New Hemp Diseases and Pests in New Zealand

Abstract This article continues the “Cannabis clinic” series, presenting diseases and pests of hemp (Cannabis sativa L.), featuring color illustrations of signs and symptoms. Hemp cultivation is new to New Zealand (NZ). Field trials began in 2001, evaluating cultivars from Europe or North America. Novel crop plants imported into new geographical areas are exposed to new diseases and pests. The imported plants often present less resistance to local problems than do indigenous plants. Many ‘local’ problems in NZ, however, are introduced organisms. Non-native birds cause the greatest crop damage. Rabbits, famous aliens in NZ, also cause problems. Invertebrate pests include the brown garden snail (Helix aspersa), brown field slug (Deroceras panormitanum), orange-soled slug (Arion distinctus), budworm (Helicoverpa armigera), passion vine leaf hopper (Scolypopa australis), caterpillars (Epiphyas postvittana), and melon aphid (Aphis gossypii). The latter species may be the vector of an unidentified virus that infests hemp. In humid regions and wet conditions, the fungi Botrytis cinerea, Trichothecium roseum, and Sclerotinia sclerotiorum rot flowering tops and stalks. For this article, image capture of invertebrate pests and fungi utilized Auto Montage software, to improve the depth of field and produce perfectly focused images.