Pest identification is an important part of becoming a successful cannabis grower. The following is a list of common pests you will encounter. It is important to be able to identify exactly what an insect is when in your grow room or outdoors. It is possible your cannabis are covered in friendly predators, who you do not want to eradicate.

Knowing is half the battle, and the following should well educate you on what pests look like, what they do and how to deal with them.

Most of the following are going to be problems for outdoor growers. A well maintained indoor grow room should never give pests or foreign entities the chance to enter. So an indoor will ideally rarely have to deal with pests - but it can happen. Something to remember as an indoor grower, is to never bring in anything from the outside. Your grow room must be a sterile and clean environment.

Before you proceed, bear in mind that a lot of solutions involve the use of pesticides. It is extremely important to use the correct type, not only for the plant's health, but mainly for yours. ONLY USE PESTICIDES CLEARLY LABELED AS SAFE FOR FOODS. If you don’t you may poison yourself when you smoke or eat your bud.

Ants

Most people know what ants are. They are small, but visible, insects that operate in coordinated colonies. You are likely to see them in large numbers as they attack your cannabis plants. Ants' coordination and teamwork can lead to the fast demolition of cannabis plants in their never ending quest to grow their colony. They will attack and take apart leaves to return to their colony for food, causing leaf discoloration and bite marks around the edge of leaves. Ants are easy to spot due to most people knowing what they are and the numbers they operate in. You are most likely to see them outdoors, but they can appear indoors as well. Ants can be removed with colony killing pesticides, but you have to be very careful using them as a lot are toxic to humans.

Aphids

Aphids are probably the most commonly seen garden pest and the bane of every gardener's world. These are the little buggers you are mostly likely to come across in your time growing marijuana, both indoors and outdoors. These soft-bodied insects are about 1/8 of an inch long and are most commonly either green or yellow, although they can be any color. They also occasionally have wings.

Aphids live off sap from the leaves and stem of your cannabis. They can often be found on the underside of new growth near nodal regions, attacking and stunting growth. Aphids leave behind a foamy waste called honeydew near their feeding sites. They also cause leaves to wilt. Although they are most commonly found in these regions of the plant, they can be anywhere on your cannabis.

They do not move very fast and are often a similar color to the leaves they are on, making them quite hard to spot. You will have to look closely and carefully to make sure. To remove them you can use various pyrethrum based pesticide sprays. You may also consider introducing friendly predators into the environment to control them naturally – this is the preferred method for organic growers. Ladybirds are a good example of a predator that can deal with aphids, you can quite often buy ladybird larvae and breeding kits online should you want to start up your own supply. See our article on friendly predators for more predator information. You can also use soapy deterrents, but this is not generally advised with cannabis as they do not play well with resin.

Caterpillars

The offspring of butterfly and moths, caterpillars can decimate your cannabis crops with their insatiable hunger. The parents themselves are often no harm, but they will lay multiple eggs, often on the underside of leaves that can spell the doom of a marijuana crop. Just one caterpillar can destroy a large cola in a matter of days in its quest for food. Whilst they will eat everything, they are particularity fond of new seedlings. You can tell a caterpillar has been around when huge portions of leaves look like they have been eaten.

The best way to deal with caterpillars is to use caterpillar and larvae replant. This is not only useful for dealing with caterpillars, but also cutworms and other insect larvae.

Deer

Only really affecting outdoor grows (you have to be really unlucky for a deer to find its way into your indoor grow room!), deer will decimate cannabis plants in their entirety. Electric fences do not keep them away, the only real way to ensure they keep their distance is to buy the urine of a predator (from a hunting shop). Spraying this around the grow site (not actually on the cannabis itself), has proven to be highly successful in keeping these beasts away.

Domestic Pets

Domestic Pets, such as cats and dogs, can be a mixed blessing. Outdoors, with enough room for them to roam freely, they should pay minimal attention to your cannabis crops whilst dissuading rodents and deer from getting too close. However, indoors they can raise havoc. Cats, and kittens especially, will use the thick stems of an adult cannabis plant as a scratching post, dogs are likely to chew on them, and both can potentially knock them over. The best course of action is to keep them out of your grow room!

Gnats

Gnats are small flying insects that resemble mosquitoes in look. They are pests that cause the same symptoms as aphids, as they to suck the sap from stems and leaves. They do not cause as much damage as aphids, but are still a problem nonetheless if left to their own devices. The best way to deal with gnats is by using a suitable pyrethrum based pesticide. You could also use sticky fly paper, hanging in your grow area, but you run the risk of killing friendly predators by doing so.

Grasshoppers

When found in small numbers, grasshoppers can be seen as tourists. They pose very little risk to your cannabis grow. Grasshoppers are often fairly large, green insects that have long legs for jumping. They are characterized by the high pitch clicking noise that the males make, and will often move on by themselves without human intervention. It is rare to find them in an indoor grow room. If they seem to be hanging about then you can hand pick them off your plants and move them on yourself. There are not likely to be many, they do not often swarm.

The only time grasshoppers are going to be a problem is when faced with a swarm (or plague) of locust. This is a member of the grasshopper family that travels in the billions. If you are unfortunate enough to live in an area where they are known to roam, then the only thing you can do is take cutting from your plants and move on. There is no way to combat this hell sent menace. Fortunately for most people, locust are not a common occurrence, and all but nonexistent in Europe.

