Spots on tomato plants

Early Blight Alternaria – Treatment For Tomato Plant Leaf Spots And Yellow Leaves

If you have noticed tomato leaf spots and the lower leaves turning yellow, you may have tomato early blight alternaria. This tomato disease causes damage to the leaves, stems and even the fruit of the plant. Keep reading to learn more about what causes tomato early blight alternaria and how to treat leaf spot.

What Causes Tomato Leaf Spots?

Alternaria Alternata, or tomato early blight alternaria, is a fungus that can cause cankers and plant leaf spots on tomato plants. It normally occurs during hot weather when there has been a significant amount of rain and humidity. Plants that have been damaged are particularly susceptible to being infected by tomato early blight alternaria.

When a plant is infected with Alternaria Alternata, it will normally appear first on the lower leaves of the plant in the form of plant leaf spots that are either brown or black. These tomato leaf spots will eventually migrate to the stem and even the fruit of the tomato. These spots are actually cankers and can eventually overtake a plant and kill it.

Treatment for Tomato Plant Leaf Spots Caused By Alternaria Alternata

Once a plant is infected tomato early blight alternaria, a fungicide can be sprayed on the plant. This can help reduce the damage from the plant, but frequently this will only lessen, not eliminate the problem.

The best way how to treat leaf spot on tomatoes is to make sure it doesn’t occur in the first place. For future plantings, make sure the tomato plants are far enough apart. Also, don’t water the plants from overhead; use drip irrigation instead.

If you find Alternaria Alternata in your garden, make sure not to plant any other plants from the nightshade family in that spot for at least a full year. Destroy any tomatoes that have tomato leaf spots. Do not compost tomato plants with plant leaf spots, as this can re-infest your garden next year with tomato early blight alternaria.

The best treatment for tomato plant leaf spots is to make sure that you don’t get it in the first place. Proper care of your tomato plants will make sure you avoid the dreaded yellow leaves and leaf spots that come with Alternaria Alternata.

Updated 8/16/19

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

When the bottom leaves of a tomato plant turn yellow with brown spots, early blight is usually the culprit. Early blight is caused by a fungus, either Alternaria tomatophila or Alternaria solani.

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.

You can see the stray stem that escaped the trellis system. Mulch will help prevent fungal spores from splashing up on the plant, but keeping the stems off the ground is a first-line defense.

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.

Clip yellow leaves of tomato plants frequently to keep it from spreading up the plant, like has happened with this Amish Paste tomato.

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.

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Sudden Outbreak of Yellow Leaves on Tomato (and Other) Plants

You’ve just described my weather and tomato plants. The best I can figure, all the rain and humidity has provided the perfect conditions for fungus to thrive. I’m thinking Septoria lycopersici.


Septoria leaf spot of tomato, caused by the fungus Septoria lycopersici, is one of the most common and destructive diseases of tomato in Virginia. The fungus can cause severe leaf spotting and defoliation is common following severe infection. Heavy leaf loss during wet seasons leads to sun scalding of fruit and failure of fruit to mature properly.


Numerous, small, water-soaked spots, which are the first noticeable characteristic of Septoria leaf spot, appear on the lower leaves after fruit set. Spots enlarge to a uniform size of approximately 1/16 to 1/4 inch in diameter. They have dark brown borders and tan or light colored centers. Yellow halos often surround the spots. Severely infected leaves die and drop off. Septoria leaf spot is easily distinguished from early blight, another foliar disease of tomato, by the uniform, small size of the spots and the lack of concentric rings in the spots; however, Septoria leaf spot is sometimes confused with bacterial spot of tomato. The presence of fruiting bodies of the fungus, visible as tiny black specks in the centers of the spots, confirms Septoria leaf spot.

Favorable weather permits infection to move up the stem, causing a progressive loss of foliage from the bottom of the plant upward. Plants appear to wither from the bottom up. Loss of foliage causes a decrease in the size of the fruits and exposes fruit to sunscald. Spotting of the stem and blossoms may also occur.

