Tuesday, September 8, 2009

Ending Powdery Mildew

Treating Powdery Mildew

Beware the cursed powdery mildew, a mold that grows on your leaves and buds. It looks like somebody sprinkled little roundish spots of talcum powder on your leaves. It saps the strength and vigor of your plants, and, when smoked, may pose a health hazard to those with compromised immune systems.

There are a few ways to fight the dreaded PM. Regular sprayings with neem oil during veg and early flowering is successfully employed by some growers. Some use Serenade, an organic bio-fungal, and there are a few other products available at the grow store that work to varying degrees. An organic “systemic” called Aqua-Shield is available from Botanicare. It is made from composted “poultry litter”. (I’m glad I’m not the guy with the job of brewing that stuff up).

 The best method, of course, is to not get the stuff to begin with. Keep the humidity way down and provide the plants with a lot of internal air circulation.

Another way to not get PM, and to successfully get rid of it if you do get it, is to evaporate sulfur. Sulfur is a naturally occurring element that has been around since forever, and the human body is used to it. As the sulfur can be used in its natural state, treatment with evaporated sulfur is within the bounds of organic gardening techniques.

In essence, a device heats up the sulfur until it melts at about 360 degrees Fahrenheit, and the sulfur fumes coat everything in the room or greenhouse. This raises the pH of the leaves and flowers to about 11, and no mold can grow at that level of pH. Greenhouses have used sulfur evaporation to prevent and treat molds and fungi for decades.

The same techniques work just as well in an indoor gro room. Sulfur evaporators are available at the grow store. They look like a paint can with a bail handle, and electric cord, and a tuna fish can on top. The operation is pretty simple. The heating element raises the temperature of the sulfur until it melts, and the fumes fill the room and coat the plants.

Beware the sulfur evaporators that come from the grow store. They cost over $100. and have a nasty habit of bursting into flame, burning up all the sulfur in a few minutes, and filling the room with enough fumes to kill all the plants immediately. (In all fairness to the sulfur evaporator manufacturers, they have changed their operating instructions to lessen the possibility of a fire by raising the sulfur cup up off the burner by an inch. I thank them for this, but I wish they would have made the change before I bought the damn thing.)

Instead of spending a hundred  on one of these, a frugal grower can go to Wal-Mart and buy a Rival electric skillet for $19.95. Buy your sulfur at the grow store. Turn off all the fans, turn off the grow lights, fill the fry pan about a half inch with sulfur, set the temperature to 400 degrees, and melt the sulfur. Turn the fry pan off after the fumes fill the room. Don’t breathe the sulfur fumes.

Sulfur fumigation does impart a sulfur taste to the produce if done too close to harvest. However, a tiny bit of sulfur in the aroma is far better than a crop ruined by PM. Light sulfuring done on a weekly basis will prevent PM from spreading or reoccurring. Heavier sulfuring every four or five days will eliminate a substantial infestation after a few weeks.

Sulfuring also treats, prevents, and eliminates bud rot. It controls thrips by interrupting their reproductive cycle, and spider mites would rather set up housekeeping somewhere other than in a sulfured grow room. Just be careful not to overdo it. Too much sulfur results in burned pistils in the buds closest to the evaporator, but the growth of the bud does not seemed to be compromised very much, if at all. Way too much sulfur turns the leaves yellow in the margins between the veins.

There is a controversy as to whether one should run a circulating fan while sulfuring. I run an oscillating fan at slow speed in the grow room for about half of the time I am sulfuring.

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About Me

Berkeley, CA, United States
Hello and Welcome to dharma Patients Cooperative! My name is D. Gold and I am the moderator of this blog. Over the years, I've written a few books on the subject of scientific cannabis study, starting with Cannabis Alchemy in 1972.I have taught many others the techniques for cultivating their own medicine. For the last two years or so, I have taught the Sunday afternoon grow class at Harborside Health Center in Oakland. (Every Sunday 2:00 to 6:00 pm. Always free!). While we cover beginning and advanced horticultural techniques, many other subjects come up in our weekly discussions that relate to medicinal cannabis and the movement. We hope to reflect these types of discussions in this blog. So feel free to start discussion topics, ask horticultural questions, share tips and new developments with other members, suggest ways that our community could be better served, promote activism, etc. Give us your two-cents worth. All suggestions are appreciated. Thanks. Dave