This is a guest post by Sandra Sleezer, an entomologist and the technical service coordinator for MGK.
As an organic gardener, you probably understand the frustration of walking aisle after aisle at your local nursery without finding the right tool for the job.
Sadly, we are somewhat limited in what is available — especially when it comes to pest control.
Without an insecticide that can effectively eliminate pests, keep your plants organic, and help contribute to a sustainable world, you might never be able to truly enjoy the fruits (or vegetables) of your labor.
Pyrethrins are one of many options out there, but also one of the most popular for organic gardeners.
Keep reading to see why more green thumbs are making sure these products are in their gardening arsenal.
What Are Pyrethrins?
Pyrethrins are found in pyrethrum extract collected from certain species of flowers in the chrysanthemum family. Chrysanthemum cinerariifolium is the species of plant that pyrethrum is harvested from currently, although others have been used in the past.
The active ingredient is considered broad spectrum, meaning it targets a broad range of insect species. They work by disrupting the insect nervous system. They also have repellent properties, meaning insects can usually detect the pyrethrins and become agitated and try to leave the area.
Because of the properties listed above, insecticide products constitute the most common pyrethrins uses — and are especially popular among many organic gardeners and plant lovers.
Pyrethrum Vs Pyrethrins
What exactly is the difference between pyrethrum and pyrethrins?
Pyrethrum is the extract from the flowers, and pyrethrins are the six active molecules that act as the pest control agent in that extract.
If all the other plant materials were removed from the pyrethrum and you only distilled the six active ingredient compounds from the pyrethrum, you would be left with the pyrethrins.
Whether a product someone buys says pyrethrum or pyrethrins, it will essentially function the same way (and is really just a matter of wording as far as the end user is concerned).
To summarize, professionally produced pyrethrum or pyrethrins will both be expertly refined products that will aid in the control of your plant pests.
How Is Pyrethrum Made and Where Does It Come From?
Most of the flowers used for processing pyrethrum these days are grown in East African countries and Australia. Once harvested, the flower heads are dried and transported to an extraction facility.
The first extract results in a dark, tarry substance with a high level of plant waxes and other residues. It is then refined further to remove those unwanted substances.
The process has been refined over decades to produce the high-quality product we have today, which is a clear to amber liquid used to formulate many different products used in homes, gardens, commercial buildings and more.
How Do Plant-Derived Pyrethrum/Pyrethrins Differ From Pyrethroids?
Pyrethroids are synthetic and based on the six active compounds extracted from the flowers — with small changes made in a chemistry lab.
Pyrethroids usually have a longer residual, meaning they remain on an applied surface for a longer period of time, and often inherently change in toxicity (higher or lower) to any organism, including insects, mammals, birds and fish.
Other changes that can happen when a compound is altered can cause the molecules to bind tighter to the nerve site or to organic matter like soil.
Additionally, these chemical changes can add stability when under UV light or create a substance that becomes more toxic as it breaks down, which can be beneficial for some applications.
Small changes can make a big difference in how a chemical reacts with the environment around it, including people, animals, plants and other chemicals. That is why every new molecule has to go through environmental impact and toxicity testing established by the EPA to more clearly understand the potential risks and benefits of it.
What Insects Do Pyrethrins Work On?
Because pyrethrins insecticides are broad spectrum, they can target a wide array of insects common in organic gardening — from aphids to zebra caterpillars and many others.
Generally speaking, insecticides (including pyrethrins) work faster on smaller insects because it takes a smaller dose to have an effect.
Pyrethrins also work better on soft-bodied insects like aphids rather than insects with thick exoskeletons like Japanese beetles because the insecticide can penetrate quicker and start working.
Another factor is the particular insect’s enzymatic system. Can the insect break down the product quickly enough to recover before the pesticide can eliminate it? When this happens you will see a “knock down” effect where the insects fall over and look as if they are dying, but if you continue to watch, they recover and walk away.
This essentially means they didn’t get a lethal dose and/or may be resistant to the insecticide.
Is Pyrethrum a Safe Organic Pesticide?
As an organic gardener, one of the questions you may have is if the products you are using are safe. “Safe” is a very charged word in the pest control industry and one that cannot be used carelessly.
