Experiments and Findings

Our interest in developing clean pesticides for the marijuana industry soon led us to conduct our own experiments. There were important questions for which there seemed to be no definitive answers. For example, which of the essential oils works best on marijuana? What type of emulsion produces the best results? Should we use several essential oils in our pesticide or just one? What is the optimum relative concentration of each ingredient in the pesticide? Like many of you, we dug into the internet and found lots of opinions, anecdotal evidence, and mythology but very little science. Scholars at universities weren’t studying marijuana because of federal restrictions so the information found in academic studies of other plant varieties had to be generalized to cannabis. When we decided to develop state-of-the-art nanoemulsions that opened the door to the complex set of chemistry issues involved in making them. It also meant that we had to test our formulations ourselves because applications of nanotechnology were relatively new.

The purpose of this short article is to share our methods and findings and to encourage others to conduct experiments of their own. If reading this article motivates at least one person to design and conduct an experiment, then I have been successful as a science writer. If you report your findings to us so that we can post them on this website, then all of us will be more successful in our gardens. As always, the goal is constant improvement.

Fortunately, you don’t need a high-tech lab full of exotic glassware to conduct an experiment that produces meaningful results. But you do need to observe basic principles of experimental design. That said, it is possible to answer important questions by conducting experiments in relatively informal settings. Of course, science gives us the methodology to frame a question so that it can be tested, design an experiment with controls in place, and evaluate the outcome (an article on this topic is in progress). Whether you are developing pesticides or trying to improve your gardening techniques, the approach is the same. So strap on your horn-rimmed glasses and let’s talk science!

Two Pivotal Experiments

This article describes two of the experiments we conducted during the development of Peppermint Fury. Specifically, the experiments were designed to answer the following questions: at what concentration does it kill two-spotted spider mites? And, at what concentration does it damage the plant (become phytotoxic)?
To answer the first question, I needed to find some bugs. A friend reported that he had some sickly plants infested with insects. I used one of these plants for the experiment. It showed signs of webbing from two-spotted spider mites, and upon closer inspection it was crawling with russet mites as well. I was delighted! I isolated the plant and labeled two branches. On one branch I planned to spray Peppermint Fury at .5% concentration, which was known to be effective. But I wanted to know if it still worked at a reduced concentration, so the other branch was sprayed with a solution at .33% peppermint oil. Before spraying the plants, they were carefully inspected with a 100x microscope to determine the extent of the infestation on each branch. The insect populations were apparent on all of the branches. Then separate branches were sprayed with Peppermint Fury at .33% and .5%. The leaves were inspected every day for four days with a microscope and took notes on what I saw. After 24 hours, the insects were dead on both branches, but the higher concentration was more devastating in terms of collapsing the bodies of the insects. These results indicated that effectiveness was improved at the higher concentration of peppermint oil. It is interesting to note that this same experiment was conducted using several other essential oils (cinnamon bark, lemongrass, rosemary, thyme, and three blends) with similar results. It appears that essential oils tend to be lethal to insects at .33% but their effectiveness is improved at .5%.

A second experiment was conducted to determine the concentration at which Peppermint Fury becomes phytotoxic (damages plant tissue). We wanted to determine the “safety window” of the product – that is, the difference between the concentration at which it kills bugs and the concentration at which it damages leaf tissue. Three matched test subjects were used for these experiments. To eliminate possible differences between the test subject, three clones taken from the same mother plant were selected. The clones were the same age, size, and appeared healthy. Thus the potential variables of genetics, size, and age were held constant across test subjects. At the time of the experiment, we were using Peppermint Fury at a concentration of .5%. Although it quickly eliminated pests, that concentration was a “best guess” based on our review of the literature on peppermint oil. No tissue damage had been observed when using the pesticide at .5% so I decided to test concentrations of .5% (baseline), 1.0%, and 1.5% (test subjects A, B, and C respectively, from left to right in the photos). The plants were labeled and photographed at pretreatment (see photo #1), 24 hours, 48 hours (see photo #2), and 72 hours later (see Photos 1.1, 1.2, and 1.3). In addition, I examined leaf samples from each test subject under a 100x microscope and took notes on what I saw, trying to be as objective as possible.

Photo #1: Pretreatment

Photo#2: 48 Hours After Treatment

Here are some excerpts from those notes.
24 Hours. No damage on “A” and “B.” Leaf twisting and distorted new growth noted on “C.”
48 Hours. No damage on “A.” Some leaf curl (claw)at top on newer leaves on “B.” Obvious leaf twist on several of the top leaves on “C,” some curl (claw) particularly on the bottom leaves but no necrotic tissue.
72 Hours. No change on “A.” Upper leaves still curled on “B”, especially at new growth on top. Lower leaves turning yellow on “C,” top leaves twisted, distorted new growth at top (deformed, blunted leaves).
All plants were able to recover, although it took longer for “C.”
Note that five other essential oils (clove bud, lemongrass, oregano, rosemary, and thyme) were tested as well as well to determine their safety window. It turns out that several essential oils, such as lemongrass, have a very narrow safety window. Of course, in hindsight this makes perfect sense. Lemongrass kills bugs by stripping off their protective coating and they die by dehydration. Unfortunately, it does the same thing to leaves at a concentration that is only slightly higher, so there is some risk involved in using this oil. Later, I discovered that lemongrass is used as an herbicide (for example, GreenMatch EX) because it does such a good job of killing leaf tissue at higher concentrations. It is interesting that lemongrass is commonly used as an active ingredients in pesticides using essential oils. I am guessing that my competitors didn’t do their homework!

Summary

These two experiments guided the final stage in the development of our first commercial pesticide, Peppermint Fury. The first experiment demonstrated that peppermint oil is effective at a concentration of .33% and it is robust at .5%, so we decided to produce our formula at .5%. By comparison with the other essential oils tested, it was clear that peppermint oil was the most lethal to insect populations. The second experiment showed that peppermint oil has a substantial safety window. It is safe to use at .5%. Only minor damaged was noted at 1.0% and the plant recovered within a few days.

Notice that these experiments were relatively simple yet provided very useful information. In academic settings the design, methods, data collection techniques, and data analyses would be much more sophisticated. And there are multiple payoffs for doing the extra work – academic researchers can make much more definitive statements about the implications of their experiments (carefully expressed in statistical language regarding sample size, analysis of variance, etc.). Such experimentation also sets the stage for programmatic research that can validate and extend the scope of ongoing investigations. I gratefully acknowledge that my understanding of essential oils as pesticides has been gleaned from academic articles, patent applications, and Ph.D. theses. While this type of detailed research certainly makes an important contribution, those of us with neither grant money nor GTFs (Graduate Teaching Fellows) make do with less sophistication. Typically this means using whatever resources you have to conduct a basic experiment that will answer the question at hand. Using just a digital camera, a microscope, and a notebook I was able to do just that.

Future Research on Peppermint Fury

Peppermint Fury is a relatively new product and our customers are constantly finding new uses for it. At GardenCare Naturals we are interested in developing IPM strategies using Peppermint Fury with other natural pest control solutions. Many questions remain. For example, does Peppermint Fury kill beneficial insects? We also need to test its effectiveness on other common pests such as stink bugs and fire ants. Be sure to check our website for new developments.