A key pest of hops in Europe is the hop aphid, which feeds directly on the hop plant, extracting cell sap and nutrients with its sucking mouth-part. Hop aphids excrete prolific amounts of honeydew. Sooty mold grows on the honeydew and can destroy a crop’s value, as mold renders hop cones unacceptable for brewing. How do European growers cope?

“Dried female flowers (cones) of hops are used for flavoring and as a preservative of beer and related beverages. They provide bitterness and aroma. … Feeding by large numbers of aphids can debilitate hop plants and may induce premature defoliation, sometimes followed by a total loss of yield. Because of the threat posed by [hop aphids], treating hops with pesticides was already being recommended in England by the end of the 17th century and has been used regularly since about 1865.”

Authors: A. Barber, C.A.M. Campbell, H. Crane, P. Darby and R. Lilley
Affiliation: Horticultural Research International, Kent, UK
Title: Cost-benefits of reduced aphicide usage on dwarf hops susceptible and partially resistant to damson-hop aphid.
Publication: Annals of Applied Biology. 2003. 143:35-44.