There is some amount of risk in every insecticide, and while this risk can be minimized, it can never be avoided completely. While pyrethrum toxicity is generally less than many other chemicals used in insecticides, there are still safety measures that must be taken (which we will review later in this article).
The most important thing to keep in mind is that you should always treat any insecticide with a healthy dose of respect.
Are pyrethrins-based insecticides safe? Not 100%. However, it has been used for decades with a very good record and few acute toxicity cases.
Something else to note is that just like any substance, certain individuals may be more sensitive to particular chemicals than others. This could be due to allergies, lowered immune systems, or compromised detoxification systems.
Anyone could have a poor reaction to a substance that to most people would be benign. Peanuts are a good example of this.
Pyrethrins and Bees
While pyrethrins target a large number of insects, the short residual time and contact spray associated with these insecticides are benefits that lessen the impact on pollinators like bees.
Yes, it can harm beneficial insects, especially if sprayed directly on them. We recommend spraying either in the early morning or late evening when most pollinators are not active.
Pyrethrins need to be directly sprayed on an insect to be the most effective. Once the product is dried on a surface, the efficacy diminishes greatly.
Additionally, the half-life of pyrethrins is about 11 hours in direct sunlight, meaning if the pyrethrins are in full sun for 11 hours, half of the product will break down into non-insecticidal compounds.
After a day or two outdoors, the product should be effectively gone. It won’t persist in the environment, continuing to eliminate insects as an insecticide with a long residual would.
Therefore, if you apply pyrethrins when pollinators are not active, the risks to them will be mitigated as much as possible.
Best Practices to Improve Safety When Using Pyrethrum
Most pyrethrins come in liquid concentrate form. The concentrate can then be diluted with water in a spray tank and sprayed over the infested area. All the instructions and safety documentation for the product will be included on the label.
Pyrethrins-based products come in different concentrations, so the amount mixed per gallon of water will vary depending on the desired end use percentage and the original percentage in the concentrate.
There are some pyrethrins insecticides that come pre-diluted and ready to use. These products will lose effectiveness over time, as water aids in the breakdown of the products.
Most concentrates have a mix of active ingredients, surfactants, and usually some oils or other non-water ingredients. For this reason, it is recommended to use a concentrate instead of a pre-diluted product.
Once you have your product, you want to make sure you are using it in the best and safest way possible.
Here is a helpful guide on how to use pyrethrum pesticides:
1. Read the label of your chosen pyrethrins product.
2. Gather all the application equipment and PPE (personal protective equipment) you will need.
3. Time your application appropriately. Apply in the early morning or late evening to avoid pollinators. Don’t apply during strong winds when the application can be blown to other areas. There will probably be a lot of other don’ts on the label. Follow the label instructions closely.
4. Wear your PPE. This will usually include things like long pants, long-sleeved shirt, shoes and socks, and chemical resistant gloves. The label will state what you need.
5. Mix the concentrate with water or oil depending on the label instructions. Mix only what you need. Remember, pyrethrins break down over time in water, so you don’t want to store mixed product for later use as it likely won’t work well.
6. Apply the product to the infestation area making sure to get solid contact with all surfaces where insects may be hiding. Many insects hide in the crevices of plants and undersides of leaves. Spray where the pests are and make sure to get good coverage.
7. Wait for the product to dry and the pests to expire.
8. Evaluate how well the product worked. If it worked, great! If not, you should reevaluate and decide if you need to try another tactic or if something was off with the application and try it again later.
Where Can Pyrethrins Be Used?
Pyrethrins are very versatile and can be used indoors, outdoors, in residential areas, commercial areas, on gardens, crops and structures. Anywhere that insecticide would need to be applied can accommodate pyrethrins.
Another added benefit for organic gardeners is that they can be used as a post-harvest application. Whether you’ve just harvested or picked up produce from the store, you can ensure your fruits and vegetables are pest-free.
The Organic Gardener’s Best Friend
What are the most important aspects to look for in an insecticide?
We want it to eliminate all the pests yet none of the beneficial insects or other random critters that happen to be nearby, including people and pets.
We want the plants and structures we are trying to protect to remain undamaged. We also don’t want to do damage to our environment and our planet.
That is a tall order to fill, but pyrethrins, if used appropriately, do a great job and check many of those boxes.