The broad mite, or polyphagotarsonemus latus, may have escaped the lists of common pests in some well-known grow guides, but this microscopic pest is quietly invading more and more cannabis gardens across the country.
At less than half the length of a grain of salt, you need at least 60 times magnification to see one. This also a great level to view trichomes up close for fine-tuning harvest time.
Broad mites lay eggs on the underside of leaves and dwell there and in crevices around the plant. They prefer feeding on newer leaves, and their toxic saliva causes malformation and stunts the growth of young plants. The effects can resemble a nutrient deficiency or pH imbalance, so always keep a microscope handy to check for these pests before changing anything else.
Keeping a clean and closed growroom and dusting with diatomaceous earth (for indoor or out) can help prevent pest invasions. Spraying with essential oil containing eucalyptol (eucalyptus and rosemary) can also help prevent insects from invading small growrooms. It might even mask some of the smell if it’s getting too loud.
If you’ve already been infested, and you’re still in the vegetative phase, a miticide containing abamectin is what most people recommend for broad mites. Abamectin is relatively safe but should be used with caution, and definitely think twice about using it outdoors. It degrades quickly in soil and doesn’t easily leach into ground water, but it is still highly toxic to aquatic life. Abamectin also kills bees, and they already have enough problems on their hands.
For the flowering stage, insecticidal soap and other organic insecticides can help quell a mite population. Hot temperatures will kill broad mites too. Soaking a whole garden’s worth of plants for 15 minutes in hot water might not be a feasible solution for everybody, but if you have the ability, turn the temperature in your growroom up to 115 °F for 20 minutes with some circulation fans. Repeating this weekly until the mites are gone might be the easiest way to kill a broad mite infestation in a small setup.
For larger grow-ops and for outdoors, predatory mites can also help you avoid the use of toxic chemicals against the broad mite.