9 Reasons For Tomato Leaves Turning Brown (And How To Fix It)

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Tomato plants are known for their issues. As fast-growing as they are, and as delicious as they can be, they can be a challenge to grow.

One common problem that we see in our garden are tomato leaves turning brown. This may come in the form of spots, wilting, crumbling, or even leaves falling off of the plant.

So, in this article, I’ll share 9 common reasons for tomato leaves turning brown. I’ll also give some advice for each issue on how to properly prevent or treat the problem going forward. Let’s get started!


1. Early Blight

The fungus that causes early blight in tomatoes (Alternaria linariae) is incredibly widespread. Growers in almost any climate may experience early blight if the conditions are right for its development.

Early blight brown lesion on tomato leaf
Early blight causes brown spots with subtle concentric rings.

To identify early blight, look for brown or black lesions on the lower leaves. The most unique trait is the concentric circles in the center of the spots. Other common spotting diseases will not have this concentric ring pattern.

Causes & symptoms:

  • Moderate or heavy rainfall
  • Warm temperatures (80°F or higher)
  • Plant debris from previous season
  • Brown or black spots with concentric rings in the center

Treatment & prevention:

It is always best to prevent disease in your plants rather than treat it. Here are the best ways to prevent or treat early blight in tomatoes:

  • Remove diseased leaves. The brown lesions on your tomato leaves are full of spores that can easily spread from one leaf to another. Avoid further spread by removing diseased foliage as soon as it is found. Also, clean your pruning shears before and after use with isopropyl alcohol.
  • Remove plant debris. After each gardening season, clean up your garden by removing the branches, stems, fruits, and roots of your plants. Otherwise, the plant matter can act as a vector for disease, potentially infecting next year’s garden.
  • Pull volunteer plants. When you leave tomatoes in the garden over the winter, the seeds can easily survive and sprout in the spring. These plants are known as “volunteers,” and can be a source for disease. Pull any volunteer tomatoes in the spring.
  • Fertilize properly. By feeding your tomatoes enough food, you can help maintain plant vigor and growth rate throughout the season. If they run out of fuel, they may become more vulnerable to pests and disease.
  • Apply fungicide. For treatment, there are many options. You can use an organic fungicide spray such as this one from Amazon. Spray the affected areas to avoid further spread.
Early blight on tomato leaf
Early blight on tomato leaf.

2. Under-Watering

If your issue does not appear to be early blight, perhaps your plants could use a bit more water. Tomato plants are heavy feeders of both water and nutrients.

Brown tomato leaves crispy and dry
Dry crispy tomato leaves turning brown.

As the weather warms up, they will drink more and more water, requiring regular irrigation. Before watering, check your soil for moisture by digging your finger a few inches below the surface. If there is any moisture a few inches down, your plant doesn’t need water.

If your plants go too long without rain or water, the leaves may turn brown and turn crisp. This is an extreme example of under-watering, but once it happens, the leaves won’t recover.

Causes & symptoms:

  • Prolonged periods of drought
  • Wilting leaves

Treatment & prevention:

  • Water to keep the soil evenly moist at all times
  • Avoid periods of excessive drought

3. Bacterial Leaf Spot

Tomato bacterial spot is a common disease caused by (you guessed it) bacteria. You may have also noticed this disease on your pepper plants, as it can affect both plant types.

Brown spots with yellow halo on tomato leaf
Bacterial spot on tomato foliage.

In tomatoes, bacterial spot is characterized by small brownish spots on leaves that often turn into holes as the disease progresses. It may also cause brown spots on the tops of the tomato fruits.

It is most common in warm, humid weather, and spreads readily in these conditions. It is best to prevent it, as treatment options are limited once an infection sets in.

Causes & symptoms:

  • Excess humidity and heat
  • Small brownish spots on leaves which do not have concentric rings
  • Spots can also be on fruits, stems, and calyx of flowers and fruits

Treatment & prevention:

  • Plant resistant varieties
  • Treat seeds before planting with the hot water method
  • Properly space and prune plants for aeration
  • Remove plant debris at the end of the season
  • Avoid eating affected fruits
  • Avoid watering over the tops of the leaves

4. Mites (Spider Mites, Russet Mites)

Various mites, including spider mites and russet mites, can cause tomato leaves to turn brown. They are most common on the lower leaves of plants, though if the infestation grows large enough, the whole plant can be impacted.

Mites feed on the nutrients in the cells of your tomato plant’s leaves. They leave behind dead cells which can cause yellowing or browning leaves that appear burnt in severe cases.

