20 Devastating Tomato Plant Diseases And Treatments

Nothing beats the taste of the fresh, juicy tomatoes eaten straight off the vines! It’s also one of the easiest vegetables to grow. This is exactly why almost every vegetable gardener grows this vegetable. However, despite being easy to grow, there are many tomato plant diseases and treatments available. As a gardener, these are the top diseases, pests and treatments.

Tomato plants are sensitive things and are susceptible to a number of common problems and diseases. I have collated all of the main common problems into one large article to help you solve a variety of devastating tomato plant diseases and treatments

However I do need help and would appreciate your own stories and photos as I want to help as many people identify and solve these problems. Please contact me and I will happily include your photos. If something has worked or not worked please leave a comment and I will help you solve the problem.

Learning about the common tomato plant problems will help you catch them in time to fix them and revive the plants. Here are some of the problems typical to tomato crops:

Tomato Plant Diseases And Treatment Leaf and Stem Problems

There are several fungal, viral, and bacterial infections in tomato plants that result in leaf and stem problems. 

1. Tomato Plant Leaves Turning Brown And Curling

There are many reasons why leaves curl as it’s a sign of stress. Once you have been through my list of fixes for tomato leaf curl it might down to disease. Brown, dry leaves curling upwards, or downwards is most likely an indication of Septoria leaf spot. It’s a disease caused by the fungus Septoria lycopersici. The disease affects tomatoes, eggplants, and other species belonging to the same family.

Why Leaves Curl

Warm and humid conditions persisting for extended periods often result in the development of Septoria leaf spot on the plants. The fungal spores can spread from the soil, gardener’s clothing, and rain droplets blown with the wind.

Symptoms Of Septoria Leaf Spot

If often begins appearing at the lower leaves as soon as the first fruits set on the plant. Initially, you will see small circular spots with brown margins and grey centers. With time, the spots grow bigger until the entire leaf turns brown. When you find your tomato plant leaves turning brown and curling, the disease is already in its advanced stage. 

Fix Septoria Leaf Spot

1. Improve air circulation to the plants and keep them off the ground by trellising or staking them. 
2. Always water at the base to maintain dry foliage. 
3. Mulch the soil to prevent splashing water from the soil.
4. Clean the garden bed thoroughly after each harvest, removing all the debris from the plants.
5. Rotate the crops. Don’t plant your tomatoes at the same site that your last year’s tomato crop grew.

Preventing Septoria Leaf Spot

After removing and disposing of the infected leaves, apply a fungicidal spray formulated for Septoria leaf spot. Although they can’t cure the plants’ infected parts, they’ll prevent its spread to the new growth. Apply the fungicide as directed on the label every 7 to 10 days throughout the growing season. An organic alternative to these chemical fungicides is Bacillus subtilis.

2. Tomato Leaf Sunburn

Tomatoes are heat-loving plants and are thankful if they get 6 to 8 hours of sunlight every day. However, prolonged exposure to intense sunlight, especially during the hotter part of summers, can result in sunscald (or sunburn) in tomato plants. Although it’s a problem that concerns many tomato growers, it can’t exactly be classified as a disease. 

Reasons For Tomato Leaf Sunburn

It typically affects tomato plant seedlings soon after they are transplanted into the garden from an indoor location safe from direct sunlight to a site exposed to the sun’s rays directly. The sudden change in lighting conditions results in a sunburn.

Fully grown tomato plants can also be affected by sunscald. It usually affects the fruits if they are growing in the shade of the upper leaves and are suddenly exposed to intense sunlight. Pests and diseases can also make your tomato plant susceptible to sunburn. This is especially the case if your plant has experienced leaf drop due to pests or diseases. The new growth will show symptoms of sunscald.

Symptoms Of Tomato Leaf Sunburn

White or yellow patches develop on upper parts of the leaves, especially on the sides exposed to the sun, and the edges dry out. 

Fixing Tomato Leaf Sunburn

Although sunscalding can be easily prevented, there’s no cure to the problem. The good news is that it’s unlikely that sunburn will kill your tomato plant. The affected leaves can perform photosynthesis, so it’s best to leave them on the plant while it is still young and developing. Use a shade cloth over the damaged plants to restrict their exposure to the sun. Expose them to the direct sunlight gradually, increasing the hours of exposure each day until they are ready to grow without the shade cover. During this period, water and feed them well so that they have all the energy to recover from the damage.  

Prevention Of Tomato Leaf Sunburn

To prevent the effects of sudden exposure to intense sunlight, gardeners use a practice called “hardening off” before transplanting the seedlings. Place them outside for an hour on the first day, 2 hours the next day, slowly increasing the duration of exposure each day until they are tough enough to be planted in the garden bed. This step gives them time to assimilate to the new environment, preventing a sunburn. 

