Hop mosaic

Hop mosaic is a viral disease caused by the Hop mosaic virus (HpMV), a member of the Carlavirus genus. This plant pathogen is a significant concern for hop growers globally, as it targets Humulus lupulus, leading to systemic infections that impair plant vigor and reduce the quality and yield of hop cones.

The characteristic symptoms of the disease include a distinct mosaic pattern on the leaves, featuring irregular patches of light and dark green. In sensitive varieties, the leaves may show signs of crinkling, cupping, or severe distortion. Stunting of the entire plant is common, especially in varieties that lack resistance to this specific viral strain.

The transmission of the virus is primarily mediated by aphids, specifically the damson-hop aphid (Phorodon humuli). The virus is acquired by the aphid during brief probes on infected plants and is transmitted to healthy plants in a non-persistent manner. Mechanical transmission, though less frequent than vector-borne, can occur through infected tools or plant-to-plant contact during harvesting or pruning.

Development and spread of the disease are heavily influenced by the presence of the vector and local environmental conditions. Periods of mild weather favor aphid colonization, facilitating the rapid spread of the virus within the hop yard. Once introduced, the virus persists in the hop rootstocks, ensuring its presence in the field year after year unless active management is undertaken.

Control measures focus on integrated pest management (IPM) strategies. These include sourcing certified virus-free planting material, rigorously managing aphid populations through insecticide applications, and immediate rogueing of infected plants to prevent inoculum buildup. Maintaining clean farm practices, such as sanitizing pruning tools, is essential to mitigate the risk of mechanical spread.