Agronomic management of industrial hemp alters foliar traits and herbivore performance

Agronomic management decisions can alter plant foliar traits, especially nutritional quality, with potential to influence plant–herbivore interactions. Herbivores balance consumption of plant tissue for nutritional gains related to growth and development while contending with plant traits that may deter herbivory or are toxic. This study evaluates the influence of management decisions on the foliar quality of industrial hemp ( Cannabis sativa ) and the impact on the performance of fall armyworm ( Spodoptera frugiperda ). We included three common management decisions in this study: fertilization rate, cultivar choice, and planting date. In a no-choice feeding trial, fall armyworm larvae were fed leaves of field-grown hemp from three different cultivars that received different rates of fertilizer and were planted on two different dates. We quantified levels of foliar nitrogen, the ratio of carbon to nitrogen, leaf mass per unit area, and concentrations of tetrahydrocannabinol and cannabidiol, and determined the influence of foliar quality on herbivore performance. Fertilization rate, cultivar, and the interactions of planting date with both fertilization rate and cultivar influenced multiple aspects of hemp foliar quality. Overall, fertilization had the largest influence on foliar quality and subsequent herbivore performance. Variation in foliar traits influenced herbivore performance. Foliar nitrogen had a positive impact on fall armyworm performance and the ratios of carbon and total cannabinoids to nitrogen had negative impacts on fall armyworm performance. Our findings show that management decisions in industrial hemp can affect plant–insect interactions through changes in foliar quality. These outcomes suggest that developing crop management recommendations for pest management will be important for a re-emerging crop like industrial hemp.