White on tomato leaves

Tomato Leaves Turn White: How To Treat Tomato Plants With White Leaves

One of the most commonly grown garden plants, tomatoes are quite sensitive to both cold and too much sun. Because of their extremely long growing season, many people start their plants indoors and then transplant later in the growing season once the soil has consistently warmed. The transplantation of the tomato seedlings is where one may run into a problem. Their susceptibility to temperature and light extremes often renders them vulnerable to white tomato leaves. Let’s explore this white leaf color on tomato plants.

Why Do Tomato Leaves Turn White?

If you’re unlucky enough to find a silver or white leaf color on your tomato plants, it is undoubtedly the result of either sun damage, cold vulnerability or some sort of disease (most likely fungal).

The most common cause of leaves turning white in tomatoes, especially young seedlings that are recently transplanted, is exposure to intense sunlight. Although tomato plants need full sun for healthy growth, a sudden change of venue from indoors to outdoors may shock the plants and cause the tomato leaves to turn white. Generally, the damage from sunlight appears as a border of white leaf color on the tomato plant. The leaves may curl and break, leaving minimal foliage on the plant. Winds in the area of transplantation exacerbate this condition as well. Mature tomato plants suffering from sunscald will include blistered or papery fruits.

The solution to tomato plants with white leaves due to sun over exposure is simple in retrospect. In the future, allow the transplants to languish in the shade for a few days and/or move them outside on a cloudy day, then gradually place them in the sun for a couple of hours each day over the course of one or two weeks. This is called hardening off. Either of these gives the plant time to acclimate to its more radical environs.

If hot, dry winds are an additional issue, try placing a windbreak around the transplants or relocate to a protected area. With either issue, if the windburn or sun scorch is not severe, the plant will likely recover; remove any afflicted leaves to discourage disease.

Fungal Reasons for Tomato Plants with White Leaves

Other than environmental exposure, another explanation for tomato plants with white leaves is disease. Primarily the disease is fungal in variety and resulting from the same cause, overwatering. Too much water in the soil stimulates the fungal spores and causes root rot, Alternaria or Septoria leaf spot, which has dark borders surrounding the white blotches on the leaves.

Transplants should be watered deeply for the first three days and thereafter, dependent on your climate, once a week to every two weeks. This promotes deep root development and deters fungal spores from taking hold. If a fungal disease has taken root, so to speak, try a fungicide made for use on tomato plants to repair any leaves that are turning white on your tomatoes.

Nutrients Causing Leaves Turning White in Tomatoes

Lastly, a potential cause of the leaves turning white in your tomatoes is a lack or surplus of nutrients. Plants lacking nitrogen or phosphorus may show whitening or yellowing of their leaves. A tomato fertilizer containing the proper amounts of these nutrients is a likely solution.

Additionally, deficiencies of calcium or magnesium will also cause whitening of leaves with the leaf veins retaining their green hue. Again, an application of the proper fertilizer is in order. Additionally, garden lime will aid in the calcium deficiency.

Tomato Powdery Mildew

Powdery mildew is a common fungal disease affecting many plants, but especially tomato plants.

This type of mildew is caused by many types of fungi that do not require high humidity to get established, and prosper under mild conditions. These qualities make them more prevalent than many other plant diseases. However, this can easily be prevented with an ingredient that has been around for hundreds of years.

Causes and Symptoms

A powdery mildew infection develops when wind borne spores land on plant tissues. A combination of shady conditions and warm weather favor the development and formation of the fungi. The fungi establishes itself through mycelial growth across the surface of the plant. The fungi completes its life cycle by producing more spores; which then perpetuates the cycle throughout the season.

Symptoms of a powdery mildew infection appear as white, chalky spots forming all over the plant, including stems, flowers and fruit. They spread rapidly, affecting large areas of the leaves and stems. The leaves will then turn yellow, die and drop off. Plants will have a lower yield and shortened fruiting season. The fruit flavor will not be as strong as it would have been without the fungal infection.

Treatments and Control

The best treatment for powdery mildews is prevention. Full-sun conditions and high temperatures will hinder its growth and spread. Choosing resistant varieties, providing proper air circulation around the tomato plants, allowing for adequate spacing in the garden, and avoiding overhead sprinkling all work as preventives.

If these measures fail, then fungicides are available for control. Fungicides can be used to protect against and destroy an infection. The least toxic of the fungicides includes neem oil, horticultural oil, sulfur, biological fungicide, and jojoba oil. The oils are better at eradicating infection when symptoms appear, but the sulfur fungicides for tomatoes protect against an infection getting established.

For hundreds of years, applications of sulfur fungicide for tomatoes prevented powdery mildew. They are only useful if applied before symptoms are evident. There are wettable sulfurs and sulfur dusts available for use on tomatoes. Copper can also be used, but it is not as strong as the sulfurs.

Application of treatment, whether sulfer, fungicides, or coppers, only works on contact, and thorough coverage of the plant is critical to stop infection. You should apply fungicides every seven to ten days. If an infection starts to become evident, the oils mentioned above are a reputable alternative to maintain control.

By Gene McAvoy|January 22, 2019

White mold on tomato also is known as timber rot. Photo courtesy of Maine.gov

Sclerotinia white mold on tomato is caused by Sclerotinia sclerotiorum. S. sclerotiorum has a wide host range, attacking more than 170 species. This disease affects a number of economically important vegetable crops including beans, cabbage, lettuce, and pepper.

In tomato, the disease is also known as timber rot. Primary infections usually occur on flowers and succulent tissues. The spores go through a saprophytic growth stage on senescent flowers before initiating further infection. Initial infection of the pathogen is on tissues within the plant canopy, often near the base of the stem at the soil line.

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Identification
Pale or dark-brown, water-soaked lesions form on flowers and at stem joints where senescent flower petals have fallen. Bleached areas and watery, soft rots form on the stems and leaf axils, and then wet, fluffy white mold develops inside and outside the plant tissue. The soft, watery rots on the stems eventually become dry and brittle, which leads to girdling. The pathogen also can attack at the base of the stem causing the plants to wilt and die.

As infected tissue decays, hard, black, irregularly shaped resting structures called sclerotia form on the inside and outside of decaying tissue. Stems are frequently hollowed out by the fungus leaving a papery shell to cover numerous sclerotia.

Survival and Spread
Sclerotinia sclerotiorum can remain dormant in the soil for five years or more as hard, black sclerotia and require a conditioning period of cool temperatures before they can germinate and form apothecia — cup-shaped fruiting bodies. The pale, brownish-yellow apothecia form just above the soil line and produce ascospores that spread through moving water, wind, plant debris, and workers.

The pathogen favors temperatures from 59°F to 70°F, and nighttime temperatures of 60°F. Sixteen to 72 hours of continuous wetness and high humidity is favorable for spore infection. Once the disease cycle is complete, spores are not produced again until the next season.

Management Methods
Effective management of white mold requires an integrated disease management approach. The disease is controlled primarily through the use of cultural practices and foliar fungicides.

Scouting is important for early detection once plants begin flowering.

Cultural practices, such as destruction of infected plant debris, eradication of weed hosts, and crop rotation with non-susceptible hosts like corn, will help reduce disease in subsequent plantings.

Good fertility management to prevent excessive canopy development and staking to improve aeration can aid in reducing problems with white mold.

Contans WG (Coniothyrium minitans, Bayer) is a biological product that limits the seasonal carryover of sclerotia and must be applied prior to and following the cropping season. Preventative fungicide applications will help prevent infections.

Consult UF/IFAS recommendations for currently labeled fungicides for sclerotinia control in Florida tomato.

