Professional Marijuana Grower March-April 2018 Issue | Page 28

stagnant environment, which is depleted of much of its dissolved oxygen content, is perfect for pythium. Put another way, overwatering is a common cause of pythium. Pythium is also common in hydroponic systems that have an insufficient amount of dissolved oxygen in the nutrient solution. The first signs of pythium can mimic a nitrogen defi- ciency, with the lower leaves turning yellow. Eventually these leaves may also have brown spots, again mim- icking other nutrient deficiencies. The entire marijuana plant will ultimately appear wilted and, in extreme cases, will die. Upon inspection of the roots, a marijua- na grower can quickly identify pythium. Brown, slimy roots are a dead giveaway that pythium lurks in the grow room. Pythium Prevention and Treatment If caught early enough it is possible to recover from a pythium attack. There are many oxygen boosting additives available in hydroponic stores. Diluted hy- drogen peroxide is one way growers can increase the dissolved oxygen content, but it should be used spar- ingly. A hydroponic grower must maintain a consistent temperature of 65-70 degrees F in the reservoir. When the temperature of the water rises, the dissolved oxygen content decreased. Pythium is notorious for showing up in hydroponic systems when the water temperature 28 • Professional Marijuana Grower reaches above 75 degrees F. Hydroponic gardeners can use a water chiller to maintain temperatures in the desired range. Powdery Mildew Powdery mildew is another common pathogen that causes trouble for cannabis growers. Powdery mildew spreads quickly and can destroy a healthy garden in a matter of days. Powdery mildew can be detected by a white, powdery coating on leaves and shoot tips. This fungus spreads fast via airborne spores. Powdery Mildew Prevention and Treatment Powdery mildew is a fungus that can only thrive when the atmospheric conditions are right. Keeping temperature and humidity levels in check are the best preventative measure against powdery mildew. Air filtration devices on the ventilation system’s intakes are also a good way to reduce the likelihood of powdery mildew. If powdery mildew is contracted, sulfur burners or organic-based fungicides can be effective during the vegetative and early stages of flowering. Treating a powdery mildew outbreak in the late stages of flower- ing can be very difficult for a cannabis grower. Most of the time, when contracted in the later stages of flower- March/April 2018