Oystershell scale, Quadraspidiotus ostreaeformis - Host plants

Oystershell scale has a wide range of host plants, mainly deciduous trees. Within the trees, most of the population lives on the trunks, stems, and branches, but the fruits are also attacked. Host plants have been reported from 41 genera in 18 families. It is most destructive on apples, pears, and stone fruits, particularly plum (European and Japanese) but also cherry, peach, prune, almond and nectarine. It has not been found on apricot in New Zealand. Oystershell scale has also been reported to occur on quince, currants, blueberry, and walnuts overseas. Willows, birches, elms, alders, poplars, mountain ash, and other common ornamental trees serve as reservoir hosts for this pest outside orchards. Shelter trees are often the most important sources of oystershell scale dispersing in the orchard environment, and the correct choice of shelter species can make a major contribution to cultural control. Shelter tree species and varietal selections differ in their susceptibility to oystershell scale. Some species of alder and birch used as shelter, such as Alnus incana and Betula pendula, have been found to support huge populations of oystershell scale next to apple blocks in Otago. Matagouri is the only New Zealand native plant recorded as a host of oystershell scale.