Gene McAvoy is the Associate Director of Stakeholder Relations for the UF/IFAS Southwest Florida Research and Education Center in Immokalee, FL. See all author stories here.

Fungicides, ( mancozeb with zinc 37.0 percent,) work to protect tomato plants against blight. Once a plant is infected, a fungicide won’t cure the disease, but may help in stopping the spread to the rest of the plant. As a precaution, you can apply a fungicide before the plant becomes diseased. Once a plant is affected, the success of treatment depends on correct application. Fungicides can be purchased as a concentrate to mix in a hand-sprayer with water or ready-to-use. Among the fungicides to choose from is liquid copper fungicide. You can buy it ready-to-use or as a concentrate. If you buy the concentrate, dilute 2 to 3 teaspoons of fungicide concentrate in 1 gallon of water. Mix well. Pour the mixture into a hand-sprayer with a hollow-cone nozzle. The hollow-cone nozzle creates the required medium-fine 0.01-inch spray of droplets for treating tomato plant blight. Be sure the spray covers the entire canopy as well as the tops and bottoms of all leaves until the solution begins to drip off the foliage. Do not store left over solution. Mix fresh solution each time you spray which should be every 7 to 14 days to be sure new growth gets treated. (see resources 4, 5 & 6). One gallon of fungicide should cover approximately 20 square feet or 8 plants. When mixed with water, the copper sulfate releases ions that are toxic to fungi but relatively safe for the treated plants. (see reference 9). Although copper is safe to use with a long storage life, it can build up in the soil and become a contaminant. Copper sulfate is toxic to fish and water wildlife. Do not apply near lakes or other natural water environments.(see resource 7) Never apply on hot days, only when the weather is mild and not windy or raining. (see references 4 & 5) When spraying with any fungicide, be sure to wear long sleeves when spraying. It is wise to wear chemical-resistant shirts and pants, waterproof gloves, shoes, and socks, and protective eye wear. Tomatoes can be harvested up to the last day of fungicidal application. (see reference 10).

Wingstem leaves turning white. Why? (photo by Kate St. John)

In July and August I noticed something I’d never seen before along the trails of western Pennsylvania — scattered instances of leaves turning white.

The leaves had been green but now their tips or even whole branches were white. The plant below had advanced to the stage where some of the stems were completely white.

Leaves in distress: top is white, 31 July 2017 (photo by Kate St. John)

The condition is called chlorosis and it means the plant is not producing enough chlorophyll to look green. Since chlorophyll uses sunlight to make food for the plant, it’s a sign the plant is in distress. But why?

Causes of chlorosis are wide-ranging. Here’s the list from Wikipedia, with my added:

  • a specific mineral deficiency in the soil, such as iron, magnesium or zinc
  • deficient nitrogen and/or proteins
  • a soil pH at which minerals become unavailable for absorption by the roots
  • poor drainage (waterlogged roots)
  • damaged and/or compacted roots
  • pesticides and particularly herbicides may cause chlorosis, both to target weeds and occasionally to the crop being treated.
  • exposure to sulphur dioxide
  • ozone injury to sensitive plants
  • presence of any number of bacterial pathogens, for instance Pseudomonas syringae pv. tagetis that causes complete chlorosis on Asteraceae.

Interestingly, the plants I photographed are in the Aster Family (Asteraceae) and one of them has complete chlorosis.

Was the 2017 growing season especially bad for the bacteria mentioned above? Or does chlorosis happen every year and I’ve just not noticed?

If you know more about this condition in the wild, please leave a comment. I’m really curious!

(photos by Kate St. John)

With much enthusiasm, I recently transplanted young cabbage plants into my garden. I took great care in doing so, excited by the prospect of a cabbage harvest. Visions of enormous round cabbage heads danced in my head, while thoughts of sautéed cabbage tickled my appetite! I love growing AND eating cabbage.

So, it came as a great shock to me when I ventured out to my garden this morning and discovered some of the leaves of my plant had turned white. Limp, pale and utterly sickly looking, I was aghast. What happened??

