Late blight of tomato

Tomato Late Blight

Potentially devastating to the home gardener, late blight can wipe out an entire tomato crop, and all the hard work that went into it, in a few short weeks. Moreover, adding insult to injury, late blight can also affect peppers, potatoes, and eggplant.

Causes and Symptoms

Late blight (Phytophthora infestans) is a fungus-like microorganism that is usually brought into the garden by the introduction of infected tomato seedlings or seed potatoes or by infected volunteer plants from the previous year’s garden. The fungus is also spread atmospherically when the live spores are blown in during periods of rain and wind. Optimum conditions for the rapid spread of the disease occurs during episodes of moderate temperatures and high moisture.

Identification of late blight on tomato plants is done by inspection of the fruit and foliage and will initially appear as gray areas on the leaves. These areas will then spread and a mold will develop on the lower surfaces of the leaves. Brown spots on the plant stems, as well as the loss of foliage, are also indications of late blight. If the weather conditions are favorable (moist), the spread will be rapid.

Treatments and Control

The first line of attack against late blight is for immediate removal and destruction of any infected plants. The plants should then be either burned or bagged and discarded through normal garbage disposal means. Infected plants should never be placed in the compost pile as this will certainly spread the disease.

Staking tomatoes and using a system of drip irrigation will reduce the potential for leaf dampness, as will allowing enough space between plants for adequate air circulation. Mulching the area around the plants is also beneficial. In addition, you can plant tomato disease resistant varieties that are specified as blight resistant.

If the infestation is not too widespread and perhaps only affecting a few plants, removing and destroying the infected plants and treating the remaining healthy ones with a fungicide spray for tomatoes may salvage some of the crop. Tomato fungicides containing copper are often recommended for the gardener wishing to avoid harsh chemicals.

Any fungicide treatments applied are likely to be successful only if the plant or plants are not showing any signs of late blight infestation. Frequent and regular applications are generally recommended with particular attention being made to spray the plants after each rainfall.

It is important the gardener rotate their tomato plantings and not plant tomatoes in the same spot every year, perhaps leaving two to three years between planting tomatoes in the same location.

Tomato Blight: How to Identify and Treat Late Blight in Tomatoes

Tomato blight, in its different forms, is a disease that attacks a plant’s leaves, stems, and even fruit.

Late blight (one form of tomato blight) is caused by a fungus, Phytophthora infestans, which also affects potatoes. The fungus was responsible for the Irish potato famine of 1845.

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What does late blight look like?

The fungus over-winters in infected potato tubers and perennial weeds (such as nightshade.) As the tubers and perennial seeds germinate during a new growing season, the fungus spreads to surrounding plants.

Late blight affects both leaves and fruit.

Leaves develop blue-gray spots which turn brown.

Leaves eventually drop.

Fruit develops irregular brown, greasy spots which can affect the entire tomato.

Spots on both leaves and fruit may develop a white, cottony ring of mold.

Late blight can overtake an entire plant quickly (within a week) if untreated.

When does late blight affect plants?

  • It’s most prevalent in mid- to late-season
  • It often strikes in cool, wet weather

How do you control and treat late blight?

  • The best control measure for tomato blight is prevention (see below).
  • Remove and destroy infected leaves (be sure to wash your hands afterwards).
  • Once blight is present and progresses, it becomes more resistant to biofungicide and fungicide. Treat it as soon as possible and on a schedule.
  • Organic fungicides. Treat organically with copper spray, which you can purchase online, at the hardware store, or home improvement center. Follow label directions. You can apply until the leaves are dripping, once a week and after each rain. Or you can treat it organically with a biofungicide like Serenade. Follow label instructions.
  • Chemical fungicides. Some gardeners prefer chemical fungicides, the best of which for tomatoes is chlorothalonil (sold as Fungonil, Daconil, or under other brand names. Check labels. You may also choose Mancozeb or Maneb, although these have longer wait times before you can harvest tomatoes safely than does chlorothalonil.

Other diseases (such as early blight, Septoria leaf spot, and gray leaf spot) can also be controlled by these biofungicides and fungicides, so application is multi-purpose.

How do you prevent late blight?

