Soil treatment for tomatoes

How to Identify, Control and Prevent Blight on Your Tomatoes

Types of Blight

Early Blight. Early blight symptoms usually begin after the first fruits appear on tomato plants, starting with a few small, brown lesions on the bottom leaves. As the lesions grow, they take the shape of target-like rings, with dry, dead plant tissue in the center. The surrounding plant tissue turns yellow, then brown before the leaves die and fall off the plant.2 While early blight does not directly affect fruits, the loss of protective foliage can cause damage to fruits due to direct sun exposure. That condition is known as sun scald.

Late Blight. Late blight can affect tomato plants at any point in the growing season and at any stage of growth. Symptoms appears at the edge of tomato leaves, with dark, damaged plant tissue that spreads through the leaves toward the stem. White mildew may grow on the lower leaf surface of the affected area. This type of blight progresses rapidly through plants in humid conditions,3 and if left untreated, can spread to fruits.

Septoria Leaf Spot. Like early blight, the first symptoms of septoria leaf spot often begin on the lowest leaves of plants after fruits appear. Rather than showing as a few lesions per leaf, septoria leaf spot appears as many tiny, brown spots on leaves. Lesions continue to grow and spread before causing leaves to fall off. This type of blight does not usually affect fruits.4

Early blight and septoria leaf spot spores survive the winter in the ground, causing the disease to return next year.1 Late blight does not overwinter in the soil because it requires live tissue to survive, but wind can carry spores up to 30 miles away from infected plants.3

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.

Contents

The Types of Tomato Blight And The Symptoms

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

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.

Blight Resistant Tomatoes – The Varieties You Should Plant

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

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.

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 to Protect the Tomato Plant

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.

Avoid Soil Splash When Watering

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

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).

Tomato Blight Soil Treatment

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:

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 or you might be able to find it in your local public library or a local bookstore.

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Protecting Tomatoes From Dread Diseases

Q. What would I put into my soil to prevent tomatoes from blighting out shortly after starting to produce fruit? Here where I live it happens every year. We can grow all sorts of other vegetables with little or no problem. Thanks…

—Frank Moneris; Boonecounty, W.Va. (just south of Charleston)

A. I suspect that your plants are being blighted by a wilt rather than wilted by a blight, Frank. Among the numerous fungal diseases tomatoes can catch are earlyblight (leaves get brown spots, then turn yellow, tomatoes rot inside) and lateblight (leaves look water spotted, develop white fuzz on undersides and smell real funky). But I think (and you hope) that your love apples have succumbed to the MUCH more common verticilliumor fusarium wilt instead. (These diseases cause the leaves to wilt and curl, then yellow and drop off.)

Both of these wilts (verticillium is more common in cooler climes; fusarium where its warmer) lurk in soil where tomatoes (and some say their relatives—spuds, peppers and eggplant) have grown in seasons past. They can persist in a plot for 15 years (!), but generally die out if you don’t plant those garden favorites in the infected area for four seasons or so. Morning sun, good drainage, high levels of organic matter in your soil and lots of airflow around the plants are all helpful in controlling the problem; chemical fertilizers are NOT—the fast, weak growth they cause is prone to such disease.

So, if you MUST grow your love apples in the same areas as seasons before, be prepared. If they’re already in the ground, check them carefully, remove all diseased parts, clean up around the base of the plants, then mulch the surface of the soil with the highest quality compost you can find—an inch deep and a couple of feet out in all directions. Living organisms in the compost will actually eat the disease spores. Yum. Then be vigilant—pull off discolored leaves as soon as they start to look funky, and remove the old compost and reapply a fresh inch every month.

Spray the plants weekly—either with a natural fungicide, compost tea (home made or one of the super-charged compost teas being brewed at larger garden centers) or The Cornell Formula: A table spoon each of baking soda and vegetable or horticultural oil, plus two drops of dish washing soap, in a gallon of water. Be sure to remove discolored leaves first, only spray first thing in the morning and really soak the undersides of the leaves.

If your love apples are not yet in the ground, try and find a new space to plant them in. Or plant at least a few in big containers that are totally free of ANY garden soil. Use a high-quality, organic potting soil containing compost or other natural fertilizers; or my famous mix of equal parts peat, perlite and compost with a tablespoon of lime or wood ash to adjust the pH. If the containers do great and the dirt does not, there’s your answer.

In future seasons, seek out disease resistant varieties; they’ll have “VF” (the initials of those wilts) and probably a few other letters, like N for root knot nematodes and T for Tobacco mosaic virus, after their name. Or try some of the huge, fast-growing heirloom varieties like the super-tasty Brandywine; these rangy vines often grow so fast they can ‘outrun’ disease! And remember— these wilts generally only harm the leaves of your plants; the actual tomatoes tend to be unaffected, and are always perfectly safe to eat.

True blight is a rarer and MUCH more serious problem. If blight it be, cry. Then do everything we’ve said and to do it perfectly: Have LOTS of room between plants; put every tomato where it gets morning sun, remove diseased leaves the second they show their spots; have a heavy hand with the compost; and alternate weekly sprays between the three disease preventers we just mentioned. Oh, and maybe try the variety “Legend” next year; it’s the only tomato I know that claims to be resistant to early and late blight.

