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Tomato Plant Diseases and How to Avoid Them

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 not only easy to grow, but it can be done in confined spaces, on balconies, and even hanging from an upside-down planter, (though we’re a bit skeptical about these. Please let us know if you’ve used them with good results and we’ll update this).

shutterstock_387680494It’s easy to get disheartened, though, when spots start appearing on your tomatoes. Other common issues with tomatoes are the leaves start yellowing, or any one of several other 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 – but 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.

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

Issue 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.

How to Avoid It

Don’t plant your tomatoes too early. What that means exactly will depend on your climate, but the soil needs to be warm when you plant your tomatoes. You can also use mulch to warm the soil around your plants.1)

Issue 2: Catfacing

Image by Irene of LedgeAndGardens.typepad

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. 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:
“I have learned that ‘catfacing’ occurs from one of two conditions and usually on the beefsteak type tomatoes. The first condition would be herbicide damage which is not an option for these since they are organic and no herbicides were used at L & G anywhere near tomatoes. The other situation which causes ‘catfacing’ is cool temperatures occurring at the time of pollination. We had cool temperatures well into July this year. The tomatoes still taste great, they just look a bit funky.”2)

How to Avoid It

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, such as:
Resistant/Tolerant Varieties: Duke, CountII, Floradade, Walter and others.

Editor’s Note: We only found the Flora-Dade variety on Amazon. We didn’t find these others anywhere. Please let us know if you know of where to find these, or, other varieties that are resistant to catfacing. You can reach us via email or post your comments on the GardensAll Facebook page.

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

Issue 3: Growth Cracks

This is just what it sounds like – cracks that run from the stem end and that can encircle the whole fruit. The cracks can get invaded by bacteria and fungi 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

Image source from Vegetable Research and Information Center VRIC, University of California Cooperative Extension: 3)

How to Avoid It

Even and consistent watering practices will help prevent growth cracks. Mulch will also keep moisture more consistent. Some varieties, such as beefsteak are more prone to growth cracks. Tomato varieties less prone to cracking they have more elastic skin, include Daybreak, Early Girl, Earl of Edgecombe, Heinz 1350, Jet Star, Juliet, Mountain Delight, Mountain Pride, and Valley Girl.


Burpee Tomatoes
Burpee Tomatoes

Issue 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 with less dramatic temperature impact. Make sure the plant is strong by using organic fertilizer, drawing pollinators by planting milkweed and cosmos, and using neem oil insecticides.

Issue 5: Poor Fruit Set

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 It

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.

Issue 6: 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. This can be caused by high temperatures, wet soil and too much pruning tomato plants can also cause leafroll.

Leafroll - Image from
Leafroll – Image from

How to Avoid It

Firstly, know that this issue shouldn’t affect your harvest. Although it looks ugly, 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.


Issue 7: Early Blight

You’ll find brown spots on tomato leaves, starting with the older ones. 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. 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, “Are 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 representativeopinion (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”.

Also know that infected fruit may not be showing signs of blight- which have not been found to make people sick, 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)

You may also enjoy this article on mulch and mulchers, plus info on avoiding blossom end rot. 6)

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