Sharp-eyed handpicking and trapping can control many garden pests, but not every insect battle can be won with hand-to-hand combat. Instead, you may need an intervention plan that affects the pest, yet causes little or no harm to natural predators and beneficial life-forms that live in your garden. This is where organic pest control products can come to the rescue. To help you match the best products with each pest, we’ve organized our guide in two ways — by pest and by remedy. Download our convenient “Organic Remedies for Garden Pests” table, and then bring yourself up to date on cures with the information following in this article. The information in the table and the text is based on current recommendations from sustainable agricultural research centers throughout North America.
In the last few years, much has been learned about the secret world of garden insects. Spraying is not your only option. Growing flowers to provide nectar and pollen for beneficial insects, and excluding pests with row covers are both remarkably effective preventive measures. And don’t forget our feathered friends — wild birds, ducks, and chickens feast on all kinds of garden pests (see “Poultry Pest Patrol” below).
Before you decide to use any organic pest control product, take the time to correctly identify the pest and see if it will respond to cultural controls, such as simple handpicking. (Using the wrong product could cost you time and money, and may backfire by killing natural predators.)
The Basic Biologicals. The oldest and best-known of biological pesticides is Bt (Bacillus thuringiensis). The subspecies B. thuringiensis ssp. kurstaki remains a top remedy for leaf-eating caterpillars. Bt is based on a naturally occurring soil bacterium that causes the insect’s gut to rupture several hours after ingesting it.
Sunlight degrades Bt after a few hours, so it’s best applied late in the day to be consumed during the nightly feeding. Keep in mind that your objective is to place the substance where the caterpillars will eat it. In the case of corn earworms, this means squirting the Bt solution into the tips of young ears of corn. When using Bt to control leaf-eating pests, repeat treatment every 7 to 10 days, or until it’s no longer needed.
Always follow label directions for diluting concentrated solutions of Bt and other natural pesticides. Some Bt products include genetically modified strains; products listed by the Organic Materials Review Institute (OMRI) include only naturally occurring forms.
Another biological pesticide, called “spinosad,” is a fermented brew of two naturally occurring bacteria that slowly paralyzes insects after they eat it. Spinosad is widely used in fire ant baits, and it’s also useful for controlling leaf-eating beetles, such as Mexican bean beetles and Colorado potato beetles. Where cabbageworms, armyworms, European corn borers, or other caterpillars require repeated treatment, experts recommend alternating Bt with spinosad to keep insects from becoming resistant.
Although diatomaceous earth feels as soft as talcum powder in your hand, under a microscope you would see that each particle has sharp edges. When enough gets wedged into the head and leg joints of soft-bodied insects, they dry up and die. Diatomaceous earth deters slug feeding, too. The effects are short-lived because it seeps into mulch and soil after rain, but a thorough, well-timed dusting can still give good control of aphids, leafhoppers, and slugs or snails. In contrast, the particles of kaolin clay are so tiny that they form a thin paint when mixed with water. Leaves covered with the stuff are ignored by many common pests, and those that do nibble on clay-coated leaves usually move on. Organically grown produce that has traces of a dusty off-white residue was probably treated with kaolin clay.
Aphids, mites, and other small sucking insects that don’t have much of an exoskeleton (shell) often can be controlled with two applications of insecticidal soap, 5 to 7 days apart. Assuming you get the soap on the insects (which is crucial), its fatty acids cause the bugs to die through desiccation. For best results, blast infested plants with a strong spray of water to dislodge offenders, then apply insecticidal soap to kill any missed by the water spray. (Once tiny sucking insects are washed to the ground, few make it back up to tender new growing tips.) Use the soap sparingly, as it can reduce yields of some crops, and know that plant leaves can be damaged if you apply insecticidal soap on a hot, sunny day.
Oils that clog up insects’ sensory and breathing systems can be useful in the control of whiteflies and a few other pests. Most horticultural oils are now made from soybean oil, made into a water-soluble emulsion. (These oils may burn plant leaves in hot weather.)
If you’re going to go the oil route, in most cases it’s best to opt for neem oil, which is derived from the tropical neem tree. After dozens of studies, neem hasn’t turned out to be the big fix for garden pests it was hoped to be, yet it has earned recognition for control of squash bugs, Mexican bean beetles, and a few other hard-to-control insects. In addition to the smothering action of neem oil, contact with or ingestion of neem’s active ingredient slows feeding and radically reduces reproduction. Neem seldom eliminates pests altogether, but it often reduces them to levels that can be ignored or managed by handpicking.
If you’re willing to pay close attention to details of timing, temperature, and moisture, you can do some amazing things with microscopic life-forms, such as wipe out every cutworm in a newly dug bed with beneficial nematodes. Japanese beetle grubs make fine hosts for nematodes, and some people have even had luck injecting these tiny parasitic eelworms into the stems of squash plants infested with squash vine borers.
Where grasshoppers are the biggest problem, the farmscaping approach that works best is to maintain a moist, grassy area away from your garden, and encourage grasshoppers to congregate there by mowing around it. In early spring, just as grasshoppers begin to emerge, place baits that contain the spores of Nosema locustae in and around the grasshopper habitat. Young grasshoppers that eat the bait will grow weak and die. Milky spore disease, applied in fall or early spring, does a similar number on underground Japanese beetle larvae.
Beauveria bassiana is a parasitic fungus, the spores of which germinate and grow on whiteflies, thrips, and several other pests, turning them into white mummies. It’s a useful tactic, but may result in unwanted casualties of lady beetles and other susceptible insects.
Possibly the largest citizen science project of its kind, The Big Bug Hunt is using reports from real gardeners to track how bugs and pests spread. The creator of the project, Growing Interactive, is devising a prediction system that will send alerts when pests are heading your way, so you can take preventative action. And with an easy identification guide available at the website, it’s easy to take advantage of this new tool in the fight against garden pests by reporting the insects in your own garden at The Big Bug Hunt.
Chickens, ducks, guineas, and turkeys can be great allies in your garden pest control endeavors. The following pests can be reduced by poultry: ticks, mosquitoes, flies, grasshoppers, Japanese beetles, fire ants, termites, pill bugs, grubs, crickets, cabbageworms, and millipedes.
Check out these books for even more information on organic pest control methods for your garden.
The Naturally Bug-Free Garden by Anna Hess
Attracting Beneficial Bugs to Your Garden by Jessica Walliser
Farming with Native Beneficial Insects by The Xerces Society
Free-Range Chicken Gardens by Jessi Bloom
Barbara Pleasant has practiced organic vegetable gardening for 30 years and has authored numerous books. Pleasant lives in Floyd, Virginia, where she grows vegetables, herbs, fruits, and flowers, and where she keeps a small flock of chickens.
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