Pests in Gardens and Landscapes: Quick Tips


Published   10/17

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Green peach aphid colony

Green peach aphid colony.

Sticky honeydew, black sooty mold and cast skins are signs of an aphid infestation.

Sticky honeydew, black sooty mold and cast skins are signs of an aphid infestation.

The convergent lady beetle is one of many common natural enemies of aphids

The convergent lady beetle is one of many common natural enemies of aphids.

Almost every plant has one or more aphid species that occasionally feed on it, but low to moderate numbers of aphids usually aren’t damaging to gardens or landscape trees. Although aphids can curl leaves and produce sticky honeydew, they rarely kill plants, and can usually be washed off with water. When aphid numbers are high, natural enemies often feed on them, eliminating the need for pesticides. When pesticides are necessary, use less-toxic products such as insecticidal soaps and oils.

Aphids are common in your garden because:

  • Aphids like lush, new growth. Don’t over fertilize; use organic or slow-release products.
  • Aphids build up on flowering plums, roses, tulip trees, crape myrtles, apples, and many vegetables. Expect aphids when you grow these plants.
  • Ants protect aphids from their natural enemies. Keep ants off plants to help beneficials do their job.

To reduce aphids:

  • Prune out infested leaves and stems.
  • Knock aphid populations off plants by shaking the plant or spraying it with a strong stream of water.
  • Protect seedlings with covers or aluminum foil mulches.
  • Wait for hot weather; some aphids are heat- intolerant and will be gone by mid-summer.

Protect aphids' natural enemies:

  • Lady beetles (“ladybugs”), both adults and larvae;
  • Lacewings
  • Syrphid fly larvae
  • Soldier beetles
  • Parasitic mini-wasps that turn aphids into crusty “mummies”.

Beneficial insects such as lady beetles and lacewings will come into your garden naturally when aphids are abundant. Protect these “good bugs” by avoiding the use of insecticides that can be toxic to them.

If insecticides seem necessary, use the safest products.

  • Use nonchemical pest control methods first to manage aphid populations. However, if you feel insecticides are necessary, choose less toxic products.
  • Insecticidal oils and soaps are the safest products. When properly used, these materials solve most aphid problems.
  • Oils and soaps work by smothering aphids, so apply these products thoroughly. Don’t apply them to drought-stressed plants or when it is very hot. A few plants are sensitive to these products.
  • Apply insecticidal soaps, soap-pyrethrum mixtures, or neem oils on vegetables or small bushes such as roses.
  • Narrow range horticultural oils—such as supreme or superior oils—are appropriate for larger trees.
  • Oils and soaps don’t kill aphids hidden within curled leaves. Prune these out. Systemic insecticides can kill hidden aphids, but they are much more toxic and might kill bees and other beneficial insects on flowering plants.

Read more about Aphids.

Minimize the use of pesticides that pollute our waterways. Use nonchemical alternatives or less toxic pesticide products whenever possible. Read product labels carefully and follow instructions on proper use, storage, and disposal.

Statewide IPM Program, Agriculture and Natural Resources, University of California
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