Harvested Tomatoes

How To Avoid Tomato Blight That Can Decimate Your Crop

One of the worst tomato diseases is blight. Learn how to avoid tomato blight so that you keep your crop and can enjoy tasty, juicy tomatoes every year.

If you have grown tomatoes outdoors for any length of time, you may have had a whole tomato crop wiped out by tomato blight. This is quite disheartening after all the work of raising strong tomato plants from seeds or seedlings.

You’re probably looking forward to a fresh tomato salad or making some tomato sauce or salsa. Those plans can instantly be upset by losing part or all of your tomatoes to this disease that can strike at any time.

But there are various pro-active things you can do to have a more blight resistant tomato crop.

The best way to prevent tomato blight is to protect the tomato foliage from soil splash.

There are also some ways to also treat tomato blight when it first starts, but prevention is more effective in the long run.

Let’s look at what you can do to secure your tomato crop against this devastating disease.

The Types Of Tomato Blight And The Symptoms

late blight on tomatoes

There are two types of blight that can hit tomatoes.

Early blight (Alternariatomatophila or Alternariasolani) can cause the lower leaves to yellow and brown spots to appear on the leaves. The fruit can also be affected, getting brown lesions and can drop off the plant.

If kept unchecked could affect the whole plant over time. Usually you will get lower harvests but in some cases the whole plant could die.

Late blight (Phytophtherainfestans) actually will kill your plants in a short time. Unlike early blight, if a plant gets infected it’s toast! Basically the plant starts to look like it has been burnt by the sun. In a short period of time it will simply wither and die.

You can try and pick the unripe tomatoes that are on the vine when you see the first symptoms of late blight and then have them ripen off the vine. But if you pick them too late they likely will be infected and rot away while you are waiting for them to ripen off the vine.

What Causes Tomato Blight

Both forms of blight are caused by a fungus in the soil. When the fungus spores get splashed up onto the plants stem or leaves, it takes hold and it’s then just a matter of time before the whole plant is infected if nothing is done about it.

The fungus loves damp and warm temperatures. So it will usually be dormant in winter and only become a problem in mid summer when temperatures warm up. Late blight gets it’s name from being especially prevalent in late summer.

So all of these control measures in this article cover controlling the fungus and trying to keep it off of your plants.

Does Tomato Blight Affect Other Plants

Eggplant and Pepper on a wooden cutting board

Other plants in the nightshade family can also suffer from the same early and late blights that affect tomatoes.

Potatoes are especially susceptible to blights. Usually blight travels from tomatoes to potatoes but it can also travel the opposite direction.

So definitely keep potatoes as far away as possible from tomato plants. In a small garden this may be difficult. You may just have to forgo one for the other.

Or you can plant the potatoes and tomatoes in separate raised beds or in separate containers so that you can keep the soil separate. Early blight however is airborne as well so that may not work reliably.

Blight can also affect peppers and eggplants. It helps to keep some distance between plants, but again in a small garden may be hard to do.

If you plant in containers, you keep the soil separate and can also move a plant if you notice it started to be affected.

How To Avoid Or Reduce The Effects of Tomato Blight

Despite the devastating effects of tomato blight, you can avoid or at least reduce the effects of it, so that you can still harvest a decent number of tomatoes from your plants.

Plant Blight Resistant Tomato Varieties

Because blight has become such a problem, tomato propagators have been working hard on breeding more blight resistant tomato varieties.

Any good seed catalogue will list as part of the seed description if that tomato variety is resistant to blight. Note that no seed company can guarantee a tomato variety is completely immune to blight, so you still need to follow the other methods in this article.

But at least with these varieties you have more of a chance in fighting blight. Here is a list of suggested varieties. (adapted from https://homeguides.sfgate.com/early-late-blightresistant-tomato-plants-60469.html)

  • Defiant – this large determinate red tomato has good resistance to early blight and very good resistance to late blight
  • Legend – another large determinate plant that is resistant to both blights
  • Black Plum – an heirloom indeterminate variety that is dark-skinned and has good resistance to both kings of blights
  • Black Krim – another dark indeterminate heirloom that is moderately resistant to both types of blight
  • Aunt Ginny’s Purple – similar to Black Krim
  • Red Currant – an indeterminate cherry tomato with good resistance to both blights
  • Matt’s Wild Cherry – another cherry with even better resistance than Red Currant
  • Yellow Currant/Yellow Pear – a small pear-shaped tomato that also is excellent at being resistant to both types of blight

For even more information, check out Late Blight Management in Tomato with Resistant Varieties from the Cooperative Extension System.

If you save tomato seed, you need to be especially careful. Never save seeds from a tomato plant that is infected by blight. You could end up with blight susceptible plants if you use those seeds.

In general when saving seeds, pick only tomatoes from super healthy plants that have seen no sign of blight or any other tomato diseases.

Cover the Soil to Protect from Soil Splash

arborist wood chip mulch

One of the easiest ways to minimize the chance of blight affecting tomatoes is covering your soil with a mulch of some sort.

I’ve already discussed the benefits of mulch in this article: 7 Benefits Of Mulch You’ll Get When You Add It Right Now

And one of those benefits is disease prevention. Especially for soil-borne diseases such as blight.

By covering the soil with some kind of mulch, you minimize the blight fungus splashing up when it rains or when you water your tomato plants.

Cover your Tomato Plants

The other more drastic measure is to cover the entire plants so that they never get rained on.

