# Powdery Mildew



## pcduck (Aug 18, 2012)

I came across this at Gp and found it an interesting read.
Figured I would post it here for our members.


*PM cures.

*  You'll know powdery mildew has paid your  plants a visit when it looks   lot like confectioners sugar has been  sprinkled on the plant leaves.   At first it may be hard to spot as it  might appear on just a small   portion of the leaf appearing as an  irregular circle. But it quickly   spreads and soon appears on the  surrounding vegetation. Soon the entire   leaf is covered and at the  same time colonies develop on the  surrounding  vegetation and in other  areas of the garden.
 So how does it all start?  Well, the plant becomes infected when an  airborne spore, or _conidia_,   lands on a leaf and germinates. It  soon grows a guide tube that   attaches tightly to the leaf. Then it  pierces the plant cell wall and   membrane and inserts a hollow tube that  sucks up plant nutrients,   weakening the leaf and slowing growth. Within a  week the fungus   produces tiny mushroom stalks that release millions of  spores, ready to   infect more leaf surfaces. The fungus also produces a  secondary  spore,  which over-winters outdoors and may also hide in a  greenhouse  or  indoor garden even after the crop has been harvested.
 Powdery mildew is most likely to attack the young leaves, up to two  or three weeks old.
 A dozen or so different fungus fall under the heading of Powdery    Mildew, but two different fungus species are the most likely culprits.  _L.  taurica, _tends to attack warmer gardens. It prefers a temperature  of about 77 F (25 C). _S. macularis _prefers   a cooler  temperature; however, the more virulent stain found in  indoor  gardens  today  has adapted to tolerate more heat. Both strains  thrive  in  moderate humidity and are not injured by water. Their  conidia can  live  in water for short periods and are mobile in it.  However, strong  water  sprays do destroy some conidia.
*CULTURAL CONTROL*
*Heat
*
 Powdery mildew is sensitive to heat. Neither species will grow at 90 F  (32 C). and will quickly perish when above 100  F (38 C).
 To get a complete kill maintain the temperature for an hour. This may    not be a feasible option in most indoor gardens for several reasons.    The first is that it may be difficult to heat the space to such a high    temperature. The second is that even a single peak of 100 F (38 C)    affects the growth of plants. Vegetative plants  with flowers or fruits    in mid stage growth (weeks 3-7) may stretch a little from the    experience. The heat treatment has relatively little effect on first and    second week flowers or flowers nearing maturity.
 You can minimize heat's impact on plants in several ways. Heat the    garden at the end of the day, as the lights are turned off. Since the    plants are not photosynthesizing, they have lower water needs.
 If the plants are being grown hydroponically, lower the temperature  of   the water to 60 degrees. Keeping the roots cool will help the upper    plant parts beat the heat. It's not difficult to do this, even if you    don't have a water chiller. Just add ice to the reservoir or flow    through system. Roots of plants growing in soil can also be cooled using    thermal ice packs at the base of the stem.
 The heat treatment should kill off most of the fungus and its spores.    The chances are there will still be some fungal re-growth. These can be    eliminated using spot treatments.
*Pruning
*
 If one particular plant seems to be infected with a few tiny white    spots on a few of its leaves, get a bag large enough to drop the leaves    into and then cut them off into the bag. Remove the bag from the room.    This prevents spores, the white powder on top of the leaves, from    becoming airborne while being removed. Remember to wash your hands and    clean the scissors or knife with soap and water, hydrogen peroxide,    alcohol or bleach.  Spray the plant with one of the sprays listed below    after pruning to prevent re-infection and encourage healing.
 If, you notice a re-infection a few days later, there is a good  chance   that this plant is very susceptible to powdery mildew and  presents a   good location for the infection to start and spread from. The  plant   should be removed immediately by placing a bag over it and  removing it   from the space. Then the space should be sprayed with one of  the  sprays  listed below.
*ORGANIC and IPM CONTROL
*

 Here are some sprays that you can use to control the powdery mildew  in   your crop. All of these are safe to use for herb or for edible crops.    Sprays are washed away by water, including rain.
*Cinnamon Oil and Tea*
 Cinnamon is an effective destroyer of powdery mildew, with an    effectiveness rate of 50-70%. It won't kill it completely but it will    keep it in check somewhat. It also potentiates other suppressive sprays    so it is good to use in combination. To make your own, boil water,  turn   off the heat and add one ounce of ground cinnamon to one and a  half   pints water. Let the tea cool to room temperature. Add half a  pint of   100 proof grain alcohol or rubbing alcohol and let sit. Strain  the   cinnamon. The spray is ready to use. A faster method is to add 2    teaspoons cinnamon oil to one pint of water and a dash of castile  soap.   Other herbs are also fungicidal. Clove, rosemary, and  wintergreen oils   are used in some botanical fungicides. The solution  should consist of  no  more than 2% oil.
*Garlic*