  • Rotate crops. The tomato blight (late blight) fungus can remain in the soil for several years. Be especially careful not to plant tomatoes in an area where potatoes were cultivated the year before.
  • Plant disease-resistant hybrids to strengthen your plant’s chances of being blight-free.
  • Plant tomatoes in a raised bed to improve drainage and prevent diseases from spreading.
  • Give tomato plants extra space (more than 24 inches) to let air to move among leaves and keep them dry.
  • Water the soil – not the plants – to prevent splashing. Avoid overhead watering.
  • Mulch with black plastic or landscape fabric to prevent fungus from spreading up onto leaves.
  • Stake tomato plants for better circulation.
  • Remove and destroy affected plants at the end of the season.

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Late Blight on Tomatoes and Potatoes

Home gardeners should be aware of Late Blight caused by Phytophthora infestans – a very destructive and very infectious disease that kills tomato and potato plants in gardens and on commercial farms across the U.S. Because the disease can move very easily from one garden or field to others, it is critical that both home gardeners and farmers know how the disease works, what to look for, and how to manage it. Given the right conditions, the spores are easily carried for miles in wind currents to infect susceptible plants in even the most remote parts in our region. All tomato and potato plants grown in home gardens and in commercial fields are susceptible to late blight!

Late blight is the same disease that caused the Irish Potato Famine in the 1840s. It has been in the US for over a century, but it has become more of a concern in the Northeast in recent years. In 2009 a widespread outbreak affected both home gardens and commercial farms on a broad scale, causing significant yield losses in both tomato and potato. Since then, it has continued to appear throughout New England in farm fields and home gardens, but fortunately it has not caused losses at the same level. Keeping the disease in check requires attention and vigilance from gardeners and farmers alike.

Symptoms

The most common early symptoms on tomato transplants are brown lesions on stems, with white fungal growth developing under moist conditions.

Symptoms on plants in the garden appear as large (at least nickel-sized) olive-green to brown spots on leaves with slightly fuzzy white fungal growth on the underside when conditions have been humid or wet. Sometimes the lesion border is yellow or has a water-soaked appearance. Leaf lesions begin as tiny, irregularly shaped brown spots. Brown to blackish lesions also develop on upper stems. Firm, brown spots develop on tomato fruit. Late blight can sometimes be confused with early blight and Septoria leaf spot, two common diseases found in home gardens. If the lesion has a yellow border and is occurring on the bottom of the plant, it is likely due to infection of either early blight or Septoria leaf spot.

Photo gallery of what to look for: http://ag.umass.edu/home-lawn-garden/fact-sheets/late-blight-on-tomatoes…

Life Cycle

P. infestans in the Northeast survives in infected potato tubers that were saved from last year for seed or that were disposed of in compost piles or cull piles, or left in the garden in soil that did not freeze during the winter. The pathogen does not overwinter in tomato plants or debris, and is not seed-borne. In more southern and tropical regions, the pathogen produces long-lived sexual spores (Oospores) that survive in infected crop debris and the soil. Fortunately, there is currently no evidence that this happens in New England.

Wherever infected tubers or plants are found, if conditions are favorable, the plants will develop late blight lesions that release sporangia. Sporangia are spread long distances by wind and wind-driven rain. In cloudy, gray weather, the clouds protect spores being dispersed in wind from the killing effect of ultraviolet radiation. Spores land on leaf tissue and penetrate the leaf, causing rapid decline and death of the plant under favorable conditions, Phytophthora infestans is favored by cool (below 77 F), wet weather. Hot, dry periods are not conducive to late blight development. An exception would be where plantings are overhead watered or are located where fog occurs regularly such as near rivers or in coastal areas.

The late blight pathogen has recently undergone changes in Florida that affect disease occurrence there and in other eastern states. Diseased tomato plants in south Florida have survived cold periods in winter allowing the pathogen to persist. Late blight has also been active into the spring as late as May indicating an increased tolerance for warmer temperatures. This means a potential source of inoculum persists into the spring, when crops are being produced north of Florida and thus a ‘green bridge’ exists for the pathogen to progress on until it reaches the northeast.

