The blue potato bush is recognized by its abundant purplish-blue flowers. It is often grown as a tall, sheared shrub.
Photograph by Shari Kaplan
Everything you wanted to know about ... aphids?
By Tony Tomeo
Aphids suck! Quite literally. All insects feed by one of several means and have mouthparts appropriate to their method of feeding.
Moth larvae have mouthparts suitable for chewing. Thrips have rasping mouthparts to scrape foliar surfaces so they can then consume the fluid exuded from the damage. There are a few other creative feeding habits.
Aphids and their relatives have piercing and sucking mouthparts. Hence, my earlier comment.
Like rabbits, aphids are extremely prolific because they are eaten by so many predators. In fact, without ideal conditions, like those found on fresh young rose shoots, aphids would be easily controlled by predatory insects. They are only able to proliferate as a result of their symbiotic relationship with ants. Scale, related to aphids, has a similar arrangement with ants.
The sticky excrement produced by aphids, known as honeydew, is a favorite sustenance of ants. (Yum!) Consequently, ants have become quite proficient at "herding" aphids. The ants relocate them to more productive foliar growth, since what was formerly grazed succumbs to overgrazing. Ants also protect the aphids from predators and even try (often unsuccessfully) to prevent sooty mold from overtaking their crop of honeydew.
Many severe aphid infestations occur without the help of ants, and can be distinguished from infestations that rely on ants by an absence of ants. (Duh!) However, most severe infestations are established and maintained by ants.
Infested plant specimens may be pruned away from contact with any of the surroundings to limit access to ants. When clear from the surroundings, the only access for ants is the point at which the main trunk or stem originates in the soil. This can easily be blocked by creating a barrier the ants cannot cross, such as grease or Vaseline. Vaseline may need to be periodically replaced as it degrades, however.
Plants that are inaccessible to ants can then be simply rinsed with a garden hose to remove much of the honeydew and some of the aphids. Blasting the aphids with as much pressure as possible without damaging infected specimens may remove most of them. Periodic rinsing or blasting (blasting is more fun) inhibits new infestation. Although there may be some aphids present, they cannot proliferate. Even if it is not practical to prune an infected host clear from the surroundings, rinsing or blasting works well.
Unlike ants, predatory insects can fly into infected hosts to consume the aphids. Some predators do not eat aphids as adults, but lay eggs on infected hosts so that their larvae can consume the aphids. Unlike aphids, populations of predatory insects remain stable even with foliar rinsing, because those that are eliminated are easily replaced from the outside.
Mildly soapy water is more effective at killing aphids because it kills those that remain attached to the host. However, it can leave a residue if not rinsed off later and can damage sensitive new growth or roots if too much soap is used. Soapy water is useful for species such as roses that can be damaged by water on the foliage. Soapy water rinsing is not necessary as frequently as rinsing with plain water.
More information concerning control of aphids as well as a few other pests--without the use of chemical pesticides--is available from the West Valley Clean Water Program at 408.354.4734.
Flower of the Week: Blue potato bush
I sometimes wonder where some of these common names originate. The blue potato bush, Solanum rantonetii or Lycianthes rantonnei, is naturally in the form of a bush, but I have yet to see it produce blue potatoes. As an informally pruned or rarely sheared shrub, it can grow rapidly to six feet tall. With support, it can grow considerably taller. Without support or shearing, it can sprawl over an area wider than its own height, but is sparse. It is most commonly grown as a standard--formally sheared into a small dense shrub on a staked, bare, vertical stem.
Blue potato bush is generally evergreen in the Santa Clara Valley, but may defoliate and experience minor frost damage during cooler winters. It can be killed by severe frosts. The size of the foliage is variable, but individual leaves are generally less than three inches long and about an inch wide. The bright purplish blue flowers with yellow centers are only about one inch wide, but very profuse from spring to autumn and often into winter if the weather is warm.
Horticulturist Tony Tomeo can be contacted at 408.358.2574 or at LGHORTICULTURE@aol.com.
Sunnyvale, California Since 1994
