Pyrethrin Pros and Cons: How to Use it Safely

Pyrethrin can be a controversial topic among gardeners. It is naturally derived and considered organic, but it can also harm beneficial insects (as well as humans) when used incorrectly. There’s also a synthetic version called permethrin that makes the topic a little confusing.

Some gardeners believe it’s best to stay away from all of it, just to be safe. But if you’re dealing with severe pest problems, pyrethrins will make your life a lot easier. It can kill common sucking insects like aphids and flying insects like whiteflies, along with stink bugs, ants, and even fleas!

We’ll get into the good and the bad of pyrethrins and pyrethroids and everything that makes them similar and different to ensure you make an informed decision that’s best for your garden.

What Is Pyrethrin Spray?

Pyrethrin is made of six naturally-occuring toxins found in the dried flower heads of Chrysanthemum cinerariifolium. Synonyms are Tanacetum cinerariifolium or Pyrethrum cinerariifolium.

You may have heard this species of chrysanthemum flowers referred to as the painted daisy or pyrethrum daisy because of this use. The toxins are extracted from the flowers, diluted, and used as an insecticide. 

Pyrethrin was first registered as a pesticide in the 1950s. It has been used to kill fleas, flies, ants, moths, mosquitoes, and many other pests. If only natural ingredients are mixed into pyrethrin sprays, the products are generally recognized as safe for organic gardening by the Organic Materials Review Institute, or OMRI.

Permethrin is a pyrethroid, a synthetic compound produced to mimic the effects of the pyrethrin. Permethrin is lab-synthesized, but it acts just like the toxins found in chrysanthemum flowers. They’re used similarly to pyrethrins but are more frequently used for insect pests in buildings, clothing, and on pets and livestock.

Permethrin was registered with the U.S. Environmental Protection Agency (EPA) in 1979, and later was brought under review due to safety concerns, but was once again deemed safe and registered again in 2006.

How Do Pyrethrins Work?

Pyrethrins and pyrethroids kill pests in a similar way. Each of them excites the insect’s nervous system once the insect touches or eats the insecticide. They eventually become paralyzed and die because their bodies can’t get rid of the toxins quickly enough. 

The pyrethrin toxin is usually enough to kill pests, but many products use another chemical or addition, called a synergist, to make it more potent and effective. The added materials used will vary between products.

Organic options include insecticidal soaps or neem oil. If an additional chemical is used, the product won’t be OMRI-rated as organic, even if the natural pyrethrin is used. Check for the OMRI rating on your pyrethrin to be sure it’s an appropriate pesticide for your needs.

Small amounts of pyrethrins won’t hurt humans or animals because their bodies are capable of breaking down the toxins. However, other mammals have slightly higher sensitivities than humans do, especially when it comes to pyrethroids.

If you have pets, take note that cats are usually more sensitive than dogs. As pyrethroid kills insects, however, these are often used for pest control collars such as flea collars.

Types

You’ll most likely find pyrethrin and permethrin in the form of a ready-to-use spray (RTU) or a concentrate that will need to be mixed with water before you use it. Both kinds can be sprayed directly on plants as needed. These two pesticides can also come in the form of foggers, dust or powder, pet shampoo, and head lice products.

Permethrin is a bit more flexible in its uses. You can find this product in insect repellent, flea collars and medication, treated clothing, and cattle ear tags. It’s commonly used in public health mosquito control programs and is sprayed over large areas to combat large infestations.

Pyrethrin is naturally derived from chrysanthemums and can be used in organic gardening. Pyrethroids like permethrin are synthetic.

Other Pyrethroids

There are other types of lab-derived pyrethroids such as bifenthrin, deltamethrin, and resmethrin. These chemicals aren’t as closely related to pyrethrin, but they’re still in the pyrethroid family.

Bifenthrin is typically used in conventional farming and is available as sprays, granules, or aerosols. Deltamethrin is used outdoors in large areas such as golf courses, but can also be used indoors in cracks where pests enter the building. Resmethrin is used in food-handling facilities, industrial facilities, or for livestock and pets to control insects such as fleas or flies. You likely won’t use these in the garden.

Many other pyrethroids are available, but these typically aren’t available to residential gardeners and are limited to commercial use. Some pyrethroids have been banned due to their potential to harm people and the environment. 

Pros of Using Pyrethrin

Pyrethrin is highly effective against most insects. It can control aphids, cabbage loopers, fleas, flea beetles, leafhoppers, stink bugs, moths, mosquitoes, and ants. You can use it in the garden around flowers, vegetables, fruits, and other plants. There are a few precautions you’ll need to take, but we’ll get into that in the next section.

Lab-derived permethrin is integrated into specially treated clothing and accessories to keep mosquitoes, fleas, and other bugs away. Flea collars will keep your pets bug-free and prevent your home from being infested. Permethrin is also available for garden use as a pesticide, although it’s generally considered more harmful to the environment than natural pyrethrin.

