Cost-benefits of reduced aphicide usage on dwarf hops susceptible and partially resistant to damson-hop aphid

Soil‐applied imidacloprid at full (125 g a.i. ha^?1) and half approved doses gave levels of control of damson‐hop aphid, (Phorodon humuli), similar to that provided by foliar spray(s) of tebufenpyrad on the aphid‐susceptible dwarf hop cvs First Gold and Herald. On those cultivars, aphid control was unreliable on plots treated with quarter dose imidacloprid and was generally no better than on untreated plants. Aphids were virtually eliminated from the leaves by the end of July each year in all treatments consistent with the action of natural enemies. Aphid contamination of cones reflected the numbers on foliage at flowering time, but varied widely between years. Yields and percentage α‐acids content of dried hops were unaffected by the numbers of aphids on leaves early in the season and in cones at harvest, but aphid contamination reduced the economic values of crops by as much as 80%. Few P. humuli colonised the partially aphid‐resistant breeding line 23/90/08 before their numbers were regulated and consistent with natural enemy activity. Yields, percentage α‐acids content, and commercial value of harvested cones were similar in all treatments on 23/90/08 whether or not plants were treated with aphicides. The commercial risks posed by P. humuli preclude substantial reductions in aphicide usage on aphid‐susceptible dwarf hop cultivars, but future cultivars expressing a similar level of partial resistance to aphids as 23/90/08 should not need treatment with aphicides.