Quickly I scoured my resources for answers and came upon a very simple one.

Sun scald

Also known as sun scorch. Basically, it means my tender transplants were not ready for a direct blow from the Central Florida sun. Not even in late September. I usually cover my tender transplants with a screen contraption, but didn’t do so this time. Thought I could “wing it.” Apparently not. The young plants were accustomed to greenhouse conditions, and needed a more gentle transition into direct sunlight. Lesson learned.

Peering down the bed of plants, my shoulders sagged. How many did I lose?

Several. And worse, I discovered something had been digging in my garden overnight. By the looks of this hole, I’d say it was in search of grubs between my broccoli plants.

But did it have to rip the entire plant from its bed in the middle of the night and toss it aside like unused bed sheet?

Yes. That cabbage plant to the lower right is no longer tucked safely in its hole. Ugh. Varmints have no manners or courtesy whatsoever. The good news: I can replant the plant. It will survive. So will my sun scorched cabbage plants. So long as there is one green leaf left, they can survive. Next time I won’t skip the screen.

Are Your Vegetable Leaves Turning White? Helpful Answers Here.

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Are your vegetable leaves turning white? That is a little disconcerting, yes? White is definitely not the color we are expecting or desiring from our plants! We want them a nice healthy, bright green right?

Why Are Your Plant Leaves Turning White?

There are a couple reasons why your plant leaves turn white. It only comes down to a few. I will give you the summary version here then we will go into more detail below. One. Your plant could have a fungus. Two. It could be sunburnt. That is about it. See. Simple answers. Maybe not so simple fixes.

Powdery Mildew Leaves Treatment

There is a fungus called Powdery Mildew. It actually just developed on my rosemary. I thought it was dust from building the new greenhouse-butIwaswrong. It was doing fine until I moved it into the greenhouse-where already (it is February) that little room is getting humid and toasty.

Powdery Mildew on Ivy Gourds Source: https://flic.kr/p/G24PdF

The mildew is easy to spot because it is bright white and you can actually wipe it off with your finger. And NO plant is immune to it. Good news first. It is rarely fatal to the plant. Yeah! The downside for me is I want to cook with those rosemary leaves-which are now covered in white mildew.

If you allow the mildew to go too long, your leaves will turn yellow or brown and curl. I discovered in my research that mildew is formed when the humidity is high <See my hand waving over here?>, light is low, temperatures are moderate <Another hand wave. It has been around 70-75F.> and the vegetation is dry.

The first thing I did was move the rosemary container out of the greenhouse and into an area that gets good circulation. It actually already looks a little better to me.

Your vegetable garden also needs plenty of sun. Like six hours or more. If it is planted in the ground, can you trim trees and shrubs around it? Try to get it a few more hours of sunlight?

Additionally, be careful you do not fertilize young plants with too much nitrogen. This makes them more susceptible. Consider using instead a time-release fertilizeror compost tea.

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Your Plant Has Powdery Mildew Right Now

Do not wait too long before addressing this issue as there are not many cures for it after it has taken over. You can cut off the offending plant parts and/or use an organic or homemade fungicide (more on this below).

That’s it. I realize it’s not much of an answer but Powdery Mildew cannot really be cured. However, it can be managed as long as you proactively monitor it.

Prevention of Powdery Mildew

  • Fertilize your plants with compost tea.
  • Find plant varieties that are resistant to the fungus.
  • Make sure you are planting in sunny areas. (Remember at least six hours each day is optimal.)
  • Space plants based on recommendations on seed packets or best practices. Actually, plant crowding can be a major factor in the development of Powdery Mildew and other fungus.
  • Prune. It will give your plants breathing room.
  • Spray fungicide regularly.

Natural/Homemade Fungicides

As a preventive method, spray natural fungicides on them. For example, this Potassium Bicarbonate from Amazon will be perfect.

