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Spots on Tomatoes | What Do They Mean?

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Tomatoes are one of the most popular vegetables, if not the most popular. Even people who really don’t garden grow tomato plants. So it’s very discouraging to do all the work to grow tomatoes only to discover they have black spots on them.

Black spots on tomatoes can be caused by a number of different things including Blossom End Rot, Buckeye Rot, Anthracnose, Powdery Mold, Late Blight, Early Blight, and Septoria Leaf Spot. Some of these are caused by diseases, some by bacteria, and some by physiological issues.

In the following paragraphs, we will discuss the diseases and problems that cause spots on tomatoes and other issues with the plants themselves, along with how they can be prevented and treated. 

Here are a few common diseases and other causes of spots on tomatoes

Anthracnose

Tomato-With-Anthracnose
Anthracnose

Anthracnose is a common disease found on ripe and overripe tomatoes but is rarely seen on green tomatoes. Symptoms appear as small sunken areas on tomatoes that may develop a black center as the disease progresses and secondary organisms get into the affected area and damage the entire tomato.

The fungus that causes anthracnose can live in the soil for up to 3 years and is spread from affected tomatoes to healthy ones by spores that are splashed from the soil onto the fruit during rain or overhead watering or irrigation.

Ways to control anthracnose include:

  1. Harvest as early as possible.
  2. Avoid overhead watering or irrigation.
  3. Apply fungicide sprays used to control leaf diseases on a regular basis.
  4. Practice a 3-year crop rotation schedule.

Blossom End Rot

Tomatoes-on-Vine-With-Blossom-End-Rot
Blossom End Rot

Blossom End Rot is found only on the blossom end of the fruit and produces dry and leathery spots that are not caused by a disease organism like Buckeye Rot is but is caused by physiological issues of either water fluctuations or a calcium deficiency.

There is no way to treat the affected tomatoes. The best thing to do is to pick off the tomatoes that have developed the spots and then to maintain a regular watering schedule of 1 to 1 ½  inches of water per week. Do not over-fertilize, especially with nitrogen-based fertilizers which could reduce the amount of calcium in the soil even more.

Buckeye Rot

Tomatoes-on-Vine-With-Buckeye-Rot
Buckeye Rot

Buckeye Rot is usually seen after periods of heavy rainfall. Buckeye Rot is caused by spores that are splashed from the soil during a heavy rainfall onto the lower hanging tomatoes. Those spores enter the fruit and may rot part of it very quickly. The rot, which can occur anywhere on the fruit, produces lighter and darker concentric bands or rings in the fruit.

Ways to prevent or control buckeye rot are:

  • Plant in well-drained soil.
  • Aerate the soil.
  • Plant in raised beds.
  • Practice crop rotation.
  • Mulch plants or stake them well to reduce the plant’s contact with the soil.

Other Diseases That Affect Tomatoes

Bacterial Wilt

Bacterial wilt is a major problem for home gardeners because the small areas they have for planting do not allow sufficient space for crop rotation. This type of wilt doesn’t cause yellowing of the plant, instead the bacteria get into the roots and stems of the plant where they clog the tissue preventing water and nutrients from getting to the plant and leaves and causing the plant to die.

Some of the ways to control bacterial wilt are:

  1. Completely remove the plant from the garden area and destroy them.
  2. Choose disease-resistant varieties.
  3. Practice crop rotation if possible.
  4. Be sure the soil has a balanced pH.
  5. Plant tomatoes in well-drained soil.
  6. Space tomato plants far enough apart to allow air circulation.

Early Blight

Early Blight is another common disease that can affect tomatoes and is caused by a fungus. The symptoms are not spots on the tomatoes themselves, but dead spots appear on the leaves and stems that may look like a bull’s-eye pattern. 

Early Blight can be controlled by spraying at regular intervals with a preventive spray.

Fusarium Wilt

Fusarium wilt is very common and is the most destructive disease of tomatoes in some areas. It is soil-borne and is most destructive during hot weather. Fusarium Wilt is caused by a fungus that enters the plant through the roots and develops inside the stem. This disease doesn’t cause spots on the tomatoes but instead kills the entire plant. The symptoms are a progressive wilting and yellowing of the entire plant starting at the bottom.

Planting varieties of tomatoes that are disease resistant is the best way to control the wilt, and even those varieties can be affected.

Powdery Mold

Symptoms of powdery mold are bright yellow uneven spots on the leaves of the tomato plants. The leaves die resulting in the unshaded tomatoes becoming sunburned.

The fungus that causes the disease is carried by the wind onto the tomato plants and is usually worse at the end of the growing season. Plants that have other problems are more susceptible to powdery mold.

Spraying with a fungicide is the only good way to treat powdery mold.

Septoria Leaf Spot

Septoria leaf spots can be identified by spotting on the lower leaves of tomato plants. Then, as the disease progresses, the leaves turn yellow and fall off. 

Septoria Leaf Spot is caused by a fungus and is one of the most damaging to tomatoes and other vegetables like potatoes and eggplants. The lesions on the leaves produce spores that can get in the soil and live to infect later crops.

The best methods to control septoria leaf spots are:

  • To remove the affected leaves from the garden and destroy them.
  • To spray with a copper fungicide.

Southern Blight

Southern blight is caused by a fungus in the soil that produces white debris on the plants at the soil line. It can be identified by the white debris and small round growths that look like white or brown mustard seeds. The fungus can live in the soil for 3 to 4 years and can easily be transferred to healthy plants by gardening tools, soil, unsterilized pots, even on the bottoms of your shoes.

The disease is fast-moving and can quickly kill your tomato plants.

Crop rotation is the best method of control for southern blight.

Is It Safe To Eat Tomatoes From Affected Plants?