Prevention and Management

  • Do not plant potato tubers from the previous year; purchase seed potatoes from a reputable source and inspect them before planting.
  • Destroy volunteer potatoes that sprout from overwintered tubers. The late blight organism requires living tissue to survive; it does not survive in the soil or carried tomato seed. The most likely source of late blight is infected potato tubers that survived the winter, tubers that were saved, or tubers that remained in the soil unfrozen and grow from overwintered tubers as volunteer potato plants. These plants should be dug up, placed in a plastic bag and discarded in the trash or completely buried deep enough so plants decompose and will not resprout.
  • Select resistant varieties were available. ‘Mountain Magic’, ‘Legend’, and ‘Plum Regal’ have excellent resistance to Late Blight. ‘Red Pearl’ and ‘Matt’s Wild Cherry’ are small fruited tomatoes with good resistance. Some heirloom tomato varieties have good tolerance to late blight. A few cultivars also have resistance to Early Blight (Alternaria solani, A. tomatophila) and should be considered. The development of triple (LB, EB, Septoria leaf spot) resistant varieties is underway at Cornell and other Universities.
  • Start with disease-free tomato transplants. Growing your own tomato transplants from seed or purchasing transplants that were started here in the Northeast from seed will ensure a healthy start to the season for you and local farms.
  • Control solanaceous weeds such as hairy nightshade, jimson weed, golden henbane, and others.
  • Plant potatoes and tomatoes where air circulation is good; stake tomatoes for more rapid dying of leaves after dew or rainfall.

If symptoms are already appearing on plants, remove plants, place in a plastic bag, seal and discard in the trash or completely bury plants deep enough underground so plants decompose and will not re-sprout. Do not put the plants in a compost pile as spores will still spread from this debris.

Fungicides

To manage late blight with fungicides, treat before symptoms appear. Use a product that contains chlorothalonil listed as the active ingredient on the label. There are ready- to- use formulations available to home gardeners. Fungicides are only effective if used before the disease appears and should be reapplied every 5-7 days if wet weather persists. Chlorothalonil is a protectant fungicide, with no systemic movement in the plant, so thorough coverage is necessary.

Copper based fungicides are another option for home gardeners, and are reasonably effective against some strains of the late blight fungus. For organic gardeners, copper based fungicides are the only allowed option. As with all pesticides, read the label carefully and follow instructions for personal protective clothing, rates, and interval between spraying and harvest. These fungicides will also reduce losses from early blight and Septoria leaf spot, which are widespread in gardens and on farms every year from July till frost. If late blight is widespread in the region and weather conditions are favorable for the disease, fungicides alone may not guarantee a healthy crop.

FAQ’s about Late Blight on Tomatoes

I think I had late blight on my tomatoes last year, will it overwinter in my garden?

Tomatoes will not carry late blight over the winter, because freezing kills the whole plant.

Will seed from any tomatoes left in the garden from last year carry over the disease?

Tomato seed, even from fruit that was infected with late blight, will not carry the pathogen, so no need to worry about the tomatoes left behind in the garden or compost pile.

What about my tomato stakes, will it carry over on my tomato stakes?

No, late blight will not survive on tomato stakes and cages. However, other diseases can survive on tomato stakes. Remove dirt and debris from tomato stakes and disinfect stakes by cleaning them with 1 part bleach + 9 parts water. Soak stakes for 30 minutes. Let dry before using them.

I grew potatoes last year. Can late blight over-winter on potatoes I may have left in the garden?

Potatoes that freeze or fully decompose will not carry the pathogen over winter. However, the biggest threat for overwintered disease in New England is on potatoes that might come up this year. In the spring, inspect last year’s potato plot and any compost or cull piles for volunteer potato plants. If you find potato plants, pull them out and put them in the trash or destroy them. If tubers were infected and survive, then the late blight pathogen could grow upward from the tuber, infecting the stem and producing spores when weather conditions are favorable. These spores could then disperse to other tomato and potato plants.

Is there anything else I can do to prevent late blight this year?

Yes, late blight is not seedborne (however, it is tuber-borne in potato), so tomato plants started from seed locally (in the Northeast) would be free of the disease. Growing your own tomato transplants from seed or purchasing transplants that were started here in the Northeast from seed will ensure a healthy start to the season for you and local farms. Disease-resistant or tolerant varieties of tomatoes exist, however seed is in limited supply this year, so you will not likely find them at your garden center. ‘Mountain Magic’, ‘Plum Regal’, and ‘Legend’ are three varieties with resistance or tolerance to late blight. Note that the variety ‘Legend’ is the only late-blight resistant variety for which seed is readily available this year.