I deliberately did not bring up Neem Oil as I have read mixed results on its effectiveness. Now, baking soda mixed with liquid soap and vegetable oil like in the YouTube video below is supposed to be quite effective if you catch the fungus right away-or want to use it as a preventative!

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Price Disclaimer This is something you will have to do on a regular basis throughout the growing season.

Vegetable Leaves are Sunburnt (Sunscald Injury)

Why do plant leaves turn white? Maybe they are sunburnt! The main reason this happens is the plants were not hardened off long enough before planting outside. In other words, they were not given enough time to acclimate to your sun before being put out there permanently.

And do not assume that because you moved a plant from a greenhouse to the outside it did not need acclimation time. Actually, it did. Greenhouse panels tend to filter UV light whereas direct sun has no filter and beats down on the plant just like it beats down on us.

It is not just new plants that suffer from this though. If you have an extended heat wave (looking at you Phoenix!), then those plants can also get too much sun.

What Can You Do About It After It Happens?

Not much. Cut the leaves off and love on the plant until it can grow new leaves.

Put up a UV sunshade as mentioned below.

Tips for Preventing White Leaves

If you know your plants will or are getting too much sun, consider putting up a temporary sunshade that filters the UV light.

I have done that and it did wonders to protect my peppers from the afternoon sun and heat. If these are new plants, start out with baby steps and only give them a short amount of time in direct sun (hardening off process). Over the course of a couple weeks, you can remove the sunshade earlier and earlier until the plants are tough enough to withstand the rays.

Conclusion

Now you know. The two most common reasons for vegetable leaves turning white are mildew or sunburn. With some proactive diligence, both are easy to prevent (says me with my powdered rosemary!). Afterwards, the damage is the damage but neither normally kills the plant-as long as you stay on top of things. Why are my vegetable plants turning white? Now you know!

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Cornell University

Powdery mildew is a disease of leaf tissue that occurs sporadically on Long Island, and elsewhere in the USA. Outdoors it tends to be more common in gardens than commercial crops, perhaps reflecting different environmental conditions and crop management practices. It also develops on tomatoes grown in greenhouses and high tunnels where it can be a very important disease.

Yield and fruit quality can be reduced by powdery mildew because the disease can develop quickly, and severely affected leaves are killed. This results in less fruit being produced, especially with cherry, Heirloom, and other indeterminant tomato plant types. Fruit that forms typically does not taste as good as fruit produced on a plant with a full canopy of photosynthetically-active leaves, and it is more likely to develop sunscald damage with less protective leaf cover.

Pathogens causing powdery mildew typically have narrow host ranges. Thus the powdery mildew occurring on tomato is caused by a different pathogen than the one occurring on squash, or on peas, or on roses. Sometimes weeds are also hosts and thus can function as a potential source of a powdery mildew pathogen.

The pathogen causing powdery mildew on Long Island and throughout the eastern U.S. is Oidium lycopersici. A different fungus, Leveillula taurica, occurs in other areas, including California. Both pathogens produce characteristic white, powdery growth. Leveillula taurica only produces this on the underside of leaves. Leveillula taurica has been observed twice on Long Island and only in pepper.

Like other powdery mildews, the white, powdery growth is mostly the asexually-produced spores (conidia) of the pathogen plus the structures the spores form on. The spores are easily dispersed by wind. A spore landing on a tomato leaf can infect and in about one week develop a new disease spot with an abundance of spores ready to be dispersed. Powdery mildew fungi do not require leaf wetness or high humidity to infect leaves, as do other fungi causing foliar diseases. Their ability to develop under a range of conditions combined with their ability to quickly produce a lot of spores, means powdery mildew diseases can develop rapidly. While moisture is not required, tomato powdery mildew develops best when the air is somewhat humid, but not above 95% RH.

Main management practices for powdery mildews are selecting resistant or less susceptible varieties and applying fungicides.

