- Soil repair after tomato season
- Fighting Tomato Blight – 3 Major Keys
- How to Grow Healthy Tomatoes
- Blight On Tomatoes – Tomato Blight Treatment And Prevention
- What is Tomato Blight?
- How to Prevent Tomato Blight
- Early blight of tomato
- Quick facts
- Host and pathogen
- Biology and disease cycle
Soil repair after tomato season
Tomatoes are susceptible to several fungal diseases and the most common is early blight. See our website for more information on prevention and control. You can also select resistant varieties next year. See the resistant list from Cornell http://vegetablemdonline.ppath.cornell.edu/Tables/TomatoTable.html
At this point it is recommended to test your soil for pH and nutrient deficiencies if this has not been done in the last several years. See our link http://extension.umd.edu/hgic/soils/soil-testing
Be sure to discard badly-diseased plants and fruits; don’t till them back into the soil. All other plant waste can be composted or directly incorporated into your garden soil. This will reduce the potential for these disease problems from next year’s garden. This debris should be bagged and put out for the trash and not put in the compost pile. Only really hot compost piles will kill off potential problems.
Lettuce, spinach, and arugula can be planted through mid October. Cover these late plantings with a cold frame, temporary greenhouse or floating row cover. Be sure to fertilize seedbeds, keep the soil moist and protect seedlings from pests. Garlic and shallots can be planted mid October -mid November.
If you decide not to plant, Do not leave the soil bare. Cover crops are preferred. If this is the first time planting or you want to plant early spring vegetables, look at spring oats. Oats are killed by the first hard freeze, leaving a brown decomposing mat in the spring.
Otherwise shredded leaves are a good alternative. Rake leaves into a loose pile and go over them with a lawnmower to cut them up. They will be much less likely to blow away if they are broken up. They can be worked into the soil next spring or seedlings can be planted through them. The mulch will act as a weed inhibitor.
Tomato blight. Two words that strike fear into backyard tomato growers everywhere!
Tomato blight is a fungal condition that can devastate and destroy otherwise healthy tomato plants. It is spread through spores, and can easily wipe out an entire crop.
There are actually three distinct types of tomato blight. Early blight, Leaf spot blight, and Late blight.
Of the three, Leaf spot blight is by far the most common to the home gardener. It begins to appear in late June to early July, with the lower leaves turning black and rotting away.
Leaf spot will steadily begin to destroy all of the foliage of the plant, usually within 30 days of first appearing.
An entire crop of tomatoes ruined by blight
Early tomato blight will appear after the tomato plants have set fruit. This blight will also show in damaged leaves, but also with dark spot appearing on the tomatoes themselves.
It can completely rot out the fruit as it tries to ripen on the vine.
Late blight starts as a small light-colored spots on the foliage of plants. It quickly progresses until the stems, leaves and tomatoes turn black.
Late blight is spurred on by cool, damp temperatures. It tends to be more of an issue in cooler climates, or in growing seasons that are extremely wet and rainy.
The bad news is that once any of the above tomato blight symptoms have arrived, it is usually too late to help. Although you can remove damaged leaves and fruit as soon as you see them, blight usually will win in the end.
The real key is in prevention. There are actually quite a few things you can do that can help you avoid tomato blight. And you might be surprised how easy they are!
Fighting Tomato Blight – 3 Major Keys
Crop Rotation / Planting In A New Space
The number one way to keep tomato blight and disease from your tomato plants is by rotating your crops.
Growing tomatoes in the same soil or garden space every year is like opening the door to blight. Tomatoes are one of the most susceptible vegetable plants when it comes to soil-borne disease.
By planting continually in the same location, soil can become infected with spores. And every year you plant, they have an easy ride to killing off your new crop.
Rotate tomatoes to a new location or soil space each year for a minimum of 4 years. If you are growing tomatoes in containers, replace the soil each season with new potting soil.
Not only does this help to prevent blight, it also keeps a fresh supply of nutrients in the soil.
Mulch Plants As Soon As You Plant
Supporting tomatoes keeps them off the ground and out of harms way
As soon as you plant, mulch the area around your plants immediately. Mulching plants helps to cut down on weeds and keeps the soil temperature regulated.
