Foliar insecticides for the control of curly top in Idaho sugar beet, 2021

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

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2022
Publication Date: 3/17/2022
Citation: Strausbaugh, C.A., Wenninger, E.J. 2022. Foliar insecticides for the control of curly top in Idaho sugar beet, 2021. Plant Disease Management Reports. 16. Article V036.

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, so foliar insecticides need to be investigated to extend control of curly top beyond early season control. Thus, seven foliar insecticide treatments were investigated, but only one treatment, Scorpion, was found to provide control of curly top similar to the Poncho check treatment. The commercial sugar beet cultivar used in the study was approved for commercial production; however, the yields for all treatments except Poncho (seed treatment check), Scorpion and Applaud 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 and supplemental foliar 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 seven foliar insecticides were screened in 2021 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 22 June. Foliar symptoms were evaluated on 10 August and 10 September 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. Two treatments (Poncho Beta seed treatment and the Scorpion foliar treatment) provided a similar level of control on the second rating and had similar root yield and ERS. The Applaud foliar treatment provided less control based on ratings, but ERS was not significantly different from the Poncho Beta and Scorpion treatments. The foliar insecticide treatments containing Asana or Spear T provided marginal control of BCTV, but these treatments were better than the non-treated check in foliar ratings, root yield, and ERS. The Venom and Ninja + Asana treatments also showed higher root yield and ERS relative to the non-treated check. The remaining treatments were similar to or worse than the non-treated check with respect to sucrose, root yield, and ERS. These data show that sugar beet production in areas with curly top would likely suffer considerably without the neonicotinoid seed treatments and the supplemental foliar treatments.