Ah, the advantages of growing your strain of choice inside. The upside seems so obvious: access to the garden 24/7, protection against the forces of Mother Nature, and practically no chance some fur-bearing creature will break in and destroy your garden.
Sounds like the ideal growing situation, so what could possibly go wrong? In truth, lots. Indoors doesn’t mean invincible.
While growing inside gives you control and protection from the elements, Newton’s 3rd Law can dull that edge with an equal and opposite reaction. These same indoor perquisites can also prove problematic. Without rainfall and wind there is nothing to help wash away the little parasites that make their way into your growroom. Beneficial insects like ladybugs and parasitoid wasps also won’t be around to help.
What’s more, in an enclosed environment like a house or greenhouse, many pest insects can build up an immunity to pesticides very quickly. The best way to keep your plants free of unwanted pest colonies is to be vigilant and practice good clean habits in your grow space.
Essentially, there are five pest insects appearing on the marijuana marquis of undesirable garden guests. Those names include thrips, fungus gnats, aphids, and whiteflies, with the headliner being spider mites. These seemingly ubiquitous little sap suckers are the bane of an indoor grower’s existence and need to be dealt with immediately upon detection. Let’s begin with the dreaded spider mite.
The twospotted spider mite (Tetranychus urticae Koch), which seems to be the most prevalent of spider mites, infests some 200 species of garden plants both indoors and out. Be it greenhouse, warehouse, or basement, they will find your Eden. Their specialized sharp mouths penetrate the skin of the leaf and suck the sap from it, leaving a skeleton in its stead and photosynthesis impossible in severe infestations.
At 1/50 of an inch long, these tiny terrors can be hard to spot with the naked eye, so a good magnifying glass is needed. Small as they are, they still leave telltale signs of their presence if you know what to look for.
Early indicators are the appearance of stippling (small dots) on the underside of the leaves. They also weave a gossamer thin webbing on the plant, hence the name. These cobwebs become the highway on which they travel from leaf to leaf and plant to plant. If left unchecked, your plant can become mummified in a short period of time. This is why you should check your plants early and often, before an infestation takes hold.
To scan for unseen mites, take a piece of white paper and place it below your plant. Now give the plant a little shake. Look for moving mites, their eggs, or larvae that have fallen onto the paper. Specks of black frass (fecal matter) may appear as well. If you detect spider mites, you need to take action.
Eradicating Spider Mites
Always isolate any infected plant from the others. Insecticidal soap or horticultural oils can be applied to the leaves to kill the mites. To make your own soap, simply combine two teaspoons of mild dish soap with a gallon of warm water. Stir it up and use a small brush or atomizer to apply to both sides of the leaves.
Mites prefer warm, dry climates. As a preventive measure, mist your plants (leaf undersides too) to create a higher degree of humidity that will help thwart their advance. A moist grow medium will also help. Rinsing your plants afterward with cool water will help dislodge the mites. Do this outside if feasible to avoid them running to another plant once rinsed off. Treatment once a week is recommended.
Thrips are slender, winged pests that dine on your plants in much the same way as mites. They pierce the leaf and suck out its essential sap. Treating thrips can be tricky, however. Having a control strategy that incorporates good cultural practices like regular inspections and effective pruning to remove injured areas of the plant can forestall or even derail an invasion.
Clean up the infected debris and promptly remove it from your grow areas. Applying neem oil and/or insecticidal soap are quite efficacious in controlling thrips. Neem oil is a vegetable oil extracted by pressing the seeds and fruits of the neem tree of India. Dish soap works well, but only if there are all-natural products available.
In their defense, there are some good thrips that prey on plant-eating bugs. If you have the time and patience to differentiate them, you can apply the live-and-let-live approach. Most growers don’t.
Whiteflies bring with them the same devastation as the others mentioned here and in the same way. White and winged, they are yet another of the sap-sucking plant predators that love their greens. Aside from seeing the insects themselves, evidence of whiteflies on your plants can be the sticky film they leave behind on the leaf. Other indicators may be shriveled or yellowing leaves.
The real damage, however, is done by the nymphs — their immature offspring. They are wingless, legless, and, for the most part, motionless. They are content to munch away at your plant while awaiting their full development. In a perfect world, ridding your plants of whiteflies would be done by predatory insects like green lacewings, ladybugs, big-eyed bugs, and others.
Eradication of Whiteflies
If you don't have a stash of those beneficial bugs handy you’ll have to take action yourself. This can be done by pruning yellowed or damaged leaves, picking the flies off manually, and by wiping the leaves with a mild soap and water solution. Of course, there is the always the old standby, neem oil.
Read also: The Best Pest Control for Cannabis
Aphids are nasty little creatures that, like their brethren, drain the life-giving fluid from a plant’s leaves. All these little buggers do primarily the same thing. They damage, or, if unchecked, kill your plants. Aphids graze in groups which increases their devastation.
Aside from the actual damage caused by their feeding, they also leave behind a sticky exudate called honeydew that can encourage a soot-colored mold fungus to form on the residue.
Aphids also carry viruses with them that can be transferred from plant to plant. Some aphid species inject a toxin into the plant causing the leaves to yellow and distort in shape.
Eradication of Aphids
Aphids are quite easy to spot and controlling them can be as simple as brushing them off by hand or rinsing them off with a stream of water. Careful with the pressure though. You don’t want to damage your plant in an effort to help it. Applying a one to two percentage of neem or canola oil to water works best. This method smothers them. As always, be sure to target the underside of the leaves. This application will need to be repeated daily until the aphids are gone.
Fungus gnats are tiny, winged insects that love moist, organically-rich soil like compost or potting soil and decaying vegetable matter. These gnats are probably the least damaging of the five pests listed here but still can be devastating to a plant. They don’t really bite or eat the plants leaves, but the larvae are born in the soil, and, being underground, go undetected.
These little devils dine on the roots of the plant, so in large numbers they can be a serious problem causing root damage and stunted growth, especially in younger plants.
Eradicating Fungus Gnats
Purchase and use only potting mix or soil that has been pasteurized. Since they thrive in moisture-rich conditions, keep your grow area dry. Clean up water spills and let the top of the soil dry out before watering. Improve the drainage of your pots by decreasing the amount of perlite or by adding sand to more clayey soil. Use sticky traps. Yellow sticky traps are great against flying insects like fungus gnats and whiteflies. Tip: the traps can be cut into smaller pieces and put on sticks, so you can place them into separate pots.
By following these simple steps of prevention and taking proactive measures, you’ll help ensure this traveling troupe of trouble won’t be attacking your cannabis plants any time soon.