3.Fusarium Wilt

If the lower leaves are yellowing, wilting and dying, it’s most likely fusarium wilt. Eventually, the disease worsens, and the plant may die. If you slice a stem with a knife, you’ll find a distinct brown discoloration. Once the plant is infected, there’s no saving it. Remove it from the garden bed, and destroy it. Treat the site with fungicides and plant disease-resistant varieties in the next growing season. 

Signs and Symptoms of Fusarium

Symptoms of this disease usually show later in the growth season, on the lower side of the older leaves. The younger leaves will be harmed as the illness spreads, and the plant will finally die. In many situations, symptoms appear on only one branch or side of the plant.

Water, insects, and garden tools spread Fusarium wilt, which may live in the soil for years. The fungal illness appears in hot weather and is most damaging when soil temperatures reach 80 degrees Fahrenheit. This plant disease thrives in dry weather and little soil moisture.

Treatment

• Fertilizers with a high nitrogen content may make tomatoes more susceptible to this disease. In the vegetable garden, test your soil and use a slow-release organic fertilizer.
• Many weed species harbor the disease pathogen, therefore. hand remove or spot treat weeds with a weed flamer or natural herbicide.
• If the signs of this disease continues in tomatoes, the best course of action is to remove the entire plant and solarize the soil before replanting.

4.Verticillium Wilt

This is another fungal disease, very similar to fusarium wilt in its symptoms. The yellowing of leaves is more gradual and less pronounced in this case. Plants usually wilt during daytime and recover by night, and the growth is stunted. They eventually die if the weather is cold. 

The infected plants must be rooted and destroyed. The soil can be treated with solarization to get rid of the fungus, which involves heating the top few inches of soil by tilling it and packing it tightly with clear plastic. 

5.Southern Blight

Southern blight is also a fungal disease and is identified by the fast wilting of the plant and a white fungal growth around the base of the plant. Remove and discard the infected plant since it’s not curable. Disinfect tools, hands, and gloves after working with the diseased plant to prevent spread to the healthy plants.

Signs and Symptoms of Southern Blight

Early blight symptoms often emerge after the first tomato fruit appears on a tomato plant, beginning with a few tiny, brown lesions on the bottom leaves. The lesions develop into target-like rings with dried, dead plant tissue in the middle as they expand. Before the leaves die and fall off the plant, the surrounding plant tissue becomes yellow, then brown.

Dark and damaged leaves of the plant are the signs of late blight. It occurs at the margin of tomato leaves and spreads through the leaves toward the stem. White mildew might form on the afflicted area’s lower leaf surface. In humid circumstances, this form of blight spreads quickly through plants, and if left untreated, it can spread to fruits.

Treatment

Take immediate action if blight has been clearly discovered to prevent it from spreading. Remove all of the infected leaves and burn or dispose of them. To prevent fungal spores in the soil from splashing on the plant, mulch around the base with wood chips, straw or other natural mulch.

6.Bacterial Wilt

Excessive soil moisture and high temperatures can often result in this bacterial disease. It turns the stem darker on the inside and usually hollow, but the diagnosis is only possible once the disease has taken its toll on the plant. Remove and discard the infected plants and don’t plant varieties susceptible to this disease in the affected garden bed next season. 

7.Spotted Wilt Virus

Spotted wilt is a viral disease that causes purple patches on the leaves in addition to wilting. As with the above conditions, there’s no cure. Just remove the infected plants and don’t plant tomatoes in the same bed for a year or two. 

8.Black Spots On Tomato Leaves

If you find black spots on tomato leaves, it’s most likely caused either by bacterial speck or by bacterial spot. Although these are two different diseases, the symptoms are quite similar. Septoria leaf spot also forms spots on the leaves, but with a black border and grey centers. 

Symptoms of Black Spots On Tomato Leaves

• Bacterial speck – Small black spots surrounded with a yellowish halo.

• Bacterial spot – Small water-soaked black, circular spots.

• Septoria leaf spot – Water-soaked, circular spots with black borders and grey center.

Fix Black Spots On Tomato Leaves

Remove and discard the infected leaves to prevent the spread of the disease. This fix will only work if the problem is caught early. Keep removing the infected leaves as they appear. If the problem persists for too long, the ideal option is to uproot and discard the entire plant.

Preventing Black Spots On Tomato Leaves

• Water at the base; avoid drenching the leaves. 

• Trellis tomatoes to keep them off the ground.

• Mulch around the plants to prevent splashing during watering.

• Don’t work with the tomato plants while the leaves are wet. 

• Rotate crops.

