Of mildew, aphids, and oleander
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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
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