Indoor-grown cannabis crops are ecological islands contained within buildings, allowing for novel pest control techniques that are not an option in field crops. Keeping insects and other pests out is the most critical first step in an effective pest management program. Here are some recommendations:
1. Check the building to make certain that it is pest-proof and make any necessary corrections.
One of the primary routes of insect entry is through vents and windows. All openings should be screened. Typical window screens found in homes will keep out tarnished plant bugs and moths, but are useless at stopping smaller pests such as thrips and spider mites. Smaller mesh screens, available from greenhouse supply companies, should be installed to block all arthropods. The downside is that small mesh screens reduce airflow significantly. Enlarge the vent and window openings to compensate for the airflow reduction.
2. Modify the perimeter landscape and environment to make it an unfavorable place for pests.
Weeds and other plants are a source of arthropod pests and plant disease organisms. Every effort should be made to have a completely weed-free zone around the building. Removal of trees and ornamental plants is also advised. When applying herbicides around the building perimeter, all windows should be closed and the ventilation should be turned off. If outdoor herbicide residues are detected on your crop, it may have to be destroyed (depending on your state regulations).
3. Clean-up the perimeter area.
Poor storage practices and debris adjacent to the building can provide harborage for rodents and insects. If long-term outside storage is necessary, elevate pallets, shelves, and crates at least one foot off the ground. Remove trash and debris that collects along fences.
4. Change the color of your clothes.
Most species of aphids, thrips, and other plant-feeders are instinctively drawn to dying, yellowing plants more than healthy green plants. If you are wearing a lime-green or yellow shirt outdoors, it is common for them to land on you. As you walk into the facility, these pests will hitchhike unnoticed through the door. Some species of thrips are also attracted to light blue clothing. The least attractive color to insects is white.
5. Review your exterior lighting.
When checking the lighting, keep in mind that insects will not actively fly to something they can not see. Wavelengths greater than 550 nanometers are out of the range of vision for most insects, so bulbs with higher wavelengths are less attractive to night-flying insects. Aphids typically fly during the day, but many do not land until after dusk. Bright blue/white lights on your building will draw them in. Most of the remaining night-flyers seen around lights are not greenhouse pests, but it is common in Colorado, for example, to have several hundred false chinch bugs flying around halogen lights. Never install exterior bug zappers (flying insect light traps). These devices only draw more insects toward your building.
6. Do not let outdoor bugs see your plants.
Install films with UV light-blocking materials below 380 nanometers (standard films are 360 nanometers). All windows must be covered with these 380-nanometer films. Research has shown when a few windows are left uncovered, significant numbers of insects will still invade the greenhouse.
7. Make it difficult for insects to find your vents.
For indoor operations that do not use natural lighting, there is a trick to reduce the number of insects that fly toward the vents. Make the roof as reflective as possible using silver-colored roofing materials, aluminum sheeting, or other similar materials. This works because it confuses most flying insects. In their natural environment, insects use polarized light from the sky to navigate, so when light is reflected up underneath them, it interferes with their normal flight behavior and disorients them.
8. Do not let pathogens come inside on your clothing.
Soilborne pathogens, such as Pythium, may be present on your shoes, so it is a good idea to have disinfecting trays immediately inside the doors of the greenhouse or grow room. If employees have been working in another grow facility, they should change clothes and footwear to reduce the possibility of spore or arthropod introduction. Even if your standard practice is to change into sterile coveralls before entering the grow area, pests in the locker room may lead to contamination.
9. Do not carelessly bring in plants, media, or tools that have pests on them.
Inspect all seedlings and starter clones meticulously. Diseases and arthropods (insects and mites) may be present on either the roots or on the vegetative portions of the plants. Successful inspections may require the services of a plant pathologist or entomologist. Use only sterile soil media. Disinfect all tools before they are brought into the facility, and do this again before each use.
These guidelines should lead to significant savings by reducing the costs associated with interior pest control.
Scott Armbrust ([email protected]) is a Master-degreed entomologist and the owner of Rid-A-Pest Exterminators in Littleton, CO. He trains pesticide applicators around Colorado and the surrounding states. He has lectured for several associations, the FDA, civic groups, elementary schools, and many others.