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{{Short description|Species of fungus}}

{{Speciesbox
| taxon = Microsphaera diffusa
| authority = Cooke & Peck
| synonyms =
''Erysiphe diffusa'' <br />
''Erysiphe glycines'' <br />
''Trichocladia diffusa''
}}

'''''Microsphaera diffusa''''' is a [[plant pathogen]] that is known to cause [[powdery mildew]] on [[soybean]]s.<ref name=SoybeanFieldBook>{{cite book|last1=Bennett|first1=J. Michael|last2=Rhetoric|first2=Emeritus|last3=Hicks|first3=Dale R.|last4=Naeve|first4=Seth L.|last5=Bennett|first5=Nancy Bush|title=The Minnesota Soybean Field Book|date=2014|publisher=University of Minnesota Extension|location=St Paul, MN|page=85|url=http://www.extension.umn.edu/agriculture/soybean/docs/minnesota-soybean-field-book.pdf|access-date=21 February 2016|archive-url=https://web.archive.org/web/20130930151502/http://www1.extension.umn.edu/agriculture/soybean/docs/minnesota-soybean-field-book.pdf|archive-date=30 September 2013|url-status=dead}}</ref>

== Importance ==
Powdery mildew is a significant pathogen of soybeans and tends to cause epidemics about every 10–15 years in Wisconsin. The first epidemic there was observed in 1975 and several have occurred since.<ref name=":0">{{Cite web|url=https://fyi.extension.wisc.edu/fieldcroppathology/files/2010/12/powdery_mildew_06.pdf|archive-url=https://web.archive.org/web/20191214053019/https://fyi.extension.wisc.edu/fieldcroppathology/files/2010/12/powdery_mildew_06.pdf|url-status=dead|archive-date=December 14, 2019|title=Powder Mildew of Soybean|last=Grau|first=Craig|date=January 2006|access-date=2019-10-23}}</ref> When 82% of the soybean leaf area is covered by ''M. diffusa'', photosynthetic and transpiration rates are less than half of normal soybeans, thus affecting soybean yield.<ref>{{Cite journal|last=Mignucci|first=Julia S.|date=1979|title=Inhibition of Photosynthesis and Transpiration in Soybean Infected by Microsphaera diffusa|journal=Phytopathology|volume=69|issue=3|pages=227|doi=10.1094/phyto-69-227|issn=0031-949X}}</ref> Different studies have found varying amounts of yield reduction due to powdery mildew. In Illinois, measured yield losses ranged up to 14 percent.<ref>{{Cite journal|url=https://pdfs.semanticscholar.org/a849/65761b9e13a044daf9194af41b6b88accd70.pdf|archive-url=https://web.archive.org/web/20191214053018/https://pdfs.semanticscholar.org/a849/65761b9e13a044daf9194af41b6b88accd70.pdf|url-status=dead|archive-date=2019-12-14|title=Powdery Mildew of Soybeans|date=1989|doi=10.2307/3758214|jstor=3758214|s2cid=37603780|access-date=2019-10-23|last1=Paxton|first1=Jack D.|last2=Rogers|first2=Donald P.|journal=Mycologia|volume=66|issue=5|pages=894–896|pmid=4612359}}</ref> Studies from Iowa recorded yield losses of up to an estimated 10 bushels per acre. In Wisconsin, yield loss was up to 5 bushels per acre. It is important to note that yield loss due to powdery mildew will be greater for soybeans planted late for a region compared to early-planted soybeans.<ref name=":1">{{Cite web|url=https://soybeanresearchinfo.com/soybean-disease/powdery-mildew/|title=Powdery Mildew - Soybean Disease|website=Soybean Research & Information Network|language=en-US|access-date=2019-12-14}}</ref>

== Environment ==
Temperature plays an important role in powdery mildew development. Powdery mildew develops favorably in cooler temperatures (65–77 °F). Temperatures above 30 °C appear to constrain disease development. Rainfall does not appear to affect the disease,<ref>{{Cite web|url=https://www.cropscience.bayer.us/learning-center/articles/powdery-mildew-in-soybeans|title=Powdery Mildew in Soybeans|website=www.cropscience.bayer.us|language=en|access-date=2019-12-14}}</ref> but it has been found that a shorter leaf wetness duration appears to be a driver of the disease.<ref>{{Cite journal|last1=Roese|first1=Alexandre Dinnys|last2=Ribeiro|first2=Paulo Justiniano|last3=De Mio|first3=Louise Larissa May|date=2017-06-16|title=Microclimate in agrosilvopastoral system enhances powdery mildew severity compared to agropastoral and non-integrated crop|journal=Tropical Plant Pathology|volume=42|issue=5|pages=382–390|doi=10.1007/s40858-017-0162-4|s2cid=8380698|issn=1983-2052|doi-access=free}}</ref> Additionally, low relative humidity is required for disease development.<ref name=":1" />

== Management ==
Variety selection is a tool that can be used to help combat powdery mildew. No variety of soybean has complete resistance to powdery mildew, but some varieties are clearly more susceptible than others. Resistance affects initial inoculation of the plant.

Fungicides may also be used as a management tool. They can be sprayed once powdery mildew is detected to kill the spores. This affects the dispersal and secondary inoculation of the plant.<ref name=":0" /> Some examples of fungicides include Topsin M, Quadris, and Headline, with the last two being less effective.<ref name=":1" />

Another management practice is the planting date. Early-planted soybeans tend to show less severity of powdery mildew than late-planted soybeans.<ref name=":0" />

== References ==
{{Reflist}}

== External links ==
* [https://web.archive.org/web/20070820101227/http://nt.ars-grin.gov/fungaldatabases/ USDA ARS Fungal Database]

{{Taxonbar|from=Q6840321}}

[[Category:Fungal plant pathogens and diseases]]
[[Category:Microsphaera|diffusa]]
[[Category:Soybean diseases]]
[[Category:Fungus species]]

Microsphaera diffusa - Revision history

imported>Cedrusaurum: Extensive copyediting