San Jose scale, Quadraspidiotus perniciosus - Host plants

San Jose scale has a wide range of host plants, mainly deciduous trees. Most of the population is on the trunks, stems, and branches of the trees, but the leaves and fruits are also attacked. Over 700 species of host plants in 240 genera and 81 families have been reported. It is most destructive on apples, pears, and stone fruits, including sweet cherry, peach, plum, prune, almond and nectarine. Damage to pipfruit can be so severe as to kill branches and main leaders of the trees, and has even caused the death of young trees in New Zealand. San Jose scale also occurs on grapes, kiwifruit, and walnuts, and has been reported on berryfruits 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 San Jose 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 San Jose scale, and some shelter species, such as Casuarina spp., are not hosts of San Jose scale. Large willow trees on stream banks and in gullies close to orchards are a large source of scale insects in some regions, such as Nelson.