UC Davis

The creation of the legal adult use cannabis industry in California necessitates a model to assess the risk that common cannabis arthropod pests may pose to the industry at the landscape scale. The current triage methods for assessing phytosanitary risks to cannabis crops are based on observational and grower reported data, which could potentially be misleading in reflecting the true risk that pests may pose to the industry. Here we present a model for assessing the risk of twenty-three common cannabis pests, weighting each according to their potential for causing negative externalities within the industry, from the industry to other industries or consumers, and the difficulty in preventing and managing those pests. Each of the taxa was evaluated for traits related to their potential to cause significant harm to cannabis growers, such as their host range, net reproductive number (R0 value), generation time, and vector competence. These biological parameters were integrated with county level hourly climate data and host acreage distributions taken from statewide crop mapping. Beet leafhopper (Circulifer tenellus) and other generalist pests with high reproductive potential are found to be the highest risk for the state’s cannabis crops. In contrast, pests like brown soft scale (Coccus hesperidum), greenhouse thrips (Heliothrips haemorrhoidalis), and hemp russet mite (Aculops cannabicola) are among the pests of the lowest risk; they lack many of the traits that correlate with the highest risk pests (vector/transmission contributions and large life history lifts), and greenhouse thrips in particular are further depressed by especially low landscape exposure (host range/acreage contribution). The hemp russet mite has rapid life cycle turnover but lacks the strong vector/transmission lift of other pests and has limited statewide exposure. The CPA model provides an estimation of which pests pose the greatest risk to the industry (and broader spillovers) and suggests methods of intervention in response.