Evaluation of adjuvants added to fungicides for controlling Cercospora leaf spot on sugar beet

Authors: BHUIYAN, ZIAUR - North Dakota State University; LUIS, DEL RIO MENDOZA - North Dakota State University; Lakshman, Dilip; Q, AIMING - University Of Hertfordshire; KHAN, MOHAMED - North Dakota State University

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2023
Publication Date: 10/12/2023
Citation: Bhuiyan, Z., Luis, D., Lakshman, D.K., Q, A., Khan, M. 2023. Evaluation of adjuvants added to fungicides for controlling Cercospora leaf spot on sugar beet . Crop Protection. https://doi.org/10.1016/j.cropro.2023.106471.
DOI: https://doi.org/10.1016/j.cropro.2023.106471

Interpretive Summary: Sugar beet is an economically important crop in the USA and Cercospora Leaf Spot (CLS), caused by the fungus Cercospora beticola Sacc., is a destructive foliar disease of sugar beet and responsible for a significant reduction of extractable sucrose. The recent development of resistance to several classes of chemicals by C. beticola coupled with untimely applications and/or regular rainfall after fungicide applications have resulted in reduced efficacy of fungicides in controlling CLS. We, therefore, tested to improve the efficacies of three different fungicides (Penncozeb®, Inspire® XT, and Badge® SC) by amending with various combinations of four different adjuvants (Complex®, Preference®, Cerium Elite®, and Transfix®), both in the greenhouse and field, to control the CLS. Our experimental analysis showed that the addition of adjuvants did not improve the effectiveness of any of the fungicides and a few mixtures even negatively impacted root yields. Future research with different adjuvants and fungicides is warranted. Our research findings will be useful to plant pathologists, extension agents, and farmers in efficiently and economically managing the CLS.

Technical Abstract: Cercospora Leaf Spot (CLS) caused by the fungus Cercospora beticola Sacc., is a destructive foliar disease of sugar beet (Beta vulgaris L.) responsible for significant reduction of extractable sucrose. Recent development of resistance to several classes of chemicals by C. beticola coupled with untimely applications and/or regular rainfall after fungicide applications have resulted in reduced efficacy of fungicides in controlling CLS. The objective of the study was to evaluate the role of adjuvants in improving the efficacy of fungicides for controlling CLS of sugar beet. In the greenhouse, the three recommended fungicides (Penncozeb®, Inspire® XT, and Badge® SC) were used alone or in mixtures with four adjuvant types (Complex®, Preference®, Cerium Elite®, and Transfix®) before and after inoculation with C. beticola. Disease severity was evaluated 14 days post-inoculation. In the field, fungicides were applied alone or mixed with three adjuvants at 14 days intervals and disease severity and recoverable sucrose were evaluated at harvest. Greenhouse trials showed that the application of fungicides before disease onset resulted in reduced disease severity. Plants treated with the systemic fungicide Inspire XT had lower disease severity than plants treated with the protectant fungicide Penncozeb or Badge SC. Field trials showed significant variations on disease severity and yield components (P<0.001). The addition of adjuvants did not improve the effectiveness of fungicides in controlling CLS and few of the mixtures negatively impacted root yields. In these studies, rain events typically occurred more than four days after spraying. Thus, it is possible the lack of heavy precipitation soon after plants were sprayed in field trials may have influenced these results.