Also, purchase certified, disease-free seed potato from a reputable source Examine your seed potatoes and plant only firm, blemish-free tubers.

I have spots on my tomato plants that show up in June or July every year. Could this be late blight?

Probably not. In addition to late blight, each year tomatoes become infected with early blight and Septoria leaf spot, which look very similar to late blight symptoms. If you have problems with early blight each year, consider growing tomato plant varieties that are resistant or tolerant to early blight, such as the varieties ‘Mountain Fresh’, ‘Mountain Supreme’, and ‘Plum Dandy’ and others.

For more information, see the

Identifying And Preventing Late Blight On Tomatoes

Late blight tomato disease is the rarest of the blights that affect both tomatoes and potatoes, but it is also the most destructive. It was the leading factor in the Irish Potato Famine of the 1850s where millions of people starved because of the devastation wrought by this deadly disease. On tomatoes, the fungus-like organism can destroy a crop within days if conditions are right. Vigilant observation and pre-treatment are the only defenses against late tomato blight.

Symptoms of Late Blight on Tomatoes

Phytophthora infestans, the pathogen that causes tomato late blight, needs tissue to survive. Sporangia from an infected plant are carried through the air, sometimes several miles, and once they land on a suitable host, germination is almost immediate. Tomato late blight needs only a few hours to take hold. All it wants is a little free moisture on the leaves from rain, fog, or morning dew.

Once infected, late blight symptoms will become visible in three or four days. Small lesions appear on stems, leaves, or fruit. If the weather

is damp and the temperature moderate – just like most rainy summer days – the pathogen would sporulate around these lesions and the late blight tomato disease will be ready to spread to the rest of the garden and beyond.

The tiny lesions of late tomato blight are hard to spot and sometimes go unnoticed. The late blight symptoms become more obvious when the area around the lesions appears water soaked or bruised and turns grey-green or yellowed. Each late tomato blight lesion can produce up to 300,000 sporangia a day and each of those sporangium are capable of forming a new lesion. Once begun, late blight tomato disease can sweep through acres in a matter of weeks. Plant foliage will be completely destroyed and the fruit will be ruined by dark, greasy looking blotches of necrotic flesh.

Preventing Late Blight on Tomatoes

Sanitation is the first step in controlling tomato late blight. Clean up all debris and fallen fruit from the garden area. This is particularly essential in warmer areas where extended freezing is unlikely and the late blight tomato disease may overwinter in the fallen fruit.

Currently, there are no strains of tomato available that are resistant to late tomato blight, so plants should be inspected at least twice a week. Since late blight symptoms are more likely to occur during wet conditions, more care should be taken during those times.

For the home gardener, fungicides that contain maneb, mancozeb, chlorothanolil or fixed copper can help protect plants from late tomato blight. Repeated applications are necessary throughout the growing season as the disease can strike at any time. For organic gardeners, there are some fixed copper products approved for use; otherwise, all infected plants must be immediately removed and destroyed.

Tomato late blight can be devastating to the home gardener and the commercial grower alike, but with close attention to weather conditions, garden hygiene and early detection, this killer of crops can be controlled.

Prevent tomato late blight next growing season

University Park, Pa. — Across the northeast, home gardeners expecting the usual bumper crop of tomatoes this season were dismayed to find their plants affected by late blight, the same fungus that caused Ireland’s potato famine in the 19th century.

According to Beth Gugino, assistant professor of plant pathology at Penn State, late blight is a fungus that primarily affects tomatoes, potatoes and certain solanaceous weeds such as bittersweet nightshade.

“An unseasonably cool spring followed by an equally unseasonably cool and wet summer facilitated late blight growth for both home gardeners and commercial farmers throughout the growing season, which is very rare,” said Gugino.

