As a tomato enthusiast I know, firsthand, the frustration of discovering black spots on tomato leaves. There’s nothing quite like the anticipation of seeing those first ripe fruits, only to be disappointed by unsightly blemishes on the leaves.
After encountering this problem in my own garden, I did some research and discovered the various causes of spots on tomato plants.
In this blog post, I’ll be sharing my experience with spotting on tomato plants and discussing some of the common culprits behind this issue. These unsightly marks are usually caused by fungal infections or bacterial diseases, which can quickly spread throughout your vegetable garden if left unchecked.
Whether you’re a seasoned gardener or a newcomer to the world of tomatoes, this post will provide valuable insights on how to prevent and treat spots on your tomato plants, so you can enjoy a bountiful harvest of beautiful, healthy fruit.
Causes of black spots on tomato plant leaves
Dark brown and black spots on tomato leaves can be caused by a number of factors, including fungal or bacterial infections, and well as insect damage, and environmental stress.
Keep reading as we dive into the most common causes of black spots on tomato leaves and provide effective, organic solutions for banishing them from your garden.
Early blight (also known as Alternaria solani) is a fungal disease that causes black spots on the lower leaves of tomato plants. If left untreated, the leaves will turn yellow and eventually drop off.
Your plants could become infected from contaminated seeds or seedlings. Early blight can overwinter on infected plant debris, in the soil and on host weeds.
What to look for
Infected plants will have spots with concentric rings and yellow halos. These spots will enlarge and spread.
Sunken spots with concentric circles may develop on the stems as well. On young tomato plants, these stem lesions can girdle the plant stem and kill the plant. (This is also known as collar rot.)
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How to treat early blight on tomatoes
Early blight tomato treatment includes practicing crop rotation, and perhaps not growing eggplants and tomatoes for a couple of years.
Other ways to treat early blight on tomato plants is to be sure to stake or cage tomatoes to prevent their leaves from touching the soil. Pruning off the lower branches will also avoid soil contact with leaves.
Cover the soil with mulch and avoid overhead watering. Also, be sure to remove suckers from tomato plants to ensure that the inner part of the plant gets good air circulation.
Avoid high-nitrogen fertilizers since they will produce lush foliage growth, which can be easily infected. Instead, choose a fertilizer that has more phosphorus. (Too much nitrogen can also lead to catfaced tomatoes.)
Also clean up and dispose of any infected plant debris and never save seed from infected plants.
One natural treatment for early blight is baking soda. The USDA recommends a heaping tablespoon of baking soda mixed with a teaspoon of vegetable oil and a small amount of mild soap, all mixed in a gallon of water.
This solution needs to be reapplied regularly to treat the disease.
Copper fungicides are also considered approved for organic gardening. They also need to be reapplied.
Late blight in tomatoes
The microorganism of late blight (also known as Phytophthora infestans) is a water mold that lives in water or soil. These pathogens overwinter on plant debris and affect mainly potatoes and tomatoes.
Late blight in tomatoes is easily spread in air or water during cool, wet conditions.
Although the conditions of early and late blight are similar, late blight affects new growth near the top of a plant, and early blight first affects the lower leaves before moving up the plant.
Late blight of tomato symptoms
Tomato late blight plants will have water-soaked spots on the younger leaves, white mold on the undersides of the leaf lesions and dark spots on both the leaves and stems.
The fruit of infected plants will become mottled with sunken spots which will turn dark and leathery.
Treating and avoiding late blight tomato disease
While tomato late blight can be a serious fungal disease that affects tomato plants and can cause rapid and widespread damage, there are natural treatments available to control it and save your precious crops.
Late blight tomato treatment includes these practices:
Inspect new seedlings carefully before planting, taking care to look for any dark spots on the leaves.
Space tomato plants well for good air circulation and keep leaves away from the soil with proper staking. Ovoid overhead watering and mulch the plants well.
Practice a three year or four crop rotation plan and choose late blight resistant tomatoes as plants. Some good choices are:
- Mountain Magic – resistant to both early and late blight
- Legend – also resistant to early blight and verticillium wilt
- Defiant – resistant to both early and late blight
- Iron Lady F1 – resistant to fusarium wilt and early blight, too
- Matt’s Wild Cherry – also resistant to fusarium wilt and tobacco mosaic virus
Some great organic treatments for late blight tomato disease include copper sprays, baking soda sprays, and neem oil.
