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How To Control Whiteflies & Aphids
by National Gardening Editors
Few insect pests are more widespread than whiteflies and aphids. They attack indoor and outdoor vegetables, flowers, herbs, shrubs, and trees. They breed quickly, and once their numbers are high, they can damage leaves, stems, fruits, and even roots by sucking plant juices. Let's look at both pests and the safest controls for them.
Tools and Materials
Pruners
Yellow sticky traps
Insecticidal spray: soap, horticultural oil, neem
Hand sprayer
Hose
An aphid's life. Aphids like the low light levels and cool conditions of spring and fall. They will attack all plant parts but prefer young, succulent growth. There are many species of aphids, some named after the plants they attack, such as pea aphids and peach aphids. In general, all are small (1/16 to 1/4 inch long) and oval-shaped, and can be black, white, green, or pink. Although most aren't very mobile, some forms have wings. All reproduce quickly, and under the right conditions a small infestation can become large in no time. By sucking plant juices from leaves and stems, they weaken the plant. More seriously, they can also transmit virus diseases that will gradually debilitate and kill some plants.
A whitefly's life. In cold-winter climates, whiteflies are mostly greenhouse or indoor pests, but they can be found in the garden. In mild-winter climates with no winter cold to kill them, whiteflies are serious outdoor pests. In recent years in the Southwest, pests such as the silverleaf whitefly have been among the most damaging to agriculture.
Adult whiteflies hide and feed on the undersides of leaves. They are most noticeable when you rustle the leaves and a cloud of whiteflies emerges into the air like "plant dandruff," as some gardeners aptly describe them.
Like aphids, whiteflies reproduce quickly, laying white eggs that hatch into white crawlers on the undersides of leaves. Whiteflies thrive in sunny, warm conditions. The crawlers and adult flies suck plant juices, weakening the plants.
Aphid and whitefly controls. The first line of defense is prevention. Check plants regularly. Avoid high-nitrogen fertilizers, which create excess succulent growth these insects love. Isolate infested plants from others and control the pests aggressively.
For whiteflies, hang yellow traps coated with a sticky substance close to the tops of plants. Whiteflies are attracted to the color yellow, and once they land will be stuck and die. Hand-crush small populations of young aphids and whiteflies. Encourage natural enemies in the garden such as ladybugs and lacewings by planting diversity of plants and not spraying harsh chemicals. As a last resort, use low-toxic sprays such as insecticidal soap, horticultural oil, and neem to reduce populations before they get out of hand. Repeat treatments every few days until the problem is under control.
Tips
Aphids can easily be removed from a plant by knocking them off with a stream of water from a hose. Once off, they tend not to climb back up to feed.
Whiteflies are sluggish in early morning and evening, so to control small populations on houseplants, vacuum the leaves, sucking up the whiteflies, too.
Photography by Suzanne DeJohn/NationalGardening.com
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