A common pest on many plants, these sap-sucking insects are often noticed feeding in clusters on new plant growth. Here’s how to control aphids organically without using toxic sprays.
There are approximately 4,000 aphid species found throughout the world. Low to moderate numbers are usually not harmful to plants and rarely require aphid control. However, heavy infestations will cause leaves to curl, wilt or yellow and stunted plant growth. A general decline in overall plant vigor will also be noticed. Several species can transmit plant diseases, particularly viruses which they pass on during feeding.
Aphids are small (1/8 inch long), soft bodied, pear-shaped insects that may be green, yellow, brown, red or black in color depending on species and food source. Generally adults are wingless, but some can grow wings, especially if populations are high. They have two whip-like antennae at the tip of the head and a pair of tube-like structures, called cornicles, projecting backward out of their hind end.
Note: As they feed, aphids secrete large amounts of a sticky fluid known as honeydew. This sweet goo drips onto plants, attracting ants and promoting a black sooty mold growth on leaves. Cars and lawn furniture that are under infested trees will also be covered with this sticky fluid.
In spring wingless female aphids hatch from overwintering eggs and soon give birth to many nymphs (males are not present). Young nymphs increase gradually in size and within a week give birth to many more nymphs. This process is repeated several times and results in huge population explosions. As the colony grows, a few of the females develop wings and fly off to other host plants to start new colonies. In late summer and early fall sexual forms (males and females) develop which mate and lay overwintering eggs. There are many overlapping generations per year.
Note: Most aphids, except for the sexual forms, do not have to mate in order to reproduce, and they produce live young, rather than eggs.
- Pinch or prune off heavily infested leaves or other plant parts.
- Use the Bug Blaster to hose off plants with a strong stream of water and reduce pest numbers.
- Commercially available beneficial insects, such as ladybugs and lacewing are important natural predators. For best results, make releases when pest levels are low to medium. If populations are high, use a least-toxic, short-lived natural pesticide to establish control, then release predatory insects to maintain control.
- Safer Insecticidal Soap or botanical insecticides can be used to spot treat heavily infested areas.
- Horticultural oils should be applied early in the season or late in the fall to destroy overwintering eggs.
- Do not over water or over fertilize – aphids like plants with high nitrogen levels and soft new growth. Use organic fertilizers which release nutrients slowly.
Tip: Ants feed on the honeydew that sucking insects produce and will protect these pests from their natural enemies. An application of Tanglefoot Pest Barrier to the stalks of roses and other woody plants will help keep ants away.