Tomato Diseases

Your tomato plants have grown and are finally starting to produce the most beautiful tomatoes in the whole world (nothing less!), unfortunately, they've been hit by some strange disease.

What is that? What did you do wrong? And above all, what can you do about it? Well, we've put together this helpful article of the main diseases and pests that destroy our tomato plants.

1- Blossom-end rot

black ass tomato

Your tomatoes are developing normally, but a spot begins to form at the base of them just as they are ready to ripen. This affected area is soft and brown at first, but quickly becomes hard, dry and black. The good news is, you can remove and still eat the tomato.

The culprit: Your plants are most likely lacking in calcium. But be careful, this lack is usually not due to a lack of calcium in your soil. It is much more often caused by the lack of calcium available at the time of forming the fruit because there was not enough water. In other words, it is very likely that your plant ran out of water at the critical stage of development.

The remedy: Start watering your plants regularly to ensure that the plant has access to all the nutrients it needs at all times and do not disturb the soil around your plants too much to avoid cutting roots unintentionally. Pay particular attention to growing in containers, which increases the risk of drought.

On the other hand, if your watering is constant you can check the pH of your soil to make sure that it is between 6 and 7 (fairly neutral) so the tomato will be able to assimilate the calcium. Also, don't use fertilizer that are too rich in nitrogen (indicated by the first number 15-10-10) as this can cause the plant to grow too quickly, which will then use the minerals for the foliage and not the fruit.

Finally, some varieties of tomatoes are more prone to blossom-end rot than others.

apical necrosis

Photo credit: Ontario Ministry of Agriculture, Food and Rural Affairs

2- Blight


Photo credit: Garden Relaxation

Towards the end of summer, small brown spots that circle around like a target begin to appear on the lower leaves of your plants. Then the whole leaf turns yellow and brown and finally falls off. The fungus progresses up the plant fairly quickly, often turning the stem brown as well. The fruit, on the other hand, develop soft brown/black depressions just before ripening. They are unfortunately no longer suitable for consumption.

The culprit: Blight, a naturally occurring mould ( Alternaria solani ) in soil that thrives in certain conditions.

The remedy: Prevention is key here. Avoid the conditions where the fungus begins to develop, i.e. persistent humidity on the leaves of the plant. So, maintain a distance of at least 50 cm between plants to ensure good air circulation so the leaves can dry completely between waterings or rains. Also, when you water, only water the ground avoiding the foliage. Finally, remember to rotate crops from one year to another or not to plant tomatoes always in the same place in your garden.

If your plants are affected, quickly remove what is diseased and apply a fungicide.


Photo credit: Smart Gardener

3- Split fruit

Your tomatoes split at the top. Often insects (e.g. ants or earwigs) are attracted by the juices of the fruit and will lodge there.

The culprit: Again the culprit is water. A period of drought followed by a period of abundant water will cause the tomatoes to grow too quickly and may then split.

The remedy: The secret is consistency in watering. It is better to water regularly rather than once in a while in large quantities.


Photo credit: Garden and Vegetable garden

4- Tomato Hornworm

Your plants were magnificent yesterday, but overnight the leaves and fruit have been devoured? Sounds like a tomato hornworm is to blame.

The culprit: The tomato hornworm (Manduca quinquemaculata) which can measure up to 10 cm and is the same green as a tomato plant. These larvae are found in our tomato plants because this is where the mother comes to lay her eggs directly in the pantry for her little babies.

The remedy: Fortunately, there is usually only one caterpillar per plant, rarely 2. It must be found and eliminated. Take the time to observe your plant well, it has a perfect camouflage :)

Now you've got the solutions for keeping your tomato plants healthy, happy harvesting!

tomato hornworm

Photo credit: Whitney Cranshaw, Colorado State University