Nothing quite says summer like a fresh tomato picked right from your own garden. Is there anything better than the juicy punch of your own homegrown tomato?  

Growing up on a farm in West Tennessee, I have great memories of eating homegrown tomatoes straight from the garden with a dash of salt. I truly believe there is nothing better in this world than a fresh-sliced tomato sandwich with a little mayo… yum!

And while tomatoes are generally a great beginner’s plant, there are still several diseases that can put a damper on your homemade salsa and fresh BLT dreams.

We’re covering 11 common diseases your tomato plants may face and how you can organically prevent or treat these.

(A big thank you to our former Ag Extension agent, Amy Dismukes, for providing us with  educational resources on these tomato diseases! We’ve used her wisdom as a guide for this post.)


But first… the basics.

Tomatoes are sunbathers: they prefer full sun for at least 8 hours each day. Otherwise, you risk spindly plants with little fruit to show for them.

Tomatoes thrive in fertile, well-draining soil that’s rich in organic matter and sporting pH levels of 5.5 – 6.8.

For more information about growing basics, check out our post: How to Plant Tomatoes for the Best Results.



If your tomato plants are experiencing unfavorable conditions (think: nights below 55°F or hot, dry days above 95°F), the flowers can drop from your plants.


This condition will improve on its own as the weather improves.


Calcium deficiencies aren’t good in people, and they’re not good in tomatoes, either. Tomatoes need calcium for normal cell growth. Too little can cause this rotting condition on the bottom of maturing fruit.


There are several variables needed for optimal tomato health. 

Ideal soil pH is around 6.5 with low nitrogen and high phosphorus levels. We recommend testing your soil prior to each growing season and amending if necessary. Check out our blog post here for details on testing your soil.

Consistent soil moisture is important. If experiencing a drought, water thoroughly 1 – 2 x per week to moisten the top 6 inches of soil. But don’t go too nuts with the watering… tomatoes hate—as our former Ag Extension agent puts it—“wet feet.”

According to Amy, “Foliar application of calcium is NOT recommended, as there is poor absorption and movement rate to the fruit—where it’s really needed.”


Just like we fight sunburn, tomatoes fight Sunscald. 

This happens when tomatoes are exposed to direct sunlight in extremely hot, dry conditions, causing white or yellow patches on the side of the tomato that’s been getting fried. (Sure, we like our green tomatoes fried, but not by the sun.)


Limit pruning to allow the plant’s foliage to provide natural shade to the fruit.


Cracks on your tomato fruit can be due to both genetics or environmental factors.

Growth cracking on the fruit often happens when the plant has absorbed too much water. When the fruit has matured, it can’t expand to absorb more water, so it splits.


To keep tomatoes from cracking, avoid overwatering. Additionally, several new tomato varieties are bred to be resistant to cracking.


Green shoulders refers to the problem of your tomatoes not ripening all the way: the base ripens to a rich red while the “shoulders,” or top, of the tomato remains an unripened green. Hence the name “green shoulders.”

High temperatures and prolonged direct sunlight can cause the chlorophyll to break down unevenly throughout the fruit.


Again, let the plant’s foliage do its duty of providing shade during extreme heat. Prune sparingly to ensure your fruit has nice leafy covering. Hybrids are bred to be resistant to this issue, so green shoulders are typically more common in heirloom varieties. (Read more about heirloom vs. hybrid varieties here.)


Not too hot, not too cold, but juuuust right. That’s how tomatoes like their weather. Many of the common tomato diseases and problems are caused by high heat, but cool temps can make your tomato plants testy, too.

Tomato leaf roll is an example of this. During extended periods of cool, rainy weather, you may notice your plant’s leaves roll upward, becoming thick and leathery.


After the weather levels out and warmer temperatures return, new leaf growth will return to normal.


Blight is a tomato lover’s nightmare when all you’ve been dreaming about is the juicy tomato you can’t wait to pick from your vine.

Early blight is an early season fungus disease that can infect just about every part of the plant: neither leaves, stems, or fruit are immune from its wrath.

Signs include yellow “bullseye” patterns of concentric rings on the leaves.


Look for tomato hybrid varieties that are resistant to early blight. Otherwise, use fungicides to treat it at the first signs of blight. Grow Organic offers several organic fungicides.


Septoria Leaf Spot is another fungal disease that occurs later in the summer.

It causes small, tan spots on the leaves usually boarded by a purple ring. Unlike early blight, this fungus does not infect the fruit.

Your tomato plants can pick up the fungus from infected plant debris remaining in the soil. The fungus spores can then spread by rain splashing from the soil to the lower leaves of the plant.


At the end of the season, THOROUGHLY remove & destroy infected tomato crop, ensuring that no remaining plant debris remains within the soil. Turn the soil deeply to bury any tiny infected plant debris. When watering, avoid wetting the foliage as much as possible. Fungicides are also useful in treating at the first signs of disease. Grow Organic offers several organic fungicides.


Southern Blight gets its name because it favors all that a southern summer has to offer: high humidity, high temperatures, and excess moisture in the soil.

This blight means business—you’ll notice rapid wilting of the entire tomato plant with this fungal disease.

As it spreads, you’ll notice white mold covering the lower stem of tomato plants and the surrounding soil. 

Dead leaves or other organic matter in the soil at the plant’s base only add fuel to the blight’s fire. This is why it’s important to keep the base of your plants as clear as possible.


Remove infected plants and turn deeply the soil to bury any remaining debris. Southern Blight can survive in soil through the winter, so it’s important to ensure that all infected debris is cleared away prior to next season’s crop.


Caused by the bacterium Xanthomonas campestris pv. Vesicatoria (try saying that ten times fast), your tomato plants are vulnerable to lesions on both leaves and fruit.

On foliage, the bacterial lesions are often easier to identify on the underside of the leaf and when wet.

On fruit, these bacterial spots will appear scabby, while some fruit go on to develop sunken centers.

This bacteria likes to travel—it can be brought into fields on infected transplants, surviving on seeds, plant debris, and tools. That’s why cleaning your gardening tools regularly is a healthy practice for your plants. Warm, moist environments also allow for quick spread of the bacteria.


Inspect your transplants to ensure they are disease-free before bringing them into your garden or fields. Avoid rotating your tomato plants with peppers, potatoes, or eggplants. 

And when admiring your lovely tomato plants, it’s best to look but not touch—overhandling can cause wounds in your plants that allow the bacteria entrance. 

Amy also recommends fixed copper sprays to reduce spread—but you must apply this as soon as you notice first symptoms. Grow Organic offers a few organic copper fungicide options.

ARE YOU A VISUAL LEARNER? If so, I am happy to send a presentation via email which contains pictures that Amy Dismukes provided us on the diseases. Just click here to request the presentation.