"Walter R." writes:
I am plagued by leaf miners on my citrus trees. No insecticides seem to
work. The leaves curl and eventually fall off. Hardly produce any oranges.

The trees are only 25 years old. May have to cut them all down, unless there
is an alternative.

Citrus leaf miners are a relatively recent pest to blight Australian
citrus. I have no idea how commercial farms control it; but the insect
is difficult to get at because it's protected from sprays by the
transparent waxy coat on citrus leaves since it lives in the green cells
sandwiched between the waxy coats. I expect that a chemical method would
have to be systemic to be effective; but as I said I don't know.

For the home gardener, local tv and radio gardening programs recommend
a fortnightly spraying with PestOil (TM) or EcoOil (TM). These are
oil emulsions which don't carry the same risk as ordinary white oil;
the risk being that a sunny day after a spraying of White Oil can cause
catastrophic leaf loss of citrus. I think the way PestOil works is that
the temporary oil coating on the leaf suffocates the insect, so you must
spray both sides of the leaf, and thoroughly, for it to be effective.
Gardeners report that not only does the oil control the miners, but it
seems to keep the trees free of aphids and scale, into the bargain,
provided you keep up the fortnightly regimen throughout the year.

There is a likelihood that these oils may not be available outside
Australia, or they may be but marketed under different names. Perhaps
other readers can offer help here?
--
John Savage (my news address is not valid for email)