Improving the Cercospora Leaf Spot Management Model for Sugar Beet in Minnesota and North Dakota

Abstract

Management of Cercospora leaf spot, caused by Cercospora beticola, is necessary for the economic production of sugar beet (Beta vulgaris). The objectives of this study were to evaluate the impact of two relative humidity thresholds (87 and 90%) on the daily infection values (DIVs) used to determine when fungicide applications were required, to determine whether current Cercospora management recommendations for northern areas of Minnesota and North Dakota could be used by growers in the southern areas of these states, and to compare the utility of calendar-based fungicide applications with the Cercospora management model. Research was conducted in Breckenridge, MN and St. Thomas, ND in 2003 and 2004. Fungicide applications significantly (P = 0.05) reduced maximum disease severity (ymax) and area under the disease progress curve (AUDPC) when compared with the nontreated control at both locations during 2003 and 2004. Fungicides applied according to DIVs calculated at RH ≥ 87% or RH > 90% gave similar results. The mandatory second fungicide application 14 days after the first application for southern areas did not significantly decrease disease severity or AUDPC, or improve root yield or recoverable sucrose compared with treatments without the mandatory application. This research illustrates that a DIV calculated at RH ≥ 87% would result in similar timing of fungicide applications compared with DIVs calculated at RH > 90%. The results further show that the recommendation of fungicide applications at initial symptom and subsequent applications based on DIV and disease severity should be used for both northern and southern growers. Finally, this research showed that fungicide applications based on the Cercospora management model provided similar, effective disease control with fewer fungicide applications compared with calendar-based applications.

Challenges and Prospects for Building Resilient Disease Management Strategies and Tactics for the New York Table Beet Industry

“…This may lead to reductions in fungicide usage with environmental and economic benefits and reduced exposure to pesticides when not warranted. However, complicating the decision to apply fungicides and maintain season-long disease control are inherently the risk-averse attitudes of growers due to the high economic impacts of CLS epidemics [73][74][75].…”

“…Studies on the effects of weather on infection and sporulation and the relationship between disease intensity and crop loss have led to the development of several forecasting systems for CLS in sugar beet [74][75][76][77]. The objective of these predictive systems is scheduling the first and/or subsequent application of fungicides to coincidence with environmental conditions that promote infection.…”

Cercospora Leaf Spot Disease of Sugar Beet

“…In this way, infested plant residues are destroyed and a lower amount of inoculum is available for a subsequent sugar beet crop. As justified by relevant pathogen survival studies (Pool and McKay 1916;Khan et al 2007), a 2-3 year rotation is necessary to reduce fungus carryover from a severely infested crop, while incorporating leaf debris in the soil by deep tillage may further contribute to the reduction of initial inoculum (Jacobsen and Franc 2007). Avoiding proximity to previously heavily infested sugar beet fields helps in delaying the epidemics, as does controlling the presence of weed hosts (Pool and McKay 1916;Jacobsen 2010).…”

“…The various models developed depend on environmental and yield damage parameters as they relate to the infection process. Some models consider only weather data favoring disease progress (Shane and Teng 1984;Windels et al 1998;Khan et al 2007), while other models take into account the resistance level of the variety as well Wolf and Verreet 2002;Racca and Jörg 2007). When properly implemented, all these models can be of great help in disease management and economic sugar beet production (Windels et al 1998;Wolf and Verreet 2005;Khan et al 2007).…”

Characterization of CbCyp51 from Field Isolates of Cercospora beticola

“…C. beticola is able to overwinter as stromata in infected sugar beet leaf residue on or directly below the soil surface (14). Control measures for leaf spot include resistant sugar beet varieties and crop rotation but the disease is managed effectively only when combined with timely fungicide applications (10,13,31). The fungus penetrates stomata to gain access to the apoplast (34), where effectors are produced by the invading hyphae that facilitate disease establishment (3).…”