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Controlling Aphid Populations

Aphids are a common pest in the garden and orchard.  Aphid infestations are greatest in the spring and fall when temps are between 65-80F. There are many different species of aphids and most will not kill plants but they can be vectors for viruses and also their honeydew can lead to growth of sooty mold fungus. Some aphids will release a toxin and cause the leaves of trees to curl. They will then go into the curled up portion to protect themselves from predators.

In our video,Getting Rid of Aphids, Tricia introduces us to several methods of getting rid of aphids. Some of these methods include cultural control, biological control, non-chemical control and lastly chemical control. Let's go a little further into some of these control methods!

Cultural Controls

leaves removed from kale

Practicing good cultural controls in the garden is the least toxic, and a great place to first focus on to keep aphid populations at bay. The following are a few suggestions:

  • Weed control - aphids may seek refuge in weeds so keep them pulled or cut down to discourage them from setting up home.

  • Control ant populations - ants will herd and protect aphids from predators in order to "milk" the honeydew produced by aphids. If you see a steady stream of ants in your trees, good chance they are going to milk the aphids. You can put sticky bands around the trunk of the tree to help stop the stream or put bait stations at the base of the tree as well. Check out our video, How to Get Rid of Ants, for helpful information on ant control.

  • Stop excess nitrogen feeding - Don't over fertilize with nitrogen; aphids are attracted to new lush growth which is promoted by nitrogen. Try using an organic, slow release balanced fertilizer for a continuous supply of nutrients.

  • Crop rotation - don't plant susceptible plants in the same part of the garden every season.

  • Put down reflective mulch - in the spring-time, putting down some silver colored reflective mulch before planting may help repel aphids. You will want to remove it when the summer heat hits.

  • Remove infested leaves - Strip the leaves infested with aphids. This will remove aphids and promotes healthy leaves as well as providing good air circulation.

  • Plants that attract beneficals - Plant things that attract beneficial insects such as sweet alyssum, yarrow, sweet fennel, sweet clover, Queen Anne's lace, or hairy vetch. Mixes such as PVFS Good Bug Blend are great choices to plant along side the garden. This mix contains seeds which will provide a perfect habitat and nectar for beneficial insects.

Biological Controls

syrphid fly larvae

Beneficial insects such as ladybugs (adults and larvae), lacewing larvae, syrphid fly larvae and parasitic wasps enjoy an aphid dinner. Keep plants around the garden that will attract these beneficials (see above) and avoid spraying with chemicals that will kill these garden helpers.

Non-Chemical Controls

Don't reach for the chemicals just yet. There are still several non-chemical controls that can be implemented. Aphids are soft-bodied and can be killed by rubbing (squishing) them with a cloth or blasting them with a strong stream of water. The Bug Blaster Spray Nozzle attached to a garden hose works wonders!

Floating rowcovers can be draped over plants before aphids have time to establish a foot hold on tasty plants. Check out our Agribon AG15 rowcover, it is lightweight enough to be left ontop of plants and should not cause heat build up. It will also protect from birds and cabbage moths. Lastly, Green Sticky Traps can be placed throughout the garden where aphids are a problem. The green color attracts aphids to the sticky card. You might also catch some thrips and hoppers with the card as well.

Organic Chemical Controls

The use of chemicals should be the last resort at controlling aphids. Organically-based chemicals are a better choice than synthetic, harsh chemicals as the organic chemicals cause less damage to beneficial insects. Products such as Insecticidal Soaps and Organocide are labeled for use on soft-bodied insects like aphids.

For more information about aphids and great photos, check out the UC IPM Online website.

Photo of the syrphid fly larvae by Beatriz Moisset.

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