Widespread Resistance to QoI Fungicides of Colletotrichum acutatum from Strawberry Nurseries and Production Fields

Strawberry anthracnose, caused mainly by the Colletotrichum acutatum species complex, is a major disease in strawberry nurseries and production fields. The use of fungicides, such as the quinone outside inhibitors (QoIs), has been extensively deployed for the control of C. acutatum for the past 20 years. C. acutatum resistance to the QoIs was first reported in 2013 in Florida strawberry production fields. In 2015, anthracnose outbreaks were reported in strawberry nurseries and production fields across the United States. To elucidate the significance and geographical extension of C. acutatum resistance, fungicide use surveys were conducted, and isolates were collected in the affected areas. QoI-resistant isolates were collected from strawberry production fields and nurseries in six states in the United States. Fungicide use surveys indicated that, in some locations, the number of QoI applications exceeded the recommendation for this fungicide group. Thus, the current situation warrants immediate changes in anthracnose management strategies that integrate other chemical as well as nonchemical strategies to limit resistant population selection and prevent future anthracnose outbreaks.