A ProMED-mail post <http://www.promedmail.org>
ProMED-mail is a program of the International Society for Infectious Diseases <http://www.isid.org>
Date: Mon 25 Feb 2019
Source: Farm Forum [edited]
South Dakota State University [SDSU] and University of Kentucky plant pathologists have confirmed that _Cercospora sojina_ that causes soybean frogeye leaf spot has shown resistance to QoI fungicides (quinone outside inhibitor, strobilurin) in South Dakota. SDSU's Febina Mathew says, "This finding warrants the need to determine the prevalence of QoI fungicide-resistant _C. sojina_ in the state."
Frogeye leaf spot is predominantly managed through fungicides.
According to Mathew, in 2014 frogeye leaf spot was ranked 4th most destructive disease affecting soybean in the southern US. _C. sojina_ resistance to QoI fungicide was first documented in Tennessee in 2010 [ProMED-mail post http://promedmail.org/post/20101027.3897] and has been detected in several other states since, including Iowa in 2017.
SDSU's Emmanuel Byamukama says. "Because this fungus has high genetic diversity and can be spread via seed, resistant isolates can develop even without extensive use of QoI fungicides." Fungicide resistance can be delayed by using practices such as planting resistant varieties, crop rotation, drainage and proper soil fertility levels.
Communicated by: ProMED-mail <email@example.com>
[Frogeye leaf spot is caused by the fungus _Cercospora sojina_, which can infect leaves, stems, and seeds of soybean. The pathogen is found worldwide but is only problematic under warm, humid conditions.
Significant yield losses of 10 to 50 percent are commonly associated with frogeye epidemics.
The fungus is spread via infected plant material and can also be seed borne leading to inferior seed quality. It is most likely to become a problem if infected seed is planted or if infected residue of a previous soybean crop serves as a source of inoculum (thus the disease may be more difficult to control in 2nd crops). Disease management includes use of disease-free seed, planting of resistant varieties, crop rotation, tillage and fungicide applications. Rotating or mixing chemical classes of fungicides is used to extend the useful life of the compounds.
Strobilurins are strongly antifungal agents produced by fungi. Being derived from natural products, they are considered environmentally safe and are used worldwide as protectants against most major fungal plant pathogens. However, like several other fungicide classes, they have single-site activity and therefore pathogens must be expected to develop resistance or tolerance over time. Pathogen resistance to this important group of fungicides is of major concern to many primary industries worldwide.
Strobilurin resistant strains of the related _C. beticola_ which causes leaf spot of sugar beet have been reported, for example, from the UK (ProMED-mail post http://promedmail.org/post/20170413.4967611]
and the US (ProMED-mail post
<http://www.mapsofworld.com/usa/usa-state-and-capital-map.html> and <http://healthmap.org/promed/p/243>
Individual states via:
<https://www.extension.purdue.edu/extmedia/BP/BP-131-W.pdf>, and <https://www.pioneer.com/home/site/us/agronomy/crop-management/soybean-insect-disease/frogeye-leaf-spot/>
_C. sojina_ taxonomy:
Information on strobilurins:
<https://www.ncbi.nlm.nih.gov/pubmed/17474024>, and <http://grounds-mag.com/mag/grounds_maintenance_strobilurin_fungicides_natures/index.html>
Cercospora leaf spot, sugar beet - UK: strobilurin resistance
Cercospora leaf spot, sugarbeet - USA: (MI,ND) new strains
Frogeye leaf spot, soybean - USA: (TN) new strain
Frogeye & leaf rust, soybean - Argentina, Brazil
Fungal diseases, field crops - Americas
Early blight, potato - Canada: new strains
Mildews, grapevine - USA: new strains
Frogeye leaf spot, soybean - USA: surveillance
Frogeye leaf spot, soybean - USA (Wisconsin) http://promedmail.org/post/20021028.5655]