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Tomato Plant Diseases and How to Avoid Them

We’ve never met a gardener who didn’t grow tomatoes. There is nothing like picking your own vine-ripened tomatoes to give you a sense of accomplishment as a gardener. Bursting with flavor and available in hundreds of hybrid and heirloom tomato varieties, this extremely versatile fruit is the most favorite “vegetable” to grow, even on balconies and in pots. However, tomato plant diseases can be a problem.

Tomato plant diseases


It’s easy to get disheartened, when spots start appearing on your tomatoes, or the leaves start yellowing. It’s like a sick child… you want to help but feel helpless to know what to do. There are several diseases and fungal attacks that can cause a set back in the ripening of those beloved tomatoes.

As the old saying goes, prevention is better than cure – however, if your tomatoes still show symptoms, it’s best to catch these early, so that you can maximize your harvest and enjoy these vitamin-packed globes right through the season. But don’t worry. There are things you can do to help, and things you can learn to prevent future damage.

First up, we will take a look at three issues that are easily preventable from day one, simply through careful preparation and planning.

Tomato Plant Disease Prevention #1: PHOSPHOROUS DEFICIENCY

Tomatoes need a good supply of phosphorous to grow, and while most healthy soil should have plenty, it isn’t bio-available to the plants at low temperatures. Too little phosphorous can kill your plants and leave you without that bumper crop.

Phosphorous Deficiency Symptoms

Veins of leaves turning purple.

How to Avoid It

Don’t plant your tomatoes too early. What that means exactly, will depend on your climate. The soil needs to be warm when you plant your tomatoes. Cold soil reduces your plant’s absorption of phosphorous. You can also use mulch to warm the soil around your plants.

We also use a laser thermometer to keep a close watch on the temps in our straw bale garden.


Tomato Plant Disease Prevention #2: CATFACING


Catfacing, is an odd term that refers to holes and scars at the blossom end of the fruit that basically make for an ugly tomato. In some instances, the puckering and indentations can look a bit like the shape of a cat’s face, thus the term. Larger tomato varieties are more susceptible than smaller ones.

Catfacing Symptoms in Tomatoes

  • Puckering
  • Cracks
  • Indentation

What Causes Catfacing on Tomatoes?

The various causes are thought to include disturbances to the flowers or flower buds during their development, cold weather during blossoming, too-high nitrogen levels and contact with certain herbicides.

By Irene of LedgeAndGarden.typepad:
“Catfacing’ occurs from one of two conditions and usually on the beefsteak type tomatoes.1)

  1. Herbicide damage
  2. Cool temperatures at the time of pollination

How to Avoid Catfacing

Don’t plant your tomatoes too early in the season or expose them to cold weather. If you live in an area with a short planting season, consider germinating seedlings and primary growth in a mini-greenhouse to help keep them warm. Also, certain varieties of tomato are more prone to catfacing than others, so if you keep seeing this, try different varieties.

Tomatoes Resistant to Catfacing

  • Duke
  • CountII
  • Floradade
  • Walter

A similar problem that afflicts even more tomatoes, are growth cracks which we cover next.


Tomato Plant Disease Prevention #3: GROWTH CRACKS

This is just what it sounds like – cracks on tomatoes that run from the stem end and that can encircle the whole fruit. The cracks can get invaded by bacteria, fungi or ants once they appear, which ruins the fruit. Growth cracks are the result of very rapid growth of the fruit, brought on by environmental conditions like when water becomes abundant after a drought.

Catfaced tomatoes, image from
Catfaced tomatoes, image from

SOURCE: Image from Vegetable Research and Information Center VRIC, University of California Cooperative Extension: 2)

How to Avoid Growth Cracks on Tomatoes

  • Even and consistent watering practices
  • Mulch for moisture retention

Some tomato varieties, such as beefsteak, are more prone to growth cracks. Some varieties are less likely to crack because they have more elastic and resilient skin. (Ha! I could use some of that! 😀 )

Crack Resistant Tomato Varieties Include

  • Daybreak
  • Early Girl
  • Earl of Edgecombe
  • Heinz 1350
  • Jet Star
  • Juliet
  • Mountain Delight
  • Mountain Pride
  • Valley Girl


Tomato Plant Disease Prevention #4: BLOSSOM DROP

With this issue, flowers appear on your tomato plants, but they fall off without tomatoes developing. This can be caused by excessive temperature fluctuations. Tomatoes need night-time temperatures between 55 and 75 degrees Fahrenheit to keep their blossoms. Too high or too low, and the flowers drop off. It can also be caused by insect damage, lack of water, too much or too little nitrogen, and lack of pollination.

How to Avoid It

While you can’t change the weather, you can try to plant them in a protected area, such as a greenhouse, or cover them with row covers when temperatures drop. Make sure the plant is strong by using organic fertilizer, drawing pollinators by planting milkweed and cosmos, and using neem oil insecticides.

