Identifying and Treating Tomato Diseases

Fast-spreading diseases like blight can be serious problems for the home gardener, especially when it comes to tomatoes. Below you'll find details on two of the most prevalent afflictions. If you see signs of these diseases or have any questions, feel free to contact our garden professionals right away.

Late Blight

Potato Late Blight is the same disease that caused the great potato famine in Ireland during the 1800's and will also affect tomato crops.

Infected Plants

Symptoms of the disease include a water soaked grease spot on foliage or dark brown, almost black spots on the stalks or fruit. Spores from infected plants can travel up to 40 miles in the air under the right conditions, so the Maine Department of Agriculture asks gardeners to destroy infected plants by burying or bagging them. This will prevent the spores from releasing in the air and spreading the disease.

Non-Infected Plants

For plants that have not been infected yet, the application of an organic fungicide is strongly recommended. We recommend Fung-onil among many approved solutions. After applying the fungicide, continue to monitor your plants for signs of infection.

Blossom-End Rot

Extended periods of wet weather can produce Blossom-End Rot, a tomato disorder that is caused by low levels of calcium. When too much water is applied to plants, the roots are deprived of oxygen and unable to produce the calcium they need for normal cell production.


Blossom-End Rot usually begins as a small water-soaked area at the blossom end of the fruit. This may appear while the fruit is green or during ripening. As the lesion develops, it enlarges, becomes sunken and turns black and leathery. In severe cases, it may completely cover the lower half of the fruit, becoming flat or concave.


Protecting your tomato plants from overwatering and stimulating calcium production should be your focus. Apply a treatment of lime to help regulate the soil's pH and encourage calcium production, then mulch around the plants to keep soil moisture levels as consistent as possible.

A treatment of Rot-Stop from Bonide would also be beneficial.