 Garlic is antifungal and anti-bacterial and has several pathways for    destroying fungi including its high sulfur content. It can also be added    to other anti-fungal sprays.  Several garlic sprays are available    commercially.
 A homemade formula: Soak three ounces of crushed garlic in one ounce    of neem or sesame oil and 100 proof or higher drinking alcohol or 70% or    higher rubbing alcohol for a day or two. Strain. Then soak the garlic    in a cup of water for a day. Strain. Mix the oil/alcohol, soaked  water   and 1 tablespoon liquid castile soap in a gallon container. Then  fill   with water and shake. The formula is ready to use.
 A simpler brew consists of a teaspoon of garlic oil in a pint of    water. To keep the oil and water mixed add a 1/8teaspoon of soap. Use    garlic as a vaccination. Spray on new growth before there is a sign of    infection.
 Garlic is a general purpose insecticide as well as fungicide, so it    should be used with caution on outdoor plants. It kills beneficial    insects as well as plant pests.
*Hydrogen Peroxide*
 Hydrogen peroxide (hp) is a contact fungicide that  leaves no residue.   It is an oxidized product of water and has an extra  oxygen atom that  is  slightly negatively charged.  When it comes in  contact with the  fungi  the oxygen atoms attach to molecules on the cell  walls,  oxidizing or burning them.
 Household hp sold in drug stores has a concentration of 3%. Garden    shops sell 10% hp. Zerotol contains 27% hydrogen peroxide and an    unstated amount of peroxyacetic acid. Together they have a more potent    chemistry than hp, with an activity of about 40% hp. It is considered    hazardous because it can cause skin burn similar to that caused by    concentrated acids.
 To treat plants with drug store grade 3% hp use 4 1/2 tablespoons and    fill to make a pint of solution, or a quart of hp to 3 quarts of   water.    With horticultural grade 10% hp use about 4 teaspoons per  pint,  5  ounces per gallon. With Zerotol use about 1 teaspoon per pint,  2 1/2   tablespoons per gallon.
*Limonene*
 Limonene is refined from the oil of citrus rinds.  It has a pleasant   citrus odor and is the active ingredient in many of  the new cleaning   products. It also has fungicidal qualities. I've used  pure diluted   limonene and it controlled powdery mildew, but did not  eradicate it.   Perhaps a higher concentration would have been more  successful. Start   using 0.5-1% limonene in water 1/2-1 teaspoon per  pint.
*Milk*
 Milk kills powdery mildew so well that both home and commercial rose    growers all over the world have adopted it for their fungicidal sprays.    Use one part milk to nine parts water. I've only used 1% milk, but   other  recipes call for either whole or skim milk and use up to 1 part   in 5  milk. Some recipes add garlic or cinnamon to the mix. When using   more  than 30% milk, a benign mold is reported to grow on top of the   leaves.  Use a milk spray at the first sign of infection then protect   the new  growth weekly.
*Messenger*
 Messenger's active ingredient is a naturally  occurring protein called   harpin that stimulates the plant's own natural  defense system. It has   been proven to promote more vigorous hardier  plants that are more   resistant to disease and have increased yields. It  is used to prevent   infection and decrease its virulence


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## pcduck (Aug 18, 2012)

Neem Oil
Neem oil is pressed from the seed of the neem tree (Azadirachta indica), native to Southeast Asia, but now cultivated worldwide. Neem oil has low mammalian toxicity. It degrades rapidly once it is applied so it is safe for the environment including non-target species and beneficial insects.
Neem oil protects plants with its fungicidal properties: it disrupts the organisms metabolism on contact, forms a barrier between the plant and the invading fungus, and it inhibits spore germination. It has translinear action, that is, it is absorbed by the leaf and moves around using the leafs circulatory system it can also be used as a systemic. When it is applied to the irrigation water it is absorbed by the roots and delivered throughout the plant. Adding a 0.5% solution, about 1 teaspoon per quart, to the irrigation water will protect the plant from infection.
Neem oil is best used before the plant or the garden exhibits a major infection. By using it before powdery mildew appears, it prevents the spores from germinating. It should not be used on buds or flowers.

