There are several species of mites that infest pome and/or stone fruit trees in Victoria and they have different life cycles and habits that growers need to understand in order to efficiently manage their impact on crops.
Spider mites
Spider mites include two-spotted mite (TSM), European red mite (ERM), and Bryobia mite.
TSM is generally the most common mite and overwinters as hibernating females amongst webbing around the lower trunk of the tree.
Overwintering females appear as tiny spider-like orange-red coloured mites, which is why they are often called ‘red spider’ mites.
In spring as the temperatures warm up, and there are leaves on the trees, the overwintering TSM start to feed on the lower leaves, change colour to the summer form (pale straw) and develop the two dark spots that give them their common name.
At this stage they start to lay spherical, pearl coloured eggs usually close to the veins on the undersides of the leaves.
As populations start to build up, the mites move upwards and outwards along the scaffold limbs of the trees.
Biological control
Predatory mites were introduced and distributed throughout Victorian orchards for biological control of TSM.
Populations of TSM resistant to many miticides are widespread and growers need to carefully plan their mite control program to maximise the benefits of biological control before resorting to applying pesticides that may disrupt the biological control agents (especially predatory mites and Stethorus beetles).
ERM
ERM is a dark red mite about the same size as TSM.
It has white tubercles, with strong hairs (setae) protruding from the tubercles, on its back. ERM overwinters as dark red, onion-shaped eggs that have a spine arising from the central top. These eggs are laid around the bud scales on twigs and shoots.
The white tubercles on the backs of the adult mites, and the spines on the eggs, are easily seen with the aid of a hand lens.
The overwintering eggs hatch around the green-tip stage of tree development in spring and the nymphs move to the developing leaves.
This pattern of egg laying means that ERM infestations are more widespread throughout the tree than are TSM infestations.
Where ERM and TSM appear on the same leaves ERM will usually inhabit the upper surface of the leaf and TSM the lower surface.
ERM does not produce much webbing. ERM appeared in orchards on the Mornington Peninsula in the 1980s and spread to Gippsland, Yarra Valley, Bacchus Marsh, North-East, and Harcourt. It has been found in small pockets in the Goulburn Valley since about 2000.
Biological control
Predatory mites were introduced to Victoria to control ERM in the 1980s and the comments regarding biological control of TSM hold equally for ERM.
Bryobia mites (cont. next month)
See this article in Tree Fruit Dec 2017
