A plant, other than the main host, on which a pathogen or pest can live. Alternate hosts, which are often weeds can provide a means for the athogen to survive when its main host is not available. For example, downy mildew of beet (Peronospora farinosa) can overwinter in wild beet. Hawthorn (Crataegus) is an alternate host and important inoculum source for the fire-blight bacterium (Erwinia amylovora), which infects pears and apples. Many *rusts
also overwinter on alternate hosts. Certain insect pests overwinter as eggs on alternate hosts, e.g. blackfly (Aphis fabae) migrates to the spindle tree (Euonymus europaeus) in the autumn. Virus diseases may be found in weed hosts near crops. The term alternative host may be used when the pathogen has a number of different hosts. Control of the alternate hosts can be an important way of reducing inoculum sources of some diseases.