How to Identify, Treat, and Prevent Early Blight in Tomatoes
Surely, if you have been gardening and growing tomatoes for some time, you have heard the term “blight,” but information surrounding it can be confusing. Where does it come from? How does it spread? Can I save my garden if my plants become infected with early blight?
Early blight can be destructive, but it is also very preventable if you follow some simple gardening steps. Take good care to keep your garden tidy, know when early blight can strike, and how to treat it if it appears.
Keep reading for tips on identifying, treating, and preventing early blight in your tomato garden.
Early blight is a common tomato disease caused by the fungus Alternaria solani or closely related Alternaria tomatophila. This disease should not be confused with late blight, which occurs later in the growing season, is much more deadly, and can spread much further and more quickly.
Plants and fruit can be affected by early blight at any maturity stage, starting from young seedlings all the way to older, stronger stages.
How it Grows
Early blight fungus lives in the soil, on plant debris like discarded leaves or compost, and on other infected plants. It can jump from soil to your plant by way of water splash or wind which makes pruning, deep watering by way of soaker hoses or drip tape, and mulching extremely vital to keeping a healthy garden.
Symptoms of early blight will start to show on the lowest leaves first and work its way up the plant. Pay close attention to the lower leaves, looking for signs of the disease and taking action quickly to prevent further spread.
Early blight tends to prey on weak, stressed, and unhealthy plants. Ensuring that your plants are healthy in general will decrease the odds of them coming down with any of the many diseases that can affect tomatoes.
Although early blight may not altogether kill your plants, yields will almost certainly be affected. Affected immature fruit may even completely fall off the plant, leaving you with less fruit to enjoy.
Fruits that make it to mature stages may not be as high quality as fruit of an unaffected plant. They may form black, leathery spots near the stem and may even fall from the plant completely.
Crops That May Deal With Early Blight
Early blight can affect both tomato and potato varieties as well as other nightshades such as eggplant and peppers. The disease may also be present in solanaceous weeds such as black nightshade and hairy nightshade.
Early blight thrives in moist conditions and can occur at any temperature but spreads the quickest when temperatures are above 75°.
Oftentimes, early blight appears after heavy early morning dew or heavy rainfall. Although it shows up earlier than late blight, it sometimes does not appear until plants are fruit bearing, and the two diseases can show up simultaneously.
Dense foliage and high humidity creates a perfect storm for early blight. Keep in mind that pests such as flea beetles and aphids can help to spread the spores of early blight throughout your garden.
If young seedlings are infected with early blight, it will generally show up by way of brown spots on the stem just above the soil line. Early blight can easily cause vulnerable seedlings to die.
Note: Early blight present in plants purchased from an outside source could be affected by damping off.
If plants are more mature when early blight strikes, the fungal disease can cause brown and yellow bullseye marks on leaves, often causing them to dry up and shrivel or fall off completely. Look for brown spots on lower, older leaves of your plants.
The spots can get up to 0.5 inches in diameter and may form concentric circles that are yellow and/or brown. Stem spots on older plants will be dry, irregular, and oval-shaped.
Since the fungus is traveling up from the soil, low-hanging and old leaves are typically affected first. If you have been experiencing long-term drought conditions, plants are more susceptible, and the disease can spread more rapidly during these periods, so keep a close watch.
Check out this Cornell article on early blight. The featured photos may help you determine if what’s going on in your garden is early blight or something else!
Proper Disposal of Plants
It’s important to completely kill the pathogen once you have identified early blight in your garden, and sometimes, the best way to do that is to destroy the infected plant.
Remember, this pathogen can travel by wind and rain as well as from plant to plant, so if you simply move the plant to a compost pile, the spores may make their way back over to your garden!
To fully and properly kill the late blight pathogen, pull out infected plants on a hot and sunny day, lay them out in the sun, bag them, or cover them with a tarp so they cannot travel and spread.
Pro tip: If you have confirmed early blight in one area of your garden, keep a close eye on others that may be affected. You could also treat your plants preemptively with a fungicidal spray. More on that a bit later.
Prevention is really key when it comes to early blight, as it is hard to eradicate once it appears in your garden for the season. Below are ways you can prevent early blight in your garden. Choose the options that work best for you and experiment often.
Upon transplant of tomatoes, peppers, potatoes, and eggplant, mulch them to get ahead of any early blight living in your soil, which could just be waiting for ideal conditions to spread. The mulch serves as a barrier between the fungus and your plant, making it more difficult for the fungus to splash up.
Just about one inch will suffice. Much more could lead to increased humidity, which will have the opposite effect that you want.
Provide Adequate Airflow
You must follow proper pruning practices to get good airflow. This includes keeping the bottoms of plants clear of spent leaves and clusters, as well as keeping suckers to a minimum. Suckers are the new growth between a leaf and the main stem. If left alone, suckers will become bigger and start competing for resources as well as crowding your plants with unnecessary foliage.
