Tomato blight can be a tomato grower’s nightmare. After nurturing your tomato plants from seedlings, the last thing you want is to lose your entire crop to this troublesome disease. Knowing what does tomato blight look like is the first step. In this guide, we’ll share practical strategies to help you safeguard your tomato crop from blight and ensure you enjoy harvests of delicious, juicy tomatoes year after year.
Understanding Tomato Blight:
If you’ve been growing tomatoes for a while, you may have encountered two common types of blight: early blight and late blight. These diseases can wreak havoc on your tomato plants, causing leaves to yellow, brown spots to appear, and fruit to develop unsightly lesions. In severe cases, the entire plant may wither and die. If you are part of a Facebook or Reddit group for growing Tomatoes you will have seen the posts of despair. People posting pictures of wilting, blackened plants asking “What is wrong with my tomatoes?” It is pretty much always blight.
Early blight affects the lower leaves and fruit, resulting in reduced harvests and potentially plant death if left unchecked. Late blight, on the other hand, is far more destructive, rapidly killing infected plants. Once late blight takes hold, the affected plants appear as if they’ve been scorched by the sun, and they wither and die quickly. When we have experienced Late Blight we have been successful with aggressive pruning.
Tomato blight, whether early or late blight, is a serious fungal disease that affects tomato plants and can lead to significant crop losses. Here are definitions and some key facts about both early and late tomato blight:
Early Blight (Alternaria solani):
- Definition: Early blight is a common fungal disease caused by the pathogen Alternaria solani. It primarily affects the leaves and fruit of tomato plants.
Key Facts and Statistics:
- Symptoms: Early blight symptoms include the development of dark lesions with concentric rings on lower leaves, which can eventually lead to defoliation. Generally starts at the lower levels of the plants and works up.
- Favorable Conditions: This disease thrives in warm and humid conditions.
- Spread: Early blight can spread through splashing water, contaminated tools, and infected plant debris.
- Impact: While it can reduce yields and affect fruit quality, it is generally less severe than late blight.
- Control: Crop rotation, fungicides, and good garden hygiene practices are common methods for managing early blight.
Late Blight (Phytophthora infestans):
- Definition: Late blight is a devastating fungal disease caused by the pathogen Phytophthora infestans. It affects a wide range of plants, including tomatoes and potatoes.
Key Facts and Statistics:
- Symptoms: Late blight symptoms include water-soaked lesions on leaves, often with a white, cottony growth on the underside of the infected areas. It can also affect fruit and stems. Stems can show brown lesions that almost look like a burn. Generally seen on newer growth.
- Favorable Conditions: Late blight thrives in cool and wet conditions, which is why it’s most problematic in late summer and early autumn.
- Spread: The disease can spread rapidly and is highly contagious. Wind-driven rain can carry spores over long distances.
- Impact: Late blight is particularly destructive and can lead to the rapid death of tomato plants.
- Historical Significance: Late blight is infamous for causing the Irish Potato Famine in the 19th century.
- Control: Management strategies include fungicides, crop rotation, and destroying infected plant material.
What does tomato blight look like
How to identify Blight is a tricky one. It seems like whenever you have a tomato plant that looks sick the answer is BLIGHT! So, what does tomato blight look like? There are some tell-tale signs that make identification easy.
Dark spots on leaves
Normally the first symptom to appear are these dark brown lesions on the leaves. It is clear to see the darker spot in the middle referred to as a bullseye. You can see some of the leaves to the bottom left showing the underside and the white mildew-like effect often defining blight. You can also see some perfectly healthy-looking tomatoes growing on the plant, as the disease has not progressed to the fruit yet.
Dark lesions on stems
Here we can see a dark brown lesion on the stem, a bit like a burn. For me, this is a slam dunk when it comes to Blight diagnoses. You can also see the start of blight spots on the leaves in this picture. Two days after taking this picture the leaf was about 50% covered in lesions.
