Powdery Mildew: Info on cause & treatment

*outdoors* · 09-14-2008, 01:41 PM

Quote:

Powdery mildew develops quickly under favorable conditions because the length of time between infection and the appearance of symptoms is usually only 3-7 days and a large number of conidia can be produced in a short time. Favorable conditions include dense plant growth and low light intensity. High relative humidity (RH) is favorable for infection and conidial survival, but infection can take place at RH levels as low as 50%. Dry conditions are favorable for colonization, sporulation, and dispersal. Rain and free moisture on the plant surface are unfavorable, however, disease development occurs in both the presence or absence of dew. Infection can occur at 50-90°F; mean temperatures of 68-80°F are favorable. Powdery mildew development is arrested at daytime temperatures of 100°F or higher. Plants in the field are often not affected until after fruit initiation. The leaves are most susceptible 16-23 days after unfolding.

So there ya go... Powdery Mildew...

Quote:

Contary to popular belief, powdery mildew generally does not require free water to establish and grow. Infection can actually occur on dry leaves. Warm temperatures and shady conditions encourage the fungus to grow and spread. However, the spores and mycelium are sensitive to extreme heat and direct sunlight.

The optimum temperature for infection is between 68 to 77 degrees F and relative humidity between 40 to 100% is sufficient for the spores to germinate. Low, diffuse light also seems to favor powdery mildew development. The mildew can spread rapidly since the disease cycle can be completed in as little as 72 hours. However, it commonly takes 7-10 days from the time of infection to the development of symptoms and secondary spore production.

Quote:

Plant in full sunlight in a well-drained area.
Do not crowd plants. Air flow and ventilation will discourage mildew growth.
Powdery mildew thrives where high rates of nitrogen have been used. High nitrogen promotes tender leaf formation, causing dense stands that are more susceptible to infections. Adequately fertilize but avoid stimulating succulent growth. Organic fertilizers or slow-release formulations of lawn fertilizers are good choices.
Prune infected plants to get rid of infected parts and increase airflow. If the infestations are severe, remove and destroy the plants that are infected.
Disinfect your pruning tool in a bleach solution of one part household bleach to four parts water after each cut.
Watering plants in the morning gives the plants the rest of the day to dry off, discouraging establishment of diseases, including powdery mildew.

Quote:

Organic Sprays
Sulfur is highly effective against powdery mildew if used in a protectant program with a minimum of 7 to 14 days between applications. Garlic naturally contains high levels of sulfur and a few cloves crushed in water can be used to make a homemade spray. Apply a sulfur-based fungicide at first evidence of mildew and repeat applications as necessary. Proper timing of fungicide applications is critical to successful control so make sure to begin at the first sign of the disease.

Another option is to spray once a week with a solution of baking soda. Baking soda increases the surface pH of the leaf making it unsuitable for the growth of powdery mildew spores. Be sure to spray the undersides of leaves as well as the upper surfaces when using any of these sprays.

Here's a recipe to make your own spray:
1 teaspoon baking soda
1 quart water
A few drops of liquid soap
Before treating your plants, test the spray on a few leaves to make sure they are not too sensitive.

There is a product on the market called "Serenade" which is OMRI certified organic and is effective
against PM and Botrytis.

Quote:

If needed during the growing season, begin fungicide applications when the first white patches are noticed. Repeat as indicated on the product label during cool humid weather. Some products with a broad range of applications for outdoor ornamentals include products containing: Bacillus Subtilis, Jojoba or Neem oil, potassium bicarbonate, sulfur or lime sulfur. Some of these products may also be used to treat powdery mildew infections in the vegetable garden. Other products may also be available, so refer to the appropriate pest management guidelines or contact your local Cooperative Extension Office for more information.

Hope this information is helpful...

Peace- OD

*outdoors* · 09-18-2008, 10:04 PM

My study continues....
This article is most helpful.

Quote:

Originally Posted by excerpt

Infection is favored by high humidity (50 to 90%) during twilight hours, and temperatures between 60° and 80° F. While there’s some ambiguity in the UC IPM literature, most sources state that not only does PM not require moist conditions to germinate and grow but that the spores can be killed or inhibited by water on the plant. Shady conditions (which are most conducive to retaining humidity) and vigorous plant growth favor disease development while high temperatures (above 90°F) have an inhibitive effect.

GreenDragon2k · 09-18-2008, 11:27 PM

Don't bother with sprays if you grow indoors or in a greeenhouse your much better off with a sulfur burner. You're gonna have to cover every square inch of leaves on your plants if you're using a spray. Now if you have enough plants, thats darn near impossible, but with a burner, everything gets covered with sulfur, even the walls and floors and equipment... Now outside though, you're gonna have to settle for the sulfur sprays, so make sure you cover those plants completely.

Two or three 8 hour burns during the dark cycle, during the first two to three weeks of flowering will take care of the problem. Completely.

Also keep that humidity @ 45 % during flowering. Very important.

Do not use the sulfur burner past 3 weeks into flowering or your buds will taste like sulfur. Do not use sulfur if you have applied Neem oil within 30 days or you'll burn the leaves.

Works like a charm though. I'll never bother with any other method of control

Sulfur burner all the way.

