Garden Series: Aphids

By Randall Mallette

Gardens are home to numerous insects, many of which can go unnoticed due to their life cycle, habits, and predation. However, not all garden bugs are bad. The presence of some garden bugs are actually very effective pest control measures. This article, however, will focus on a serious pest: aphids.

Aphids are small bugs that can have a big impact on your garden. They are slow moving insects with pear-shaped bodies and usually have spine-like projections from their abdomens. Aphids are commonly black, green, yellow, or grayish in color and feed on the stems, leaves, flowers, and developing fruits of garden plants. In small numbers, aphids may go unnoticed, however, under the right conditions they can reproduce extremely quickly, and are hard to overlook.

Aphids have piercing-sucking mouthparts, which they use to remove plant juices. Heavy infestations can cause leaves to yellow or drop from the plant. Plant growth can be stunted due to heavy feeding, and yields can be affected, especially when aphids feed on the developing fruit, pods, etc. Aphids can also spread diseases in their saliva when they pierce the plant. Additionally, aphids secrete a clear sticky liquid called honeydew. Ants are attracted to the honeydew in large numbers, and are often seen tending the aphids and feeding on the honeydew. Sooty mold also grows on honeydew, and if allowed to build up thickly on plant leaves, sooty mold can interfere with photosynthesis.

The good news is that aphids have many natural enemies. Ladybug adults and larvae are voracious predators of aphids and should be encouraged in the garden. Assassin bugs are solitary insects that roam gardens killing many different types of pests including aphids. A few types of flies prey on aphids, while wasps and hornets also feed on the pesky bugs. Some parasitic wasps even lay their eggs in aphids and the larvae develop inside the aphid, killing it after a short amount of time. Lacewing larvae are fierce predators, and even earwigs consume some types of aphids. In addition to these insects, spiders also feed on aphids. Many beneficial insects can be bought and released in the garden, however be aware that these adults often fly off after release instead of sticking around. Releasing beneficial bugs can be more effective in greenhouses.

If natural predators are not controlling the aphid population sufficiently, it may be necessary to spray. There are several different options, including some effective natural products that work quite well. Malathion is a contact insecticide (must contact the insect to kill) that kills aphids effectively, however, it is a broad spectrum insecticide so it will also kill beneficial insects. Imidacloprid and Bifenthrin are also effective against aphids. Insecticidal soaps and oils are effective against aphids as well, and can be sprayed often. In some cases they can be used on the day of harvest. These work by suffocating the aphids. The drawback is that they require thorough coverage of the plant, including under the leaves. Also, these cannot be used in hot weather because they coat the leaf surface, preventing transpiration. Use these products early in the morning or late in the evening when temperatures have cooled sufficiently. As with any pesticide, thoroughly read and follow the label instructions. Be especially careful using insecticides during bloom to avoid affecting pollinators.

For more information contact Randall Mallette, County Agent, at the local LSU AgCenter Extension Office 318-357-2224. You can also visit us on the web at http://www.lsuagcenter.com or at 624 Second St, Natchitoches.