Of mildew, aphids, and oleander

STEVE KAWARATANI

“I feel coming on a strange disease ...”

--Frank Lloyd Wright

“Why this is very midsummer madness.”

--Bill Shakespeare

As a consequence of our on-and-off warm, humid and overcast

weather, I have been busy dispensing advice on pest and disease

management to clients and friends. During my Design Review rounds, I

find that questions regarding insects and mildew often take

precedence over ocean views and privacy. I don’t mind. My patients

are plants, routinely infested and injured by a familiar gang of

pests or diseases -- but not always.

Seasoned gardeners recognize the usual problems riding roughshod

in their garden. Powdery mildew, aphids, caterpillars and mites are

expected this time of year. There are many tried and true control

options available with varying degrees of efficacy -- depending on

your toleration of plant damage versus pesticide pollution. But what

happens when something bad occurs in your garden, and you don’t

recognize the problem?

Identification is the key to proper management of plant pests and

diseases.

Many of the “problems” I see at first display symptoms similar to

insect or disease damage. However, closer inspection often reveals

that the damage is the result of either natural occurrences, such as

extreme heat or sunlight, or unsound cultural practices -- improper

watering or windy locales.

Environmental factors may even predispose a plant to be attacked

by weakening its natural immune system. Before dusting off that old

bottle of nerve gas or calling Western Exterminator, one should first

ascertain what is really ailing your plant. It may be as simple as

moving the plant around the corner into the shade. If you are

uncertain of the problem, consider consulting your favorite nursery.

One thing I have learned over the years is that there is a nearly

inexhaustible horde of pests and diseases waiting to invade our

garden borders.

They arrive primarily through natural migration and contaminated

shipments of live plants and foodstuffs. That is the reason

California has strict regulations governing the inspection of plant

material into and within its boundaries.

Giant whitefly has appeared again in a big way. Not only are the

adults huge -- many times larger than whitefly -- but they quickly

multiply and create a trademark colony of white threads that hang

from the undersides of infested plants. Washing the leaves constantly

with a stream of water and applying horticultural oils and

insecticidal soaps are the best line of defense.

Eugenia was once a popular plant in Laguna, useful for hedges and

topiary, but the invasion of psyllids has curtailed its use at the

present time.

Infested leaves become curled, distorted and covered with

blisterlike galls. Pesticides are rarely effective; consistent

watering and fertilization to maintain a vigorous plant has been the

best solution.

The ubiquitous oleander has departed nurseries and the landscape

even faster. A relatively new insect, the glassy-wing sharpshooter

leafhopper, is infecting oleanders with a deadly bacterium. Oleander

leaf scorch is an apt name; the foliage appears to have been burnt by

a blowtorch. At this time, there is no remedy other than removing

infected plants.

Although the last drought may just be a faint memory for some, it

left its mark on the Monterey pine and eucalyptus population in the

village and canyons. Both were stressed by lack of water and became

susceptible to attack. The Ips engraver beetle became the nemesis of

the Monterey Pine, while the Eucalyptus long-horned borer and, more

recently, lerp psyllid have proved fatal to a number of eucalyptus

trees. A program of supplemental watering and removal of diseased

trees would have saved dozens of trees.

Seventy-seven degrees and overcast -- I close my eyes, and I’m in

Costa Rica or Baja. Before it becomes hotter, I think I’ll step on a

few snails, cut a hornworm in half and trap some whitefly on sticky

paper. This weather just puts me in a mood... I’ll complete my dark

brooding by reviewing a few plans for Thursday nite. See you next

time.

* Steve Kawaratani can be reached at 949.497.2438, or E-mail to

plantman2@mac.com.