Foliar insecticides for the control of curly top in Idaho sugar beet, 2022

Authors: Strausbaugh, Carl; Majumdar, Raj; WENNINGER, ERIK - University Of Idaho

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2023
Publication Date: 3/15/2023
Citation: Strausbaugh, C.A., Majumdar, R., Wenninger, E.J. 2023. Foliar insecticides for the control of curly top in Idaho sugar beet, 2022. Plant Disease Management Reports. 17. Article ST004.

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 only 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 and alternatives to neonicotinoid seed treatments would also be desirable, so foliar and seed treatment insecticides need to be investigated to extend control of curly top beyond early season control and find new seed treatments. Thus, seven foliar insecticide treatments were investigated. The Poncho Beta seed treatment provided better control than all other treatments based on curly top ratings, root yield, and estimated recoverable sucrose (ERS). The Actara, Asana, Transform, and Violacein treatments all reduced curly top ratings compared to the non-treated check, but the control was not adequate to avoid serious reductions in root yield and ERS. These data show that sugar beet production in areas with curly top would suffer greatly without the neonicotinoid seed treatments and supplemental foliar treatments. Additional evaluations will need to be conducted with other insecticides if alternatives to the neonicotinoid (Poncho Beta) chemical class are to be identified for curly top control.

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 seven foliar insecticides were screened in 2022 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 15 June. Foliar symptoms were evaluated on 20 July and 15 August using a scale of 0-9 (0 = healthy and 9 = dead). Curly top symptom development was uniform and no other disease problems were evident in the plot area. The disease pressure in the test was severe with good symptom development in the non-treated check. The Poncho Beta seed treatment provided better control than all other treatments based on curly top ratings, root yield, and estimated recoverable sucrose (ERS). The Actara, Asana, Transform, and Violacein treatments all reduced curly top ratings compared to the non-treated check, but the control was not adequate to avoid serious reductions in root yield and ERS. These data show that sugar beet production in areas with curly top would suffer greatly without the neonicotinoid seed treatments and supplemental foliar treatments. Additional evaluations will need to be conducted with other insecticides if alternatives to the neonicotinoid (Poncho Beta) chemical class are to be identified for curly top control.