Aphids are common pests to house plants, vegetables, annual and perennial flowers, ornamental trees and shrubs. They can often be found in the garden, on trees and shrubs and sometimes on houseplants.
Look for aphids on susceptible plants in the late spring. If they are present they can often be found clustered around leaf or flower buds, or on the under side of leaves. Catch aphid infestations early as one aphid can produce up to 80 offspring in as little as a week and is capable of doing this several times over.
Many aphid species are monophagous which means they feed on only one plant species. Aphids passively feed on the sap of phloem vessels in plants. During feeding, many aphids secrete a clear, sticky, sweet substance, called honeydew. It is often found on or below the host plant and may act as an attractant for other insect pests, such as ants, who use it as a food source.
Honeydew also acts as a host for a harmless black fungus called sooty mould which often grows in the secretion. Sooty mould is a secondary symptom of an aphid infection. In addition to sooty mould, aphids often transmit plant viruses to the plants they are feeding on. These viruses can sometimes kill the plants.
There are several natural enemies which feed on aphids like lady beetle larvae, lacewings, assassin bugs, syrphid fly larvae, various wasps and spiders. Lady beetle larvae consume the largest number of aphids. As these insects are only effective when they are present in the garden, avoiding the use of pesticides will help conserve the populations of these natural enemies.
When there are not enough of the aphid’s natural enemies to keep the infestation under control, try one of the physical control methods listed below:
Spray a steady stream of water at the host plant to knock aphids off. This treatment may have to be repeated several times. I always use this method as the first step and then catch the aphids missed by the shower with any of the following methods.
Rubbing or hand picking aphids from affected plants will also reduce populations. If only a few small colonies of aphids are present, prune affected areas of trees and shrubs to remove aphids and overwintering aphid eggs and dispose of in a tightly sealed plastic bag or container.
Pyrethrum insecticides or insecticidal soap can be sprayed on infested areas of plants to control aphid populations. Pesticides only work on contact so it is important to apply it directly to the aphids. Always carefully follow the label directions when using pesticides.
Make homemade insecticide, using dish soap, preferably Sunlight, mixed to a ratio of 1 tablespoon per gallon of water. This can be put in a spray bottle and applied directly to the aphids. The soap washes off the aphid’s protective waxy coating and causes dehydration.
With some vigilance and the knowledge gained from this column, you are now ready to battle aphids. A careful eye and these tips can help you stay in control.