Remember, you can remove about ⅓ of a plant’s foliage when pruning without any negative effects on its overall health, so don’t be shy!
Another thing you can do to provide good airflow is to space your plants out properly when planting out your garden. You want to be sure leaves from one plant aren’t touching the leaves of its neighbor because that’s an easy way to spread diseases of all kinds. If you have the space, try to give each plant at least 2 ft of its own space.
Pro tip: Read seed packets and do research on new varieties you are growing before transplanting. Oftentimes packets will indicate if lots of foliage can be expected. You should plan to give this plant even more space.
Grow Disease-Resistant Cultivars
You can select tomato cultivars more resistant or tolerant of early blight than others. On many seed company websites, you can filter for specific disease resistance (look for the code EB if you don’t see the option early blight).
Below are a few examples of these cultivars, which are pretty widely available and have been bred for early blight resistance.
|– Plum Regal
– Verona F1
– Cloudy Day F1
– Defiant PhR
– Mountain Magic
|– Geranium Kiss
– Honeybunch F1
– Summer Sweetheart
– Supersweet 100 F1
– Coyote Cherry
– Marnero F1
– Matt’s Wild Cherry
– Old Brooks (great for canning)
– Tommy Toe
Remember that you may still experience early blight even when growing a so-called resistant cultivar because the resistance bred into these cultivars makes the plants more tolerable but will not 100% prevent the pathogen.
Always check your plants for symptoms so you can catch it quickly, and your plants have a chance to recover if early blight appears.
Practice Crop Rotation
You can help prevent early blight in future years by practicing proper crop rotation. Try not to plant tomatoes, potatoes, or other members of the Solanaceae (nightshade) family for at least 3-4 years after experiencing early blight in that plot, as the pathogen can continue to live in the soil.
By moving crops that early blight attacks out of the infected soil area for a few years, you are starving the fungus. This might not always be possible for growers with limited space, so do your best to rotate.
- Take care to keep your pruning tools clean and dry.
- Avoid long periods of humidity or wetness.
- Avoid overhead watering and working with plants when they are wet.
- Select disease-resistant cultivars.
- Purchase plants from reliable sources.
- Have a plan in place for treatment.
- Keep your gardens weeded.
- Keep any trimmings and clipped leaves off your garden floor.
Growing in a Greenhouse or High Tunnel
Typically, growers decide to install protected spaces, such as a greenhouse or high tunnel, to grow valuable crops such as tomatoes. Usually, there is a decreased chance of getting early blight. This is because you can control the humidity and airflow.
It allows you to close the sides on windy days so pathogens don’t fly in and keep rainfall off plants, which helps keep them dry. However, condensation forms easily in this enclosed environment from moisture dripping off the ceiling onto the plants.
Remember that when growing in a protected space and early blight does appear, it may be harder to control the spread. Be sure to space your tomatoes properly to avoid any leaves touching those of other plants, and prune regularly to increase airflow.
Start walking through your tomato tunnel as soon as conditions are ideal.
The fungus that causes early blight feeds on decaying plants and plant matter. It will survive in your soil after the growing season.
Early blight spores will survive on support cages or stakes, so take caution when reusing these items year after year. Disinfecting and storing them away from plant debris will help keep them clean and blight-free.
Early blight can cause fruits to rot more quickly or not ripen properly at all. However, fruit infection is quite rare with this fungus. And although the infected fruit is not the prettiest, you can remove the infected area and eat the remainder of the fruit. Early blight cannot be transferred to humans as it is a plant pathogen, so the fruit is not dangerous to ingest.
Pro tip: Infected fruits should not be used for canning of any sort. For preservation, you should always select the healthiest fruits for the best results.
Contacting your local cooperative extension office is a great starting point. There is likely an agent assigned to your county or region who can look at photos of suspected blight to help you diagnose the pathogen and answer any questions you may have.
Also, most state cooperative extension offices track early blight, so it’s a good idea to reach out if you have confirmed early blight in your garden.
If you have early blight, your neighbors might too, so it’s also a good idea to communicate about it. You could also join a local online board about tomato growing in your region.
Copper fungicides are the only approved treatments for organic growers that seem to have substantial results in the fight against early blight. Some home gardeners rely on potassium bicarbonate for another eco-friendly and inexpensive option. While this does not get rid of the risk completely, it should help keep it under control.
Prevention is key so if you decide to spray, it is best to do so before you see symptoms and then continue a treatment plan all season long. It is recommended to spray every 7-10 days once treatment begins. As with any treatment plan, read all labels before applying anything to your garden.
Although early blight is a nasty soil-borne disease that can destroy gardens, it is avoidable if you crop rotate or pre-treat early in the season to avoid it altogether. Focus on reputable seed and plant sources, deep root watering, mulching and pruning, pruning, pruning!
Creating good airflow between your plants and allowing plants to dry out before working with them will drastically cut down on lots of tomato issues, especially this one. Do your research and be sure you know what to look out for so you can keep your garden safe from early blight.