But more importantly, it helps prevent the spread of soil borne disease! Spores that are alive in the soil can easily be splashed up foliage directly.
Every time a hard rain hits, your plants have the chance to become infected by the spores splashing up.
It is also important to remove the bottom 6 to 12 inches of your plants foliage for this same reason. Keeping the plants up off the ground helps to keep disease away by keeping soil from directly touching the foliage.
Supporting plants with stakes or cages helps keeps plants off the ground as well. Product Link : See Tomato Square Cage
When and how you water can make all the difference in keeping tomato blight at bay. Water in the early morning so tomato plants have time to dry off.
Wet and damp leaves are the ideal ingredient for spores to grow. Watering late in the day or at night will keep plants too moist. That leads to heavy dew, making plants more prone to disease.
When you water, be careful to water only the root zones around tomato plants and not the foliage.
By watering this area, you reduce the chance of splashing spores from plant to plant. Watering is one of those mundane tasks that seem so simple on the surface, but can cause immense damage if done incorrectly.
See : The 4 Secrets To Watering Plants
You may not be able to treat tomato blight effectively once it occurs, but you can definitely help prevent it. As the old saying goes, an ounce of prevention is worth a pound of cure!
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You have visions of homegrown tomatoes dancing in your head. . . Homemade tomato sauce canned and stacked neatly on shelves, stewed tomatoes in jars, tomatoes on salads and just taking a big juicy bite out of one straight out of the garden – you can almost taste it! You go out to your garden to do your checkup and daily watering and see something odd on one of your tomato plants. The leaves are watery and rotten looking and there is a brown lesion on the stem. What is going on? You guessed it: you may have tomato blight.
What is tomato blight?
Early tomato blight is caused by a fungus called Alternaria solani. This fungus can affect almost every part of the tomato such as the stems, leaves and fruits. It may not outright kill the plant but it will weaken it and the yield may be smaller.
Early blight loves damp weather and heavy dew, it can be in the soil, or it can overwinter in diseased plants from the year before if you didn’t clean up the vegetable garden promptly. Like with most pests and diseases, plants which are stressed or just in plain poor health are more susceptible.
Early tomato blight forms spots on the leaves, which then turn yellow and die. The spots may start out small and shrunken and as they get bigger they get longer. Spots which are on the stem near the ground can cause the stem to girdle. When it’s on your fruit, the spots show up near the stem. The spots will be dark leathery and sunken with concentric rings and it will affect your ripe and unripe tomatoes. Your plants may survive this attack but there won’t be as many tomatoes. While early blight is a nasty disease, it’s not as devastating as late blight.
Late tomato blight is just plain bad news all the way around. The name of this fungus is called Phytophthora , which means “plant destroyer”. It can ruin a whole crop and infect other plants quickly. It’s highly contagious and can spread from your garden to a neighboring gardener’s plot in the breath of a spore carrying wind. If a plant becomes infected, it has to be destroyed and taken off-site (not composted).
Late blight shows up as blue-gray spots which then turn brown, and it affects both the leaves and the fruit. The fruit will have brown greasy spots which are shaped irregularly. The spots on the leaves and fruit may have a cottony looking ring of white mold and the leaves will eventually fall off. Late tomato blight shows up in cool and wet weather in mid-to-late season and can kill a plant within a week.
California’s Humboldt County and the coastal Pacific Northwest has such cool, damp summers that our tomatoes often suffer from blight – though it’s by no means limited to the Northwest region. Gardeners across the country suffer from both early and late blight.
The heartbreaking look of late blight.
Plant blight-resistant tomato varieties
- ‘Iron Lady’
- ‘Jasper’ – red cherry
- ‘Lemon Drop’ – yellow cherry
- ‘Pruden’s Purple’
- ‘Red Currant’
- ‘Defiant PhR’
- ‘Jasper’ red cherry
- ‘Mountain Magic’
If you can find grafted versions of tomatoes that are bred for disease-resistance, all the better. Grafted tomatoes can be much more vigorous and better able to shake off stresses.
Preventing early tomato blight
- First of all buy your starts and seeds from a reliable source – don’t just take starts off friends or well-meaning neighbors.
