What are the best organic pesticides for my garden?
Pest populations can explode even if you keep your soil healthy and maintain a balanced garden ecosystem. Pest management is a natural part of growing plants and occasionally gardeners need to rely on external control measures like spraying pesticides. Organic gardeners shy away from using pesticides for some very good reasons. Sprays, particularly if they are not organic, can kill beneficial bugs and insects, like the bees that pollinate your raspberries or the insects that cycle nutrients through your soil. Pesticides also find their way into the food chain because plants absorb chemicals through roots and leaves. Fortunately you can mitigate the risk of using pesticides by relying on ones certified for organic use, which tend to be derived from plants or bacteria.
Note: Certified organic or not, you want to keep pesticides in their original containers, out of reach of pets and children and in a dark and dry place that never drops below 40 degrees or gets hotter than 100 degrees. I keep mine in a dark closet in the house and avoid leaving it in the garden shed.
PESTICIDES CERTIFIED FOR ORGANIC USE
NEEM OIL: Using Neem oil is a great preventive control measure. It comes from the bark and leaves of the Neem tree, a common evergreen grown in tropical and subtropical regions. Azadirachtin, the active ingredient in Neem oil, makes insects grow slowly and eat less. It also makes them lose interest in laying eggs so there are fewer of them to begin with. Neem is particularly effective against fast growing beetles, small caterpillars, and aphids.
Use Neem on plants as soon as you see the first adult bug, and spray weekly. Keep your bees safe by covering treated plants with a row cover. Don’t expect Neem to instantly rid your garden of pests. It works over time by limiting the reproduction and growth of bad bugs. If you want to speed up the process, you can also hand-pluck adult bugs from plants.
How to prepare it: Most Neem products come as a concentrate that needs to be mixed with warm water before spraying it onto your plants. Follow the label instructions to know the proportions to use. Apply the mixture weekly to the tops and underside of leaves. Avoid spraying in direct sun, since it will burn oil-covered leaves, much in the way baby oil causes skin to burn.
Store: Concentrated Neem can be kept for up to two years.
INSECTICIDAL SOAPS: Insecticidal soaps are an effective way to control soft-bodied insects if no beneficial bugs are around to do the job for you. The fatty acids in insecticidal soaps break down the protective cuticles of soft-bodied pests like aphids and caterpillars, which become dehydrated and die.
Soap sprays only kill insects that are sprayed directly so be sure to thoroughly wet both sides of leaves and avoid spraying beneficial insects, like bees and spiders. Repeat applications every five to seven days, as new pests hatch and form colonies. I keep a few premixed spray bottles on hand so I can spray pests as soon as I see them.
How to prepare it: Make your own soap spray by mixing one tablespoon of dishwashing soap per quart of water. You can also buy an insecticidal soap concentrate. Follow label directions for diluting it because using too much can harm plant leaves. If you have hard water at home, use bottled water to make sprays, because the minerals in hard water reduce the effectiveness of insecticidal soap.
Mix only as much concentrate as you need for the day and keep spray bottles out of the sun, which will degrade the quality of your spray and make it less effective. Any unused sprays that haven't been used in a week can be diluted with more water and poured out in the garden far from any storm drains.
Store: Soap concentrates can last for up to five years.
DIATOMACEOUS EARTH (DE): DE is made from the pulverized fossils of tiny sea creatures and looks like broken glass if you peer at it under a microscope. It kills insects by slicing up their protective outer layer and causes fatal dehydration when they walk through the dusty white powder. You can dust the leaves of your plants to kill leaf-eating bugs or create a barrier of white powder at the base of your plants to stop slugs.
DE is great for killing slugs, newly hatched Japanese beetles, and wireworms. It works best in dry conditions because rain makes the powder congeal in clumps and lose some of its sharp edges. If it rains, reapply once your plants have dried.
Store: Make sure to store your DE in an airtight container to keep it dry. Properly stored DE can last indefinitely.
BACILLUS THURINGIENIS (Bt): Bacillus thuringiensis, or Bt, is a naturally-occurring bacteria that ruptures the internal organs of leaf-eating insects like caterpillars. It only works on the bugs that eat treated leaves. It has no impact on pests that are directly sprayed so bees and other pollinators are left alone.
Direct sunlight degrades Bt after a few hours, so apply Bt late in the day when the sun is low. It will work to kill pests during their nightly feeding. You can use Bt every 10 days to control caterpillars and other leaf-eating insects until they're no longer a problem.
Store: Powdered Bt products can last for five years, while liquid Bt products last only about two years.
SPINOSAD: Spinosad is another naturally occurring bacteria, Saccharopolyspora spinosa, which produces a deadly neurotoxin that makes infected insects excited to the point of utter exhaustion. After eating it, insects immediately stop feeding and die within a few days. Spinosad works to control all types of caterpillars and some beetles that eat a lot of leaf tissue.
Apply spinosad to dry leaves as soon as you notice leaf-eating pests in the garden. Thoroughly wet both sides of leaves. Much like Bt, spinosad breaks down in direct sun, so late afternoon applications are the most effective.
Spinosad is somewhat absorbed by plant leaves so one treatment can last up to 10 days. Within the first 24 hours of spraying be careful not to let treated leaves come in contact with beneficial insects, like bees. You can protect your good bugs by draping treated plants in row covers, or fabric, for a day.
Store: Spinosad products last about three years.
PLANTSKYDD: I know people who swear by this. Plantskydd is environmentally safe and works against rabbits, voles, moose, chipmunks, squirrels, nutria, beaver, groundhogs, and deer. It can last up to six months - even over the winter season. It repels, according to company literature, by "emitting an odor that browsing animals associate with predator activity, stimulating a fear-based response that will have garden feeders looking for somewhere else to dine."
Acadia Tucker is a regenerative farmer, climate activist, and author of Growing Perennial Foods: A field guide to raising resilient herbs, fruits & vegetables and Growing Good Food: A Citizen’s Guide to Backyard Carbon Farming. She currently lives in Maine and New Hampshire with her farm dog, Nimbus. When she isn’t raising perennials in her own backyard, she grows hops to support locally sourced craft beer in New England.