Microsphaera diffusa

{{Short description|Species of fungus}}

{{Speciesbox

| taxon = Microsphaera diffusa

| authority = Cooke & Peck

| synonyms =

Erysiphe diffusa

Erysiphe glycines

Trichocladia diffusa

}}

Microsphaera diffusa is a plant pathogen. M. diffusa infections on soybeans are referred to as powdery mildew.{{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}}

Importance:

Powdery mildew of soybeans is an important pathogen and tends to cause epidemics about every 10–15 years in Wisconsin. In 1975 the first epidemic there was observed and several have occurred since.{{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}} Powdery mildew affects the soybean plants. 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.{{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}} Different studies have found different amounts of yield reduction due to the powdery mildew. In Illinois, measured yield losses ranged up to 14 percent.{{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}} From Iowa studies, measured yield losses were estimated up to 10 bushels per acre. In Wisconsin, the yield loss was up to 5 bushels per acre. And it's 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.{{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}}

Environment:

The temperature plays an important role in powdery mildew development. Powdery mildew favors cooler temperatures (65–77 degrees F). Temperatures above 30 degrees C appears to constrain disease development. Rainfall does not appear to affect the disease.{{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}} But, it has been found that a shorter leaf wetness duration appears to be a driver of the disease.{{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}} Additionally, low relative humidity is required for disease development.

Management:

Variety selection is a tool that can be used to help combat powdery mildew. It's not entirely effective because no variety of soybean has complete resistance to powdery mildew, but there are definitely some varieties more susceptible than others. Resistance affects initial inoculation of the plant. The currently effective management tools are fungicides. They can be sprayed once powdery mildew is detected and they kill the spores. This affects the dispersal and secondary inoculation of the plant. Some examples of fungicides include Topsin M, Quadris, and Headline, with the last two being less effective. Another management practice is planting date. Early-planted soybeans tend to show less severity of powdery mildew than late-planted soybeans.