Why Leaves Get White Spots: Powdery Mildew
Summary
TLDRIn this video, Jason from Fraser Valley Rose Farm addresses the common issue of powdery mildew affecting plants, particularly during certain seasons. He explains the fungal infection's appearance on a variety of plants and emphasizes its varying impact on their health. Jason discusses the conditions that favor powdery mildew, such as humidity and cooler temperatures, and offers practical advice on prevention, including choosing resistant plant varieties and maintaining good air circulation. He also suggests less harmful alternatives to chemical sprays, like neem oil, horticultural sulfur, and even milk, for managing the disease.
Takeaways
- 🌱 Powdery mildew is a fungal disease that appears as white patches or a fuzzy covering on the upper surface of leaves.
- 🍃 Susceptible plants include squash, cucumbers, melons, grapevines, roses, phlox, menardes, and certain broadleaf trees like horse chestnut and big leaf maple.
- 🌡️ The fungus thrives in humid conditions and cooler temperatures, making early season greenhouses particularly prone.
- 🌳 While powdery mildew can affect many plants, its impact varies; it's often less severe on trees and perennials but can be devastating for annual crops and those intended for fruit or flower harvest.
- 🌱 To prevent powdery mildew, choose resistant plant varieties, such as the Jacob Kline monarda or powdery mildew-resistant (PMR) squash and cucumbers.
- 💧 Good air circulation, proper watering, and maintaining plant health are crucial for preventing powdery mildew; avoid overhead watering that keeps foliage wet.
- 🌬️ In greenhouses, use circulating fans to manage humidity and prevent the buildup of fungal spores.
- 🌱 Neem oil and wettable sulfur are less harmful alternatives to heavy chemicals for controlling powdery mildew, effective as preventive measures early in the season.
- 🥛 A baking soda and oil spray, or a milk solution (one part milk to two parts water), can also be used as home remedies to deter powdery mildew, though they may have drawbacks like cost or unpleasant smell.
- 🛡️ Once a significant amount of powdery mildew is present, it's challenging to eradicate, emphasizing the importance of early detection and prevention.
Q & A
What is powdery mildew and how can it be identified on plants?
-Powdery mildew is a fungal disease that appears as white patches or a white, sometimes fuzzy, covering on the upper surface of leaves. It's fairly unmistakable and can affect a wide range of plants.
Which plants are particularly susceptible to powdery mildew according to Jason?
-Jason mentions that squash, cucumbers, melons, grape vines, roses, phlox, menardes, and broadleaf trees like horse chestnut and big leaf maple are particularly susceptible to powdery mildew.
How serious is a powdery mildew infection for the health of a plant?
-The seriousness of a powdery mildew infection varies by the host plant variety and the severity of the infection. For most healthy trees and perennials, it's more of a nuisance and doesn't significantly impact health, but for fast-growing plants like squashes, cucumbers, and melons, it can ruin the crop.
What conditions favor the spread of powdery mildew?
-Powdery mildew thrives in humid, wet conditions on leaves and prefers cooler or moderate temperatures. It can also be more prevalent in greenhouses due to higher humidity levels.
How can aphids contribute to the spread of powdery mildew?
-Aphids can make plants more susceptible to powdery mildew by puncturing the leaves with their sucking parts, creating openings for the fungal spores to infect the plant.
What are some preventive measures for powdery mildew?
-Prevention includes choosing resistant plant varieties, ensuring good air circulation, proper watering and feeding to establish healthy plants, and strategic watering to minimize foliage wetness.
What is the role of resistant plant varieties in managing powdery mildew?
-Resistant plant varieties can delay or reduce the severity of powdery mildew infections, which is beneficial especially for crops where the disease can impact the harvest.
Why is air circulation important in preventing powdery mildew?
-Good air circulation helps to reduce humidity around plants, which is a condition that powdery mildew favors. It also prevents the buildup of fungal spores on plant leaves.
How can proper watering practices help in managing powdery mildew?
-Watering practices should avoid wetting the foliage, using methods like drip irrigation or watering early in the day to allow for evaporation, thus reducing the risk of infection.
What are some less harmful alternatives to chemical sprays for treating powdery mildew?
-Less harmful alternatives include neem oil, wettable sulfur, and homemade solutions like a baking soda and oil spray or a milk spray, which have been shown to be as effective as heavier chemicals in reducing powdery mildew.
