Organic Damage Control
- Drench plants with strong sprays of water from a garden hose to kill aphids.
- Keep your plants as healthy as possible. We have customers who swear they never get aphids because they regularly use Seaweed Extract on their plants to keep them vigorous and healthy.
- Introduce lady beetles and lacewings into your garden.
- Control ants that guard aphid colonies in trees from predators by placing sticky bands around the trunks.
- Spray aphids with insecticidal soap such as Safer, neem oil (on tolerant plants), and homemade garlic sprays.
As the season heats up, you’re no doubt starting to see aphids on your plants. These tiny, soft-bodied insects reproduce like crazy and have long, slender mouth parts that they use to pierce stems, leaves, and other tender plant parts. Aphids can be green, yellowish, black, red or powdery gray (almost translucent). As our friend and Master Gardener Pam Perry likes to remind folks, the appearance of aphids does not mean that you have failed as a gardener – it’s just a sign that summer is coming. It’s also a sign that you’ve got some yummy winter greens still in your garden nearing the end of their season and just ripe for an aphid’s appetite!
Both adults and nymphs suck plant sap, which usually causes curled leaves, buds, branch tips, and stunted plants. Severely infested leaves and flowers may drop. As they feed, aphids excrete a sweet, sticky honeydew onto the leaves below.
Although they may be found singly, aphids often feed in dense groups on leaves or stems. And unlike other insects, most aphids do not move rapidly when disturbed. Although aphids rarely kill a mature plant, they can make a mess of if with the honeydew and stunted growth.
Check your plants regularly for aphids – at least twice weekly when plants are growing rapidly. Many species of aphids cause the greatest damage when temperatures are warm but not hot (65° to 85°F). Once their numbers are high and they have begun to distort and curl leaves, it is often hard to control them because the curled leaves shelter aphids from insecticides or natural enemies. It’s likely you won’t win the fight against aphids, so continue to harvest your infested plants. Just wash your produce in a bit of salted water to dissolve and kill the aphids.
Important natural enemies of aphids are various species of parasitic wasps; they lay their eggs inside aphids. The skin of the parasitized aphid turns crusty and golden brown. Many predators also feed on aphids. The most well known are lady beetle and lacewing. Naturally occurring predators work well, especially in a small backyard situation. Commercially available lady beetles may give some temporary control when properly handled, although most of them will disperse away from your yard within a few days.
How Long Do They Live?
Most aphids reproduce asexually throughout most or all of a mild season. Female aphids can reproduce without mating, giving birth continuously to live nymphs. Nymphs mature in 1 to 2 weeks and start producing offspring themselves.
When days become shorter in the fall, both males and females are born. They mate, and then females lay eggs on stems or in bark crevices. The eggs overwinter and hatch the following spring. In very mild climates and in greenhouses, aphids may reproduce year-round.
Weather also impacts aphids. They start to die out when the summer heat regularly goes past 100 degrees in the desert.
Before You Plant, Check The Area
Before planting vegetables, check surrounding areas for sources of aphids and remove these sources. Some aphids build up on weeds, moving onto related crop seedlings after they emerge. Always check transplants for aphids and remove them before planting.
Where aphid populations are localized on a few curled leaves or new shoots, the best control may be to prune out these areas and dispose of them.
High levels of nitrogen fertilizer favor aphid reproduction, so never use more nitrogen than necessary. Slow-release fertilizers such as organic fertilizers or urea-based time-release formulations are best.
Because many vegetables are susceptible to serious aphid damage primarily during the seedling stage, reduce losses by growing seedlings under protective covers in the garden, in a greenhouse, or inside and then transplanting them when the seedlings are older and more tolerant of aphid feeding. Protective covers will also prevent transmission of aphid-borne viruses.
Another way to reduce aphid populations on sturdy plants is to knock off the insects with a strong spray of water. Most dislodged aphids won’t 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.
Here’s our best advice on controlling aphids
Use a hose to vigorously wash them off daily.
Use beneficial insects such as ladybugs and green lacewings. The trick is to release them when you begin to see aphids so that they have enough to eat, but before the infestation becomes overwhelming.
If you want to go the next step, insecticidal soap – such as Safer – and neem oil provide a bit of temporary control if applied thoroughly to the infested plant. To get thorough coverage, spray these materials with a high volume of water and target the underside of leaves as well as the top. Soaps and neem oil only kill aphids present on the day they are sprayed, so daily applications may be necessary.
Predators such as lady beetles often become abundant only after aphids are numerous, so applying non-persistent insecticides like soap or oil may provide more effective long-term control. Although these materials do kill natural enemies that are present on the plant and hit by the spray, because they leave no toxic residue, they do not kill natural enemies that migrate in after the spray. Do not use soaps or oils on water-stressed plants or when the temperature exceeds 90°F or you will burn your plants.
Sources: University of California Integrated Pest Management Program, Organic Gardening Magazine, University of Arizona Cooperative Extension Yavapai County