Foliar insecticides for the control of curly top in Idaho sugar beet, 2019

Authors: Strausbaugh, Carl; WENNINGER, E - University Of Idaho

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2020
Publication Date: 3/9/2020
Citation: Strausbaugh, C.A., Wenninger, E.J. 2020. Foliar insecticides for the control of curly top in Idaho sugar beet, 2019. Plant Disease Management Reports. 14:CF041.

Interpretive Summary: Curly top in the semiarid sugar beet production areas of the United States is caused by Beet curly top virus and vectored by the beet leafhopper. Resistant sugar beet cultivars became available in the mid-1930s prior to which curly top combined with drought almost eliminated the sugar beet industry in the western United States. However, resistance is typically low to intermediate in commercial sugar beet cultivars and has a tendency to be associated with lower yield potential. The neonicotinoid seed treatments have been a good management option to supplement host resistance for good early season control of curly top. However, the influence of the seed treatments ends around 77 days after planting, so foliar insecticides need to be investigated to extend control of curly top beyond early season control. Thus, eight foliar insecticide treatments were investigated, but all were found to have little to no influence on control of curly top. The commercial sugar beet cultivar used in the study was approved for commercial production; however, the yields for all treatments except the insecticide seed treatment check indicate that the cultivar was severely infected during the study. These data show that sugar beet production in areas with curly top would suffer greatly without the neonicotinoid seed treatments.

Technical Abstract: Curly top caused by Beet curly top virus (BCTV) is a widespread disease problem vectored by the beet leafhopper in semiarid sugar beet production areas. Host resistance is the primary defense against this problem, but resistance in commercial cultivars is only low to intermediate. The neonicotionoid seed treatments currently supplement this resistance to provide early season control. In order to identify other management options eight foliar insecticides were screened in 2019 on a commercial sugar beet cultivar approved for production. The plots were arranged in a randomized complete block design with eight replications. A curly top epiphytotic was created by releasing six viruliferous beet leafhoppers per plant at the eight-leaf growth stage on 24 June. Foliar symptoms were evaluated on 11 August and 16 September using a scale of 0-9 (0 = healthy and 9 = dead) in a continuous manner. Curly top symptom development was uniform and no other disease problems were evident in the plot area. The disease pressure in the test was moderately severe with good symptom development in the non-treated check. Based on visual ratings, root yield, and estimated recoverable sucrose, the foliar insecticides provided little or no influence on the control of curly top. However, the yields for all treatments except the insecticide seed treatment check indicate that the cultivar was severely infected during the study. These data show that sugar beet production in areas with curly top would likely suffer considerably without the neonicotinoid seed treatments.