Fungus on the fruits
This is what Blight looks like on tomatoes. The structure of the skin starts to break down and wrinkle, and the blight starts almost like a brown bruise. This rapidly progresses to shriveled and brown fruit that smells of rotting. Really not nice!
What causes Tomato Blight:
Both types of blight are caused by soil-borne fungi. These fungi thrive in damp, warm conditions, typically becoming active in mid-summer when temperatures rise. Late blight is especially prevalent in late summer. To combat tomato blight, it’s essential to focus on controlling the spread of the fungus and preventing it from infecting your plants.
Common misconception regarding soil and Late Blight
While Late Blight can indirectly impact the soil, it typically doesn’t persist in the soil for extended periods on its own. Instead, its survival depends on the presence of infected plant material, such as decaying plant debris or infected potato tubers. So it is important that you remove any infected material from the soil to avoid it overwintering.
Is the joy of Blight just for Tomatoes?
It’s important to note that other plants in the nightshade family, such as potatoes, can also fall victim to early and late blights. Do you remember learning about the Irish potato famine at school? Well, that was caused by conditions that were perfect for Blight infections. Blight can spread from tomatoes to potatoes, and vice versa. To reduce the risk, keep potatoes away from tomato plants. If space is limited, consider planting them in separate raised beds or containers to keep the soil apart. However, be aware that early blight can also spread through the air.
Plants susceptible to different types of blight
Various plants can be susceptible to different types of blight, which are fungal diseases. Here is a list of common plants that can be affected by blight:
- Tomatoes: Both early and late blight can infect tomato plants.
- Potatoes: Late blight, known as the cause of the Irish Potato Famine, primarily affects potato plants.
- Peppers: Pepper plants, being part of the nightshade family, can be vulnerable to blight.
- Eggplants (Aubergines): Similar to peppers, eggplants are also susceptible to blight.
- Peaches: Peach trees can suffer from a fungal disease known as peach leaf curl, which is a form of blight.
- Apple Trees: Apple scab is a fungal disease that affects apple trees and can be considered a form of blight.
- Pear Trees: Pear scab, similar to apple scab, affects pear trees and is another form of blight.
- Grapes: Grapevines can be affected by downy mildew, a disease that shares similarities with blight.
- Cucumbers: Cucumber plants are susceptible to cucumber blight, which can affect the leaves, fruit, and stems.
- Squash: Various types of squash, including courgette (zucchini) and butternut squash, can be vulnerable to different types of blight.
- Lettuce: Lettuce plants can contract lettuce blight, particularly if grown in damp conditions.
- Beans: Bean plants can suffer from a range of fungal diseases, including bean blight.
- Cabbage: Blackleg, a type of blight can affect Cabbage plants.
- Brussels Sprouts: Brussels sprouts are closely related to cabbage and can also be susceptible to blight.
- Roses: Rose bushes can experience rose blight, which affects the leaves and stems.
One thing to consider is that as Blight is soil-borne, you need to ensure that you do not plant Tomatoes where Potatoes were grown previously. this can increase the chance of Early Blight sticking around in the soil. The advice ranges from one year to several years. However, I think that a year should suffice in most areas.
Preventing and Managing Tomato Blight:
Despite the challenges of tomato blight, there are effective measures you can take to protect your crop:
- Choose Blight-Resistant Tomato Varieties: Select tomato varieties that have been bred for blight resistance. Notice the keyword here is “Resistant” rather than immune. You cannot guarantee that Blight cannot take hold, but they put up a brilliant fight! Some recommended options include our own personal favourite Primabella along with Crimson Crush, Crimson Cocktail, Mountain Magic and Lizzano. We have done a review of Primabella on the Kettle Whistle and you can find that here: https://thekettlewhistle.com/the-best-primabella-tomato-review-2023-blight-resistant/
- Don’t be confused by Blight Tolerance when it comes to varieties. It is commonly suggested that Ferline and Legend are varieties that are blight-resistant, but they are blight-tolerant. They put up a fight, but are not fully protected and will eventually succumb.