Symptoms first appear on the foliage of plants as pale green to brown lesions. These areas expand rapidly during moist conditions and a white downy mold appears on the margin of the affected area on the lower surface of the leaves. Eventually, the greasy greenish-brown lesions begin to appear on the fruit and can enlarge until the entire fruit is covered. According to Gugino, the most important sources of the pathogen early in the season are infected potato tubers and infected tomato transplants. “During the season, late blight can be spread long distances from diseased tomatoes and potatoes to healthy ones via windblown spores. Within short distances, like in a garden, spores can also move between plants in splashing rain.”

To help prevent late blight next growing season, Gugino recommends making sure that all late blight-infected tomato and/or potato plant tissue from this past season is dead and home gardeners refrain from composting diseased plant material. “Late blight cannot withstand the freezing winter temperatures of the northeast, but may be able to live in the center of a warm compost pile. As long as the plant tissue is alive, the pathogen can survive.”

There is no need to remove the dead tomato plant tissue this late in the season or treat the soil over the winter, since the freezing temperatures will kill both the plant tissue and late blight. However, late blight can survive in infected potato tubers overwinter and can be a potential source of the disease the following year. If they are infected, Gugino recommends they be dug up and disposed of in the regular trash. “If volunteer potato plants grow next season make sure to quickly destroy them.”

Fortunately, the late blight pathogen can’t survive in or on tomato seeds, or on tomato cages and stakes between the seasons and therefore cannot be a source of the disease next season. However, Gugino said many bacterial diseases can survive in the seeds and on the cages so it is still important to purchase high quality seed and to disinfect cages and stakes to help control these diseases.

Currently there are no tomato varieties resistant to late blight, however growers and home gardeners have observed that some may be less susceptible than others.

“Fortunately, there are some potato varieties including Elba, Kennebec, Allegany, Sebago, Rosa, Defender, Jacqueline Lee and Ozette, that are described as having some late blight resistance,” Gugino said.

Breeding work is under way and some resistant varieties are in the final stages of development and are expected to be available as soon as 2010.

Gugino recommends gardeners plant healthy disease-free transplants next year, and examine the plants regularly for symptoms of late blight, especially if the weather is cool and wet. Plants or plant parts that have late blight symptoms should be removed quickly to prevent the spread of the disease to other plants. Avoid wet leaves by watering at the base of the plant or watering in the morning so the leaves dry quickly. She also recommends spacing the plants further apart to improve air circulation and eliminate weeds, which can be carriers of the pathogen. Preventative applications of a fungicide containing chlorothalonil may also help before late blight symptoms appear. Utilizing a combination of these integrated pest management practices will also help with the management of other common foliar tomato diseases. Integrated Pest Management (IPM) aims to manage pests — such as insects, diseases, weeds and animals — by combining physical, biological and chemical tactics that are safe, profitable and environmentally compatible.

For more information on late blight, visit http://www.ppath.cas.psu.edu/EXTENSION/VEGDIS/Vegetable_Pathology_Home.htm online or contact the closest Penn State Cooperative Extension Office.

The Pennsylvania IPM program is a collaboration between Penn State and the Pennsylvania Department of Agriculture aimed at promoting integrated pest management in both agricultural and urban settings. For more information, contact the program at (814) 865-2839, visit http://www.paipm.org/ online.

For the video-related story on late blight, visit: /video/173083/2013/02/09/video-no-title

Late blight of tomato and potato

Quick facts

  • Late blight is a potentially devastating disease of tomato and potato, infecting leaves, stems and fruits of tomato plants.
  • The disease spreads quickly in fields and can result in total crop failure if untreated.
  • Late blight of potato was responsible for the Irish potato famine of the late 1840s.

Host and pathogen

Late blight infects leaves, stems and fruit

Late blight is caused by the oomycete Phytophthora infestans. Oomycetes are fungus-like organisms also called water molds, but they are not true fungi.

There are many different strains of P. infestans. These are called clonal lineages and designated by a number code (i.e. US-23). Many clonal lineages affect both tomato and potato, but some lineages are specific to one host or the other.

The host range is typically limited to potato and tomato, but hairy nightshade (Solanum physalifolium) is a closely related weed that can readily become infected and may contribute to disease spread. Under ideal conditions, such as a greenhouse, petunia also may become infected.