How does the baking soda and oil spray recipe work for treating powdery mildew?
-The recipe involves mixing one tablespoon of potassium bicarbonate (baking soda) and three tablespoons of horticultural oil or canola oil per gallon of water. This spray is less phytotoxic and can be as effective as chemical treatments.
What is the milk spray method and how effective is it against powdery mildew?
-The milk spray method involves mixing one part milk to two parts water to create a 33% milk solution. It can be effective in preventing powdery mildew, but it may leave an unattractive coating on foliage and has a strong odor.
Outlines
🌱 Understanding Powdery Mildew
Jason from Fraser Valley Rose Farm addresses a common gardening concern about white patches on plant leaves, identified as powdery mildew. He explains that this fungal infection affects a wide range of plants including squash, cucumbers, melons, grape vines, roses, and some perennials and trees. Jason emphasizes that the severity of the infection varies by plant type and the progression of the disease. While it may not significantly impact the health of most trees and perennials, it can be more serious for annual crops and ornamental plants, potentially ruining the crop or affecting the plant's appearance. He also discusses how powdery mildew spreads, the conditions it thrives in, and the importance of early detection and prevention.
🌿 Preventing Powdery Mildew
Jason provides insights on how to prevent powdery mildew, starting with choosing resistant plant varieties. He mentions specific cultivars like Jacob Kline for bee balm and variegata to Bologna for roses that show resistance. He also stresses the importance of good air circulation, proper watering, and feeding to establish healthy plants that are less susceptible to the disease. Jason advises on cultural controls like spacing plants appropriately, pruning for air flow, and using irrigation methods that minimize foliage wetness. He also touches on the use of less harmful solutions for disease management, such as neem oil and wettable sulfur, which are effective in preventing powdery mildew when applied early in the season.
💧 Natural Remedies for Powdery Mildew
In this segment, Jason discusses alternative, non-chemical methods for treating powdery mildew. He recommends a baking soda and oil spray, providing a recipe that uses potassium bicarbonate and horticultural oil to minimize phytotoxicity. He also suggests a milk spray, which, despite its unpleasant smell and the need for a high milk concentration, has been shown to be effective in controlling powdery mildew. Jason concludes by inviting viewers to ask further questions about powdery mildew or other plant diseases, indicating his willingness to continue the conversation.
Mindmap
Keywords
💡Powdery mildew
💡Fungal infection
💡Susceptible plants
💡Prevention
💡Cultural controls
💡Resistant varieties
💡Air circulation
💡Watering practices
💡Organic sprays
💡Phytotoxicity
💡Disease management
Highlights
Gardeners often ask why their plants' leaves turn white, which is usually due to powdery mildew.
Powdery mildew appears as white patches or a fuzzy covering on the upper surface of leaves.
Certain plants like squash, cucumbers, melons, grape vines, and roses are particularly susceptible to powdery mildew.
Powdery mildew can also affect perennials such as phlox and menardes, as well as broadleaf trees like horse chestnut and big leaf maple.
The severity of powdery mildew's impact on plant health varies by plant variety and the progression of the infection.
Most healthy trees and perennials can withstand powdery mildew without significant health issues.
Powdery mildew is more of a nuisance for ornamental plants, potentially reducing flowering but not usually threatening their lives.
For crops like squash, cucumbers, melons, and grapes, powdery mildew can ruin the harvest if not managed.
Powdery mildew spreads via fungal spores that travel in the air and thrive in humid conditions.
Greenhouses are at higher risk due to increased humidity, and early season conditions are particularly conducive to powdery mildew.
Aphids can make plants more susceptible to powdery mildew by creating openings for fungal spores.
Prevention of powdery mildew should start with choosing resistant plant varieties.
Cultural controls like good air circulation, proper watering, and feeding can reduce the risk of powdery mildew.
Resistant cultivars of plants like monarda and roses can delay or reduce the impact of powdery mildew.
Spraying with less harmful solutions like neem oil or wettable sulfur can be effective in preventing powdery mildew.
A baking soda and oil spray, or a milk spray, can be used as natural alternatives to chemical treatments for powdery mildew.
Proper watering practices, such as using drip irrigation or watering early in the day, can help prevent powdery mildew.