- Mulch to Protect the Soil: Covering your soil with mulch helps prevent soil splash, a common way for the fungus to infect tomato plants. Mulching also offers additional benefits for soil health and moisture retention which we have an article all about here:
- Consider Protective Covers: Growing tomatoes in a greenhouse or using a covering/shelter can shield your plants from rain, reducing the conditions that promote blight infection. This approach provides better control of wet conditions, but depending on where you are growing and available space and cost, may be unsuitable.
- Trim Lower Foliage: Remove lower leaves from your tomato plants to reduce the risk of blight infection. Pruning at least a foot above the soil surface is recommended, though the distance may vary based on your specific gardening practices. The secondary benefit of this is that you also promote the growth of fruit rather than leaves. This can actively reduce the time to ripen and ensure that if late blight strikes, you have managed to harvest as much fruit as possible. It is worth noting that you should sanitise any tools used to trim tomatoes after use, to reduce any spread of potential disease.
- Be Mindful When Watering: Watering practices can impact the spread of blight. Avoid splashing water onto the leaves, as this can transfer the fungus. Use low water pressure, fine rose attachments, and water in the morning to ensure rapid leaf drying. We always take extra care to only water the roots on our allotment, which can take longer but reduces the chance the leaves stay wet.
- Maintain Cleanliness: Regularly clean up fallen leaves and debris under your tomato plants to prevent the fungus from spreading. Proper disposal of infected foliage is essential to minimize the risk. You are best not to compost infected foliage for example.
- Crop rotation: One thing to consider is that as Blight is soil-borne, you need to ensure that you do not plant Tomatoes where Potatoes were grown previously. This can increase the chance of Early Blight sticking around in the soil. The advice ranges from one year to several years. However, I think that a year should suffice in most areas.
Tomato Blight Treatment:
Now we know what tomato blight looks like, should disaster strike what do you do?
As a first step, our recommendation is to prune out as much of the blight as you can. This can be pretty aggressive to the plant, but less so than having blight attack it. So many people rip up their plants at the first sign. You have to ask yourself, if I rip them up I get no chance of any tomatoes. If I leave them in and prune, I might equally get no tomatoes, but there is a chance that your plants can survive and continue to fruit. We choose to prune them every time, and we have continued. to get edible fruit. You can see our video here documenting our fight with blight on the Kettle Whistle allotment:
You can try homemade sprays as a chemical-free option:
- Baking Soda Spray: Create a solution of 2 teaspoons of baking soda per litre of water with a few drops of washing-up liquid. Spray this mixture on your tomato leaves during early morning hours – basically not in full sun when the chances of leaf burn is possible.
Then there are the more aggressive fungicides that are certainly not organic:
- Copper-based Fungicides: Copper-based fungicides, such as Bordeaux mixture, can help control the spread of blight. Apply according to the product’s instructions and avoid excessive use, as copper can accumulate in the soil.
- Fungicides Containing Chlorothalonil: Products containing chlorothalonil can be effective against blight. Follow the recommended application rates and safety guidelines.
Minimise the risk of tomato blight
To minimise the risk of late blight affecting your garden in subsequent growing seasons, it’s essential to practice good garden hygiene, including:
- Remove and dispose of infected plant material promptly, including leaves, stems, and fruit.
- Properly dispose of infected potato tubers to prevent their reuse.
- Clean and sanitise gardening tools and equipment to avoid contamination.
- Rotate crops to different areas of the garden each year to reduce the risk of disease buildup in the soil.
Tomato blight could spell disaster for your crop of tomatoes. With these proactive measures, you can protect your precious tomato crop. I would highly recommend choosing resistant varieties as a first step. Practice good soil management, and be diligent with plant hygiene to enjoy a fruitful tomato-growing experience. Don’t be put off growing tomatoes because of the risk of blight. Worst case, just grow blight-resistant varieties and you can’t go too far wrong.
Thank you for reading, hope to see you again soon.
If you would like to get all geeky on Tomato Blight a good link for that information can be found here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5666701/