I don't really know anything but I can tell you what our gardener told us. We have a tangerine that we've been working very hard to save - long story but it's finally on the road to recovery. We had simultaneous infestations of whitefly, scale and aphids for more than a year.
Remember that infestations begin initially as a SYMPTOM of an unhealthy tree. You'll need to treat the infestation, but you'll also need to address whatever was wrong with your tree to begin with.
In our case, it was too much damp (brought on by our former gardener planting too many other plants nearby and mulching the whole bed). Citrus need their roots to be dry between waterings, like cactus. This means well-drained soil, NO mulch, and NO other plants or grass nearby.
Lacewings are a good biological control for all of the above infestations.
Ants are not destructive in themselves, but they're a marker for the presence of other insects, particularly aphids.
We tried knocking the insects off with water spray, but that has a downside when you're trying to keep the roots dry! And you really do have to do it every day to control the insects. When all else failed on the aphids we used insecticidal soap (1 tbsp Dr. Bronner's in a quart of water). It was VERY effective and obviously it's non-toxic to mammals and birds. Of course any broad-spectrum insecticide is a last resort, since it will kill the beneficials along with the destructive insects. But I wouldn't worry too much about whether the fruit would be edible as a result of the insecticide, since a tree that badly damaged probably won't set fruit this year anyhow.
Last edited by OakLeaf; 11-10-2008 at 05:26 AM.
Speed comes from what you put behind you. - Judi Ketteler