Tomato Fruit Problems

Failure to set fruit, poor fruit set, or discolored or disfigured fruits can result from a variety of issues. Here’s a list of the most common fruit-related problems:

9. Poor Fruit Set

Poor fruit set may result from:

1. Temperatures below 55°F or higher than 90°F during the flowering time can cause the blossoms to drop without developing fruit. Shade, mulch, and water the plants well if it’s hot and cover them with clear plastic if it’s too cold to prevent the damage. 
2. Dry soil or excess nitrogen in the soil also caused blossom drop. Water regularly and fertilize with a low-nitrogen fertilizer during the flowering and fruiting period. Avoid over-fertilizing. 
3. Lack of air circulation can prevent pollination, preventing the fruit set.
4. Viral diseases, such as curly top can prevent fruit set.

10. Blossom End Rot

A brown spot appearing at the blossom end of the developing tomato is a blossom end rot. It can result from calcium deficiency in the plants due to excess nitrogen levels or dry soil. Use bone meal fertilizer and don’t use nitrogen-based fertilizers during fruiting. 

Signs and Symptoms of Blossom End Rot

Blossom end rot usually occurs as a single canker that starts tiny and expands over time, but it can also emerge as two or three lesions. They are always on the fruit’s blossom end, never on the top.

The tops of the tomatoes appear normal, but when the gardener removes them from the plant and turns them over, the black lesion on the bottom of the fruit is visible.

Treatment

If your plants have already a few tomatoes with black cankers, it is not too late to correct the problem for the remainder of the growing season. Change the way you water your plants. Deeper waterings and fewer frequent waterings are recommended.

The cankers that are already there will not go away. Those fruits should be thrown away. New fruits will emerge with no evidence of rot for the rest of the growing season if properly watered and a layer of mulch is applied.

11. Catfacing

Deformities near the blossom end of the tomatoes with deep grooves, but no cracks, is an indication of catfacing. Varieties with larger fruits are more prone to the problem. It most often results from cold temperatures during blossoming, but high-nitrogen levels in the soil can also cause catfacing. Cover the plants with clear plastic from late evening until morning to keep them warm.

12. Cracking

Tomatoes can have radial cracks originating at the blossom end, or concentric cracks surrounding the fruit. It’s caused when the peel grows slower than the inside of the fruit. Sudden changes in temperature or moisture typically cause it. The cracks make tomatoes more susceptible to fungal infections, so pick them quicker than others and leave them in a cool, dry spot to ripen. 

13. Yellow shoulders

Hard, yellow stalk and white internal tissue indicate yellow shoulder disorder in the tomato fruits. It’s associated with unsuitable weather or soil conditions. High pH or low potassium levels in the soil often result in such fruits. Select disease-resistant varieties and amend the soil to suit the varieties you are planting after conducting a soil test. 

Tomato Pests

14. Hornworms

If you find holes in your tomato plant leaves and fruits, you most likely have tomato hornworms at your hands. They’re green colored caterpillar pests that appear in late spring, a week after the adult moth lays eggs on the lower portions of the leaves. After feeding on the tomato crop for about 4 to 6 weeks, they create a cocoon and overwinter. 

Holes chewed in the fruits and leaves, about the size of a cigarette are symptoms of a tomato hornworm. They typically begin feeding on the top portion of the plants, so that’s where you’ll find the signs. Look for black or dark green droppings on the leaves and stems. You may also spot a hornworm closeby, which confirms the cause of this trouble.

Handpicking and destroying the caterpillars is the most effective solution to deal with the hornworms. If you have a large garden to manage, pesticides can be used. Bacillus thuringiensis is an excellent organic option to get rid of the pests. Insecticidal soaps are also useful.

Plant them with dill, basil, or marigold. These are helpful companion plants to deter hornworms.

15. Slugs

Holes chewed only in the fruits indicate the presence of slugs. Handpick and destroy the slugs and surround the plants with diatomaceous earth. Plant slug-resistant varieties if these pests are a common problem in your area.

16. Aphids

A team of tiny insects, nibbling on the stems and leaves, are aphids. Handpick and crush them, pinch out the leaves with a dense population, and throw them in the trash. Use insecticidal soap if the pests still don’t leave your plants alone.

17. Cutworms

These are small caterpillars with earthy skins that eat young plants at night. Enclose seedlings in collars made out of cardboard or aluminum to ward off the pests.

18. Flea beetles

Flea beetles eat the leaves while their larvae feed on the roots. Place traps to capture adults, use row covers, and dust diatomaceous earth on the plants to control the population. Use insecticides if the problem continues. 

19. Hornworms

These green caterpillars eat the leaves and fruits, leaving holes as they feed. Handpick and destroy them or use Bacillus thuringiensis on the plants. 

20. Whiteflies

Whiteflies have developed resistance to many insecticides. You can tell they are infested on your plants because they leave behind a sticky secretion sometimes called honeydew. They can be controlled by sticky traps, ladybirds or thoroughly hosing down the plants.