Around San Diego · Home & Garden

Watch for Aphids in Spring

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[Pictured Above: Larvae of the convergent lady beetle feeding on aphid.  The larvae is often mistaken for a pest. Photo Credit: Jack Kelly Clark, courtesy University of California Statewide IPM Program.]

Article By: Vincent Lazaneo

Each spring as swallows return to Capistrano colonies of aphids appear in gardens.  The insect feeds on plant sap and can be a troublesome pest.  Watch for aphids in your garden and take steps to control them before plants are damaged.

Aphids are small, soft-bodied insects less than 1/16 inch long and have pear-shaped bodies with long legs and two antennae.  Their color may be green, yellow, brown, red or black depending on the species of aphid and the plants they feed on.  Some aphids are covered with a white or gray substance and have a waxy or woolly appearance. Most adult aphids are wingless but winged aphids are produced when populations are high.

Aphids feed on tender new leaves, shoots and flower buds.  They use their piercing mouth parts to suck nutrient laden sap from plant tissue.  Excess liquid is excreted as droplets of sugary honeydew.  Plants and objects beneath infested plants are soiled by the sticky residue which is often colonized by dark sooty mold.  Certain ants feed on honeydew and protect aphids from natural enemies which allows the pest to proliferate.

Aphids reproduce rapidly under favorable conditions.  Most aphids are female that do not need to mate to give birth to live young which are also female.  The ability to reproduce by cloning can enable a single female aphid to quickly create a large colony.

Most plants can tolerate a few aphids but dense populations may stunt or kill young plants especially herbaceous flowers and vegetables.  Established woody plants are rarely killed but aphids distort and soil leaves which may be aesthetically undesirable.  Aphids also transmit harmful viruses that infect and weaken plants.

Use the following methods to protect your plants:

  • Inspect weekly for signs of aphids. Check new growth and the undersides of leaves.
  • Remove aphids.Use your fingers to squish aphids on a single leaf or rub them off a stem. Dislodge aphids by washing infested plants daily with a forceful spray of water until aphids are gone.
  • Control ants.Use toxic baits that ants take back to their nests for the colony to feed on. Baits take a while to work but can eliminate the entire colony.  When ants climb trees, block their access with a sticky barrier like Tanglefoot.  To protect the bark apply a strip of plastic or other material around the trunk, then apply a ring of the sticky barrier on it.
  • Protect beneficial insects. Do not apply insecticides with a persistent toxic residue such as malathion, carbaryl (Sevin) and pyrethroids.  They can kill beneficial insects for days or weeks after treatment.  Use insecticidal soaps or horticultural oils that kill aphids on contact and quickly break down.

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