Identification

Signs and symptoms

Leaf infections are large brown blotches with a green gray edge

  • Leaves have large, dark brown blotches with a green gray edge; not confined by major leaf veins.
  • Infections progress through leaflets and petioles, resulting in large sections of dry brown foliage.
  • Stem infections are firm and dark brown with a rounded edge.
  • Firm, dark brown, circular spots grow to cover large parts of fruits. Spots may become mushy as secondary bacteria invade.
  • In high humidity, thin powdery white fungal growth appears on infected leaves, fruit and stems. Infected fruit have a dry brown rot In high humidity, powdery white spores form on infected fruit, leaves and stems
  • In cool, wet weather, entire fields turn brown and wilted as if hit by frost.

Environment

  • Spreads most in cool (60°F to 70°F), damp weather.
  • Prolonged hot dry days can halt pathogen spread.

Biology and disease cycle

Phytophthora infestans can overwinter in Minnesota if protected in potato cull piles. Overwintering in a tomato production system is unlikely but infected tomato fruits may give rise to infected volunteer seedlings the following season.

The most common routes of introduction each season are infected potato seed tubers, infected tomato transplants shipped in from other regions, or windblown sporangia (asexual spores) from the south.

Under cool, wet conditions, P. infestans can infect and produce thousands of sporangia per lesion in less than five days. These sporangia easily become air-borne, resulting in prolific spread of the pathogen.

The disease can potentially destroy entire fields in a short period of time if left unmanaged. Long-distance spread to other fields is also likely, particularly under cloudy conditions.

Management

Resistant varieties

Even a resistant variety will show some late blight symptoms when conditions are highly favorable for disease. Levels of resistance vary between cultivars and may be more or less effective depending on the P. infestans clonal lineage present. Several resistant varieties are listed below. Check seed catalogues and the Cornell vegMD webpage for new varieties with resistance to late blight.

Cultural control

  • Destroy potato cull piles before the growing season begins by burying them, spreading and incorporating them into fields, or feeding them to animals.
  • Control volunteer potato plants, as infected plants can grow from infected tubers.
  • Seed infection is unlikely on commercially prepared tomato seed or on saved seed that has been thoroughly dried.
  • Inspect tomato transplants for late blight symptoms prior to purchase and/or planting, as tomato transplants shipped from southern regions may be infected.
  • If infection is found in only a few plants within a field, infected plants should be removed, disced-under, killed with herbicide or flame-killed to avoid spreading through the entire field.

Chemical control

Fungicides are available for management of late blight on tomato. Late blight does not occur every year in Minnesota. Growers should watch for late blight symptoms in their regular scouting, particularly with weather conditions that favor disease. Reports of regional outbreaks of late blight can be found at the USAblight website.

Fungicide applications should be made prior to infection when environmental conditions favor disease to be the most effective. Phytophthora infestans is a water mold and not a true fungus. Fungicides specific to water molds must be used and applications repeated according to label instructions. For a current list of fungicides for late blight management visit the Midwest Vegetable Production Guide. Rotate fungicide groups and/or tank mix fungicides to avoid producing fungicide-resistant isolates.

Because late blight disease development is so dependent on weather, disease forecasting computer programs such as TOM-CAST have been developed to estimate when the pathogen is most active. The program uses temperature, humidity and rainfall data from a weather station. The program will determine whether a fungicide application is necessary. Following this system rather than just applying fungicide every 7 days may save several fungicide sprays per season while still providing good disease control.

Anna Johnson; Michelle Grabowski, Extension educator and Angela Orshinsky, Extension plant pathologist

Reviewed in 2016

Found on tomato and potato plants, late blight is caused by the fungus Phytophthora infestans and is common throughout the United States. True to its name, the disease occurs later in the growing season with symptoms often not appearing until after blossom.

Late blight first appears on the lower, older leaves as water-soaked, gray-green spots. As the disease matures, these spots darken and a white fungal growth forms on the undersides. Eventually the entire plant will become infected. Crops can be severely damaged

Unlike other fungal diseases, this plant problem does not overwinter in the soil or on garden trash. Instead the spores are introduced by infected tubers, transplants or seeds. Wind will also carry the disease from nearby gardens. Warm temperatures (70-80˚F) and wet, humid conditions promote its rapid spread.