- Make sure there is enough space between your plants for air circulation.
- Add a layer of mulch or use those red plastic tomato mulches they sell as a barrier between tomato foliage and soil, as the fungus can be carried in the soil.
- Check your plants frequently during wet weather or if they are stressed.
- If you see anything that even remotely looks like blight, begin a spraying program of alternating organic copper spray, and Serenade biological fungicide, both of which are safe to use on edibles. Don’t spray them together on the same week as there is some question as to whether the copper inactivates the Serenade. Do use caution with the copper – spray early in the morning to avoid harm to bees, and because it can build up in the soil and cause toxicity, don’t grow tomatoes in the same spot every year if you’re going to use copper frequently.
- Make sure your garden area is cleaned up promptly at the end of the summer gardening season and there isn’t any plant debris lying around.
- If you have an outbreak, rotate your crops even if you have to plant in containers.
Preventing late tomato blight
- Don’t overwinter your plants and remove any volunteer tomatoes and potatoes that come up. Potatoes can carry blight too.
- Use trellis and plant supports to keep your plant branches off the ground, and as noted above, use mulch!
- Don’t water your plants from above, and water early in the day so your plants are dry by nightfall.
- A product called Actinovate, which has the beneficial bacteria Streptomyces lydicus in it, can be used as a preventive measure.
- Oxidate, made of activated peroxide, is another safe and effective product to keep plants sterile and clean of blight.
- However, the above methods are for prevention. If late blight shows up, you need to pull out all the plants which are affected and put them in a trash bag. Don’t compost them as this highly contagious disease can infect the rest of your plants, and even your neighbors’ plants!
While in cool, moist climates, tomato blight can’t be totally beaten, by using preventive measures you can go a long way towards reducing the likelihood of outbreaks.
Tomato photo at top courtesy of J. Regan of Flickr (via the Creative Commons Attribution License)
Late blight photo courtesy of C. Paquette of Flickr (via the Creative Commons Attribution License)
How to Grow Healthy Tomatoes
Start reading about tomato pests and diseases and you begin to wonder how any tomato ever makes it at all. After weeks of episodic rain my tomato plants are growing like kudzu, but I noticed something this morning that sent me looking for fungicide recipes: yellowing around large brown spots on the lower leaves of one of the plants. I am not happy about this.
Early Blight is a fungal disease that is easily transmitted from infected soil, tools, some insects, (ex. aphids), or any type of physical contact. It can live up to two years. Wet seasons like the one we’ve been having provide ideal conditions for it to survive and thrive. The lower leaves are affected first, yellowing and falling off.
Some of the most effective controls are:
- Removing the lower leaves, especially those which contact the ground
- Mulching to reduce splattering of the fungal spores up to the leaves
- Watering the soil, not the plant, to keep the plant dry and inhospitable to fungus growth
- Spraying with copper or sulfur–use caution, too much copper can harm earthworms
- Serenade Disease Control has gotten some good buzz. It’s listed as approved by OMRI (Organic Materials Review Institute)
- Neem oil, especially as a preventative before the blight appears
I removed the lower, affected leaves, added some fresh mulch, and sprayed with a baking soda solution (1 T. baking soda, 1 T. oil, squirt of liquid soap/1 gallon of water). Of course, 30 minutes later it rained again, so I’m anticipating a battle with this. For the benefit of the plants yet to show signs, I am going to hit them with neem oil. I’ve heard a milk solution (1 part milk to 9 parts water) is also helpful so I may try that, too– if it ever quits raining! Remind me how I wouldn’t quit whining about the nonstop rain when the next drought hits . . .
This is an article about pruning the lower parts of the tomato plant for this reason.
And this is a discussion about Early Blight on GardenWeb, one of my favorite resources.
Disclaimer: This post may contain a link to an affiliate.
Blight On Tomatoes – Tomato Blight Treatment And Prevention
What is tomato blight? Blight on tomatoes is caused by a fungal infection and like all fungi; they are spread by spores and require damp, warm weather conditions to flourish.
What is Tomato Blight?
What is tomato blight? It’s actually three different fungi that attack tomatoes in three different ways at three different times.
