Sunday, June 23, 2013

Aphids by Bernadette Costa

Aphids on Leaf
Aphids are very common.  Sometimes called plant lice, they are small, soft-bodied, pear-shaped insects, generally less than 1/8” long.  Most are green or black but they can also be found in a variety of other colors as well.  A characteristic common to all aphids is the presence of cornicles, or tubes, on the back ends of their bodies, sort of like “tailpipes”.  These cornicles secrete substances that help protect the aphids from predators.  Over winter, aphids exist as eggs on perennial plants and hatch in the spring.
Aphids are found on almost all types of plants and a few species can cause plant injury. Some aphid species can curl the new leaves of some types of plant. Feeding aphids excrete honeydew, a sticky fluid that can cause nuisance problems. Natural enemies of aphids include lady beetles, flower fly larvae, lacewing larvae, and parasitic wasps.

Physical and Cultural Controls
On shrubs and garden plants, aphids can sometimes be managed by simply washing them off of plants with a forceful jet of water. Hosing plants can lethally injure aphids and very few surviving aphids that are knocked to the ground can successfully find their way back onto their host plant. Exposed aphids can be controlled by insecticides, insecticidal soaps and sometimes with a strong jet of water. 
  • Most dislodged aphids will not be able to return to the plant, and their honeydew will be washed off as well.  Using water sprays early in the day allows plants to dry off rapidly in the sun and be less susceptible to fungal diseases.
  • Some flowers that are perennial, but dieback to the ground in fall, have problems with aphids in the spring. Columbine, lupines and perennial asters are examples. With these plants the eggs of the aphids are laid on the stems in fall, near the point where new shoots will emerge the following spring. Spring problems with these aphids can be prevented by removing the old top growth that contains the eggs before plants emerge in spring.
  • Also check transplants for aphids and remove them before planting.  Wash off before planting.

Organic Aphid Control
Killing aphids naturally is better for your plants, the environment and beneficial bugs in your garden. Here are some natural deterrents for controlling aphids:
  • Grow young plants under row covers. Remember to remove the covers when the plants begin to flower.
  •  Use aluminum foil or reflective mulch on the ground beneath the plants. While you may not want to do this in your flower garden, reflective mulch in the vegetable garden is a very effective deterrent.
  • A strong spray of water from a hose will knock many of the aphids off the plant, and they won’t be able to return. It also rinses off some of the honeydew. Spray the plant every day until the plant is aphid free.
  • Grow plants for a homemade aphid control. Plants such as the following are attractive to aphids and good for organic aphid control. Growing these far from other garden plants will lure aphids away and keep the garden aphid-free: Nasturtium, Aster, Mum, Cosmos, Hollyhock, LarkspurDahlia, Zinnia.

You may also wish to add some herbs known to repel, if not kill, many common garden pests.  You can also try planting garlic or onions near infested plants, as the smell drives aphids away. Try a handful of any of the following: horseradish, cayenne pepper, garlic, or onions.category includes beetles, wasps, and other insects that are predators and parasites of garden pests. Eat aphids.
For a more aggressive approach, you can try insecticidal soaps, at your local garden center. Ask for a contact insecticide without residual activity insecticidal soaps which contain pyrethrins. "Without residual activity" means no harm to the plant.  Using regular household liquid detergent or clothing detergent is not really a good idea and could cause damage to the plant.

For more detailed information on Aphids and insecticidal soaps and oils for getting rid of aphids, see CSU Extension Fact Sheets:   
Insect Control: Horticultural Oils