Medical Cannabis Is Grown For Human Consumption

It doesn’t matter if it is smoked, vaped or used in an edible form, every effort should be made to grow the crop without the use of chemical insecticides, fungicides or herbicides. When plants are grown in protected environments, they can be grown all year round, at a faster rate and with less physical damage. The protected environment however, also tends to make it easier for the pests to become established and to get out of control due to the exclusion of natural enemies from the surrounding environment.

PRIOR TO PLANTING

The greenhouse or growth chamber must be adequately cleaned of old plant material, obvious fungal residue and non-essential apparatus. A thorough cleaning with a detergent is highly recommended.

The climate must be appropriate for growing conditions. Stressed plants are much more susceptible to fungal pathogens and insect pests. Care must be taken to ensure that air circulation is efficient but not too intense, as a strong wind passing through the plant causes displacement of the “humidity umbrella” that the plant normally forms by transpiration. If the plant surface becomes desiccated, pests such as the two-spotted spider mite will thrive.

Before placing the crop, put a few bush beans in pots throughout the greenhouse. The beans will attract any pests that were missed by the clean-up, allowing you to redo the clean-up or use a more thorough technique.

GETTING STARTED

When the pots are first watered, a soil mite such as Stratiolaelaps scimitus or Gaeolaelaps gillespiei should be applied to the soil surface at a rate of 25,000 mites / 100m2 (1,000ft2). They can be broadcast over the spaced-out pots or trays. These soil mites will control fungus gnat larvae in the root zone, leading to a faster growth rate and healthier plants. Both mites also feed on pupating thrip larvae, helping thrip management by breaking the reproductive cycle.

Yellow sticky traps should be applied, at least 1 trap for every 500 square feet. Care must be taken to ensure that the height of the traps does not exceed the height of the plants. Traps higher than the plants will not trap a representative sample of thrips.

SPIDER MITES

Spider mites are the most common and serious pest. This is due to the environment, plant stress and the plant itself. In general, spider mites greatly dislike high humidity. If you are not battling botrytis or similar molds, try misting the affected areas on a regular schedule for a few days. Prevention of spider mites is possible by applying Neoseiulus fallacis at a rate of 2 mites per square foot. This generalist mite predator evenly establishes itself throughout the crop, preventing spider mite establishment under normal conditions. Hot spot outbreaks should be treated with Phytoseiulus persimilis at a rate 5 persimilis /m2 with no webbing and 5 persimilis /ft2 if you have webbing. Fallacis and persimilis are compatible and do not interfere with each other. Fallacis does not do well on webbing while persimilis specializes on it.

Stethorus punctillum is a tiny black beetle that thrives in low humidity situations. If you are unable to manage the climate effectively and the conditions for spider mite are extreme, Stethorus could save the crop. They should be applied at a rate of 0.1 per square foot, in extreme cases, or 0.01 per foot in moderate cases. These beetles find spider mites by smell and quickly move to new infestations, leaving behind their eggs and larvae to finish the job.

Another strategy to try is using bush bean plants amongst the crop. In some crops, such as tomato, this is a very effective strategy for pulling spider mites off the crop. Bean plants are also easy to monitor, as they show spider mite damage within hours. If the beans are moderately successful, apply persimilis to them to create a “banking” system, generating more persimilis that will move into the crop. If the beans are highly successful, carefully remove them and the spider mites and plant some more beans.

FUNGUS GNATS

Fungus gnats search out moist soil in which to lay their eggs. These insects can infest a crop from wet, algae-covered areas in the drainage system within your greenhouse, or from contaminated potting soil or by flying short distances from plant to plant. While the adults rarely cause plant problems they will lay many eggs and the young larvae will feed on the fine root hairs of your plants causing them to lose vigor and develop yellow leaves. They can also tunnel into the base of cuttings or plant stems, which can be devastating. While adult fungus gnats are not usually a problem in cannabis plants they are vectors of disease and bacterial pathogens that can have serious repercussions in your crop.

Beneficial nematode, Steinernema feltiae, is the nematode of choice for controlling the larvae stage of flying insects. Nematodes will enter the larvae of soil pests like the fungus gnat and release a bacterium which is lethal to it, thus, breaking the lifecycle of the pest. A bi-weekly inoculation of nematodes is recommended as well as using yellow sticky traps to catch adults. The sticky cards should be placed on the soil sticky side up as fungus gnats are not very good flyers and tend to hop as much as fly.
Sentry : Steinernema feltiae (Sf) beneficial nematodes can be used preventatively at a rate of 25 million per 1,000 ft2.

APHIDS

Almost every plant gets aphids if the conditions are right. Over fertilizing leading to rapid soft growth is what aphids look for. In general, very few aphids cause permanent damage, but their excrement, honeydew, can lead to sooty mold. If you have aphids, you must eliminate any ants first, ants “farm” aphids, feeding on the honeydew. They will protect the aphids from predation and will actively move aphids around to “greener pastures” within your crop.

Once the ants are gone, aphids can easily be controlled by using Aphidoletes aphidimyza at a rate of 250 / 2,000ft2, weekly, until the aphids are eliminated. If you have a history of aphids, continue at this rate weekly for the duration of the crop.

THRIPS

Thrips cause damage that is similar to spider mites. There is a subtle difference however, Thrips tend to scrape the leaf surface while spider mites pierce the leaf tissue and extract the chlorophyll. Thrips are tiny pests, capable of flying, although they are quite poor flyers. They are attracted to yellow and blue sticky traps, which when used in sufficient quantities can be effective management tools. Adding a cotton ball so you can drip vanilla or almond extracts can increase the trapping by a factor of 10.

Biological controls are limited. The predatory mite Amblyseius cucumeris is the best choice. These mites attack the first and second instar larvae. If enough cucumeris are present they are extremely effective, as they can sense the thrip emerging from the leaf, they wait for it to stick its head out, biting it off. The presence of Stratiolaelaps scimitus in the soil will ensure that the thrips cannot effectively cycle within your facility

WHITEFLY

Whitefly is not a common pest with a medical cannabis crop, but pests tend to adapt, so we should discuss them briefly. Whiteflies are a close relative to the aphid. Both of them suck and both can quickly create excessive honeydew that will lead to sooty mold. If any whitefly is seen on the yellow sticky cards, begin applying the parasitic wasp Encarsia formosa at a rate 1 – 4 Encarsia /m2 (10ft2), weekly.

SUMMARY

This is a difficult crop as the plants have not been bred for protected climates. As a result, the plants are usually in some state of stress. Do what you can to minimize the stress by aggressively humidification and careful watering and nutrient balance.

The application of the soil mites is a critical first step, ensuring healthy root development by controlling fungus gnats and thrip management, by predating on the pupating thrips.

Spider mite is the traditional pest and can be prevented with the predatory mite fallacis. Outbreaks are best treated with persimilis and severe infestations due to poor climate are best dealt with by applying the beetle, Stethorus. The use of bush beans as monitoring/trapping plants should be investigated in this crop. If the crop ends with a spider mite problem, apply more Stratiolaelaps scimitus to the floor area, focusing on cracks and any other breaks in the floor where the spider mites overwinter. The Stratiolaelaps scimitus will feed on the dormant spider mites, reducing their return numbers significantly.

There is little you can do to prevent thrips. If they become a pest, apply cucumeris to the plants and apply vanilla spray or almond to the sticky traps by using cotton balls.

The importance and value of Medical Cannabis is well worth the effort to grow this crop using organic methods to insure its health consumption.