It is possible to set up and cultivate medicinal marijuana indoors and completely avoid common indoor cropping problems without ever resorting to sprays or other controls. Don't ever think you should “get used to” problems in your garden.
The issues usually come from the outside (cuttings from outside sources are an easy entry point) and are amplified by an unbalanced environment. The good news is that by following simple environmental guidelines most issues can be controlled easily or eliminated all together without using potentially harmful substances in the garden.
A healthy exchange of air flow is essential for crop health. Whether your grow with an IN/OUT exhaust set-up or a sealed and climate-controlled growing environment, the air should never be still. Besides keeping the air moving with fans, grow room air should pass through an activated carbon or HEPA filter when being introduced from outside or continuously re-circulated in an enclosed environment. A pre-filter makes filters work better and lengthens work life, and cleaning away dust from the pre-filter is always good maintenance.
Too strong of an air flow coupled with warmer and drier-than-optimal conditions will create and compound a wide array of problems, especially insects like spider mites. Soft and weak plant tissue and optimal breeding (hot and dry) conditions for spider mites can produce a new generation of these aggressive and sometimes hard-to-treat pests in as little as five days.
Plants like some temperature difference in light-to-dark cycles; in a fine-tuned growing operation this can be varied to improve cannabis growth and bud quality. However, marijuana plants will not fare well when they receive drastic swings or extremes. A similar principle also applies to relative humidity levels in the garden.
Extremes or rapid changes in temps will create stressed plants with a low yield, and plants that are far more susceptible to pathogens.
Just like human beings, when healthy and in good condition, plants are able to better resist all the stuff around them that can potentially make them sick.
If you had crop problems in your last harvest, thoroughly clean your growing area and all equipment and tools. Let the grow room sit empty for a few days after scrubbing and sterilizing -- make sure there is no plant material left where problems can hide and infect the next crop.
Adding CO2 (carbon dioxide) enrichment helps create healthier plants that grow faster: Experienced growers find that boosted plants seem to encounter fewer problems.
Maintain temperatures between 65 and 80 degrees Fahrenheit, and relative humidity in the 45 to 65 percent range. Novice growers often don't realize how devastating excessively hot and dry conditions can be to their crop until it's too late.
If you spot a problem, do not wait to treat it. There are lots of resources for making the right diagnosis. When treated early, most issues like insects or diseases can be safely eliminated.
Ultimately, if you see a problem, remember that it is a symptom: After treating, figure out what's not in sync in the environment and adjust accordingly.