One insecticide that will be in many gardener's sheds is pyrethrin spray. Pyrethrin can be controversial among gardeners because, while naturally derived, it can be harmful to beneficial insects and humans in large quantities. There's also a synthetic version called permethrin, which can make things a bit confusing. Some gardeners think it's best to stay away from all of this, just to be safe.
But at the same time, pyrethrins will make your pest control life a whole lot easier, especially when you're dealing with large outbreaks that you need to control quickly. It can kill sucking insects like mosquitoes and aphids and flying insects like whiteflies. Not to mention that it also kills stink bugs, ants and even fleas!
While pyrethrins can cause problems, many brands are classified by OMRI as safe for use in organic gardens, so you can use them if you prefer to keep synthetic chemicals out of your garden. And while permethrins aren't organic, you can still use them in the garden, and they can also be found in treated clothing and flea collars to repel pests while they're being worn.
We'll go over the good and bad of pyrethrins and permethrins, and everything that makes them similar and different.
What is pyrethrin spray?
Pyrethrin spray (with or without insecticidal soap) is an organic pesticide. Source: Lorin Nielsen
Pyrethrin consists of six naturally occurring toxins found in the dried flower heads of a specific chrysanthemum flower, Chrysanthemum cinerariifolium. Synonyms for its botanical name are Tanacetum cinerariifolium or Pyrethrum cinerariifolium. You may have heard this type of chrysanthemum flower called a painted daisy or pyrethrum daisy because of this usage. The toxins are extracted from the flowers, diluted and used as an insecticide.
Pyrethrin, sometimes called pyrethrum, was first registered as a pesticide in the 1950s. It has been used to kill fleas, flies, ants, moths, mosquitoes and many other pests. When only natural ingredients are mixed in pyrethrin sprays, the products are generally recognized as safe for organic gardening by the Organic Materials Review Institute (OMRI).
Similar to pyrethrin is permethrin. Permethrin is synthesized in the lab, but works in the same way as the toxins found in chrysanthemum flowers. They are used in a similar way to pyrethrins, but are more commonly used for insect pests in buildings, clothing, and pets and livestock.
Permethrin was developed in 1979 by the U.S. Environmental Protection Agency (EPA) registered and later reviewed due to safety concerns, but was again deemed safe and re-registered in 2006.
How do pyrethrins work?
Pyrethrins and permethrin kill insect pests in a similar way. Each of them excites the insect's nervous system as soon as the insect touches or eats the insecticide. They eventually become paralyzed and die because their bodies can't get rid of the toxins fast enough.
The pyrethrin toxin is usually enough to kill pests, but many products use another chemical or additive called a synergist to make it stronger and more effective. The added materials used vary by product. Organic options include insecticidal soaps, neem oil, or similar organic options. If an additional chemical is used, the product will not be assessed as organic by OMRI, even if the natural pyrethrin is used. Pay attention to the OMRI rating of your pyrethrin if you're organic gardening just to be sure it's an appropriate pesticide for your needs.
Small amounts of pyrethroids are not harmful to humans or animals as their bodies are able to break down the toxins. However, other mammals have a slightly higher sensitivity than humans, especially when it comes to permethrins. If you have pets, be aware that cats are usually more sensitive than dogs. However, because a pyrethroid kills insects, these are often used for pest control collars such as flea collars.
Types of Pyrethroids
You will most likely find pyrethrin and permethrin in the form of a ready-to-use spray (RTU) or a concentrate that needs to be mixed with water before use. Both types can be sprayed directly onto plants if required. These two pesticides can also come in the form of misters, dusts or pyrethrum powder, pet shampoo, and head lice products.
Permethrin is a bit more flexible in its use. You can find this product in insect repellents, flea collars and medications, treated clothing and cattle ear tags. It is commonly used in public health mosquito control programs and sprayed over large areas to control large infestations.
Remember that pyrethrin is naturally derived from chrysanthemums and can be used in organic gardening and that permethrin is synthetic but works the same way as pyrethrin.
There are other types of lab-derived pyrethrin-like products such as bifenthrin, deltamethrin, and resmethrin. These chemicals are not as closely related to pyrethrin, but they still belong to the pyrethroid family.
You probably won't be using these in the garden, but you might still want to know what they're used for. Bifenthrin is typically used in conventional agriculture and is available as a spray, granules or aerosol. Deltamethrin is typically used outdoors in large areas such as golf courses, but can also be used indoors in cracks where pests are entering the building. Resmethrin is used in food processing plants, industrial plants or on livestock and pets to control insects such as fleas or flies.
Many other pyrethroids are available, but these are generally not available to home growers and are limited to commercial use. Some pyrethroids have been banned due to their potential harm to humans and the environment.
Benefits of using pyrethrin
The pyrethrum daisy belongs to the chrysanthemum family. Source: KENPEI
Pyrethrin is highly effective against most insects, making it a favorite choice of many gardeners. It can control aphids, cabbage loopers, fleas, flea beetles, leafhoppers, stink bugs, moths, mosquitoes and ants. Because it is a natural insecticide, you can use it in the garden near flowers, vegetables, fruits and other plants. There are a few precautions you need to take, but we'll get to them in the next section.
