Beneficial predators control insects and mites, and they may be a key to controlling powdery mildew, too.
There is always, as they say, a bigger fish. Spider mites, aphids, russet mites, fungus gnats and other pests that plague growers all have natural enemies, and the use of beneficials in the cannabis industry is being boosted by significant pesticide restrictions.
The Butterfly Pavilion in Colorado used beneficials in the 1990s when Kerrie worked there, and a recent tour of the Pittsburgh Botanic Garden conservatory showed us that beneficial predators still remain a popular control choice wherever pesticides are prohibited, limited or need to be avoided.
Beneficials are a perfect fit for the cannabis industry (though there is no better pest management approach than prevention).
Tip 1: First ask the question: What do you need to protect against? There are many more pests than mentioned in the chart on p. 86, but those are the ones that do serious damage to cannabis crops, so they are the pests we recommend targeting initially.
Tip 2: Add (to your list) locally unique pests that have been known to cause severe losses.
Tip 3: The list of threats should encompass both canopy and root-dwelling pests.
Tip 4: Once we know the threats, we can turn to suppliers for recommendations on which predators to use. Suppliers provide each predator's targets along with usage information. Each supplier is a little different in its documentation, so we viewed information from a number of suppliers and summarized the predators and their targets in the chart to the right. A downloadable copy of the complete table with less common pests is available at Otokehort.com/integrated_pest_management/beneficials.
We warn users to use this chart as a guide and to check with your supplier to get their latest information.
It would be great if there was one predator that would target all of the usual suspects; but according to this chart, few growers will ever be able to get by with one predator.
Tip 5: Green lacewings attack aphids, mites and thrips in the canopy, so they would be a good base for a beneficials program.
Tip 6: If green lacewings are not available for some reason, the grower could target canopy aphids with two-spotted ladybeetles, use Amblyseius andersoni against mites, and turn Orius, the minute pirate bug, loose on thrips. Many effective combinations exist, and the choice may depend on availability of certain predators from suppliers.
Tip 7: The table notes only one predatory mite that attacks eriophyid (aka russet) mites, so Galendromus occidentalis will likely be a part of any beneficials program that looks to control eriophyid mites.
Tip 8: Beneficial suppliers also offer soil-dwelling pest predators like Steinernema feltiae nematodes or Stratiolaelaps scimitus (Hypoaspis mites) and Atheta Coriara (rove beetles). These predators target root-damaging fungus gnats and thrips larvae to provide protection to plant’s root zone.
Tip 9: Unfortunately, discussions with beneficial suppliers failed to produce a recommendation for a predator that is effective against root aphids that dive deep into the root zone beyond the reach of most soil predators. Lack of a predator places the grower between a rock and a hard place on root aphids, so we suggest that growers consider using approved drench-applied pesticides in the root zone without endangering beneficial predators in the canopy.
Tip 10: The initial list of predators may be whittled down by looking at which predators will do best in the environment of a cannabis flower room. This is where it is a good idea to work with your supplier. We turned to the person who introduced us to beneficials, Chris Daye, who is now at Beneficial Insectary.
Tip 11: Daye advises: “You have to match the proper beneficial to the conditions of the growing area. All biocontrols perform well against their prey, but some stand out under extreme conditions. For example, Neoseiulus californicus should be chosen over Phytoseiulus persimilis for better results against spider mites in hot and dry conditions.”
Tip 12: The layout of plants in cultivation spaces also influences the choice of predators. A shop that maintains separation between plants to interrupt pest movement may want to choose flying predators like wasps that can easily move from plant to plant. A shop where a sea of green, continuous-canopy approach is followed can count on crawling predators to spread far and wide.
Tip 13: Beneficials are not suitable for controlling outbreaks in progress. The folks at Rincon-Vitova Insectaries note that predators work best when the pest population involves no more than 10 percent of the leaves. If you have a big outbreak, weather the storm (once an overwhelming outbreak occurs, predators are of no value and the grower must fight pests with other pesticide-free means like daily water sprays to disrupt the pests until harvest), then introduce beneficials on a clean crop.
Tip 14: The number of predators released and the frequency of releases is usually stated on a per-plant or per-square-foot-of-canopy basis. As a preventive treatment, determining the exact quantity/frequency of predators required may take some experimentation, after the supplier has made its initial recommendations on what to release. If there are no pests to eat, predators released will all die off in a short period of time. Repeated quick die-offs indicate the inherent pest pressure on the facility was low during this time frame, but that does not mean that the pest pressure will be low for the next several crops. Beneficials are an insurance policy, and you let it lapse at your own risk.
Tip 15: A more common scenario is the presence of a constant pest pressure that predators can make a living on. The grower needs to find the number of predators in a release and the release frequency that keeps pest populations below the point of economic impact. This creates what amounts to a living zoo of pests and predators living in equilibrium.
Tip 16: Pest management depends on spotting pest and disease outbreak quickly.
Tip 17: When using beneficial predators, scouts must also carefully monitor the predator populations. In the living zoo scenario, the scout would be looking to see if the density of predators and pests is within the control limits set for the shop. Shifts in these densities will be common, but the grower also will see trends he can react to with more predators before economic loss occurs.
Tip 18: People can count pest and predator densities directly on the plants or by counting pests that fall onto a piece of paper held under shaken branches. Knowing whether populations are growing, declining or holding steady is the core knowledge that drives the decision to apply more, fewer or different predators for the next inoculation. Develop a tracking scheme and use it.
Tip 19: The final key to the successful use of beneficial predators in your cannabis operation is the ultra-cautious use of pesticides. If you are just starting a beneficials program, be sure that pesticide residuals are allowed to degrade for the appropriate time before introducing beneficials. For example, a grower should wait for two weeks following use of pyrethrins to introduce beneficials.
Tip 20: Powdery mildew has no insect or mite feeders (predators), so spraying for it is common in shops that use beneficials. If beneficials and pesticides are mixed, careful pesticide screening for compatibility with your beneficials helps prevent killing off your expensive army of predators. A list of pesticides that affect different beneficials is shown below. This list is limited to pesticides that some states have approved for use on cannabis. Sulfur is the only pesticide on this list used for insects and mites, as well as powdery mildew.
Tip 21: Perhaps the most important reason to use beneficials is they can eliminate spraying. Some grape growers partnered with the University of California, Davis, to see if they could predict when powdery mildew outbreaks are most likely to occur based on weather patterns; prediction allows for preventive action. The models that resulted from the partnership point to three key variables that affect outbreaks of powdery mildew: temperature, humidity and leaf wetness. (Source: “Disease Models: Powdery Mildew (Uncinula necator),” Thomas, C. S., Gubler, W. D., and Leavitt, G. 1994.) The latter indicates that coastal fogs in California play a key role in creating the conditions favorable for powdery mildew outbreaks. In cannabis cultivation, spraying may be the “fog” that sets off outbreaks, so it may be a wise experiment to see if avoiding spraying reduces powdery mildew levels.
Tip 22: Daye of Beneficial Insectary lends some support to this notion, saying it is good growing technique to keep your crop “dry" and only spray when necessary. Beneficial predators reduce the need to wet plants with pesticides, resulting in cleaner, healthier plants.
General practice advice and anecdotal tales do not prove an association and are not scientific enough to base decisions, but they do suggest the possibility that beneficial predator use reduces the spraying so much that growers may be able to ditch the rest of their pesticides and gain mastery over powdery mildew. With powdery mildew being the problem it is, beneficials users may want to try this theory out.