Groundhogs

Ground hogs are medium sized rodents often found in North America and Canada. They will not be a problem if you grow indoors. Groundhogs are a burrowing rodent that will eat the leaves of your cannabis plants. If you find any signs of groundhogs around your grow, apply dry chlorine to the area of entry, this should keep them away.

Mealy Bugs

These look like armored versions of aphids. They attack your cannabis in the same way as aphids and can be dealt with using the same methods.

Rabbits

Another mammal that you have to be wary of when growing outdoors. Rabbits are burrowing animals that will eat the entire cannabis plant. They work quickly and can decimate a crop in no time. They will stay away from cats and dogs (who in turn present their own problems). Rabbits can also be kept away with predator urine, which can be obtained from hunting shops. Once a rabbit has found a patch to eat at, it can be hard to dissuade them from returning until there is nothing left. Keep a vigilant eye out.

Scale

Scale is an insect closely related to the aphid. They start off mobile, but quickly hunker down in a permanent location, becoming immobile. When they are in this state they will have a tenacious grip on your cannabis plants. They tap into the marijuana, feeding off its sap. If you catch them before they hunker down, you can hand pick them off your crop. Otherwise, you can use a scouring pad to remove them, or spray them with dormant oil. Dormant oil is an organic pest control found in most gardening centers. You will want to be careful should you decide to scrape your cannabis with a scouring pad, as it is very easy to destroy cannabinoid-containing trichomes. It should also be noted that scale spread mold, so you will want to deal with them as fast as you possibly can, lest they cause you more problems.

Snails and Slugs

Another common garden pest, slugs and snails are mollusks that come in a range of sizes. They are relatively slow moving, but will quite happily eat their way through your cannabis crop. You can tell when slugs and snails have been about because they leave behind tell tale slime trails in their wake. They can be hand picked when you see them, but the best method of preserving your cannabis is deterrence. There are a few methods of preventing slugs and snails reaching your crops, you can use shop bought slug pellets, put rings of salt around your plants, put copper tape around pots, or place beer traps around your grow. If you use salt, put it a good distance away from any cannabis plants, you don’t want salt being watered into the ground and killing your plants. We have always found that placing a bowl of beer near your plants is a good method of dealing with these pests. They will be drawn to the beer, entering the bowl and, rather stupidly, drowning. Try a few methods and do what you find works best for you.

Spider Mites

Spider mites are a disaster waiting to happen. They are one of the main reasons you NEVER bring an outside plant into an indoor grow room. Spider mites are a bane to cannabis plants, who are extremely vulnerable to them. Always keep a bottle of spider mite pesticide on hand – they can decimate a crop in a matter of days.

Spider mites are tiny little bugs that are quite hard t see individually. What gives them away is that they often congregate into large numbers where they feed, making them easily identifiable. They also weave webs around affected areas, so you should be able to tell when things are getting bad. They, much like aphids, tap into the cannabis plant and drink it dry. The problem is that they come in such vast numbers that your cannabis plants don’t have a chance to resist; and like aphids, they are extremely common.

Termites

Termites, whilst not too common, can pose a real danger to your crop - even if it is just a few of them. Like ants, termites are a colony insects that operate collectively as a hive. They are notoriously known for eating wood, but they can rip through cannabis in a matter of days, they will not discriminate – especially when you consider that cannabis stems are high in wood-like substances.

If you are indoors and have termites, your cannabis crop is going to be the least of your worries. If you are outdoors then a good way to keep termites away is to over water the area surrounding your cannabis. They do not like water and are unlikely to cross sodden soil. You can also buy commercial products, but refrain, there are not any that we know of that are suitable for use on plants, especially plants that will later be consumed by humans. The best method is to find the nest and drown them at the source.

Thrips

Thrips are little, slender insects that develop wings in the later stages of their lives. They tend to attack leaves and flowering parts of the cannabis plant. You can often tell where they have been as part of the flower may start to turn silvery or crumble apart. If you are outdoors than an infestation is unlikely to last long as thrips have a lot of natural predators. However, indoors you will need to use a sage thrip pesticide, or one that is pyrethrum based.

Whitefly

Whitefly, the scourge of the allotment grower, is well known for feasting on growing vegetables. They will also quite happily feast on your cannabis plants given the chance too. Whiteflies are roughly 4mm in size but can vary depending on species. They have way white wings that they use to fly short distances, hence the name. Whitefly feed by sucking the juices from you cannabis plant and are deadly in large numbers. They make quite a distinct buzzing noise when in large groups, so you should be able to identify them quite easily.
Whitefly leave behind honeydew in their wake, making your cannabis vulnerable to mold. They have a lot of natural predators, but can also be dealt with by using soapy pesticides – be careful with these though as they destroy trichomes. Whiteflies are very common, so keep an eye out.

Woodchucks

Much like the groundhog, a woodchuck is a small rodent that will feast on a cannabis crop. Instead of going for leaves like groundhogs do, woodchucks will target stems. This makes them much more deadly as they can fell your crop quite quickly. A good way to prevent and dissuade them is to use predator urine from hunting shops, or create a mesh fence around the grow area, stopping them from entering.