Laboratory-derived permethrin can be incorporated into specially treated clothing and accessories to keep mosquitoes, fleas, and other insects away while you're wearing them. These products are great for camping trips or trips to the lake. Flea collars keep your pets free from insects and prevent your home from being infested. Permethrin is also available as a pesticide for garden use, although it is generally combined in sprays with other insecticides and is only one of the active ingredients.
Both insecticides are effective forms of bug control, and you don't even have to use large amounts for them to work. Spraying just a little bit of insecticide where you need it will be enough to control the outbreak, but it won't be enough to harm you or your loved ones.
Pyrethrin sprays are popular in the garden, but there are many other forms that are typically used indoors to control fleas and other insects. Misters are powerful and kill pests instantly, while Dusts are slower acting but offer a longer lasting solution.
Disadvantages of using pyrethrin
The insecticide pyrethrin has its concerns that you should consider before using it, as does permethrin. The biggest concern is that it is highly toxic to bees and other beneficial insects. The problem mainly occurs when the spray is wet. Once it dries and begins to decompose in the environment, it becomes less of a concern.
The best way to avoid harming friendly animals is to apply the spray early in the morning so it has time to dry before they come out to pollinate. When spraying, aim for the leaves and stems and avoid the flowers unless actively infested with pests. Alternatively, wait until just before sunset and then spray your plants, as by this time most bees will have retired to their hives for the night.
Another disadvantage is that small amounts of pyrethrins are irritating to humans and animals, and large amounts can be harmful. If it comes into contact with the skin, eyes, or mouth, or is inhaled, it can cause a variety of symptoms, including burning and irritation, runny nose, coughing, difficulty breathing, vomiting, and asthma-like symptoms. If you come into contact with a small amount, you are unlikely to experience anything more than irritation and burning. However, you should always wear protective gear and keep children and pets away from it at all times.
Pyrethrins are also highly toxic to a variety of aquatic animals such as lobsters, oysters, shrimp, fish, and insects. According to the National Pesticide Information Center, studies have shown that minnows exposed to pyrethrins laid fewer eggs over time. Luckily, the toxins usually break down in the soil before they can reach groundwater, so they don't pose much of a threat to aquatic life if you're just using them in the garden.
Use of pyrethrin insecticides
The OMRI label means that it is approved for use in organic horticulture. Source: Lorin Nielsen
Follow label directions carefully, as each brand will likely have their own directions for the product.
You can find pyrethrin spray in the form of a concentrated solution that needs to be mixed before use, or as a pre-mixed ready-to-use (RTU) spray with a hand-held sprayer. Concentrates require a small portion, typically up to a few tablespoons, to mix with water. Some products require you to add neem oil or soap to the mixture. Some RTUs may already have neem oil or soap in the mix.
Once you have mixed the concentrate according to the label directions or removed the packaging from your RTU spray, you can spray the mixture directly onto the infested plants. Try to avoid flower heads and buds so you don't risk bees and other pollinators coming into contact with the spray as it is toxic to them.
Although this step is not required, you can cover the plants with a row cover until the spray dries to protect pollinators. The spray becomes less dangerous once it dries, so you can remove the cover at that point.
Another way to protect pollinators is to selectively spray the areas that need attention, rather than spraying the entire plant or bed. If you notice a few specific plants or a specific bed that has a pest problem, try spraying just those plants first before spraying your entire garden. You can minimize the risk not only to the bees but also to yourself and others who may be in the area.
When spraying your yard, wear protective clothing and gear so you don't come into contact with it, even if you're using an organic form of pyrethrin insecticide. Goggles, face masks, and long sleeves prevent you from accidentally inhaling or coming into contact with the spray. This is an especially important step if you're using foggers or dusters, as these can get in your eyes or nose more easily than sprays.
Pyrethrin sprays can be applied to fruit and vegetables up to a few days before harvest. When exposed to sunlight, the National Pesticide Information Center reports that pyrethrins break down within a few days, making them safe for use in edible gardens. Of course, follow the directions on the label of your bottle; The instructions on the label indicate the ideal waiting time before harvest. They are also effective on ornamental plants.
frequently asked Questions
Dried Pyrethrum Daisies. Source: Museum de Toulouse
Q: Is pyrethrin harmful to humans?
A: The insecticide pyrethrin is harmful to humans in large amounts. Small amounts may cause irritation, be it burning or difficulty breathing. It is important to ensure that you are properly protected when handling pyrethrins so that you are not accidentally exposed. The small amounts you put on your plants won't be enough to harm you as long as you avoid direct exposure. Most mammals are not harmed by the small doses used for typical pest control applications.
Q: What kills pyrethrin?
A: Pyrethrins kill almost every insect! Ants, many flying insects, mosquitoes, moths, cicadas and aphids are just a few of the many pests it will kill if exposed. The downside to this is that it can kill beneficial pollinators that every garden needs, including bees. Avoid spraying pyrethrins on flowers and buds, and avoid spraying during the time of day when these insects are out. Early morning applications or just before sunset are the safest times of day to apply to your crop.
Q: Is pyrethrin banned?
A: Pyrethrin is not prohibited, but some forms of pyrethroids are. Pyrethroids are synthetic, man-made versions of pyrethrin that behave similarly to the natural pyrethrin found in chrysanthemum flowers. When the risks of pyrethroids were reassessed, some of them were banned due to risk concerns. Both pyrethrins and permethrins are considered safe for most gardening applications, and these are the ones you're likely to find in retail stores.
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