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Tomato Diseases: Blight, Charcoal Rot, Target Spot, and Anthracnose

Updated on December 15, 2013
Late blight on leaves of tomato plant
Late blight on leaves of tomato plant | Source


In this section I am going to focus on blights. Blights are weather related, which is something that we are unable to control. However, that being said, we are able to take preventive measures to help our crops out as well as treat them with certain appropriate methods to control or cure the blight. There are three types of blight. All three types are much the same, but point to the time of the growing season in which the blight occurs. There is an early, mid-season, and late blight. Cold, rainy weather is a very favorable condition for spreading the pathogen known as "plant destroyer" in Latin. However, even without rain if the humidity is at a high point of 90% or greater this also is a favorable condition for spreading. Tomatoes are in the same family as eggplant and potatoes. In the 1840s blight was the cause for the potato famine in Ireland. Most often there are potatoes that are left in the ground to over-winter that are infected with blight and thus is starts all over again in the spring. If you see your tomatoes plants or potato plants with blight at any point in the growing season you should immediately pull up the infected plants and throw them out. Fungicides can be used to help manage blight if you choose. However, being diligent about watching your crops is a must and managing the blight really only works on tomatoes if you catch it very early, and even then sometimes the blight may have already spread to such a degree than no amount of managing it will help. There is no "cure" for blight and plants that are infected do not have the ability to "heal" like animals or humans. With that being said the best thing to do is to use preventive measures by spraying fungicide when the weather conditions are favorable for blight and to get rid of any plants that have been infected by immediately discarding them.

Late blight on tomato plant stem
Late blight on tomato plant stem | Source

Charcoal Rot

Charcoal rot is caused by a fungus and other than using preventive measures such as proper spacing of plants, starting plants early so they are larger when the warm weather hits (making a shading canopy to keep roots cool) and keeping them maintained with potassium and phosphorus there isn't much you can do about charcoal rot. Charcoal rot is the cause of many different plant and fruit casualties. It can affect the stem, root, and fruit. This type of rot starts out as an amber sticky substance on the stems that eventually dries and turns the stems brown. The stems get dried out and crack, plants and leaves turn yellow and wither away. Tomatoes themselves have black lesions that are black and hard like a canker.

Black rot on stem of tomato plant
Black rot on stem of tomato plant | Source

Target Spot

This fungal disease can last up to 2 years in leftover plant debris from your garden. So appropriate cleaning out of your garden every year will be a good preventive measure to keep this disease off your plants and fruit. The leaves will have small back dots when target spot is beginning. Spraying with a fungicide periodically is the only other known preventive measure to keep your tomatoes from the target spot disease.

Target spot on a tomato
Target spot on a tomato | Source


Anthracnose is a fungal disease that affects the tomato itself. It starts as a small sunken spot and progressively worsens as the time goes on until the tomato is of no use. Temperatures of 80 degrees are favorable for the spread of this fungus as well as warm rainy weather. Puddles of water that splash up on the plants/fruit also spread this fungus. Preventive measure include planting in well-drained soil, spraying fungicide as the first cluster of tomatoes begin, as well as crop rotation every 3-4 years to prevent the fungus from accumulating in the soil. This particular disease has been a bane for me as it decreases my tomato yield which in turn decreases my canning production.

Anthracnose in tomatoes
Anthracnose in tomatoes | Source

Prevention Of Fungal Diseases

The best prevention methods for fungal diseases is really to clean your garden out every year after you're done harvesting. Pulling all the leftover plants/debris out will go a long way to keep many of these diseases at bay. After pulling out all the plants/debris, I recommend throwing them in a spot not used for gardening and nowhere near your garden area and compost them along with diatomaceous earth with help in killing some of the pathogens. I would not recommend using this compost for a few years especially if you know that the plants were from infected plants/fruit. After cleaning your garden out I also recommend sprinkling your entire garden with diatomaceous earth as it kills parasites and pests as well including annoying flies that lay their eggs in the soil waiting for warm weather to hatch their eggs. Tilling up your garden before the snow hits or ground freezes is also a good step in prevention as it will uproot any leftover roots/potatoes/ or other root type veggies that may have been missed. Good luck in your tomato growing ventures and I hope this article has been beneficial to some degree for someone.


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    • Daniel Bixby profile image

      Daniel Bixby 4 years ago from Stottville, New York

      Great Job and Very informative and will prove to be quite useful!!

    • profile image

      Danny 4 years ago

      This is a fantastic article and well written. Great job lady keep them coming!