Causes & symptoms:

  • Warm dry weather, commonly in mid and late summer
  • Tiny brown spots on leaves, especially on lower part of plant
  • Webbing on leaves and between branches
  • Drying leaves that eventually fall off

Treatment & prevention:

  • Avoid excessively dry soil by irrigating regularly
  • Control nearby weeds, as mites overwinter on these non-garden plants
  • Attract beneficial insects to feed on the mites – plant flowers like alyssum and cosmos to attract minute pirate bugs, lacewings, and hoverflies

5. Nutrient Deficiency

One of the essential plant nutrients is phosphorus. When your tomato plants can’t access enough phosphorus, the leaves will turn dark purple, almost brown.

Tomato leaf with purple bornw color from nutrient deficiency
Purplish brown leaves can be an indication of a phosphorus deficiency.

The cause of the deficiency may be a number of things. First, it is possible that your soil has been depleted of phosphorus. This is unlikely if you are growing in the ground, but can happen in potted plants.

Another cause for phosphorus deficiency is cold soil. Cooler temperatures in the soil can lead to poor nutrient absorption. Using a clear plastic mulch in the early spring can help warm up the soil.

Causes & symptoms:

  • Purple or dark brown coloration along leaf veins (see picture)
  • Cold root zone can cause poor phosphorus absorption
  • Depleted nutrients (especially in potted plants or very sandy soils)

Treatment:

  • Warm the soil in early spring with clear plastic mulch
  • Fertilize with liquid nutrients (and remember that phosphorus deficiency is very rare in ground soil)

6. Leaf Scorch (Sunburn)

In the spring, a common cause of leaf discoloration is leaf scorch. Seedlings grown indoors can be vulnerable to sunburn when the first move outdoors.

Leaf scorch on tomato leaves
Leaf scorch causes white and brown, dry and crispy leaves.

At first, the leaves may turn white and crispy. After a few days, the leaves can turn brown or black. The best way to avoid this is to properly harden off your tomato plants when moving outdoors.

Causes & symptoms:

  • Improper hardening off causes leaves to burn in direct sunlight
  • White, crispy leaves that may turn brown

Treatment:

  • Harden off tomato seedlings by gradually adjusting them to the outdoors over 1-2 weeks

7. Frost Damage

During the very early or very late season, your tomatoes may experience unexpected freezing temperatures. Anything below 32°F can be highly stressful to tomato foliage, potentially causing damage.

Frost damage on tomato leaves
Frost damage on tomato leaf.

Affected leaves often turn brown or black, and will quickly wilt and die thereafter. New foliage near the top or sides of the plant is most at risk, as it is the most exposed.

Watch the weather forecast in the early spring or fall and pay attention to overnight temperatures. Cover the plants with plastic or row cover to help insulate them from damaging cold.

Causes & symptoms:

  • Temperatures below 32°F
  • Pale black or brown leaves, often starting at the edge of a leaf and working back towards the stem

Treatment:

  • Cover plants in temperatures below 40°F
  • Move potted plants indoors overnight

8. Septoria Leaf Spot

Another common tomato disease is septoria leaf spot (or septoria blight). This infection is caused by a fungus (Septoria lycopersici) and causes a distinctive brown, water soaked spotting with a white or gray center (see picture).

Like early blight, septoria leaf spot overwinters on plant debris, so cleaning up the garden in the fall is essential to avoid reinfection. Removing diseased foliage and fungicides can help, but prevention is ideal.

Causes & symptoms:

  • Wet conditions are favorable for septoria leaf spot
  • Small, brown or black spots on lower leaves that often have a white center
  • Spots can be surrounded by yellowing on the foliage

Treatment:

  • Remove affected leaves as they appear
  • Clean up plant debris in late fall
  • Rotate crops on a 3-4 year basis

9. Late Blight

If you’re new to gardening, you may think that blight is a single disease. However, there are many different forms of blight, including early blight, southern blight, septoria blight, and late blight. Late blight is the worst of all.

Late blight on tomato
Symptoms of late blight on tomato fruit.

Late blight is caused by a mold (Phytophthora infestans), which thrives in cool, rainy weather. It is an airborne pathogen, so avoidance is difficult, especially when the weather conditions support it.

The symptoms of late blight start as brown or gray water-soaked marks on leaves that quickly grow. Late blight looks similar to frost-damage, affecting both young and older foliage.

Infected fruits will have large, irregular brown spots that quickly rot and have an unpleasant odor. Needless to say, late blight is a terrible tomato disease!

Causes & symptoms:

  • Cool, rainy weather
  • Brown, irregularly shapes spots on leaves and fruits
  • Fruits rot quickly and smell bad

Treatment:

  • Remove affected plants from the garden
  • Clean up plant debris in the fall
  • Plant late blight resistant tomato varieties
  • Rotate crops, especially avoid replanting tomatoes and potatoes
  • Use fungicide as a preventative measure in late summer and early fall

I hope this article helps you figure out why your tomato leaves are turning brown. Unfortunately, tomatoes can be a bit tricky to grow, especially when the weather is wet. To set yourself up for success, use our guide to growing tomatoes in raised beds here!

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