While there are many diseases and pests that can affect tomato plants, the most common threats are fungal diseases. Causes include improper watering, excess humidity, overcrowding, and poor air circulation. Remedy these issues, keep planting areas free of debris, plant disease-resistant varieties, and you will increase your chances of having healthy and productive tomato plants.

More on growing tomatoes:
How to Grow Tomato Plants
Different Types of Tomatoes to Grow
Tomato Gardening Tips

TOMATO TROUBLESHOOTING

Photo by: Jean Faucett / Shutterstock.

BLACKENED FRUIT ENDS

This is likely due to blossom end rot, which signals a calcium deficiency. Uneven watering practices, too much nitrogen, and temperature fluctuations are contributing factors.

Solutions:

  • Dispose of affected fruits and provide regular, deep waterings.
  • Use a fertilizer that is lower in nitrogen and high in phosphorus.
  • Check your soil pH before the growing season and adjust calcium content by adding lime, gypsum, or crushed eggshells to the soil.

Photo by: emmanine / Shutterstock.

BLOSSOM DROP

Flowers drop off the plant without fruit development. This is usually caused by extreme temperature fluctuations. Tomatoes need nighttime temperatures between 55-75 degrees F to successfully set flowers and fruit. Other causes include not enough water, insect damage, lack of pollination, and too much or too little nitrogen.

Solutions:

  • Use warming aids on cooler nights.
  • Adjust watering and fertilizer.
  • Plant flowers nearby to attract insect pollinators.

Photo by: Miyuki Satake / Shutterstock.

FRUIT CRACKING

Solutions:

  • Cover plants or harvest ripe fruit before a heavy rain.
  • Provide consistent water through the growing season.
  • Cherry tomatoes are more prone to cracking, so should be harvesting just before fully ripened.

Photo courtesy Missouri Botanical Garden.

WHITE OR YELLOW PATCHES ON FRUIT

As fruits develop and ripen, yellow patches form on the skin, turning white and becoming paper-thin. This creates an unattractive appearance and poor flavor. This is likely due to sun scalding.

Solutions:

  • Leave enough branches and foliage to shade fruit.
  • Provide other protection from direct sun during the hottest part of the day.

Photo courtesy Missouri Botanical Garden.

POOR FRUIT SET

Plants exhibit some flowers, few or no tomatoes, and poor fruit development. This can be caused by too much nitrogen, which causes plants to develop lots of foliage at the expense of flowers and fruit. This can also be due to lack of pollination or uneven temperatures.

Solutions:

  • Test soil pH early in the season and adjust fertilizer accordingly.
  • Plant flowers close by to attract insect pollinators.
  • Space plants at least two feet apart to avoid crowding, which can affect pollination.

Photo courtesy Missouri Botanical Garden.

DEFORMED TOMATOES WITH VEINING

Fruits are misshapen with irregular brown scarring. This is due to catfacing, which is caused by blossom drop when temperatures fall too low. This primarily affects the first tomatoes that develop. It doesn’t affect the flavor, so fruits can still be eaten once the affected parts are cut out.

Solutions:

  • Plant tomatoes later in the season.
  • Use a warming aid such as black plastic or row cover.

Photo by: AmBNPHOTO / Shutterstock.

BROWN SPOTS ON LEAVES

Blemishes on leaves up to 1/2 inch diameter have tan centers with concentric rings and yellow edges. This can be an indication of early blight.

Solutions:

  • Remove affected leaves as they appear and discard in the garbage; do not compost.
  • Plant tomatoes in a different area the following season to prevent spread of pathogens.

Photo by: Plant Pathology / Shutterstock.

MANY SMALL LEAF SPOTS

Multiple small spots (1/16 to 1/4") with dark brown edges and tan or gray centers on leaves can indicate Septoria leaf spot, one of the most devastating diseases for tomato foliage. Infection starts with the lower leaves and moves up the plant. Particularly severe in wet, humid weather.

Solutions:

  • Remove affected tomato leaves and discard; do not compost.
  • Improve air circulation around the plants.
  • Apply mulch to reduce splashing water on the lower leaves and water only at the base of the plant.
  • Implement crop rotation and do not grow tomatoes in the same location for 1-2 years.

