Skip to main content

Common plants diseases to watch out for in your tomato plant

Tomatoes are a favorite fruit for many. They’re great in a medley of dishes and come in different shapes, sizes, and even flavors. When it comes to care requirements, tomatoes aren’t always the easiest plant to grow, although they’re far from the most difficult. Diseases can devastate any plant, and tomatoes are no different. The best way to keep your tomatoes safe and healthy is by being prepared. In this handy guide, we’ll cover a few of the most common plant diseases that impact tomatoes and what you can do to prevent or treat them.

Blight

There are multiple types of blight, but the two most common types in tomatoes are early blight and late blight. As you might surmise from the names, early blight is more common earlier in the year, while late blight is more common later in the year.

Early blight is caused by fungi in the alternia family. It occurs during warm, humid conditions, making it most common during warmer than average springs and summers. The first signs of early blight are visible at the base. Brown spots, which are more or less circular, appear on the lowest parts of the plant. If left untreated, the spots expand and merge together, resembling tree rings, causing massive damage to the plant. Eventually, the blight spreads to the fruit and the fruit rots.

Late blight is caused by the fungus Phytopthera infestans. This fungus prefers cooler, wet weather, so it’s most common in fall and early winter. Similar to early blight, the earliest signs of this infection are brown spots on the lowest parts of the plant. However, these spots are more irregular in shape and don’t form rings. As the blight spreads, the spots form white fungal growths, especially when conditions are damp. If left untreated, parts of the stem can collapse entirely.

Despite their differences, the treatments and preventative measures are largely the same. Test your soil for the fungi before planting and plant tomatoes that have a natural resistance to blight. Be diligent in your weeding and keep your tomato plants spread out to prevent any potential infections from spreading. Most importantly, keep the leaves dry when you water your plants. Be careful not to over water them.

Tomato plant infected with early blight
Image used with permission by copyright holder

Anthracnose

Anthracnose is another fungal infection, caused by fungi in the colletotrium genus. This fungus prefers warm, wet conditions, and can live in the soil for up to a year. Anthracnose affects the fruit of the tomato plant. It begins as small dimples in the tomato fruits, which grow and darken in the center. The spots then develop yellow spores, which can be spread easily through water. By the time the spores are visible, the spots have often deepened, so that a large section of the fruit is rotten.

Tomatoes can be exposed to the fungi that cause anthracnose in the soil when they’re planted or from the plant they’re harvested from as seeds. To keep your plant safe from soil-borne fungi, keep the ground free of weeds, avoid getting the leaves and fruit wet when watering your plants, and test your soil before planting. To be sure your tomato seeds are healthy and not infected, make sure to buy them from a reputable source. If you aren’t sure, you can soak your tomato seeds in hot water for 25 to 30 minutes, which should kill the fungus. Since this fungus affects the fruit specifically, it’s a good idea to harvest your tomatoes as soon as they ripen, to help prevent them from becoming infected.

A tomato infected with anthracnose
Image used with permission by copyright holder

Damping off

Damping off is also sometimes called seedling disease because it affects, you guessed it, seedlings. Damping off can cause seedlings to die before they even break the soil, or wilt and die soon after planting or transplanting. It’s caused by two fungi; pythium and rhizoctonia, and primarily occurs when seedlings are planted too early, when the soil is still cold and damp. The best way to prevent this is to wait until the soil warms in spring to plant your tomato seedlings. You can further increase your seedlings’ odds of survival by soaking the seeds before planting them. This helps to boost germination.

A tomato plant infected with septoria leaf spot
Plant Pathology/Shutterstock

Septoria leaf spot

Septoria leaf spot is caused by the fungus Septoria lycopersici. As the name suggests, the primary way to identify this infection is by the spots that form on the tomato plant’s leaves. These spots are fairly small, with dark edges and lighter centers. As the spots increase, the leaves gradually die and fall away. This weakens the plant overall, leaving it vulnerable to other diseases and infections.

The good news is that the fungus that causes this disease doesn’t survive long in the soil. The bad news is that there are fewer preventative measures that can be taken. Clearing out old, dead, and diseased plant matter is the primary prevention measure. As always, avoid getting the leaves wet when watering them.

These are the most common plant diseases that tomato plants are prone to. In general, the best way to prevent any of these is to practice good garden maintenance. Clear away diseased or dead plant material, keep your garden free of weeds, don’t water your plants from above, and space your plants out. Doing these things can greatly increase your chances of growing healthy, delicious tomatoes.

Editors' Recommendations

Cayla Leonard
Cayla Leonard is a writer from North Carolina who is passionate about plants.  She enjoys reading and writing fiction and…
9 low-maintenance outdoor potted plants your patio needs to be its brightest, most inviting self this summer
Add color to your patio with these low-maintenance potted plants
A patio with colorful potted plants surrounding a bench.

It's hard to resist the call of warm weather. Sitting outside on your patio with your friends or just a good book can be so relaxing, and adding your favorite flowers to the mix makes it even more so! Some bright colors and interesting plants could liven up this gathering spot, but what if your thumb isn't even remotely green? No problem. We've collected our 9 favorite low-maintenance outdoor potted plants for you to add to your patio. Whether you need sun-loving flowers, plants that prefer shade, or shrubs to fill the space, this guide to low-maintenance patio plants is sure to satisfy.

Have a patio that gets baked by the sun all day? Try these plants
Many of our favorite plants would wither up and die if exposed to the harsh sun all through the day. Here are some sun-loving beauties that thrive in full sun and are resistant to drought. 
Marigolds
Marigolds are one of the most popular flowering plants to place in pots on front porches or back decks. With their bright yellow and orange blooms, it's easy to see why! Not only are they gorgeous flowers, but they require almost effortless care. They prefer to dry out between waterings, and they love full sun. That means you can let them hang out in the sun and not worry about killing them if you miss a watering day.

Read more
When should you harvest watermelons? What you need to know
Get the timing right for your watermelon harvest
Freshly cut watermelon slices

Knowing when to harvest watermelons can be tricky, especially if you’re used to growing crops like tomatoes, where there’s an obvious physical change (like turning from green to red) that indicates ripeness. Watermelons go through more subtle changes, so they can be difficult to spot if you don't know what to look for. If you're wondering if your watermelons are ready to harvest, this is the guide for you. We'll break down everything you need to know about when to harvest watermelons for the perfect summer snack!

How to tell your watermelons are ready for harvesting
Most watermelon varieties are ready to harvest roughly 1 month after the plant has bloomed, or 2 to 3 months after planting your watermelon seeds. The exact time can vary depending on the type of watermelons you're growing, what the weather has been like, and whether all the plant's needs have been met.

Read more
Are you asking, ‘Why is my tomato plant wilting?’ Here’s how to be the hero in your garden
Properly water and inspect your tomatoes to prevent (or treat) wilting
Tomatoes on a tomato plant

Tomatoes are probably the most popular veggies grown at home. Even novice growers can grow these plants with little to no experience in growing anything. Even better, many of these beginners are successful because tomatoes are so easy to care for and grow in your own home. However, one of the most common questions about growing tomatoes is, "Why is my tomato plant wilting?" Well, it could be due to a few reasons. We'll take a look at them here and give you tips on how to get your tomato plants back into tip-top shape. 

Why do people grow tomato plants?
Let's first talk about why you want to grow tomato plants. Growing tomatoes at home has a lot of benefits. First, they're healthier than store-bought tomatoes, and they taste better, too! There's no denying that tomatoes grown at home have a richer flavor. Once you eat your own tomatoes, you'll likely find the store-bought ones flat and watery by comparison.

Read more