Cannabis indica is a very enjoyable plant. Not only for humans. Pests, unfortunately, adore it too.
One of the worse, difficult to control things that could happen to your cannabis plantation, is an invasion of some pests that could eventually, if untreated, damage and kill your plants. Be it small, white spiders, leaving tiny webs near the plants tops, or common ants - presence of any kind of living creatures other than cannabis itself (and its symbiotical bacteria and funghi) is definitely not desired in your grow area.
Another grower's nightmare are various diseases. Your plant's leaves are turning brownish, yellowish, twist and turn, fall or dry without visible reason? It could be either overdose or lack of some sort of nutrient, or a plant disease.
In both cases it is easier to prevent than to cure. Dedicated protective chemicals exist, available both in form of fluid and spray, that could make the environment more hostile for all sort of unwelcomed guests. General plant enhancer - as with vitamins for human - make it more resistant versus all sort of diseases. Another important thing is to remove all dead matter, keep the grow area clean, using quality soil and trying not to introduce any filth from the outside world. Once the situation gets critical, you can still try saving your cannabis plantation using specialised treatment products. It is important not to use any of these shortly before harvest, as some of these substances might be harmful if ingested. Always read the label carefully!