Home & Garden

How to control garden pests

Snails cluster on a plant leaf at the garden of the sun, while snail damage is evident on the leaves.
Snails cluster on a plant leaf at the garden of the sun, while snail damage is evident on the leaves. Fresno Bee File Photo

The garden pests that cause damage to plants in spring are not necessarily the same as those we try to control in summer. Snail and slugs are most active in the cooler spring and fall months with some rainfall; in summer they go into a state of semi-hibernation.

Aphids, which feed on flushes of tender new green growth, are also most active in spring and fall. Hoplia beetles are only actively chewing on the petals of white or light-colored flower petals (especially on roses) for a few weeks in spring.

Pesticides have changed greatly during the 40 years I’ve been gardening. Broad spectrum insecticides such as malathion that left a long-lasting residue killing all insects that come in contact were once the first choice, but in the last couple of decades the importance of eliminating the use of more toxic insecticides in order to maintain a good balance in the garden of beneficial insects and the pest insects they prey upon has become more accepted by most home gardeners.

Elinor Teague

Metaldehyde snail and slug baits are still widely available. Metaldehyde is toxic to pets, children and wildlife. The pellet baits are often formulated with apple pectin that is very attractive to dogs; the flake baits are less so.

Iron phosphate baits including Sluggo, Escar-go and Bayer’s Slug and Snail Killer Bait are much less toxic and can be applied in areas where pets, children and wildlife can reach them. (Still not a good idea!) The gardener will seldom see the empty shells of dead snails after applying iron phosphate baits. The bait is carried back to the hiding places and the snails and slugs die there.

When applying iron phosphate baits, don’t make big piles. Instead, sprinkle the bait near the hiding places you found by following the slime trails. Reapply every two to three weeks as needed.

Aphids can be killed easily with a blast of water from the hose that knocks them down so suddenly they leave their sucking mouthpieces behind. Lady beetle and syrphid fly larvae (both look like tiny gray and orange alligators) will eat 100 aphids a day. Insecticidal soaps kill only the aphids they contact, leaving no toxic residue. Do not spray insecticidal soaps, horticultural oils that smother soft-bodied sucking insects or neem oil if you see lady beetles, syrphid flies or their larvae nearby, or if bees are actively foraging. Let them do the work naturally.

Hoplia beetles are small, square, gray or bronze-ish-colored beetles that prefer to feed on flower petals, burrowing into the center of the blossoms and hiding from predators. Even highly-toxic broad spectrum insecticides have little effect on hoplia beetles since their hard shell protects them.

Control for hoplia beetles begins with killing them at the grub stage, before they destroy every white rose and all light-colored flowers in the garden. The beetles lay eggs that hatch into grubs in lawn areas and the grubs can be killed in October by applications of beneficial nematodes. The nematodes, which are alive and shipped in cold boxes, can be ordered online.

Reduce the springtime hoplia beetle population now by handpicking them and dropping them into soapy water or by stepping on them and allowing the birds to clean up the mess.

Elinor Teague: etgrow@comcast.net