Septoria blight, also called leaf spot, is the most common blight on tomatoes. It usually appears at the end of July with small black or brown marks on the lower leaves. While fruits may remain uninfected, the leaf loss can affect yield as well as exposing fruit to sunscald. Overall, it is the least harmful tomato blight. Solutions to the problem include watering at the base of plants and avoiding the garden while foliage is wet.
Early blight appears after heavy fruit set. Rings resembling targets develop first on the leaves and cankers soon grow on the stems. Black spots on the almost ripened fruit turn into large bruised spots and the fruit begins to fall. Because the crop is almost ready for picking, this may be the most disappointing tomato blight. Treatment is simple. To prevent tomato blight from invading next year’s crop, burn everything the fungus may have touched including fruit and foliage.
Late blight is the least common blight on tomatoes, but it is, by far, the most destructive. Pale green, water soaked spots on the leaves quickly grow into purplish-black lesions and stems turn black. It attacks in rainy weather with cool nights and quickly infects fruits. Infected fruits show brown, crusty patches and rot quickly.
This is the blight that caused the Great Potato Famine of the 1840s and will quickly infect any potatoes planted nearby. All potatoes should be dug and disposed of as should all tomato plants and fruit affected by this tomato blight. Treatment is simple. Burn everything the fungus may have touched.
How to Prevent Tomato Blight
Once a blight on tomatoes takes hold, it’s very hard to control. After identification, tomato blight treatment begins with fungicide treatments, although when it comes to tomato blight, solutions really lie in prevention. Use fungicides before the fungus appears and they should be applied regularly throughout the season.
Fungus spores are spread by splashing water. Stay away from the garden while foliage is wet from dew or rain. Avoid watering in late afternoon or evening so that water can evaporate from the leaves and, if possible, water the ground and not the foliage. Most fungi grow best in the warm, wet dark.
Rotate crops as often as possible and never turn any tomato debris back into the soil. Use healthy transplants from a reliable nursery and remove damaged lower leaves regularly since that’s where most fungi attacks begin. Remove all plant debris at the end of the growing season so the spores have nowhere to over winter.
What is tomato blight? It’s a series of recurring fungal infections that can be curtailed with good garden housekeeping and simple fungicide treatments.
Early blight of tomato
- Early blight is one of the most common tomato diseases, occurring nearly every season wherever tomatoes are grown.
- It affects leaves, fruits and stems and can be severely yield limiting when susceptible cultivars are used and weather is favorable.
- Severe defoliation can occur and result in sunscald on the fruit.
- Early blight is common in both field and high tunnel tomato production in Minnesota.
Host and pathogen
Leaf spot symptoms of early blight on tomato
Early blight can be caused by two different closely related fungi, Alternaria tomatophila and Alternaria solani. Alternaria tomatophila is more virulent on tomato than A. solani, so in regions where A. tomatophila is found, it is the primary cause of early blight on tomato. However, if A. tomatophila is absent, A. solani will cause early blight on tomato.
Both pathogens can also infect potato, although A. solani is more likely to cause potato early blight than A. tomatophila. Both pathogens can also infect eggplant and several Solanaceous weeds including black nightshade (Solanum ptycanthum), and hairy nightshade (Solanum physalifolium)
Signs and symptoms
Initially, small dark spots form on older foliage near the ground.
- Leaf spots are round, brown and can grow up to half inch in diameter.
- Larger spots have target-like concentric rings. The tissue around spots often turns yellow.
- Severely infected leaves turn brown and fall off, or dead, dried leaves may cling to the stem.
Early blight stem infection
- Seedling stems are infected at or just above the soil line. The stem turns brown, sunken and dry (collar rot).
- If the infection girdles the stem, the seedling wilts and dies.
- Stem infections on older plants are oval to irregular, dry brown areas with dark brown concentric rings.
- Fruit can be infected at any stage of maturity.
- Fruit spots are leathery and black, with raised concentric ridges. They generally occur near the stem.
- Infected fruit may drop from the plant.
- Disease develops at moderate to warm (59 to 80 F) temperatures; 82 to 86 F optimum
- Rainy weather or heavy dew, 90% humidity or greater
Biology and disease cycle
Early blight fruit rot symptoms
- Alternaria tomatophila and A. solani overwinter in infected plant debris and soil in Minnesota.