Insect damage can cause black spots on tomato leaves
Insect damage on tomato plants can be frustrating for any gardener, but there is a silver lining. Black spots caused by the insects can actually serve as an early warning sign, allowing you to take action and prevent further damage to your plants.
The black spots on tomato leaves and stems can be caused by a variety of insect pests. These include:
- Aphids – They often cluster on the undersides of leaves and stems of tomato plants, leading to black spots or discoloration.
- Spider mites – These tiny insects feed on plant sap by piercing the cells of the leaves, resulting in tiny, pale spots on the leaves. The presence of webs on tomato plants is a common sign of a spider mites. As the infestation progresses, the affected areas on the leaves may turn yellow, bronze, or brown.
- Flea beetles – These are small, jumping beetles that feed on the leaves of tomato plants. They create tiny holes on the leaves. In a severe infestation, the affected areas may turn black.
- Whiteflies – These small, winged insects cluster on the undersides of leaves and suck the plant sap, which can cause yellowing and wilting of leaves. In severe infestations, whitefly feeding can lead to the development of black sooty mold sticky secretion produced by the insects.
- Tomato russet mites – These tiny pests feed on the undersides of leaves. Infested plants may display yellowing, browning, or a rust color on leaves, which can eventually turn black.
Tomato black spot treatment (caused by insects)
By taking a proactive approach and implementing organic pest control methods, you can effectively manage the pest population and prevent further damage to your tomato plants.
Inspect plants regularly for signs of any insect infestation. Look for any black spots on leaves, stems, or fruit. If you find any damage, remove the infected part immediately to prevent the spread of the infestation.
Insects can build up in the soil over time. Practicing crop rotation helps to prevent this.
Some great natural remedies for insect pests on tomato plants include neem oil, insecticidal soap, and trying to attract beneficial insects such as ladybugs and lacewings.
Keep your garden clean and free of plant refuse that can harbor pests.
Environmental factors that cause black spots on tomato leaves
In addition to the diseases and insects mentioned above, black spots on tomato plant leaves can be caused by environmental factors. Some include:
- extreme temperatures (sunscald can also produce black spots on the underside of the fruit and is more of a problem when the foliage of the plant is limited)
- lack of moisture (ground level, consistent moisture is best)
- too much moisture (this can also lead to blossom end rot in tomatoes)
- fluctuations in humidity levels can lead to many fungal diseases where black spots are the end result.
In cases like these, the spots are often associated with tissue damage to the plant.
Best practices for maintaining healthy tomato plants to prevent black spots
No matter the cause of black spots on tomato leaves, you can maintain healthy plants and have more success in prevent these unsightly spots by following good tomato gardening practices. These include:
- Planting disease-resistant varieties: Choose tomato varieties that are known to have resistance to the common diseases which cause black spots.
- Providing proper spacing: Plant tomato plants with adequate spacing between them to allow for good air circulation.
- Practicing crop rotation: Avoid planting tomatoes in the same location every year. Rotate the tomato plants to a different part of the garden each year to prevent the build up of pathogens in the soil.
- Watering consistently: Water the plants at the base, preferably in the morning, to allow the foliage to dry out during the day.
- Mulching the soil: Mulch helps to maintain soil moisture, suppress weeds, and prevent soil-borne pathogens from splashing onto the leaves.
- Staking or caging the plants: This helps keep the foliage off the ground, reducing the risk of soil-borne diseases from splashing onto the leaves.
- Practicing good garden hygiene: Remove any diseased plant material promptly to prevent the spread of diseases. This includes removing infected leaves, stems, and fruit.
- Monitoring the plants regularly: Regularly inspect your tomato plants for any signs of diseases or pests. Early detection will allow you to take preventative action sooner.
By following these best practices, you can reduce the chances of black spots caused by diseases or environmental factors. Then, you’ll be able to say goodbye to those pesky black spots and hello to a great tomato harvest!
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