These diseases and other problems affecting tomatoes do not make the tomatoes unfit to eat. If the affected tomatoes have not been completely damaged, you can just cut out the damaged area of the tomato and eat the rest.

Tomatoes – Fruit or Vegetable?

The tomato is quite unique and there has been much debate as to whether it is a fruit or a vegetable. Botanically, it should be classified as a fruit because of its method of reproduction, which is from seeds. But, back in 1893, the United States Supreme Court declared that for the purposes of tariffs on imported produce, the tomato is a vegetable. And, the tomato is currently listed as a vegetable under USDA (United States Department of Agriculture) guidelines.

Tomatoes are native to Central and South America where they grow wild and for 400 years were considered poisonous. However, In the late 1800s, tomatoes began to be considered as an edible fruit although still primarily considered an ornamental.

In the 1870s, the first commercial tomatoes were developed, and now there are hundreds of varieties in the United States to choose from. 

Growing Tomatoes – General Tips

Beginner-Tomato-Tips-Image-Graphic

Growing tomatoes is currently and has been for many years an important commercial enterprise, but many home gardeners also grow tomatoes. Tomatoes can be grown in a garden bed or in containers, and although they take up a small amount of space if they are staked or tied up properly, each plant has the potential to produce up to 5 pounds of tomatoes per year. 

It is possible to grow a continuous crop of tomatoes throughout the year by planting spring, summer, and fall plantings, although spring planting is usually the most successful. 

Here are some guidelines for successfully growing tomatoes:

  • Tomatoes need a soil pH of 6.5 to grow properly.
  • Plants grown in the garden bed should be planted 16 to 18 inches apart on 6 to 8 inch high beds that are 4 to 6 feet wide, or they can be grown in a number of pots and containers.
  • Tomatoes need full sun, but can also produce fruit in partial sun.
  • For summer and fall tomato crops, heat-set varieties are recommended.
  • The soil should be fertilized before planting.
  • Plants should be side dressed at the first cluster and again at the third cluster.
  • Tomato plants should be staked or tied up as the plant grows to keep limbs and tomatoes from touching the ground.
  • Watering should be done as early in the morning as possible.
  • Watering should be done from the bottom and not from the top.
  • Fruit cracking can occur when a large amount of water is absorbed by the fruit during the ripening process.
  • Spraying plants with a fungicide and an insecticide every 7 to 10 days starting when fruit first appears until harvest helps to reduce insect problems.
  • There are 4 types of beneficial insects/organisms that are important to any type of garden vegetable by helping to control populations of destructive insects. They include predators like assassin bugs, yellow jackets, lady beetles, and dragonflies; parasites like braconid wasps, and Eulophids; biologicals such as spinosad and logic; and the pollinators like honeybees, beetles, and butterflies that help produce the food we eat.
  • Practice good weed management as uncontrolled weeds compete for water, fertilizer, food, and sunlight and can make pest control and harvesting more difficult. Weeds can be controlled by spraying an herbicide such as Roundup, Monterey Weed Stopper, or Over-The-Top II.

Please note that when using herbicides and pesticides for gardening purposes, it is very important to read all directions before use and to follow those directions exactly.

Tips for growing tomatoes in pots:

  • Choose a plant that is more suited to growing in pots. According to Bonney Plants, determinate (Plants grow to a certain size then stop growing and produce tomatoes at the ends of the branches.) tomato varieties grow better in pots than do indeterminate (Plants continue to grow throughout the growing season and produce fruit all along the branches.) varieties.
  • Use only containers at least 5 gallons in size, preferably up to 20 gallons in size.
  • Make sure there is proper drainage in all the pots used for growing tomatoes.
  • Use only good potting soil.
  • Use a slow-release fertilizer before planting and supplement with a water-soluble fertilizer. Be sure to follow package directions for fertilizing. Tomatoes require a fertilizer that is higher in potassium than nitrogen.
  • Place pots in an area where they can have 6-8 hours of sun daily. If full sun conditions are not possible, consider using a grow light. Here are a couple of options: This is the light that I use and can highly recommend it. However, these grow-light bulbs used with a regular lamp or light fixture will work quite well.
  • Allow plenty of space between plants for proper light and air flow.

Tips for growing tomatoes in raised beds:

  • Choose plants appropriate for the season.
  • Before filling the raised bed with soil, remove or kill all the weeds, grass, and other plants in the beds.
  • Raised beds must be at least 8 inches in depth.
  • Raised beds must be no wider than you can reach halfway across.
  • Untreated wood will rot usually by the end of the first or second growing season, and fresh creosote-treated wood may burn the roots of the plants. Only wood treated after 2003 is safe for vegetable gardens. However, several construction materials like bricks, stones, and pavers can be safely used for raised beds.
  • Make sure there is proper drainage in all containers used for raised beds.
  • Use a garden blend of soilless soil or media and choose a blend that isn’t primarily made of large bark pieces.
  • The soil should have a pH of 5.5 to 7.0.
  • Use a slow-release fertilizer and supplement with a liquid fertilizer.
  • Space plants far enough apart that they are not competing for water, nutrients, and sun.
  • Remove any weeds that crop up in your raised beds.
  • Check plants regularly for insect or disease damage.

Final Thoughts

Growing tomatoes is not difficult, but there are a lot of things that can go wrong and many diseases and issues that can damage your tomato crop. My recommendation for anyone interested in growing your own tomatoes is to have your soil tested at your local USDA Agriculture Center before planting and follow their recommendations for amending the soil. Then, if your tomatoes exhibit any symptoms of any of the various diseases or other issues, ask for recommendations for treatment from either your Ag Center or some other trusted source.

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For more, don’t miss How to Can Tomatoes Using the Water Bath Method | 10 Steps.

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