3. Borers
• A type of beetle, the branch and twig borer makes holes into the twigs of
olive trees to lay eggs. Once hatched, the new borers dig deeper into the
tree and eventually, twigs and branches die. The American plum borer, on
the other hand, is a type of moth, but is so named because it also bores
into olive trees to provide shelter for its young. Avoid injuring olive trees,
which makes them susceptible to damage from both pests. Prune infested
branches.
4. Scales
• Tiny hard-shelled insects that affix themselves to plants, scales of various types
threaten olive trees. Gray olive scales, greedy scales, California red scales and
oleander scales eat fruit, leaves and twigs using their piercing mouths, damaging
fruit and decreasing the tree's productivity. To control them, treat olive trees with
horticultural oil or introduce natural pests, such as wasps.
5. Olive Fruit Flies
• A formidable pest, the olive fruit fly can decimate entire crops when its
hungry larvae burrow into olives and devour them. In California, the fruit
flies are active year round and often spread to other crops. Always remove
unwanted olives from trees and collect fallen olives for disposal. Fight
aphid infestations, as the honeydew they secret attracts adult olive fruit
flies. For ornamental trees that needn't bear fruit, spray them with an
anti-fruiting chemical to prevent the problem.
6. Root Weevils
• Dark brown root weevils feed on the foliage of olive trees, while their offspring,
white grubs, devour the plant's roots. Established olive trees can cope with root
weevils, but young ones need protection. Branches that touch the ground and
allow the flightless weevils access to the tree should be pruned. Also, wrapping the
trunk in cellophane, covered in a commercially-made sticky substance for trees,
will trap the weevils as they make their way to the leaves.
7. Olive lace bug
• The olive lace bug is a very damaging pest as it causes severe leaf damage, which can cause
yellowing of leaves and leaf fall. Stressed trees may fail to bear fruit for the next one or two
seasons.
• No chemicals are registered specifically for this pest. The olive association is currently seeking
minor use permits from the National Registration Authority for the use of other chemicals to
control this important pest. Examples of pyrethroid insecticides registered for a range of
other insect pests in orchards are Ausgro PY-Cap insecticide and Multicrop pyrethrum
insecticide. They are fairly broad spectrum, but fairly safe for operators and not very
persistent. Insecticidal soaps are also available for use against some pests. Use of such
insecticides may help suppress lace bug populations when applied for control of other pests.