Skip to content

Tomato Disease Part 1: Crop Destruction

healthy tomato growthStanding among a growing tomato field or greenhouse is a lovely sight. The deep red fruit ascending the supports or trellised the ceiling of a greenhouse shows us the beauty, functionality and sustainability that can occur when man works alongside nature. Of course, tomatoes also offer growers a great way to make money, and for these reasons tomatoes are one of the most commonly grown crops in America. Second to only the Chinese in production, Americans spend countless hours every growing season producing fresh tomatoes for households everywhere or processing purposes.

Unfortunately, just as nature provides nourishment for these plants, it can also be the source of their destruction. Tomato diseases affect growers everywhere, but many of these diseases can be prevented and their proliferation stopped by just following proper growing practices. Below we’ll take a look at some common diseases that affect tomatoes, and over the next few weeks review some of the most common conditions and diseases that can harm your tomato harvest.

Early Blight

early blightEarly blight, along with late blight, is one of the most devastating diseases, and if it isn’t addressed quickly it can wipe out an entire field. Early blight is a fungal disease that is caused by Alternaria soloni. It exists in a wide range of temperatures, and growers can recognize it by the 1/2” lesions that show up on the leaves. The lesions usually have dark circles within them, and these lesions work their way up from the bottom of the plant and can cause fruit rot, collar rot and stem cankers.

One of the reasons why early blight is so dangerous is because it is able to persist in the same environment for years. The fungus can be found in the soil or plant debris, and it can be passed from plant to plant via water, wind and animals. There are a number of steps that can be taken to prevent early blight. First of all, make sure that the plants are properly nourished. Healthy plants are far less likely to succumb to early blight. Keeping plants properly spaced is also important, because it can maintain the proper air circulation. This will help to dry out any standing water and reduce waterborne illness. Controlling the insect population in the area can also be beneficial, as well as rotating your crops every few years. It is also essential to remove crop debris at the end of each season.

Late Blight

Late blight is a fast moving disease that can affect farms and gardens of any size. It is commonly found in cool, moist places, and it is caused by Phytophthora infestans. This organism cannot survive without a living host, so it is constantly seeking live tomatoes to infect. One of the first symptoms to appear is grey or dark-green spots. They grow rapidly, darken and many times a yellowish outline may appear. Eventually large, black spots will appear on the fruit, and when the weather is wet and cool a white fungus can develop over the lesions. This can be a warning sign that a particularly fast spreading form of late blight is occurring and should be addressed immediately. These plants need to be removed, because they can destroy all of the tomatoes in just a few days.

late blightPreventing late blight can be difficult, but it certainly isn’t impossible. Since it needs a living host, starting out by planting seeds is a good place to start. If you’re going to buy seedlings it is essential to buy them from a reputable seller. Once the tomatoes have been planted, regular use of fungicides can help and keeping plenty of space in between plants may limit the spread of late blight. If late blight does occur, it can sometimes be stopped by removing plants in the infected area, so precautionary measures and early detection are important.


Anthracnose is caused by another fungus, Colletotrichum coccodes, and, after infection, it can cause the fruit to rot. Anthracnose creates an indent that forms rings within it. It tends to spread in warm, wet weather, and the spores can spread through splashing water. anthracnose infected tomatoThe darkened lesions that are created by anthracnose contain fungal structures that house spores. These spores can be released in damp weather and infect surrounding plants. This fungus is able to survive during the winter, so it is essential to remove crop debris at the end of the season. Besides this, tomatoes should be planted in dry land with proper drainage. Using fungicides can also help and rotating crops may reduce the buildup of fungus in the soil.

We’ve mentioned fungicides quite a bit, and the following chemicals may be helpful in fighting off tomato diseases: acibenzolar-S-methyl, boscalid, captan and chlorothalonil. If you’re looking for an organic option there are a number of natural fungicides, and these include sulfur, neem oil, baking soda, as well as herbal oils, like garlic, fenugreek, cumin, mint and clove.

That’ll do it for today. Next week we’ll take a look into a few diseases that can cause wilt.

tomato plant affected by wilt

No comments yet

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s