Most of us have become acquainted with aphid in one form or another. They may be pale green, pale yellow, tan, black or pink, and may or may not have wings. They are very small, about the size of the head of a pin. In small herds, they attach themselves to young leaf and flower buds. Once they have inserted their piercing mouth-parts, they are immobilized. They are so sensitive that they can be killed with slightly soapy water, slightly saline water, or even a few drops of Tabasco sauce in water. (Soap or salt residue can damage foliage, so should be rinsed off after a few minutes.)

Minor infestations on smaller plants can be blasted off with a strong stream of water. This process may need to be repeated daily for about a week or more because aphid are so prolific, but it is easy and not as potentially damaging as soap or salt solutions or contact insecticides. Large infestations, such as in willows or tulip trees, may require professionally applied systemic insecticides.

Fortunately, aphid are usually controlled by natural predators, even if nothing else is done. Parasitic wasps, syrphid flies, ladybugs and lacewings all like to snack on aphid. If the aphid are sprayed off with water, or killed with soapy, salty or even saucy water, the predatory insects simply get out of the way and return later for what remains of their feast. Hopefully, they will like the selection of added condiments.

Systemic insecticides kill insects that eat affected plant parts, but not predatory insects that eat only aphid or other insects. However, contact insecticides will also kill predatory insects, so they will not be around to eat the next generation of aphid. To make things worse, aphid are so much more prolific that their numbers increase faster than new predators can move in.

Ants cultivate aphid because they like to eat the sticky "honeydew" excreted by the insects. The ants not only protect aphid from natural predators, but will also relocate juveniles to greener pastures. Aphid are not as mobile as ants, so rely on ants to get to fresh new shoots.

Although it is nearly impossible to keep ants out of most plants, blocking access into some trees is rather simple. If a tree is not touching other plants or structures, the only access the ants have is the trunk, which can easily be circled with any sticky substance, such as grease. There are actually products that have been formulated for this purpose, and other household substances are certainly cleaner than the axle grease I use on my pear tree. This procedure does not eliminate the aphid, but will make them much more susceptible to predators.

Sooty mold is a messy but harmless fungus that proliferates in honeydew as it rains down from aphid infestations. In severe cases, it can get rather grungy on citrus fruits and patio furniture, and may need to be scrubbed off. Fresh honeydew is more soluble than moldy honeydew, so does not accumulate below trees that are sprayed with water for aphid control.

Tree of the Week:
Pygmy date palm

The largest pygmy date palm, Phoenix roebelenii, that I have ever seen was in the Conservatory of Flowers in Golden Gate Park. It was only about 12 feet tall. Most mature specimens are less than about half that tall. Growth can be so slow that the coarsely textured trunk may be short enough to be obscured by the finely textured arching leaves for a few years.

Pygmy date palm is quite happy in large pots located indoors or out, or in a sheltered area of the garden. It likes a sunny location as a houseplant, but does not like direct sun exposure in the garden. It likes to be watered regularly and is grateful for occasional application of nitrogen fertilizer.

Horticulturist Tony Tomeo can be contacted at 408.358.2574 or at LGHORTICULTURE@aol.com.