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Common Cannabis Pests - How To Spot, Treat, and Prevent

Whether you’re looking into expanding your crop or you’re entering the growing industry for the first time, it’s essential to know how to get the best yield. One of the most devastating things that can happen to your marijuana fields is an infestation from common cannabis pests. These insects and other creatures can quickly decimate your plants and harm your yield if you don’t take steps for cannabis pest control.

Originally posted on 2 February 2016, Updated on 2 May 2020

Types of Cannabis Pests

Many of these insects will eat the plant leaves or roots, taking the nutrients away from the plant so that it dies. Plants that do not die can have significant reduction of their yield or quality of cannabis buds produced. However, it isn't difficult to identify the symptoms and prevent the common cannabis pests before they destroy your grow.  In this section, we will look at the most common cannabis pests and and show you exactly what they are, how to spot them, and how to prevent and control the pests.

Spider Mites

Marijuana plant plagued with spider mites

Spider mites aren’t spiders, but they are related to spiders as part of the mite family. These mites can be difficult to eradicate. Their tiny mouths have sharp teeth that pierce plant cells and suck out the matter inside. They are very tiny and look like tiny black dots on the underside of the leaves. You’ll also know you have spider mites when yellow, white, or orange spots begin to show up on the top of the leaves. If the infestation isn’t caught in the beginning stages, a webbing will begin to appear between leaves.

Spider mites are less common when using hydroponics but can affect your plants no matter where they are grown. Spider mites must be killed, and Azamax is a common cannabis pest control killer.

Aphids

Cannabis pest aphids on cannabis leaf underside

Aphids often resemble tiny flies with wings and pierce through leaf matter to suck out the contents inside. Aphids also live in colonies and cluster together on the leaves causing significant damage quickly. They also leave a sticky residue behind, which attracts sooty mold and turn leaves black and unsafe to consume.They can be dark or pale in multiple colors, and are found on the underside of the leaves. Most aphids that attack marijuana plants are green and leaf-shaped.

Aphids can be sprayed off of the plants using a power sprayer. Heavily infested plants may need to have leaves and stems pruned. Growers can also use insecticidal soap to kill aphid colonies. Another option is to use Neem oil extract to keep the insects away.

Fungus Gnats

Cannabis pest gnats on green leaf

Fungus gnats are a nuisance to the soil cannabis plants grow in, and the larva will damage plant roots as they eat through the biological materials in the soil. They can be common indoors and out.

Fungus gnats are dark brown or black and are usually found buzzing about the soil of marijuana plants as their larva grows in the dirt. They often begin to appear when the soil has been too saturated for too long. Fungus gnats are only 2mm long but are easy to spot as they fly.

To prevent fungus gnats, you must focus on water management and not overwater the soil. Sticky cards can be used to attract and kill many of the gnats or use Neem oil, which prevents many types of cannabis pests. Diatomaceous earth is a powder that can be applied to the soil to improve soil health as well.

White Flies

Cannabis pest whitefly on the leaf

Whiteflies eat the cannabis leaves and suck the nutrients from the veins of the leaves. They look like small moths that fly around cannabis plants and hang out on the underside of leaves. They also lay white eggs that stick to the leaves and are hard to remove.

Insecticidal soaps can be sprayed onto the plants for cannabis pest control. Neem oil can also be used for prevention, but care must be taken not to spray the Neem oil on the buds as the taste will become bitter. There are also other organic pesticides such as Spinosad that can be used to eradicate cannabis pests.

Thrips

Cannabis Pest Thrips on leaf

Thrips bite the marijuana leaves and suck out the nutrients leaving behind shiny metallic-looking spots. The leaves will eventually lose enough nutrients that they begin to die.

They are tiny insects that move fast and look like pale worms as larvae but can have dark or gold wings as adults. The insects are often seen on the leaves, but growers will also see the shiny spots left behind on the front side of the leaves.

Like many cannabis pests, insecticidal soaps, and organic cannabis pest killers can be effective at treating and getting rid of thrips. Neem oil can be sprayed on the plants to prevent thrips from returning as the oil is bitter and aversive to the insects.

Caterpillars

Cannabis Pest Green Caterpillar - Hypena Scabra on a cannabis leaf

Caterpillars crawl across cannabis leaves and munch their way right through, leaving large holes in the leaves. Caterpillar poop can be seen on leaves, and the caterpillars themselves are easy to spot and often significant. Some of them are brightly colored, hairy, and can be fast-moving. They are most commonly seen in outdoor operations.

Caterpillars can be eradicated with a biological insecticide that kills the larva and starves out the adult caterpillars without harming other insects such as pollinators. Caterpillar sprays can also help with other cannabis pest control.

Leaf Miners

Cannabis pest leaf miner on a green leaf

Leaf miners live inside of the leaves and mine tunnels as they eat away the inner plant material. They are not a specific insect but refer to the larva of any of the insects that can make their way inside of the leaves, including flies, beetles, and moths.  They leave behind long, discolored trails that appear on the leaves.

To be rid of leaf miners, growers must remove the affected leaves since the bugs are living inside. Spinosad products can also be used to kill the insects as they eat the leaves. Neem oil and caterpillar spray are natural ways of preventing and treating leaf miners.

Slugs and Snails

Cannabis pest slug on cannabis leaf underside

Snails and slugs eat the entire leaf of the cannabis plants, killing the leaves. They leave behind a trail of slime and eat big chunks from the leaves of marijuana plants. Holes in the leaves will also have scalloped edges and can be confused with caterpillar damage. They are most likely to come out at night when temperatures are cooler and are most common in crops grown outdoors.

Getting rid of slugs and snails is hard, but one thing growers can do is allow frogs, beetles, and toads to remain in their outdoor fields as they eat slugs and snails. Physical barriers using eggshells, lime, or diatomaceous earth can also prevent slugs and snails from reaching the plants.

More Measures of Prevention

The best way to control your cannabis pests is to prevent them from happening in the first place. If you are growing your plants indoors, make sure your grow room is completely sealed as most of these pests come from outside. You should also focus on quality of your grow operations. Grow from seeds, not clones, whenever possible and if you do use clone seeds, you should thoroughly check for pests before planting. Growers should also buy high-quality soil and check the soil for signs of pests before using it. Growers can also sterilize the soil before use.

One of the best ways to prevent pests organically, and also helps with soil quality is to plant more than just marijuana. Companion plants such as basil and garlic can be planted around your marijuana crops to help with cannabis pest control. Many cannabis pests do not like the smell or taste of basil or garlic and these plants make useful boundaries to keep insects away.  You can also introduce natural predators in your grow spaces such as toads, frogs, ladybugs, and birds. These animals eat insects and can often rid your crops of more insects than sticky pads can if you are growing organically.

Summary

Nearly all cannabis pests are most common when marijuana is being grown outdoors. Most of the preventive methods used in cannabis pest control are very useful outdoors, including all of the pest control sprays, though they are effective indoors as well. Sprays such as insecticides are also very fast-acting and often the best way to completely rid pests from your fields.

The best way to prevent pests from decimating your cannabis plants, however, is to grow indoors and keep your buildings sealed against pests whenever possible.

MSNL Team MSNL Team / 2nd June 2020

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