough years, I cut yellow leaves and stems off just about daily.
Tie Up Long Stems
Toward the end of the season, the stems of many indeterminate tomato plants will grow so tall that they could fall over on the ground. Tie up any stems that touch the ground, even if they are healthy. They run the risk of being affected eventually. A good tomato trellis should eliminate this step.
Can early blight be reversed?
No, the yellow leaves will not return to green. Once a leaf is affected, there really isn’t hope for that leaf and even that stem. Cut it off as quickly as possible to stop the spread of the disease. Most likely, your upper leaves — which receive the light anyway — are still healthy if you caught it early enough.
What if I’m Not Sure Why My Tomato Leaves are Yellow?
Yellow tomato leaves are most commonly caused by early blight, but that’s not the only cause. If you’re not sure, you’ll want to read 5 Causes of Yellow Tomato Leaves, where I discuss transplant shock, early blight, Septoria leaf spot, verticillium wilt, and fusarium wilt.