Controlling Aphids in Your Garden

CONTROLLING APHIDS IN YOUR GARDEN

Most plants can tolerate a low to moderate population of aphids without noticeable damage. On some plants, however, large numbers of aphids can distort foliage and flowers and stunt plant growth.

Aphids excrete "honeydew," a sweet substance that forms a sticky coating on leaves. The honeydew is soon colonized by a fungus called "sooty mold," making leaves look black and dirty. Generally sooty mold is harmless and can easily be washed off with a forceful stream of water on sturdy plants.

If aphid populations are high, there will often be ants present, since they feed on the honeydew. (See the Ant article in this series).

DETECTION

Aphids are very small insects with soft, pear-shaped bodies. They have long legs and antennae, and most have two tube-like structures called cornicles on their hind end. Adults of some species have wings.

Aphids come in many colors and are usually on buds, plant tips, and on the undersides of leaves near the veins. A few species secrete a waxy substance onto their bodies, giving them a white or gray wolly appearance.

LESS -TOXIC CONTROLS

Learn to recognize beneficial insects. Among the most important natural enemies of aphids are the tiny parasitic wasps that lay their eggs inside the bodies of aphids. These tiny wasps cannot sting people. Others include spiders, ladybugs and lacewings. Beneficial insects rarely appear until after aphids have begun attacking plants, so learn to tolerate a low to moderate number of aphids.
Attract beneficials to your garden by planting a wide variety of flowering plants or certain insectory plants (See article in this series Naturally Managing Pests... With a Healthy Garden") can provide beneficial insects with the habitant they need (food and shelter).
Use a forceful stream of plain water on sturdy plants to wash off aphids and honeydew.
Wipe off colonies of aphids from tender plant leaves and buds.
Prune away severely infested portions of the plant. Dispose of properly and do not compost.
Use insecticidal soaps to kill aphids on contact while causing less harm to beneficial insects. These products do not leave toxic residues, sparing injury to the natural enemies.
Use spray (horticultural) oils to control aphids. This minimizes adverse effects on natural enemies.
Don't purchase beneficials before you have aphids. You will be releasing them into your garden to starve. If you have an aphid emergency, first use soap or oil sprays to knock-down the population. Then, if necessary, release beneficial insects. Lacewings are more likely to stay in your garden than commercially available ladybugs.

PREVENTION

Inspect new plants carefully. Don't purchase infected plants.
Use slow-release fertilizers. Maintain healthy plant growth, but do not over-fertilize with high nitrogen fertilizers. Too much nitrogen can over-stimulate succulent plant growth, prompting some aphids to reproduce more quickly. Organic fertilizers are better because they slowly release moderate levels of nutrients.
Avoid excessive pruning because it stimulates aphid-attracting growth.
Use a row cover on new plants and seedlings to exclude aphids and other pests but allow air, light, and irrigation water to reach plants.
Control ants by spraying or painting a 4" wide sticky barrier around woody shrubs or trees. (See the Ant article in this series.) For many sensitive trees, such as citrus, a protective barrier of white latex paint should be applied to the trunk before the sticky barrier.

FOR MORE INFORMATION

The Ventura Certified Master Gardener Program, operated by the University of California Cooperative Extension, provides a free assistance at the Helpline and offers a variety of workshops.

email: mgventura@ucdavis,edu or call (805) 645-1455

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