Note: Late Blight was responsible for the Irish potato famine (1845-1849).

Treatment

  1. Plant resistant cultivars when available.
  2. Remove volunteers from the garden prior to planting and space plants far enough apart to allow for plenty of air circulation.
  3. Water in the early morning hours, or use soaker hoses, to give plants time to dry out during the day — avoid overhead irrigation.
  4. Destroy all tomato and potato debris after harvest (see Fall Garden Cleanup).

If symptoms are observed, treat plants with one of the following fungicides:

  • Apply a copper based fungicide (2 oz/ gallon of water) every 7 days or less, following heavy rain or when the amount of disease is increasing rapidly. If possible, time applications so that at least 12 hours of dry weather follows application.
  • Used as a foliar spray, Organocide® Plant Doctor will work its way through the entire plant to prevent fungal problems from occurring and attack existing many problems. Mix 2 tsp/ gallon of water and spray at transplant or when direct seeded crops are at 2-4 true leaf, then at 1-2 week intervals as required to control disease.
  • Safely treat fungal problems with SERENADE Garden. This broad spectrum bio-fungicide uses a patented strain of Bacillus subtilis and is approved for organic use. Best of all, SERENADE is completely non-toxic to honey bees and beneficial insects.
  • Monterey® All Natural Disease Control is a ready-to-use blend of naturally occurring ingredients that control most plant foliar diseases. All stages of the disease is controlled, but applying before infestation gives the best results.

Solanaceous, Late Blight

Cultural Controls & Prevention:

  • Eliminate initial inoculum. The most likely source of late blight is infected tubers that survived the winter in cull piles or compost piles, tubers that were saved, or tubers that remained in the soil unfrozen and appear as volunteer potato plants. The late blight organism requires living tissue to survive; it does not survive in the soil or carried tomato seed.
  • Select resistant varieties were available. ‘Mountain Magic’, ‘Legend’, and ‘Plum Regal’ have excellent resistance to Late Blight. ‘Red Pearl’ and ‘Matt’s Wild Cherry’ are small fruited tomatoes with good resistance. Some heirloom tomato varieties have good tolerance to late blight. A few cultivars also have resistance to Early Blight (Alternaria solani, A. tomatophila) and should be considered. The development of triple (LB, EB, Septoria leaf spot) resistant varieties is underway at Cornell and other Universities.
  • Start with disease-free tomato transplants.
  • Rotate tomato fields with non-solanaceous crops. Crop rotation is for the early blight and Septoria leaf spot diseases which are an annual problem, not late blight.
  • Control potato and tomato volunteer plants as well as solanaceous weeds such as hairy nightshade, jimson weed, golden henbane, and others. The ornamental plants petunia and calibrachoa are also hosts for late blight; grow ornamental bedding plants and vegetable transplants in separate greenhouses.
  • When late blight is found in small, localized areas, promptly destroy all symptomatic plants plus a border of healthy appearing plants to prevent disease spread. Pull up affected plants, kill them with a herbicide, or disk them under. When physically destroying plants, a fungicide application can prevent equipment contamination and release of spores into the environment. Pressure wash disking equipment after operation.
  • Apply late blight specific fungicides in affected fields and nearby fields on a regular basis according to a disease forecast model (Blight Cast) until tomato harvest is complete. Shorten spray interval when disease pressure is high or environmental conditions remain favorable for the late blight pathogen (cool and wet).
  • Alternate fungicide applications among different chemical classes as indicated by FRAC code. Include a contact (protectant) fungicide in each application (chlorothalonil, mancozeb, or copper). Addition of a protectant fungicide enhances resistance management and fungicide effectiveness; it is often specified on the label and thus is a requirement. A fungicide with protectant fungicides alone becomes challenging when plants are actively growing as new growth is rapidly left unprotected.
  • Good fungicide coverage is necessary. Work in affected fields last and clean equipment between fields.
  • Disk under the field or kill with herbicide after harvest is complete.

Chemical Controls & Pesticides:

For Current information on disease recommendations ins specific crops including information on chemical control & pesticide management, please visit the appropriate crop section in the New England Vegetable Management Guide website.

Crops that are affected by this disease:

  • Potato
  • Tomato, Field
  • Tomato, Greenhouse

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