Both insecticides are powerful forms of insect control. Spraying just a little insecticide where you need is enough to control an outbreak.

Pyrethrin sprays are popular in the garden, but there are many other forms that are typically used indoors to combat fleas and other insects. Foggers are potent and will kill pests instantly, while dusts work slower but provide a more long-term solution. 

Cons of Using Pyrethrin

Even though pyrethrin is labeled organic and natural, it does have its drawbacks. The biggest concern is that it’s highly toxic to bees and other beneficial insects. The concern is mostly when the spray is wet. Once it dries and begins to break down in the environment, it becomes less of a problem. 

The best way to avoid harming friendly critters is to apply the spray early in the morning so it will have time to dry before they come out to pollinate. When you spray, aim for the leaves and stems and avoid the flowers unless they’re actively infested by pests. Alternately, wait until just before sunset and spray your plants then, as most bees will have retreated to their hives for the night by that point.

Another drawback 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 several symptoms, including burning and irritation, runny nose, coughing, difficulty breathing, vomiting, and asthma-like symptoms. 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. According to the National Pesticide Information Center, studies have shown that minnows exposed to pyrethrins laid fewer eggs over time. The toxins usually break down in the soil before they’re able to reach the groundwater, making them less of a threat to aquatic life if you’re only using them in the garden.

How To Use Pyrethrin Insecticides Safely

If you do need to use pyrethrin in the garden, follow these essential steps to do so safely.

Check the Ingredients

Always check the ingredients of your chosen product. You should know what you’re working with and what negative effects it may have. Choose pyrethrin rather than pyrethroids and determine whether there are any other ingredients that may impact plants and insects in your garden.

Follow the Instructions

The instructions may differ from product to product, so read them carefully. You’ll find pyrethrin spray as a concentrated solution that needs to be mixed before you use it or as a pre-mixed ready-to-use (RTU) spray with a hand sprayer. Some products require you to add neem oil or soap to the mixture. Some RTUs may have neem oil or soap in the mix already.

Pyrethrin sprays can be used on fruits and vegetables up to a few days before harvest. When exposed to sunlight, the National Pesticide Information Center reports that pyrethrins will break down within a matter of a few days, making them safe for edible garden use.

Of course, follow the label directions on your bottle. The label directions will indicate the ideal amount of time to wait before harvesting. They’re also effective on ornamental plants. 

Wear Protective Equiptment

When you spray your garden, wear protective clothing and gear. You shouldn’t come into contact with it, even if you’re using an organic form of pyrethrin.

Eye goggles, face masks, and long sleeves will prevent you from accidentally inhaling or coming into contact with the spray. This is especially important if you use foggers or dusts since those can make their way into your eyes or nose more easily than sprays can. 

Spray Carefully

Once you’ve mixed up the concentrate according to the label instructions, spray the mix directly onto the infested plants. Try to avoid flower heads and buds so you won’t risk bees and other pollinators coming into contact with the spray.

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 one particular bed that has a pest problem, try only spraying those plants before you spray your entire garden. This minimizes the risk to not only the bees but to yourself and others that may be in the area.

Use a Row Cover

Although this step isn’t required, you can cover the plants with a row cover until the spray dries to protect pollinators. The spray becomes less of a threat once it’s dry, so you can remove the cover at that point.

Pyrethrin Alternatives

Due to the potentially harmful effects on the environment (particularly in the case of pyrethroids), it’s best to opt for safer environmental controls first before reaching for pyrethrin.

We’ve covered 9 Pollinator-Safe Pest Control Methods for Your Garden you can try before you look to insecticides. Following an integrated pest management strategy, use pyrethrin for severe infestations only if other less harmful methods of control have failed.

Frequently Asked Questions

Q: Is pyrethrin harmful to humans?

A: Pyrethrin insecticide is harmful to humans in large amounts. Small amounts may cause irritation, whether it’s burning sensations or breathing difficulties. It’s important to make sure you’re properly protected when handling pyrethrins so you aren’t accidentally exposed. The small amounts you’ll put on your plants won’t be enough to hurt you as long as you prevent yourself from being directly exposed. Most mammals won’t be harmed by the small doses used for typical pest control applications.

Q: What does pyrethrin kill?

A: Pyrethrins will kill almost any insect. Ants, many flying insects, mosquitoes, moths, leafhoppers, and aphids are just a few of the many pests it will kill when they’re 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 sundown are the safest times of day to apply to your plant.

Q: Is pyrethrin banned?

A: Pyrethrin is not banned, but some forms of pyrethroids are. Pyrethroids are synthetic, man-made versions of pyrethrin that behave in similar manners to the natural pyrethrin that comes from chrysanthemum flowers. Both pyrethrins and permethrins are considered safe for most garden use, and those are the ones you’ll likely find for retail sale.