Oil Spray
Growers have used different oil sprays to prevent and cure fungal infections. Until recently most horticultural oil sprays were made from petroleum distillates. However, most organic growers have switched to using botanical oils. Aside from the safety factor botanicals such as cottonseed, jojoba, neem and sesame oils have fungicidal properties. They can be used in combination with other spray ingredients listed here. The oils are mixed at about 1-2% concentrations. A 1% solution is about a teaspoon per pint or 3 tablespoons per gallon. Add castile soap to help the ingredients mix. Oil sprays should only be used on the leaves, not the buds or flowers. Use weekly on new growth.
pH Up
pH-Up is a generic term for alkaline pH adjustors, used to increase water pH in indoor gardens. They come as either a powder or liquid. Its active ingredient is usually lye (KOH) or potash (K2CO3).
Fungi require an acidic environment to grow and die in alkaline environments. Changing the leaf surface environment from acidic to alkaline clears up the infection. An alkaline solution with a pH of 8 will make the environment inhospitable for the fungus and will stop its growth. This is one of the simplest means of controlling the fungus. It can be used on critically infected plants.
Potassium/Sodium Bicarbonate
Potassium bicarbonate (KHCO3) and Sodium bicarbonate (NaHCO3) are wettable powders that change the pH of the leaf surface toward alkaline. Another reaction takes place; the fungus cell wall actually bursts in the presence of bicarbonate. Potassium is one of the macro-nutrients used by plants and therefore is preferred over sodium, as sodium can build up in the soil. Sodium bicarbonate can be found in your kitchen (baking soda), so some prefer it for ease of obtaining. Both are more effective when used with an oil and spreader such as castile soap. They can be used to cure bad infections and prevents new ones.
Use one teaspoon of bicarbonate powder, a teaspoon of oil and a few drops of castile soap in a pint of water, or 3 tablespoons each potassium bicarbonate and oil and a half teaspoon soap in a gallon of water. Spray on new growth.
Serenade and Sonata
Serenade and Sonata are composed of different bacteria. They use different pathways to stop mycellial growth. They are considered totally safe to humans and animals since the bacteria attack only fungi. Watch out if you are a mushroom, otherwise you are safe. The two bacteria work well together.
They are easy to use, quite safe and effective.
Sulfur
Sulfur has been used to control powdery mildew for centuries. Sulfur sprays can be used indoors but they are not popular because of residue that remains on the plant. In greenhouses gardeners use sulfur vaporizers that heat elemental sulfur to the point of vaporization. The sulfur condenses on all surfaces including the leaves. A fine deposit of very low pH sulfur granules covers the leaf surfaces. The low pH environment inhibits fungal growth. The heaters use a 60 watt light bulb to heat sulfur which is held in a container above the light. The bulb supplies enough heat to evaporate the sulfur, but not enough for it to ignite. The problem with vaporizers is that they also leave a fine sulfur film on the leaves and flowers.
Active mildew: 7 to 8 hours per night 1 to 2 times a week.
Preventative maintenance: 4 to 5 hours once a week
Vinegar
Apple cider vinegar is toxic to powdery mildew because of its high acidity (low pH). Use it at the rate of 1 tablespoon per quart of water several times a week . Some gardeners recommend alternating using vinegar with potassium bicarbonate and milk.
PREVENTION

    Isolate all new plants in a separate area where they can't infect other plants.
    Filter incoming air to prevent spores from entering the room in the airstream.
    Install a germicidal UVC light, like the ones used in food handling areas. The light is fatal to all airborne organisms passing through the appliance. This will kill powdery mildew spores that are airborne.
    Spray the leaves with neem oil weekly. Neem oil presents both a physical barrier and a chemical deterrent.
    Cinnamon oil and cinnamon tea can also be sprayed as a powdery mildew preventative. If you are using cinnamon oil use 1 part oil to 200 parts water. (1 teaspoon oil in a liter of water.


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## AluminumMonster (Sep 3, 2012)

Very informative PCduck, thank you for posting this!


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## 4u2sm0ke (Sep 3, 2012)

Yeah *duck*..I was just talking to another member on Powder...thanks for shareing this with us...have ya tried any of these methods?.....the heat of 100 for hrs  scares me

take care and be safe


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## pcduck (Sep 3, 2012)

Have not tried the heat method.

Tried the milk method and it worked for me.


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## tastyness (Sep 3, 2012)

> When it is applied to the irrigation water it is absorbed by the roots and delivered throughout the plant. Adding a 0.5% solution, about 1 teaspoon per quart, to the irrigation water will protect the plant from infection.


*
Does anyone use Neem in their water? * 
I'm thinking if it poses no risk to my plants- better safe than sorry.
Still fighting humidity in flower a bit and thinking this might help.


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## gourmet (Sep 3, 2012)

Great info, thank you.


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