- The pathogen also survives on tomato seed or may be introduced on tomato transplants.
- Lower leaves become infected when in contact with contaminated soil, either through direct contact or through rain-splashed soil.
- Spores can germinate between 47° and 90° F and need free water or humidity of 90% or greater.
- Spores infect plants and form leaf spots as small as 1/8 inch diameter in as little as five days.
- Spores can be spread throughout a field by wind, human contact or equipment, resulting in many reinfection opportunities throughout a growing season.
There are many resistant tomato cultivars available, often designated with an “EB” in seed catalogs. There is also an extensive list of resistant cultivars on Cornell University’s vegetable pathology website. Resistant varieties are not immune to early blight. Rather moderate levels of resistance to either leaf infection, stem infection or both are present.
A few common cultivars with early blight resistance include:
- Iron Lady
- Mountain Supreme
- Mountain Magic
- Defiant PhR
- Use pathogen-free seed, or collect seed only from disease-free plants.
- Rotate out of tomatoes and related crops for at least two years.
- Control susceptible weeds such as black nightshade and hairy nightshade, and volunteer tomato plants throughout the rotation.
- Fertilize properly to maintain vigorous plant growth. Particularly, do not over-fertilize with potassium and maintain adequate levels of both nitrogen and phosphorus.
- Avoid working in plants when they are wet from rain, irrigation, or dew.
- Use drip irrigation instead of overhead irrigation to keep foliage dry.
- Stake the plants to increase airflow around the plant and facilitate drying. Staking will also reduce contact between the leaves and spore-contaminated soil.
- Apply plastic or organic mulch to reduce humidity and provide a barrier between contaminated soil and leaves.
- In the fall, remove or bury infected plants to reduce the likelihood of the pathogen surviving to the following year.
- For greenhouse production, early blight has been reduced by as much as 50% by covering houses with UV-absorbing vinyl film.
Below is a partial list of fungicides available for control of early blight on tomato. Applications should be made when environmental conditions favor disease to be the most effective and repeated according to label instructions.
It is important to alternate between different chemical families to avoid the development of pathogen insensitivity to particular active ingredients. Some insensitivity to the chemical family 11 has become more common in some areas, so particular care should be taken to rotate these with other chemical families. Also, if insensitivity is already present in a given field population of early blight, fungicides in chemical family 11 will not provide good control.
Common fungicides for control of early blight on tomato.
|Active ingredient||Common product names||Chemical family|
|Boscalid||Endura, Lance WDG||7||Very good|
|Pyraclostrobin||Cabrio||11||Very good, but insensitivity is becoming more common|
|Fenamidone||Reason||11||Very good, but insensitivity is becoming more common|
|Azoxystrobin||Quadris||11||Very good, but insensitivity is becoming more common|
|Cymoxanil and Famoxadone||Tanos||27 and 11, respectively||Good, but insensitivity is becoming more common|
|Fluxapyroxad and Pyraclostrobin||Priaxor||7 and 11, respectively||Good, but insensitivity is becoming more common|
|Difenoconazole and Cyprodinil||Inspire Super||3 and 9, respectively||Good|
|Mancozeb||Dithane, Manzate, Penncozeb||M||Good|
|Mancozeb and Zoxamide||Gavel||M and 22, respectively||Good|
|Difenoconazole and Mandipropamid||Revus Top||3 and 40, respectively||Good|
|Cyprodinil and Fludioxonil||Switch||9 and 12, respectively||Good|
|Chlorothalonil||Bravo, Echo, Equus||M||Fair|
|Copper (copper hydroxide, copper oxychloride, etc.)||Kocide 2000, Champ Formula 2, Nu-Cop 50DF, C-O-C-S WDG||M||Fair. Some copper products OMRI listed as copper are best option for organic production|
Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law. When treating fruits or vegetables, make sure the plant you wish to treat is listed on the label of the pesticide you intend to use. Also be sure to observe the number of days between pesticide application and when you can harvest your crop.
Anna Johnson, Michelle Grabowski, Extension educator and Angela Orshinsky, Extension plant pathologist
Reviewed in 2018