Willows are extremely susceptible to gall induction and growth manipulation and
Salix is one of the plant genera with the highest known numbers of associated galler species.
Rabdophaga rosaria is probably a group of closely related, unnamed species, possibly each restricted to one species of willow. Galls should be recorded as
R rosaria and the host plant should also be recorded. The gall consists of from thirty to sixty leaves, shortened and crowded together in rosettes on
white willow (
S. alba),
crack willow (
S. fragilis),
goat willow (
S. caprea) and
purple willow (
S. purpurea) willows as well as the
eared sallow (
S. aurita) and
grey sallow (
S. cinerea). The oviposition of this species results in a chemical interaction that halts the lengthwise growth of infected willow shoots, the leaves however continue to develop and thus the characteristic "rose" forms at the tip of the affected shoot.
Characteristics Rabdophaga rosaria is found on willow branches and the gall diameter depends upon the species, being larger on
Salix caprea at than on
Salix alba at . The development in the United Kingdom begins in May / June with leaf expansion and reaches maturity in August / September while the leaves are still green. The gall becomes brown and remains on the tree over winter until it is forced off by new growth in spring. ==Causer, inquiline and associations==