And no matter what else you do…

Make sure you add eggshells to your planting holes! Later this season I’ll get tons of emails from people who want to know what disease is making their tomatoes turn black and rot down at the bottom. That’s no disease—that’s blossom end rot, and it’s caused by too much water, too little water, or just plain uneven watering. Once you get to the rotten bottom point, there’s no real cure—but you can prevent it now. With eggshells.That’s right—eggshells First of all, I hope you all know to plant your tomatoes deeper than other garden plants. Tomatoes form auxiliary roots along their buried stems, allowing them to take up more food and water and anchoring them better in the ground. If you’ve got a foot tall start, remove the bottom leaves and bury 8 or 9 inches of the stem BELOW ground. And add the dried, crushed shells of a dozen eggs to that planting hole. The calcium they provide will allow your tomatoes to regulate their water needs so well, they simply can’t get blossom end rot. And they’ll taste better too! MUCH better!

The flavor of tomatoes comes mostly from volatile aromatic oils that we perceive not with our taste buds, but with our noses. And tomatoes NEED calcium to produce those oils. So if you haven’t been adding eggshells and think your tomatoes taste great, wait till you see the improvement calcium can make—you’ll never go eggshell free again.

Now, if your tomatoes are already in the ground, don’t panic. If you didn’t bury them deep in that wonderful heavy clay of yours to begin with, dig ’em up and do it again—this time, nice and deep, with a dozen eggshells and a handful of compost in the hole for good luck. Do this in the evening, water well afterwards and again the next morning and they’ll be like 5 year olds being carried in asleep from the car; they’ll just wake up in bed the next morning with no idea anything happened.And if you did everything right except the shells (or are in a blind panic trying to figure out where to get enough eggshells right now) use a calcium-rich organic fertilizer instead. Just be sure and check packages or product descriptions carefully; even though almost all our soils are deficient in calcium and plants need it, a lot of fertilizers don’t contain it.

IDENTIFY, PREVENT, TREAT TOMATO BLIGHT

There are two broad types of blight, late and early, with late blight being the main disease as far tomato plants are concerned. Distinguishing between early and late blight is a bit irrelevant for the amateur gardener, both will render your crop useless and there is no treatment when plants have been infected.

As at August 2015 there is only one tomato variety in the UK which is claimed to be resistant to tomato blight. It is called Crimson Crush and a full review of this variety can be found here.

SYMPTOMS OF TOMATO BLIGHT

The likely symptoms are listed below in the order in which they normally occur:

  1. Small brown marks appear on the leaves which enlarge as the blight takes hold.
  2. Leaves on the lower part of the plant may well have light coloured patches of fungal infection on the undersides.
  3. Brown spots will then appear on the stems and branches, quickly turning to deep brown black. These marks will expand and at this stage the general health of the plants will begin to fail, the stems and branches will begin to turn to mush and possibly collapse. It will be clear that your tomato plants are suffering badly.
  4. Finally the fruits, both green and ripe, will show brown marks on them. The affected leaves will dry up, shrivel and fall off.

Tomato Blight

HOW TO TREAT TOMATO BLIGHT

If your tomato plants are suffering from tomato blight there is no cure, even farmers who have access to strong pesticides are helpless once the disease has hit. There are however measures you can take next year to greatly reduce the likelihood of the disease occurring again. Plants affected with blight in any form should be dug up and burnt, under no circumstances put them on the compost heap.

There are several things you can do to prevent tomato blight and these are listed below:

  1. Practice good hygiene throughout the entire growing season. Remove decaying leaves from the plant and the surrounding soil.
  2. Practice crop rotation every year. Tomatoes should never be grown in the same soil two years running. Blight, especially, stays in the soil over winter and will re-infect tomato plants grown in the same soil two years running.
  3. Burn all parts of infected plants, never put them on the compost heap and do not dig them into the soil.
  4. Remove lower leaves and side stems so that none are toughing the ground and preferably are at least 5cm / 2in above the ground. This will go a long way to preventing infection which often occurs when rain splashes on the soil and transfers soil to the lower leaves.
  5. Space plants correctly. This will allow good air circulation to dry off leaves and stems and reduce the risk of fungal infections. Follow seed packet instructions but as a general rule 45cm to 60cm (18in to 24in) between plants should be sufficient.
  6. Water the soil and not the leaves. Damp conditions amongst the foliage provides ideal conditions for tomato blight.
  7. Grow blight resistant tomatoes. There is currently only one tomato variety which shows exceptional resistance to tomato blight, it’s called Crimson Crush and was first made available to the public in 2014 / 15. Read our full review of this variety here.
    Other varieties of tomato such as Ferline claim to have resistance to blight but in reality it is only minimal. At the moment, Crimson Crush is the only variety with significant resistance.
  8. Sprays for Tomato Blight. There are no effective sprays or chemical treatments available to amateur gardeners in the UK to treat tomato blight. Copper based sprays were believed to have helped but these were withdrawn in 2014.
    Many articles (online and in books) mention copper sprays (including Bordeaux Mixture) but they are simply out of date now.

LIFECYCLE OF TOMATO BLIGHT

It may help in preventing tomato blight if you understand the lifecycle of this disease.

Movement of the spores (called Phytophthora infestans) cause blight. Their movement and infection rate is highly dependant on a combination damp wet weather and specific temperatures. When it is damp and warm the danger of infection is high. The spores are released into the atmosphere from late spring to late summer and they travel on wind and / or rain drops.

It’s very difficult for the amateur gardener to predict when danger periods occur however the website Fight Against Blight offers a blight prediction service which is well worth signing up to if you plan to spray your tomatoes (see below), It’s run by the Potato Council but what works for potato blight also works for Tomato Blight. The service is free and you can receive email or text warnings for free.

Other common pests and diseases which affect tomato leaves include:

  1. Tomato Blight
  2. Tobacco Mosaic Virus
  3. Nutrient Problems
  4. MAIN INDEX TOMATO PESTS AND DISEASES

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