A Homegrown NH listener recently asked how to keep their garden safe from a variety of pests plaguing her plants and flowers.
I don't like to use pesticides, but a natural approach would be good. Anything I can do to be proactive and not harm beneficials would be great. I haven't used diatomaceous earth in years, but would that help?
Homegrown NH host Emma Erler, lead horticulturist at Kirkwood Gardens, says the first step is to accurately identify the pest that is causing issues in your garden.
"Every single product that you use will be labeled to control pests, so it's possible you could be applying one type and it will not have any effect whatsoever on the pest destroying your plant," says Erler.
Erler says many times hand-picking pests is the best option for a small home garden. It is surprisingly effective for large, slow-moving bugs like caterpillars, japanese beetles, and tomato hornworms. It also prevents them from laying eggs.
It is easiest when the temperatures are cooler and bugs are slower, so try to get out in the early morning or evening. Knock the bugs off the plant into a container of soapy water. Be sure to look under the leaves for bug eggs and wipe them off.
Neem oil, diatomaceous earth, and insecticidal soap are useful garden tools, but many pest issues can be resolved without them. Using a pesticide, even one labelled organic, should always be a last resort, according to Erler.
Neem Oil
How it works: Neem oil suffocates soft-bodied pests on contact, and disrupts their life-cycle.
Benefits: It can deter a range of insects, including aphids, beetle larvae, caterpillars, lacebugs, leaf hoppers, leafminers, mealy bugs, thrips, and whiteflies. It can also manage some fungal diseases, such as powdery mildew.
Drawbacks: It can harm beneficial insects, not just pests. It can also damage plants by burning their foliage. Test a small area before covering the whole plant.
Insecticidal Soap
How it Works: Insecticidal soap works on direct contact by dissolving the protective waxy layer of an insect's outer shell and causing dehydration.
It must fully coat the pest to work. Bugs that land on the plant after the soap dries are unaffected.
Benefits: Most effective on soft-bodied pests such as aphids, adelgids, lacebugs, leafhoppers, mealybugs, thrips, sawfly larvae, scale insects, and spider mites.
Drawbacks: It can burn or scorch certain sensitive plants, although it is more likely with home brewed concoctions as opposed to commercially-formulated insecticidal soaps. It is toxic to fish and other aquatic organisms so do not apply near bodies of water.
Diatomaceous Earth
How it Works: Diatomaceous earth is a powder made from fossilized remains of microscopic aquatic organisms called diatoms. It causes insects to dry out and die by absorbing oils and fats from the cuticle of the insect’s exoskeleton.
Benefits: Effective on soft-bodied crawling insects such as caterpillars and slugs.
Drawbacks: Only effective in dry conditions. If it rains, it must be re-applied.
Getting ahead of pests is always easier if you catch them before they multiply so keep a wary eye out while enjoying your garden.
If you have a gardening question for Homegrown NH, email or send a voice memo to HomegrownNH@NHPR.org.
Homegrown New Hampshire is a collaboration between Squam Lakes Natural Science Center and NHPR.