Chemical Control

Apply fungicides on a preventative schedule before the disease first appears on the lower leaves. Begin sprays when the first fruits of the first cluster are visible after blossom drop. Apply fungicides every 7 to 10 days or more often when the weather is warm and wet. In home gardens the fungicides, chlorothalonil (e.g. Daconil 2787) or maneb (e.g. Maneb), can be used.

After weighing my options of copper sulfate mix, ferrous sulfate, or a chemical fungicide, I quickly ruled out copper because I don’t want to cause a copper imbalance in my soil… that and copper is toxic to everything (plants, fungi, bacteria). I didn’t want to be burdened by wondering if I’m applying too much.

I went to lowes and reviewed the selection of fungicides. Many were neem oil based and seem to treat more trivial infections, which excludes septoria. Only one treated seemingly everything fungal, Daconil. So I bought it.

After reading the label and considering the degree to which I had to protect myself from the chemical, and after using it once and feeling a little trepidatious to work around the tomato plants, I decided to shelve the Daconil pending further research into its safety.

I settled on ferrous sulfate (Its called Copperas, its about $5 for 5lbs). Its safe for me and the plants, yet it makes things uncomfortable for fungi. Additionally, the iron and sulfate will help green the leaves. Due to heavy rain, sulfate will be one of the first nutrients depleted in soil because of its negative charge.

To enhance fungicidal activity and correct possible iron chlorosis of the grass, Cutting recommends adding ferrous sulfate to the tank mixture at a rate of 1/2 oz./1,000 square feet of turf area. Ferrous sulfate is an inorganic chemical of iron and sulfate, and iron is an important component of photosynthesis. “We’ve been using ferrous sulfate with our fungicides since the early 1950s to increase the green of grass and improve the finish of turf,” he explains. Data show that when turf is under stress, particularly during hot summer months, the grass plants have difficulty absorbing iron from the soil. When applied as a spray, iron can be foliarly absorbed through the leaf tissue.


The result was Ferbam (sodium dimethyl dithiocarbamate + ferrous sulfate) is an excellent fungicide.

I’m not going to claim the ferrous sulfate by itself is an excellent fungicide, but it does have some fungicidal properties. I mix about a teaspoon in a squirt bottle with water. While out pruning off branches having yellow stems or clusters of yellow leaves, I keep the bottle with me and give the plant a good squirting.

Its important to remove the dead and dying branches, thereby eliminating some of the innoculum, and increasing airflow around the plant. I’ve even considered setting up a box fan in my garden.

I also prune branches growing in the middle of the plant or those which never receive sunlight. The idea is to open up the interior to airflow.

Is important to keep the plant healthy. This includes fertilizer with plenty of potassium and calcium. Lack of calcium causes blossom end rot. Lack of potassium generally produces brown spots (necrosis) and necrosis at leaf margins in a wide array of plant species. A good fertilizer blend for tomatoes would be 30% N, 5% P, 40% K, 20% Ca, 5% Mg. I’ll leave you to decide how to mix your favorite water soluble fertilizer with potassium sulfate, calcium nitrate, and epsom salts to arrive at those percentages 🙂

The distinction between overwatering and too much rain is that overwatering is drowning the roots producing a condition of suffocation to oxygen and starvation of nutrients a plant needs, while too much rain washes soil nutrients out of the root zone, starting with the anions (NO3, SO4) and then affecting the cations (Ca, K, Mg, etc). If you have well-draining soil, you can water a lot and not produce root-suffocation, yet you’ll wash away nutrients. If you have heavy clay soil, you can water a little and still manage to suffocate the roots. Root suffocation would be similar to yanking the plant out and tossing it on the ground… the whole plant will suffer. Rather, in this case we have healthy plants with the exception of yellow leaves on the bottom. This wouldn’t be root-suffocation or overwatering, though, it could be that the rain leached away enough nutrients to leave the plant in a malnourished state, weak enough to succumb to a fungal infection.


The more I contend with these sickly tomato plants, the more I think the cause is nutritional.