Tempting Tomatoes® 'Garden Gem' tomato plant.
Photo: Proven Winners.

Tempting Tomatoes®

One of the easiest ways to ensure healthy tomatoes is to grow disease-resistant varieties, such as:

Photo by: Plant Pathology / Shutterstock.

YELLOW, WILTED PLANTS

Yellowing that begins with lower leaves and often found on one side of a plant, can be a sign of Fusarium wilt. This soil borne fungus is common in warmer regions and develops quickly in soils that are high in nitrogen and low in potassium.

Solutions:

  • Remove infected plants and discard.
  • Fusarium fungi can survive in the soil, on plant material, and even on tomato cages and tools for years. Soil should be removed and replaced and cages and tools cleaned thoroughly.
  • Avoid applying high-nitrogen fertilizers to the soil.
  • Avoid planting plants from the Solanum family in the area for a minimum of 4 years.
  • Plant resistant varieties, including 'Celebrity' and 'Better Boy'.

Photo by: krolya25 / Shutterstock.

DISCOLORED MOLDY LEAVES

Spots start out pale green, turning to brown and black. Fuzzy mold can appear on undersides of leaves. Eventually stems and fruit will also be affected. This is a sign of late blight, one of the most serious tomato diseases. An entire plant can be killed in a short amount of time.

Solutions:

  • Immediately pull affected plants and place in trash rather than the compost heap to prevent disease spread.
  • Select disease-resistant varieties the following season and plant in a different area.

Photo by: Plant Pathology / Shutterstock.

YELLOW LOWER LEAVES

Yellow blotches appear on lower leaves, which will develop brown veining, then fall off. This signals the early stage of verticillium wilt, which is caused by soil borne pathogens, attacking the roots and moving up the plant stem. It prevents normal flow of water and nutrients to the leaves.

Solutions:

  • There is no cure, and affected plants should be disposed of in the trash rather than compost.
  • Don’t plant tomatoes in the same spot for four years and choose disease-resistant varieties.

Photo by: ccpixx photography / Shutterstock.

HOLES IN LEAVES AND SUDDEN DEFOLIATION

This can be caused by hornworms, the larvae of sphinx moths. These large caterpillars 3-4 inches long can consume a large quantity of foliage and stems, decimating an entire plant in a short amount of time.

Solutions:

  • Hand pick and dispose of the worms.
  • Introduce predator insects such as parasitic wasps or ladybugs, which will eat the eggs and babies.

Photo by: JA King / Shutterstock.

STEM DAMAGE ON SEEDLINGS

This is likely caused by cutworms, which emerge at night and eat through the stem at nearly soil level.

Solutions:

  • Make a paper collar from cardboard or newspaper and surround the stem area to keep them out.
  • Remove the collar once seedlings have developed several sets of leaves.

Photo courtesy Missouri Botanical Garden.

BLACK MOLD INSIDE TOMATO

There are several possible causes, which include internal blossom end rot, anthracnose, or skin cracking that allows fungal disease to enter the fruit.

Solutions:

  • Keep fruits off of soil and maintain good cultural practices.

Photo courtesy Missouri Botanical Garden.

ROUND HOLE IN FRUIT

The most common cause is tomato fruit worm, which tunnels into the center of the fruit, causing it to rot.

Solutions:

  • Look for a brown caterpillar with distinct striping and dispose of the insects as well as any eggs that might be present on the foliage.
  • Avoid planting near corn, which is a favorite of these worms.
  • Use row covers when plants are young to keep adult moths from laying eggs.
  • Dispose of any affected fruit.

Photo by: Olya Maximenko / Shutterstock.

DARK BULL'S EYE ON BOTTOM OF FRUIT

The large round spot is sunken and mushy to the touch. This is likely a fungus called anthracnose, which develops in hot humid weather and is aggravated by overhead watering and poor drainage. It most often affects ripe rather than green fruit, and will cause fruit to rot.

Solutions:

  • Dispose of affected fruits in the trash rather than compost to prevent spread of disease.
  • Make sure to water early in the morning and around the base of plants.
  • Keep planting areas free of debris.

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