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Pest control for cannabis growing without chemicals

For decades, certain growers have been successfully growing high-yielding, healthy crops without the use of chemicals for pest management. This is hard to believe for most growers who have attempted chemical-free pest control in grow rooms. It doesn’t take long for an unnoticed hot-spot of pests to overwhelm the crop a few days later. But every pest has a predator and eliminating the use of chemicals is possible with the proper use of quality beneficial insects. Healthy cannabis plant


To minimize cost and maintain control, working preventatively is essential. At any given time, a pest is making its way into the crop and will multiply exponentially if there are no predators present. No matter what method of blocking their entrance you try, they’re still getting in through the ducts, living in the bag of soil you just bought, and navigating the cracks in the floor and baseboards. Here are some key preventative steps:
  • Cover your bases by introducing a small number of predators for each of the major pests on a regular basis.
  • Place sticky traps at different heights throughout the crop and inspect them daily. Try some right at floor level and some near the tops and see what kind of critters show up. Put a few drops of fresh vanilla or almond extract on a cotton-ball and stick it to the trap to increase the luring.
  • Plant a yellow marigold and position it near the entranceway or air ducts to attract incoming thrips.
  • Plant bush beans throughout the crop. They are a magnet for spider mite and spider mite damage is easily visible on the foliage.
  • Scout the entire crop regularly with your magnifying glass. Get to know the microscopic world in your crop and you will learn to recognize the warning signs of increasing pest pressure.

Plant Health

Plant health is critical for slowing pests down. When marijuana is grown indoors, it is out of its natural habitat and in a state of stress. This attracts pests like no other. Do your best to mimic the natural habitat by fine-tuning the humidity, watering carefully, and keeping a nice air flow throughout the crop. The best resistance to disease is the immune system of a healthy plant. Marijuana plant with whitefly

Outdoor Crops

Unlike indoor growing where pest ingress is physically limited, you’re completely at the mercy of whatever nature throws at you when growing outdoors. This makes it even more important to keep the chemicals out of the crop. With chemical sprays having less and less effect on pests every day, you’re taking a big risk by introducing them to your crop. This is going to kill the natural predators that have come to your crop after sensing the pest pressure, which is going to lead to a severe pest infestation with no way to control it. That being said, your aim should be to maintain a healthy environment for the plants and the local natural predators. In most situations you get a bit of pest damage and not long after you have noticed it, natural predators are already knocking down the population. Do not take away from the natural cycle. Plants get pests and pests get predators. There is a whole “web of life” which the grower must embrace to have healthy crops season after season. To combat the lag-time between the pests and the predator, introduce a small amount of predators periodically so they can pounce on incoming pests.

Purchasing and Applying the Predators

The critical factor in purchasing predators is their health. Like animals in a zoo in the wrong climate, stress level, activity, reproduction, and health is severely impaired. This is why the predators should never be exposed to temperatures below 46F (8C). It is essential to purchase predators that are fresh from their production, never stored and never starved. If you buy predators that are in a giant bucket that have been sitting on a shelf, you just wasted your money. This is the challenge of the Biocontrol industry because it means that the grower must place an order when they have scouted pest pressure and the producer must ship it immediately fresh out of the production facility, also ensuring it never goes below 46F during shipment. Every effort must be made to limit the amount of time between the production facility and the crop to ensure healthy predators do the job right. Make sure you know where your product is coming from and the conditions it will experience en route. Release them into your crop immediately. Depending on the species, application rates and methods vary. Your supplier will tell you how to use them properly. With some products, you will need to sprinkle the media carrying the predators throughout the crop. Others, you will simply need to open the lid and they will begin the hunt immediately. I stress again, the predators must be fresh and never exposed to temperatures below 46F.

Major Pests and Ideal Predators

Spider mite: Introduce the predatory mite A. fallacis. Fallacis is a generalist predator and will spread itself throughout the crop. If a hot-spot breaks out, apply P. persimilis. Persimilis excel on spider mite webbing and quickly knocks down hot spots. Introduce the predatory beetle S. punctillum (Stethorus) for added control. Stethorus uses its flying ability and sharp senses to locate any new spider mite hot spots before you will. Fallacis attacking spider miteThrips: Introduce the predatory mite A. cucumeris. Cucumeris is an effective thrips predator and generalist mite. Apply them throughout the crop but especially to the marigold you’re using as thrips bate. Fungus gnats: Introduce the soil-dwelling mite S. scimitus (Stratiolaelaps) or G. gillespiei (Gaeolaelaps) to the soil and cracks or penetrations in the floor. Stratiolaelaps will feed on fungus gnats, flower thrips, spider mite in diapause, and more. Stratiolaelaps eating a root weevilIf you have moist conditions introduce the rove beetle D. coriaria (Atheta). Atheta will go wherever their prey is located, whether it’s down the floor drains or at the very tops of the plants. Rove beetle attacking pestWhitefly: Introduce E. formosa (Encarsia), a parasitic wasp. Regular introductions of Encarsia will prevent whitefly numbers from increasing. Introduce D. catalinae (Delphastus), the predatory beetle. Delphastus has a massive appetite for whitefly of all shapes and sizes and will knock down any escalating populations. Encarsi Forosa hunting for WhiteflyAphids: Introduce A. aphidimyza (Aphidoletes), the predatory midge. The larval stage is a fierce predator with surprisingly efficient mobility. The adult stage is capable of flight, thus locating new hot spots and distributing throughout the crop. Predatory midge attacking larger white Aphid Another alternative to combat Aphids is to introduce Brown Lacewing. Unlike green lacewing, brown lacewing is predatory in all stages of its lifecycle. The adults do most of the feeding, usually at night time. Great for the outdoor crop. Large range of prey including aphids, whitefly, and mealy bug. Adult Brown Lacewing Introduce the parasitic wasp Aphidius matricariae. They inject their eggs into aphids, the aphid becomes a “mummy”, and out comes a new Aphidius. They have a remarkable searching ability. Parasidic Wasp attacking Aphid


Consult with your supplier of beneficial insects to design a low rate of predator application and set up a standing order. Once or twice a month is often adequate for maintaining control through the entire life of the crop. At different times of the year, pest pressure outside of the building will fluctuate which makes keen scouting so important. Monitor the plants, sticky traps, and marigolds carefully to detect any rise in pest population. Add the predator to the next order and let nature take its course. Natural pest control is easy once you’ve learned to scout and identify the activity in the microscopic world. Chemical applications more often kill the beneficial insects than the pests which leads to disaster in most circumstances. By eliminating the presence of insecticides, herbicides, and fungicides, and using beneficial insects to do the dirty work instead, you’re saving time, keeping costs down, limiting the stress to the crop, and, most importantly, producing a healthier product for the consumer. This article has been written by Adam Spencer the Chief Operating Officer at Appliedbio-Nomics.com, world leaders in biological pest controls since 1980. If you have any questions you would like answered on pest control please post your comments below: