Powdery mildew
Powdery mildew prevention is key for many gardeners.

Powdery mildew can be the bane of gardeners' lives!

Those fuzzy white spots on cannabis plants can rapidly take over a crop and ruin an entire harvest.

But it's not all bad news – there are dozens of ways to prevent mildew, which mostly focus on ensuring your environmental conditions are optimal.

A word to the wise – it's a very good idea to implement powdery mildew prevention EARLY ON, so that you avoid having to fight a catastrophic infection once it's taken hold!

Adding to this – if you wait until your plants are flowering, your range of possible options diminishes drastically.

Powdery mildew prevention is especially important in cool, damp environments, or if the variety of cannabis you are growing is susceptible to mold.

Powdery mildew may be caused by dozens of different species of fungus in the Erysiphaceae family.

Many other plants are susceptible to mildew, and if you notice that other plants (house or garden plants, or even trees on streets or in local parks) in your vicinity are showing signs, you should ramp up your efforts accordingly.    

So let's learn how to prevent powdery mildew – before it ever takes hold.

Maintain Your Environment

Another indoor cannabis grow
Are your cannabis plants in the best possible environment? Very important for powdery mildew prevention.

This is basic stuff that every grower should know – but in practice, it can be very hard to get right.

Essentially, ensuring that your environment doesn't get too moist is key to powdery mildew prevention.

High relative humidity and cool-to-moderate temperatures offer the perfect conditions for it to thrive.

Temperature and RH

For indoor growers, one of the biggest problems is the temperature drop at night. Remember, it's all about relative humidity (RH) – how much water the air can hold at certain temperatures.

If you have an air temperature of 77 F and an RH of 50%, then your temperature drops to 60 F, your RH will be at 100% unless you do something to dry the air.

Generally, proper ventilation should deal with this issue, but if not, you may have to use a dehumidifier or a heater.

For outdoor growers in the temperate zones, the riskiest times for getting mildew are in spring and autumn, when it's generally cooler and rainier than summer.

If you're in an area with particularly cool, damp autumns, it's wise to practice light-deprivation techniques and kick off flowering early, so you avoid the worst of the cold and rain.

If you have cool, rainy springs, start your plants off indoors. Autoflowering strains are also ideal for cooler, damper environments.

For outdoor growers in tropical regions – yes, there are plenty of tropical mildew species too, and for that reason, most growers avoid growing in the rainy season!

Give Your Plants Space To Breathe!

Indoor cannabis grow
Your precious plants need space!

This is another important aspect of powdery mildew prevention.

Whatever your environment, you need to ensure that your plants have adequate space between them, and that leaf coverage is not too dense.

Crowded foliage prevents good airflow and provides the perfect, stuffy, moist environment for mildew spores to take hold in hidden corners of your garden! It also blocks sunlight, keeping temperatures lower and preventing antimicrobial UV light from getting through.

Light Distribution

It's essential to ensure that adequate light gets to all above-ground parts of the plant. If you're growing in containers, you may wish to periodically rearrange your plants so that any shaded parts are brought into direct light.

Your plants may also benefit from selective pruning of shaded lower branches and leaves, which are unlikely to develop to their fullest in any case, and can offer the perfect breeding ground for powdery mildew on cannabis plants.

Note – if you are defoliating because you have already noticed powdery mildew spots, MAKE SURE you dispose of the waste properly and wash hands thoroughly before handling cannabis plants again!

So, if you follow these basic guidelines on how to prevent powdery mildew you shouldn't have to worry too much.


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