Witches’-broom

Witches’-broom is a plant growth deformity characterized by the dense, cluster-like proliferation of shoots, branches, or roots. This condition is primarily caused by phytoplasmas, but can also result from viral or fungal infections, including species within the Taphrina and Crinipellis genera, which disrupt the plant's hormonal balance and apical dominance.

The disease affects a wide variety of economically important plants. Documented hosts include staple crops such as potatoes, common beans, peanuts, and cassava. Additionally, various horticultural and woody plants are susceptible, specifically sweet cherries (Prunus avium), sour cherries (Prunus cerasus), various Azalea species, and members of the Passiflora genus.

The hallmark symptoms of the condition include the mass development of adventitious buds that would normally remain dormant. These buds grow into stunted, thin, and often chlorotic shoots. As the plant diverts its energy to sustain this excessive vegetative growth, normal physiological processes, such as flowering and fruiting, are significantly hindered or completely suppressed.

Transmission occurs mainly through insect vectors, such as leafhoppers and psyllids, which transmit pathogens while feeding on plant phloem. The disease can also spread through infected propagation material, including grafts, cuttings, and infected nursery stock. Environmental factors, particularly warm and humid conditions, facilitate both vector population growth and pathogen transmission.

Managing the disease requires a rigorous integrated pest management (IPM) approach. This includes the exclusive use of virus-free, certified nursery stock and the rapid eradication of symptomatic plants to prevent spread to healthy hosts. Controlling insect vector populations through targeted pesticide application and practicing good sanitation, including the sterilization of pruning tools, are essential steps in limiting the impact of this disease.