There are many ways to do this. One way is to grow your tomatoes in a greenhouse or in a poly tunnel. This is a more expensive solution if you don’t already have such as structure. You still need to practice clean soil hygiene but at least you more control.

Another way is to setup a temporary structure over your tomato crop. A family friend of ours in Germany setup this simple cover over his tomato plot.

fibreglass panel cover for tomato plants to avoid tomato blight

From what I could see, he simply uses some wooden stakes, a cattle panel made from welded steel wire mesh (used as fencing for cattle and livestock) and a piece of translucent corrugated fiberglass. 

It still allows airflow and won’t overheat like an enclosed greenhouse would. When we were there it was over 35°C (95°F) and standing underneath the canopy was bearable still.

A cover will also give the tomatoes added warmth and protection from cold nights early in the season and into the fall if the summer ends earlier than expected.

Trim Lower Foliage On Your Tomato Plants

Usually the lower leaves of your tomato plants don’t produce any fruit.

However those lower leaves are prime candidates for becoming infected from the blight fungus when it splashes up from the soil against the underside of the leaves.

You won’t measurably affect the plant’s growth or fruit production if you snap off the lower leaf trusses. I recommend going up at least a foot. It really depends on whether or not you’ve followed the other tips here. If you mulch and are careful with watering, you can get away with less distance between the lower leaves and the soil.

If they are still healthy with no signs of blight, you can simply compost them.

If you already see the affects of blight on the lower leaves, unless you have a very hot compost you need to dispose of the leaves in a municipal compost that does attain hot temperatures to kill off the fungus.

To see how this looks, check out this short video:

Avoid Soil Splash When Watering Tomatoes

green and black watering can watering a garden

Water drops falling on the soil and bouncing back up against the lower leaves will transfer the fungus to your plants. Less so the stem, but that can happen as well.

You can’t do much about rain. A gentle rain likely won’t have drops bouncing very high, but if you get heavy rains, then those drops will have quite the rebound. And the other methods here will help protect your plants.

But if you hand water either with a hose or with a watering can, you can be careful and only water the soil. Use a low water pressure if using a hose and a fine rose attachment on your watering can.

It also can help to water in the morning rather than in the evening, as any water splashed onto the leaves can dry quickly in the sun, rather than sit on the leaves all night.

If you do automatic watering, avoid using overhead sprinklers. The best way to water is with either drip irrigation or soaker hoses. I’ve covered all the different ways to water in this article: Watering Plants: 7 Watering Systems Evaluated

Clean Up Under Your Tomato Plants

Sometimes fruit or leaves will drop off by themselves and end up accumulating under your plants.

Be sure to clean up this debris regularly to reduce the chance that the blight fungus migrates to the debris and then ends up on your plants.

Just be sure to dispose of the foliage properly as mentioned above, depending on whether it is infected or not.

This preventative measure is something you can do when you do your regular Garden Maintenance Walks (you are doing them, right?)

Tomato Blight Spray Recipes

a spray bottle being used in the garden

So after all this, if you still get infected plants, what can you do?

There are of course chemical sprays and treatments you can buy and apply if you’re allowed to.

But if you are averse to using these and want to garden naturally and chemical-free, here are two “organic” sprays you can create yourself.

Compost Tea

Assuming your compost is disease free, you can brew up some compost tea and spray it on your tomato leaves. This will also foliar feed your plants as an additional benefit.

Just place some compost in a bucket, add water (ideally rainwater) and let sit for a few days, stirring regularly.

Then strain, put in a spray bottle and spray on your plants.

Baking Soda Spray

Baking soda is mildly fungicidal. Make up a solution of 1 teaspoon baking soda to 1 quart or litre of water. Add a few drops of a liquid dish soap to help the solution stick to the tomato plant’s leaves.

Put in a spray bottle and spray the leaves when they are not in full sun (early morning works best).

Soil Treatment Against Tomato Blight

If you want to try and treat your soil to remove or minimize the fungal spores, there are a few things you can do.

I’ve seen suggestions that say to deeply till the soil, but that can cause the fungal spores to simply be spread more widely, including to neighbouring beds. And it has other issues such as breaking soil structure and bringing up weed seeds and multiplying perennial weed rhizomes.

So a better option is to amend your soil with a deep layer of disease-free compost every year in the fall or early spring before you plant your tomatoes out. This will act as a mulch keeping the fungal spores deep in the soil.

You should also rotate your crops and not grow tomatoes in the same soil year after year. I’ve covered crop rotation in more detail in this article: Vegetable Crop Rotation: How To Increase Your Harvests

If you’re growing in containers, make sure to replace the soil every year with clean compost or potting soil. While the containers are empty, give them a good scrub with a mild bleach solution as well.

Also clean any stakes or tomato cages you use at the end of the growing season. And keep your garden tools clean as well.

More Tomato Growing Resources and Information

For more information on growing tomatoes including some of the other diseases that can affect tomatoes check out these resources.

An article by Clemson Cooperative Extension Home & Garden Information Center: Tomato Diseases and Disorders

Epic Tomatoes: How to Select and Grow the Best Varieties of All Time – This is one book I need to add to my gardening library. It’s well reviewed and written by an expert on growing tomatoes, Craig LeHoullier. You can get it on Amazon with my link below or you might be able to find it in your local public library or a local bookstore.

Tomato blight doesn’t need to devastate your crops if you take some of the precautions in this article.

Hope you have a great tomato harvest!

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