The video concludes with a call for viewers to ask questions about powdery mildew or other plant diseases in the comments section.
Transcripts
hi again it's Jason from Fraser Valley rose farm I want to answer a question I
get a lot from gardeners this time of year which is why are the leaves of my
plants turning white now the white they're talking about is like this and
I'm not sure if you can see this real close up so I'll get a close-up picture
of it but it's a white patches or white covering sometimes fuzzy on the upper
surface of leaves and it's actually fairly unmistakable
it's called powdery mildew and there are some very susceptible plants so if you
see this and it's combined with a plant that I list here pretty much it's
confirmed it's powdery mildew so let's talk about squash we talked about
cucumbers and melons grape vines get it quite frequently also my favorite roses
they get powdery mildew fairly frequently in perennials you'll
sometimes see it on phlox's and menardes and a host of other perennials as well
and sometimes you'll see it on broadleaf trees like this one here this is a horse
chestnut but also we get it quite a lot on our local big leaf maple so that's
what it is powdery mildew and it's it's over a wide range of plants let me talk
to you a little bit about how it spreads what are the conditions how you can try
to prevent it and how do you treat it if you have it on your plants so I've just
told you that your plant has a fungal infection on its leaves I guess your
next response should be to ask how serious is that for the health of my
plant and the answer is it varies an awful lot by the host variety the host
plant variety and how severe that infection progresses to be so on that
tree that I have out there and basically most healthy trees will never be set
back too far by a powdery mildew infection they'll come through it just
fine they're a long life cycle plant and one season with powdery mildew and
leaves or even every season with powdery mildew on the leaves isn't going to set
them back much like wise on my roses I have to say it's more of a small
nuisance than anything else I don't think any of my roses lives are being
threatened by a powdery mildew infection most it's going to do is it's gonna be a
bit unsightly it might reduce the deflowering on my plants for one season
if it gets particularly bad but typically it does not impact the health
of the plant significantly similarly with the perennials the phlox's and monardas
are can get powdery mildew every year later
in the season and still come back healthy the next spring so the ones you
really do have to concern yourself with a little bit more unless it gets to be
an out of hand infection is things like the squashes the cucumber's the melons
zinnias and grapes those things that you're trying to get a crop off of them
so you're trying to get the fruit or you're trying to get the flower from
them and they're fast growing and their inability to get that sunlight through
to those healthy leaves because powdery mildew is in the way and the health
deteriorates in the plant means that your crop can be ruined
dead stop so that's where it's more serious is usually in those short cycle
annual crops or those ones you're trying to get a-goin trying to get an actual
physical crop off of whereas for ornamental plants it's usually a little
bit less severe unless you're trying to sell them which I do so let's talk about
how you prevent it now the truth is it is a sport it's a fungal spore it
travels in the air it blows in from everywhere you can't really stop it from
coming into your greenhouse even if I grow in a greenhouse like this closing
the sides isn't going to keep it out in fact you're at a special risk in a
greenhouse because humidity levels are up so let's talk about the conditions
that powdery mildew likes it likes humid wet on the leaves and it's actually a
little bit better in cooler or moderate temperature conditions so early in the
season in a greenhouse like this you're very susceptible to powdery mildew
particularly on a cloudy day that's when it's really going to bring bring up the
high humidity inside the plants cooler temperatures you're going to have the
germination of those those spores on your leaves I will say one other thing
is they sometimes tag-team with aphids so if you get a lot of aphids a healthy
plant may be resisting the the germination of the fungal spores on the
leaf surface but once you get the aphids in there they stick their little their
little sucking parts into your leaves and it leaves an opening for those for
the powdery mildew to infect your plant so they sometimes go hand in hand all of
those stresses sometimes go hand in hand so any kind of a physical stress on your
plants either by under watering or aphids can sometimes make them a little
bit more susceptible to powdery mildew all right let's talk about prevention
because honestly once there's a good covering of powdery mildew on your
foliage it's pretty hard to wipe it out and your consideration for prevention
should always start by looking at resistant varieties of plants let me
give you an example in perennials monarda or bee balm is quite widely
susceptible to powdery mildew but there is one cultivar one well-known cultivar
called Jacob Kline which is a beautiful red one that actually holds off the
powdery mildew or at least doesn't get it until much much later in the season
so you don't have to worry about it quite so much now in roses you there are
