Currently there is a garden pest that is affecting many citrus trees and has a lot of people coming into my work place asking me what is wrong with their plants. Citrus leafminer, Phyllocnistis citrella, is a common pest that is currently active in the garden at this time of year when the weather isn’t very consistent. But they can also prove to be a problem in the early months of spiring, when the new season’s growth starts to emerge. The adult is a tiny moth that is silver-white in colour with yellow markings, and they have an approximant wingspan of 5mm. The adult moth lays their eggs onto the undersides of the new foliage, and once these eggs hatch that is when the symptoms and damage is most noticeable.
When the eggs have hatched the larvae begin to tunnel in between the fine layers of the leaf. This process usually takes the young caterpillar 5 days to do. Affected trees will show symptoms in the foliage and overall appearance. Silver aztec maze designs appear on the leaf surface and can cause the foliage to discolour overtime. Foliage can also be distorted and curled. Other symptoms can cause plants to wilt and in heavy infestations can cause affected trees to suffer from stress and remain unhealthy for long periods of time.
When the affected foliage starts to curl along the margins the larvae are fully grown. The larvae curl the sides of the leaf to create a ‘shield’ to protect itself as it goes through pupation. The pupation can take up to 3 weeks to complete and then the adult wasp emerges and the cycle repeats.The best method of control is to prune off all affected growth then follow up by spraying an organic pesticide such as EcoPest Oil by Multicrop or Pest Oil by Yates. Avoid using pesticides that contain toxic chemicals on your edible trees because in most cases the chemical residue can be carried into the fruit that you harvest. Citrus leafminer can be found on other plants so make sure to check over surrounding plants.
By Bonnie-Marie Hibbs