Seed treatments, in-furrow fungicides, and in-furrow biocontrol agents in sugar beet for the control of rhizoctonia crown and root rot in Northwest Minnesota, 2024

Authors: LIEN, AUSTIN - University Of Minnesota; Kandel, Shyam; CHANDA, ASHOK - University Of Minnesota

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2024
Publication Date: 1/21/2025
Citation: Lien, A.K., Kandel, S.L., Chanda, A. 2025. Seed treatments, in-furrow fungicides, and in-furrow biocontrol agents in sugar beet for the control of rhizoctonia crown and root rot in Northwest Minnesota, 2024. Plant Disease. https://doi.org/10.1094/PHP-12-24-0136-PDMR.
DOI: https://doi.org/10.1094/PHP-12-24-0136-PDMR

Interpretive Summary: Rhizoctonia crown and root rot (RCRR) is a common disease in sugarbeet in the red river valley of Minnesota and North Dakota and beyond. Yet, no reliable measures are available to minimize the crop loss associated with RCRR. In this study, we have evaluated the effectiveness of seed treatments, in-furrow fungicide treatments, and in-furrow biocontrol agents for controlling incidence and severity of RCRR using the field plot experiments. Experiments were performed at the University of Minnesota, Northwest Research and Outreach Center in Crookston, MN; and disease incidence, disease severity and yield parameters were recorded at the seedling stage and harvest, respectively. Overall, in-furrow fungicide treatments found effective to minimize the RCRR severity, while highest sugar percentage was found in in-furrow biocontrol treatments.

Technical Abstract: Plots were established in a randomized complete block design with four replicates at the University of Minnesota, Northwest Research and Outreach Center in Crookston, MN, in Hegne-Fargo silty clay soil with an organic matter content of 4.8%. Prior to planting, whole-grain barley infested with four Rhizoctonia solani AG 2-2 isolates was hand-broadcast across plots at 44.6 lb/acre and incorporated with a Rau Kombi seedbed finisher. Seed of ‘Crystal 793RR’ treated with standard rates of Allegiance, Thiram, and Tachigaren (1.59 oz/unit) was sown in 6-row by 30-ft long plots at a 4.5-in. spacing in 22-in. rows on 10 May. The application method of fungicide treatments included seed treatments and in-furrow applied fungicides (see table). The nontreated control did not include any seed or in-furrow fungicide treatment that would suppress or control R. solani. Plant stands were evaluated beginning 17 May (7 days after planting [DAP]) through 13 Jun (34 DAP) by counting the number of live plants in the center two rows of each plot. Data were collected for root rot severity, the number of harvested roots, and yield at harvest. On 17 Sep, plots were defoliated, and the center two rows of each plot were harvested mechanically and weighed for root yield. Twenty roots per plot were arbitrarily selected, and surface rot was rated for the severity of Rhizoctonia crown and root rot (RCRR) using a 0 to 10 scale with a 10% incremental increase per each unit of rating (i.e., 0=0%, 5 = 41-50%, 10=91-100%). Each rating was mid-point transformed to percent severity for statistical analysis. Ten representative roots from each plot were analyzed for sugar quality at the American Crystal Sugar Company Quality Tare Laboratory, East Grand Forks, MN. Statistical analysis was conducted in R (v 4.3.1, R Core Team 2023). A mixed-model analysis of variance was performed using the package lmerTest (v 3.1-3), with treatment defined as the fixed factor and replication as the random factor. Means were separated at the 0.10 significance level using the package emmeans (v 1.8.7) with no adjustments. Analysis by application type was performed similarly, with application type defined as the fixed factor and replication as the random factor. A weather station located 12.8 miles southwest of the Northwest Research and Outreach Center, Crookston, MN recorded a total rainfall of 2.33 and 4.49 in. for April and May, which was more than the 30-year average of 1.42 and 2.86 in., respectively. Average temperatures and adequate soil moisture at planting facilitated normal emergence of sugarbeet seedlings and generally high plant populations of 222 plants per 100 ft of row averaged across all treatments in this trial on 13 Jun (34 DAP). There were significant differences among at-planting treatments for plant stands only on 20 May (10 DAP) in which Zironar and Bexfond had a greater number of plants compared to Priaxor (data not shown), the other treatments were not statistically different. Additionally, comparisons of application type showed a significant difference on 20 May (10 DAP) in which the in-furrow biocontrol agents had a greater number of plants compared to the other in-furrow fungicide treatments and fungicide seed treatments, but not the nontreated control (data not shown). By 13 Jun (34 DAP), fungicide seed treatments had the greatest number of plants and was significantly greater than the in-furrow fungicide treatments, but not the in-furrow biocontrol agents or the nontreated control. There were no significant differences among plant stands by the time of harvest. Average temperatures in May and June and above-average rainfall in May likely contributed to a favorable environment for R. solani early on; however, lower-than-average rainfall later in the season was unfavorable for disease development and resulted in moderately low disease pressure throughout the se