Great thread OD

*outdoors* · 09-21-2008, 08:40 PM

Today I followed a link that took me to an article on using baking soda (sodium bicarbonate) as a fungicide. It was a scientific kind of article so it took me awhile to muddle
thru it.

I also read this year about Greencure... an outdoor grower swears by it.
It's active ingredient is potassium bicarbonate

This excerpt from that article talks about the different bicarbonates.

Quote:

An article in the February, 1996 issue of GrowerTalks magazine follows up on the continuing research at Cornell. Testing with a variety of bicarbonates revealed that selecting the correct bicarbonate for a particular disease is important.
Dr. Horst's research team found that ammonium bicarbonate had the strongest effect on some diseases, while potassium and sodium bicarbonates worked best against others. Potassium bicarbonate provided the best control of PM. "Sodium bicarbonate is okay, but it's not as good," Horst is quoted as saying. "And ammonium bicarbonate doesn't do the job on powdery mildew."
He points out that while conventional chemical controls for PM are preventatives only, bicarbonates can eliminate the disease after it has already appeared on certain crops—he mentions roses and an unspecified ornamental—provided the infection is not severe.

The only plant damage associated with bicarbonates applied in the trials was foliar burning when application rates exceeded recommended concentrations.

Testing established that sodium bicarbonate does not increase the levels of sodium in plant tissues, soil, or runoff water. While their precise mode of action against fungi is not understood, Horst states that bicarbonates seem to damage the cell wall membrane in PM spores. He also believes pH to be a factor in bicarbonate effectiveness. In any case, bicarbonates are contact fungicides, and kill PM within minutes.

giantwang · 09-21-2008, 09:57 PM

I have had PM issues, and think I finally have it whooped. It was a pain, but if I was diligent with baking soda sprays I could keep it to the lower fan leaves. But I often burnt my plants with the sprays, so be careful. I use a little less than 1/4 teaspoon in a quart of water. I even used it to spray down the walls and floor of the GR.

Even when it burnt the plants prety bad the buds still came out fine. It sucks that PM thrives in the conditions that are pretty much right in the range of MJ. I have no idea how it got into my garden. Anyway that is my

.

I didnt follow the links you posted, but here is one that Buzzmobile set me up with when I was having trouble. I found it useful enough to add it to my favorites.

GOOD LUCK!

*outdoors* · 09-29-2008, 09:57 PM

A pretty classic example of Powdery Mildew on Cannabis.

giantwang · 09-29-2008, 10:30 PM

OUCH! That is way worse than I have ever gotten it indoors. Good Luck!

Sending some good vibes your way...

**bobbooty** · 09-29-2008, 10:51 PM

i have powdery mildew that ive been battling, ive tried everything, the soap sprays, burned my plants, the milk sprays burned my plants. ive been keeping it in "check" with fungicide 3 by gardensafe. works good for about a week then the pm just comes back and i reapply, makes the plants look all sexy and stuff with the shine of the neem.

been real interested in this stuff:

SM-90 Pest Inhibitor from Growco Indoor Garden Supply

but unfortunately it says this in the small print at the bottom of the page:

Quote:

No shipments to California allowed.

*outdoors* · 09-30-2008, 09:50 AM

Interesting stuff Bobbooty... have you tracked
down the label information with the list of ingredients and the active
ingredients? Check this site out.

There is no cure for it, maybe indoors you could get rid of it because
you could avoid contamination after you got rid of it.

Outdoors is something different.

Everything I've read, and I've read alot, there will need to be reapplications
every few days to keep it away.

My current mixture is using a combo of Serenade (Did you read about
that Bobbooty?), Neem Oil, and dishwashing detergent.

Burning is common with the bicarbonate sprays. 1/4 tsp to a quart of water
is what is recommended; its a tiny amount, it's easy to over due it.

Spraying the pistils is not something I ever want to do because they are
nearly always damaged in someway.

The plants that I doused heavily with this mixture have stayed "clean" for
over a week. My problem is that I have so many plants and it's hard to
keep up.

Using the Serenade on it's own, left a powdery residue on the leaves
that I really didn't like. Adding the Neem oil seems to be the answer
and the Neem lays down a protective layer on the leaf so the PM
can't take hold.

You can see why reapplication is necessary.

I have no experience with sulfur products. Because I have the Serenade
on hand I'm using that.

You might be interested to know that when I bought the wettable powder
form of the Serenade it wasn't supposed to be shipped to California
either; even though the premixed stuff in spray bottles was on the shelves
everywhere.

I found an internet provider who was willing to send the stuff my way.
So, now I have about 9 pounds of this powder still on hand.

It takes diligence to keep the PM at bay especially in a large garden.

Peace- OD

GreenDragon2k · 09-30-2008, 10:45 AM

Quote:

Originally Posted by Outdoors

It takes diligence to keep the PM at bay especially in a large garden.

I'm tellin ya. Sulfur burner worked wonders on my grow. I just fired mine up, I expect two burns during first two weeks of flowering to do the job for the entire grow. Easy to use, very little effort involved... covers every square inch of your garden... and very effective. Just gotta foot the bill for the burner and sulfur is pretty cheap...

That fungicide 3 worked for me but it was just a temporary fix... I dont like spraying my buds with all kinds of junk... Mostly neem oil that stuff, with some kind of spreading agent.

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