Resistance to powdery mildew caused by Leveillula taurica has been bred into a few varieties (see Tomato Resistant Variety Table)that are adapted for being grown under greenhouse conditions because this disease has been more problematic under those conditions than outdoors for growers. Grace is a greenhouse variety that grew well and demonstrated good suppression of Oidium lycopersici under field conditions in an experiment conducted in CT (see report). Noticeable differences in susceptibility to powdery mildew caused by this fungushave been observed among other varieties growing outdoors.

Powdery mildews are relatively easy to control with fungicides. There are several conventional and biological products that have proven effective in efficacy experiments with this and other powdery mildews. Plants cannot be cured of a disease with a medicine as can animals, thus successful control of any disease in a plant necessitates starting treatment with fungicides at the very first symptom or beforehand. Many foliar diseases, including powdery mildew, begin when plants are stressed including by fruit production, thus this is often a good time to start treatment. Conventional fungicides include those containing sulfur, copper, chlorothalonil or mineral oil as the active ingredient. Botanical oil (including sesame, rosemary, and thyme), plant extracts (giant knotweed), biocontrol microorganisms (including species of Bacillus and Streptomyces), and potassium bicarbonate are some of the active ingredients in biological fungicides, most of which are approved for organic production. Typically fungicides need to be applied weekly to maintain control.

Removing affected leaves is not considered a viable approach to managing any powdery mildew disease because once spots are seen spore dispersal has likely already occurred from the spots, spores will likely be disrupted in the process of removing leaves, and there likely will continue to be sources of spores from other plants in the area.

Rotating where tomatoes are grown is not a viable practice because these are obligate pathogens, thus they need living host plant tissue to survive (they cannot live in diseased crop debris over winter). Some other powdery mildew pathogens are able to produce a special structure (cleistothecium, chasmothecium, ascocarp) that can survive in a dormant state like a seed over winter. Ascospores form within it. Production of this structure and spores typically occurs when powdery mildew pathogens reproduce sexually, which requires interaction among two pathogen strains of opposite mating type (fungal equivalent of gender).

Leaves below from a high tunnel have the characteristic fungal growth of the powdery mildew pathogen on the leaf surface but lack the typical fuzzy appearance as there are no spores due to a high infestation of mites which eat spores.

White spots on tomato plants

Howdy Michelle and HomeDepotCraig,

Well, it seems “Hortman” identified one of the most common reason for white spots in Tomatoes. I’d like to add to his answer with common reasons for white spots on tomatoes here on the West Coast.

Powdery mildew occurs in most soft leaf plants like tomatos. The fungus is carried by spores that are carried by wind to plants. Watering too late in the day, poor drainage, and lack of sun increase disease development.

To treat this mildew use multiple applications of non-systemic fungucides like Danconil,Lilly Miller Sulfur Dust, or Safer Garden Fungicide.

Leaf Spot can also be a problem. This disease begins in the leaves of tomatoes, starting with the oldest leaves. Both light and dark spots can be seen on both the top and bottom surfaces of the leaves. The spots enlarge and turn a grayish brown. Plants affected by gray leaf spot disease should be treated or removed from the garden to avoid affecting the other plants.

Fungicides like the ones mentioned above are effective if applied on a every week for at least 3-4 weeks. If you discover you have Leafspot, do not plant in the same place the following season to prevent reintroduction of fungus. The following year should be fine.

Another common pest is the Leafminers. These bugs are regarded as pests by farmers and gardeners because they cause damage to plants. They can be difficult to control with common insecticide sprays because they are protected inside the plant’s leaves.

Spraying the infected plants with an non systemic insecticide like Bayer Advanced, Bonide,Ortho Fruit and Vegetable, or Monterey Garden are all effective treatments.

The most important part of dealing with garden problems is addressing the problem quickly rather than putting it off till it’s too late. Please feel free to ask more questions you might have concerning your tomatoes.

Happy Gardening,

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