Gardening: The benefits of bugs

While “benefits” and “bugs” seem like antonyms, certain insects actually help organic gardens be healthier.

“Beneficial insect is a term applied to insects that have a positive role in the garden,” said Candace Simpson, a University of California Extension master gardener. “Some (bugs) are pollinators of plants; others are predators or parasites of pest insects. ”

The key is not to be too liberal with bug sprays, she said. “It is important to avoid broad-spectrum pesticides, even so-called ‘organic’ or plant-based insecticides, as they will kill beneficial insects as well as pests,” she said.

Instead, Simpson, who teaches a class on bug benefits to gardens, suggests that home gardeners should manage pests through things like physical barriers and traps, hand removal, and encouraging natural enemies to prey upon plant parasites.

When pests do multiply too quickly to be brought under control by natural enemies, Simpson suggests choosing pesticides that have the least negative effect on the environment or any organism other than the one to be controlled. Good options include dormant oils, which might be used to smother insect eggs on dormant fruit trees, and insecticidal soaps, which might be used on a very bad aphid infestation.

Also, a bacterial pesticide called Bacillus thuringiensis, or “Bt” for short, can be used to destroy cabbage worms, according to Simpson. She said Bt wouldn’t affect bees or other beneficial insects, though it can kill caterpillars.

“Fortunately, many butterflies lay their eggs on plants that are not for food,” said Simpson. “So if you just apply Bt carefully to food plants that are being eaten by caterpillars, only those caterpillars will be affected. Or a good alternative is to handpick caterpillars that are eating your veggies and skip the Bt. That is what I do.”

Caterpillars are not the only insects that blur the line between beneficial bugs and pests, Simpson said.

“All insects have a role to play in the ecosystem. Flies and mosquitoes can pollinate flowers, and ants eat insect eggs and also aerate the soil. Pest insects and snails, which are not insects but mollusks, and their eggs are food for other organisms,” she said.

Although mosquitoes may contribute to pollination, Simpson recognizes the annoyance and danger of their bites and the reasons for eliminating them. She only advises against using a pesticide that will kill other insects as well.

“Mosquitoes can be prevented from breeding by making sure there are no containers of standing water where they can lay eggs,” said Simpson. “Or by using ‘mosquito dunks,’ small solid cakes of a bacterial pesticide that you float in water. They only kill mosquito and fly larvae. Or we can smash them. Or wear protective clothing or use insect repellent.”

Palo Alto resident Sue Luttner also likes the “smashing” approach in some cases. She said she keeps an eye on all the leaves in her garden, and as as soon as she sees holes, she checks out the backs for eggs and larvae of pest insects, and then she smashes them.

“I like to spend time in the garden, and that gives me a chance to intervene early,” said Luttner. “Most of the native plants don’t seem especially susceptible to insect damage, but the vegetables and the fruit trees are, so I try to stay alert to bad bugs and kill them whenever I see them.”

Gardeners can also discourage exploding insect populations by intermixing different crops — placing tomato plants in ones or twos around the garden, for example, with beans or onions or something in between, so that if one patch gets infected, the bugs won’t necessarily march unimpeded right through the entire crop, Luttner said.

“I’ve learned not to crowd the crops, because that invites aphids. When I do see signs of aphids, I either cut off the affected shoots or pull out the plant immediately,” she said.

When it comes to aphids, Palo Alto Master Gardener Callie Elliston said she would wait for ladybugs to eat them. “Ladybugs can eat 30 to 50 aphids in an hour,” said Elliston. “Some of my rose buds are covered with black and green aphids. I used to hose them off with water, but now I know that if I’m patient, the ladybugs will soon come to the garden and eat all of the invaders.”

Ladybugs and their larvae help control aphids as well as other pests such as beetle larvae, white flies and mealybugs, said Elliston. She said ladybugs often lay eggs on the underside of leaves and gravitate to certain plants, such as cilantro, oregano, dill and yarrow. Some local hardware stores carry live ladybugs for purchase, something that can delight child gardeners.

Another idea is to get a good look at bugs with a magnifying glass. “An inexpensive 10X hand lens is a good investment for a gardener, to get a better look at insects and their activities,” Simpson said.

Even with magnification, some beneficial bugs may be hard to distinguish from pests, Simpson said, adding that she can help people learn what to look for in terms of insects during her upcoming seminar on beneficial insects on April 21, 7-8:30 p.m. at Rinconada Library, 1213 Newell Road in Palo Alto.

Freelance writer Crystal Tai can be emailed at crystal2@stanfordalumni.org.

Freelance writer Crystal Tai can be emailed at crystal2@stanfordalumni.org.

Freelance writer Crystal Tai can be emailed at crystal2@stanfordalumni.org.