Powdery Mildew

What is powdery mildew? 

Powdery mildew is a fungal disease that can affect many plants including your favorite plants.  If left untreated, at best it will significantly reduce yields and at worst, it will destroy your crop. 

What causes powdery mildew? 

Powdery mildew is caused by many different species of fungi that flourish in environments with high humidity and moderate temperatures.  Powdery mildew spores can be transported to your plants on the wind, through air ventilation systems, from pets and any other living thing that moves (including yourself).  Indoor grow rooms and greenhouses are most susceptible to the disease given they are the hardest environments to control. 

What does powdery mildew look like? 

Powdery mildew is one of the easier plant diseases to identify, as its symptoms are very obvious.  Infected plants show white powdery spots / blotches on the leaves and stems.  Typically, the lower leaves are most affected, however the mildew can show up anywhere on the plant. 

How do I prevent powdery mildew? 

You can greatly minimise the risk of getting powdery mildew by maintaining temperatures for seedlings and vegetative plants between 22-30C/72-85F and flowering plants between 20-26C/68-79F, while maintaining humidity levels for seedlings and vegetative plants between 50-70% and flowering plants between 40-50%.  Overcrowding grow spaces where plants leaves are touching needs to be checked.  Try to water plants earlier in the light cycle as humidity rises considerably in the dark.  Regular pruning of larger lower unlit leaves is recommended.  It also helps to know if the region you are growing in is particularly susceptible to PM and if so, try to pick strains that are more resistant to the disease and try to stay on the lower side of the recommended humidity levels previously mentioned.  It also pays to maintain good airflow across the bottom of the plants using fans etc.  UVC lights can be installed in air ducts to control circulating or incoming spores.  Amino acid chelated calcium, as contained in Dutch Master’s Commercial Edition Cal-Mag, along with silicon found in Commercial Edition Sila-Guard will also provide great protection/resistance to powdery mildew as they bolster/strengthen the plants own cellular structure and immune system against many forms of pathogenic attacks including powdery mildew, bud rot and even root rot and is definitely a worthwhile investment! 

How do I treat powdery mildew effectively? 

As mentioned previously, a good calcium and silicon additive is your first line of defense.  Sulfur burners are effective, however be very careful with use around humans and animals and beware of overdosing the plants as you can do serious damage.  Customers have also reported dipping/spraying clones/plants with a combination of Commercial Edition Zone and Saturator.  Clones can be fully dipped into a bucket (not including the media - rockwool etc) using Zone @ 5-10mL/gallon of water and Saturator @ 20mL/gallon of water.  This should help knock down potential nasty leaf borne pathogens like powdery mildew.  Adult plants can be sprayed using Zone @ 10mL/gallon of water and Saturator @ 20mL/gallon of water to help control outbreaks of powdery mildew.  NOTE: Always spot test any of the above applications on 1 plant/clone prior.  Some strains may be more sensitive than others.  Negative effects from too much Zone usage will show as a brown necrotic (dead) splotch on the leaves, however this symptom will stop with reducing the use of Zone.  There are fungicides you can also purchase, however be sure of withholding periods and compatibility with a plant sold for human consumption.