Consider this:

1) Why doesn’t it affect the upper limbs until the plant has been severely weakened by the loss of lower limbs? 2) Why doesn’t it affect fruiting limbs? 3) Why do symptoms only show after fruit-set? 4) Why does a fungus, which is naturally present in the air all the time, only attack sometimes and only some plants? Can a fungus be specific to only the tomato plant? 5) Septoria strikes after a wet season, which is conducive to fungal growth, but leached soil is also associated with increased rainfall.

My Theory

Heavy rains leach soil of calcium, sulfur, magnesium, and potassium (in that order – per The Nature and Properties of Soils – Harry Oliver Buckman, Nyle C. Brady). The leached soil leaves the plant vulnerable to disease while, at the same time, the increased humidity favors fungal infestation. This explains why lower limbs, the limbs less defended by the plant, are attacked first. It also explains why limbs not containing fruit are attacked first, the plant defends the fruit, not the leaves. And it also explains why the disease strikes most often after fruit-set, since the plant is having to divide its nutrition with the fruit.

Therefore the cause would be nutritional. The mechanism (fungus or bacteria) for decay isn’t important.

My Treatment

I applied lime everywhere. I dusted the plants as well as covered the ground in liberal amounts. I want to accomplish 2 things with this. 1) To add calcium to the soil and plant (if possible). 2) Rain can have quite a low ph, therefore I want to neutralize that acid before it hits the soil. The acid rain will also break the calcium loose in the lime. A possible third effect may be to raise the ph on the leaves, making it uncomfortable for the fungus (if so, I would consider this more of a side-effect than the main idea).

I started fertilizing with calcium nitrate, potassium sulfate, and magnesium sulfate (epsom salts).

I also found this page to be interesting:

The bottom line is that if you are having disease and insects in your tomatoes, something is out of balance. The first things to check are your calcium and phosphate levels. For quick fixes, liquid calcium nitrate and liquid phosphoric acid can prove to be valuable aids.

I will update this answer as I discover more.

Don’t let those potential problems scare you away. Growing healthy, pest- and disease-free tomato plants is relatively simple. Keep your plants healthy by rotating crops, planting disease-resistant varieties, spacing plants properly, mulching, and watering at least 1 inch per week.
Start your tomatoes off right.

As tomato plants grow, keep an eye out for tomato pests and tomato plant diseases such as tomato wilt that may come in the form of fungi, bacteria, or viruses.
Get tips for growing healthy tomatoes.

In the fall, if you have had tomato plant disease problems or tomato pests of any kind, remove the entire plant.

Rotate tomatoes so they grow in the same ground only every four years or so. Many tomato plant diseases and tomato pests lurk in the soil.

Tomato leaves have yellow or whitish spots

by Kesha
(Chicago, IL)

Q. I am trying to grow tomatoes in a container and have noticed that some of the leaves have yellowish or whitish spots. We have been getting a lot of rain in our area. I also have it planted in a self-watering containers. Will my plant still bear tomatoes or should I start over?

A. There are several possible culprits that could be causing these light colored spots on your tomato leaves, even this early in the season.

  • Early blighthref>, caused by a fungus in the soil, can start as yellow or light-colored spots. Early blight is common in wet, humid weather. But if you used the sterile potting soil that comes with the self-watering planter, then it’s not likely that the fungus was present to infect your plant. Treat early blight with a biofungicide or a fungicide.
  • Your wet conditions are also right for powdery mildew, which appears like yellow-colored spots. Looking closer, you may notice they’re grayish. Treat powdery mildew with sulfur dust or spray.
  • Leaf mold flourishes in wet weather and spreads eagerly in wind. It appears as greenish-yellow patches on leaves’ surfaces, with brownish-purplish on the the underside. Treat with a biofungicide or fungicide.
  • We noticed what looks like holes in the leaves near the light-colored spots. Check for aphids (soft-bodied) or spider mites (reddish pin dots). Spray to dislodge pests and then treat with horticultural oil or neem oil.

With quick and proper treatment, your tomato plant can turn around and produce healthy tomatoes this season.
Good luck ad happy gardening!
Your friends at Tomato Dirt

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