Tomato Plant Disease Prevention #5: Poor Fruit Set

Symptoms of Poor Tomato Fruit Setting

  • Fewer flowers, even less tomatoes
  • Tomatoes small and tasteless
  • Nice green leaves


Causes of Poor Tomato Fruit Production

  • Too much nitrogen
  • Plants too close together

You have some flowers but not many tomatoes. The tomatoes you do have on the plant are small or tasteless. Fertilizing is great, but too much nitrogen in the soil encourages plenty of green leaves but not many flowers. If your plant doesn’t have enough flowers, there won’t be enough tomatoes.

Another cause may be planting tomatoes too closely together. Tomatoes are self-pollinating, meaning that each flower contains both the male (stamens) and female (pistils) parts. Wind typically pollinates tomatoes, but if plants are too close together, the wind can’t reach the flowers.


How to Avoid Poor Tomato Production

Have your soil tested and don’t over-fertilize, especially with nitrogen-rich fertilizer. If you’re planting tomatoes in the spring, leave at least two feet or more between plants so that good air circulation can help pollinate them. If your plants are already in the garden, you can simply shake the flowering branches to simulate wind and get the pollen from the stamens to the pistils.

Tomato Plant Disease Prevention #6: Leaf Curl, aka, Leafroll

Mature tomato plants suddenly curl their leaves, especially older leaves near the bottom. Leaves roll up from the outside towards the center. Sometimes up to three-quarters of the plant can be affected. High temperatures, wet soil and too much pruning tomato plants can also cause leafroll.


Leafroll - Image from
Leafroll – Image from


Causes of Leaf Curl

  • Wind damage
  • Herbicide
  • Broad mite
  • Viruses

Firstly, know that this issue shouldn’t affect your harvest unless the cause persists or increases. Although it looks ugly, a little bit of leaf roll won’t affect tomato development, and you will still get edible tomatoes. Avoid over pruning tomato plants and make sure the soil drains excess water away. However, if the cause of the damage isn’t removed, the leaf curl can ruin your harvest.3)


Tomato Plant Disease Prevention #7: Early Blight

If you find brown spots on tomato leaves, starting with the older ones, keep an eye out. With tomato blight, each spot starts to develop rings, like a target. Leaves turn yellow around the brown spots, then the entire leaf turns brown and falls off. Eventually the plant may have few, if any, leaves.

Symptoms of Early Blight

  • Leaves have brown spots that develop rings around them
  • Leaves turn yellow around the brown spots
  • Entire leaf turns brown and falls off


Causes of Early Blight

This is caused by a fungus called Alternaria solani. This fungus can live in the soil over the winter, so if you get this problem one season, planting tomatoes in the same area the next season may cause you to get this again.


How to Avoid It

Treat infected plants with a fungicide, and make sure you’re practicing good crop rotation. Don’t plant tomatoes or related plants, such as potatoes, peppers or eggplants, in the same soil, or you could lose these crops.

For more on how to grow the best tomatoes, you may enjoy this article how to grow the best tomatoes, and how to build strong tomato cages for huge tomato plants.4)


Are Blight Infected Tomatoes Edible?

The question arises, “Can blight infected tomatoes be eaten?” There is no black and white answer. It all depends on the extent to which the fruit itself is infected and one’s own particular standards.

Of course, we’d not wish to steer anyone in the wrong direction so the caveat should be (as usual) use your own judgement and do your own research. That said, here’s a representative opinion (repeated in numerous articles addressing the question) that to us makes the most sense as to eating or not eating blight infected tomatoes.

Generally if the plant itself is found to be infected, but the fruit bears no signs of an infection, it’s OK to eat. Make certain you wash each tomato with soap and water or mix up a quick-dip 10% bleach solution (9 parts water to 1 of bleach) followed by a good washing.

The fruit may be carrying spores and while showing no outward signs might be contaminated–hence the washing/dipping procedure. Any lesions on the tomato can be cut out and the rest of it washed and eaten. , you may choose to cut these out, wash the remainder of the fruit and use it. If you are uncertain as to the quality of any fruit, just follow the old adage, “if in doubt, toss it out”.

If in doubt, toss it out.

Also know that plants can be infected with blight, but not yet showing signs. If you get sick from eating any fruit, even if the plant doesn’t show any, there may be other pathogens there which could potentially cause illness. Once again, better safe than sorry.

If a plant looks like it is being compromised by a disease but many unripened fruit still cling to the vine and appear OK, you can attempt to pick them and allow them to ripen on their own. These will need a good washing as well since they could be harboring spores. In spite of your attempt to rescue, the disease can still prevail and proceed to rot out your salvaged crop. 6)

We’d love to hear your experience. You can reach us via email or post your comments on the GardensAll Facebook page.

We've never met a gardener who didn't grow tomatoes. There is nothing like picking your own vine-ripened tomatoes to give you a sense of accomplishment as a gardener. Bursting with flavor and available in hundreds of hybrid and heirloom tomato varieties, this extremely versatile fruit is the most favorite "vegetable" to grow, even on balconies and in pots. However, tomato plant diseases can be a problem.

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