Pest and Mildew Management for Cannabis Cultivation Sites
Marijuana pest management will be among the most annoying and vexing problems associated with running an indoor marijuana cultivation business. As usual, prevention is a much better option than perpetual treatment of an existing infestation, but just about every garden eventually gets infected, and this usually happens from workers coming from other infected gardens, or infected clones being carelessly brought in. Some problems, such as powdery mildew or aphids, can come from air intake and cracks in the building.
Several steps can be taken to minimize the risk of pests being brought into the site, including positive-pressure entry ways with locker rooms between the entrance and the plant cultivation area, where all workers must shower and change clothes before entering the grow room. Medium and large-scale operations should build their sites with this taken into account.
If marijuana clones must be brought into the site, they should have a special quarantine room with great lighting, where the clones sit for 2 weeks before getting integrated into the main plant area. 10-40x magnifiers should be used on a daily basis to examine the clones and the surface of the medium to look for small moving objects. If possible, start from seed to avoid this problem.
Workers should be incentivized to look for bugs by giving them “bug find” bonuses. The sooner an infestation is found, the easier it is to contain. Certain bugs are common and easy to handle, such as fungus gnats or caterpillars, whereas others will change everything about daily operations and company profit for some period of time, until they are controlled or eliminated. These include mites of all kinds, some types of aphids, and also powdery mildew, which is not an insect, but it does fall under the “pest” category as a living infection that commonly afflicts marijuana plants.
Each type of infestation or infection has its own treatment regimen that must be swiftly and comprehensively applied in order to work properly. Sprayers that apply biological or chemical controls should use small micron-sized water particles that essentially humidify the room with the treatment substance, such that complete coverage happens without question. Beyond that, biological controls are always best for consumable products, and sometimes they work better as well. This is true, for example, in the case of Spinosad for thrips, or BTi and BTk for gnats and caterpillars.
Spider mites, broad mites, and russet mites are the biggest challenges for indoor growers. Once you have these bugs, it’s easy to get stuck in a mode of constant treatment and application of toxic, and sometimes illegal, chemicals. No one has yet found or invented an easy solution to deal with marijuana mite infestations. Hopefully a non-toxic biological solution will present itself in the near future, but for now, the options include heat treatments, horticultural oils, essential oils, diatomaceous earth, micronized sulphur, and OMRI-listed sprays such as Green Clean, Nuke ‘Em, Azadirachtin, Pyrethrum, as well as various combinations of all of them.
No satisfying pest treatments exist for flowering plants past the 2nd week of the 12/12 light cycle. At this point in the plant’s development, even Safer’s Soap can harm the fragile white hairs that begin to emerge from the plant nodes, and other sprays that might not cause the white hairs to suffer might have a residual effect on the finished product, either in terms of taste or unhealthy residues.
Financially desperate growers are notorious for using toxic chemicals such as Avid (abamectin) and Floramite to save their crops from complete failure. This is because mite infestations can emerge and dominate a grow room very quickly, and growers just can’t come to terms with taking a complete loss on the crop, so they do whatever they can to salvage it. For clones and mother plants, chemicals like these aren’t such a problem for the end consumer since they have much more time to degrade before end-user consumption. Each licensed facility must work within the guidelines of the state, and each state publishes a list of acceptable pesticides and banned cannabis pesticides. Most of these substances require regular foliar re-application.