a lot of the newer varieties that are much more power really resistant you can
go on to the site that I've recommended before help me find roses and that one
will show you in the description whether the plants are resistant or not this one
here is a variety called variegata to Bologna which is a bourbon rose
unfortunately fairly susceptible to powdery mildew I grow it anyway for
historical purposes and because it has a beautiful flower but I'm aware of that
and so I always watch it for the symptoms of powdery mildew early in the
season you will also see that in squash cucumbers and melons that oftentimes
when you go to the seed catalogs they will actually relist in the name of the
plant PMR or powdery mildew resistant and if
they don't list it in that then it's well worth reading into the description
of the plant to make sure that it has good resistance to powdery mildew
because again it may not be a case of avoiding the disease entirely but if it
can hold it off into the later part of the season after you've already got your
harvest in place that's just as good or almost as good so I know I'm gonna have
to talk about spraying here at some point because spring is the go-to in
dealing with fungus but give me a couple more minutes to talk about cultural
controls here the importance of which the first of which is to talk about good
air circulation in a greenhouse here we manage that very carefully because we
know that humanity can build up around those plants so we install circulating
fans to keep the air moving outdoors you want to manage it with the same thing in
mind so don't plant your plants so tight
together there's no way circulation space them appropriately and
prune them for good air circulation through the plants I know this on roses
I teach this on roses is to prune it to allow air to flow through the bottom
edge of that plant so we don't get powdery mildew down low that then
progresses up high and the plant also let's talk about watering feeding and
establishing your plants well the healthier the plant the less susceptible
it is to powder and mildew and particularly on roses I will say that a
lack of water will lead to powdery mildew in susceptible varieties every
time so that may sound paradoxical to you to talk about watering a plant well
but then also not letting the foliage stay too wet ways you can manage that
use drip irrigation or some other form of irrigation that keeps the water down
low where it isn't getting onto the foliage or if you are using overhead
irrigation be a little strategic about it if you see a sunny day with a bit of
a breeze water early in the day when it has plenty of time to evaporate off
those leaves that's good enough all right now let's talk about spraying then
I don't really encourage the heavy chemicals two reasons first of all I
don't want to spray where a spray suit I don't want to expose my family and my
farm to heavy chemicals but the second thing I'll say is that the studies show
that there are some less harmful solutions that are just as effective as
the heavy chemicals two of those that you would use as directed on the bottle
so look for neem oil for horticultural use that can do a good job also wettable
sulfur does a good job of reducing the incidence and severity of powdery mildew
usually again as a preventive early in the season and both of those products
are good in the cooler part of the season not so great in the later part of
the season when it's warmer because they can be phytotoxic at higher temperatures
so a couple that I'm going to talk about here I talked about a baking soda and
oil spray that I've recommended before when it comes to black spot I'm also
going to talk about a milk spray so the baking soda spray by recipe and this
time I'll give it to you in gallons is if you had a gallon of water with one
tablespoon of preferably potassium bicarbonate baking soda and say three
tablespoons full of horticultural oil or you can use canola oil
as a substitute now the reason I say potassium bicarbonate preferably and
also horticultural oil preferably is that these two ingredients are proven to
be less phytotoxic they don't burn the leaves quite as much so if you do
substitute them with canola oil or with sodium bicarbonate go ahead and do so
just I would probably either cut back the recipe or dilute it slightly or test
it first so you don't see higher you can see how much phyto toxicity there is
this and again in studies that that preparation has been shown to work as
well as the heavier chemicals in reducing powdery mildew the final what
I'm going to talk about is milk now milk does work and the solution that I've
seen mixed again in the studies is that it's it has to be at a fairly high rate
somewhere in the range of about one part milk to two parts water about a 33%
solution of milk you spray that on preferably on a warm hot day it will
smell really bad it may leave in an unattractive coating
of its own on the foliage but it does a good job of holding off powdery mildew
only thing I would say about that is in comparison to the oil and baking soda
spray you have it's probably a little more expensive to prepare and apply on a
regular basis and you do have to deal with the stink so that's my conclusion
on the spraying all right I hope this answers some of your questions on
powdery mildew and if you have any other questions on powdery mildew or other
plant diseases please drop those below the video
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