Verticillium Wilt is a plant disease that can result in severe damage and high yield losses in hop fields. It is caused by two fungi, Verticillium albo-atrum and V. dahliae. An infection initially produces yellow patches on the hop leaves, which become black as the tissues die. Eventually, the leaves turn yellow and black and curl upward at the edges, before they become withered. Once a field is infected, the disease generally spreads rapidly and can affect entire growing areas.

The fungi are wide-ranging and can be transmitted to hop plants from weeds, from other crops such as lucerne, and from the soil where spores often survive for years. Insects, too, can spread the disease over long distances, as can seeds moved from one area to another. Infections typically start at the roots and pass through the plants to the leaves and flowers. Dry conditions encourage the growth of the parasite, as the plants become drought stressed.

Virulent varieties of Verticillium wilt were recorded in the 1930s in the UK and continental Europe, where they caused severe damage. In North America, however, outbreaks of V. albo-atrum have been more limited, and V. dahliae is the more common threat because of its preference for warmer temperatures.

Resistant hop varieties have been developed in recent years, but good farming practices have reduced the impact of the disease, too. These include removing plant residues from fields after the harvest, keeping hop plants separated by patches of grass, and the use of fungicides. Restrictions on plant movement and sourcing of new plants have also been effective.