b'Provysol: A Recently Developed DMI Fungicide For Early Blight Management by Dr. Julie Pasche; Associate Professor and Neil C. Gudmestad Endowed Chair of Potato Pathology Dr. Neil C. Gudmestad; University Distinguished Professor Emeritus Potato growers in the region fight adotmanagement.Wealsorecom- toSDHIfungicidesisconveyed complexofleafblightsandspotsmend the application of a premiumthrough at least 5 mutations. These includinglateblight,earlyblight,early blight fungicide in the succi- mutationsaffectSDHIfungicides brown spot, black dot, and Botrytis.natedehydrogenaseinhibitordifferentially;however,allfungi-Late blight is an acute disease that(SDHI;FRAC7),demethylationcidesareaffectedtosomedegree. can be devastating under conduciveinhibitor (DMI; FRAC 3) or anilino- Reduced-sensitivity has been report-conditions,butchronicdiseasespyrimidine(AP;FRAC9)classated to DMI, and AP fungicides, but is such as early blight offers a seriousearlytuberbulkingandasecondnot widespread. plighttogrowerseveryyear.Earlyapproximately 2 weeks later. These blightiscausedbythefungusapplicationsshouldbetank-mixedThreeDMIfungicides,Provysol, Alternaria solani. Most cultivars areandusedinrotationwithRevus Top and Quash, are cur-susceptible to the pathogen; there- chlorothalonilormancozebuntilrentlyregisteredforthemanage-fore,growersrelyonafull-seasonvinedesiccation,maturityorhar- ment of early blight. The newest of foliarfungicideprogramtomini- vest.these is Provysol, registered by BASF mize disease impact and maximizein 2020. NDSU has conducted field yield. The early blight pathogen is catego- trials at the Northern Plains Potato rizedbytheFungicideResistanceGrowers irrigated research site near Early blight is characterized by dark,Action Committee (FRAC) as a high- Inkster, North Dakota for 10 years circular spots with concentric ringsriskfungusandisnotoriousforand trials to evaluate the efficacy of (target).Lesionsfrequentlydevelopingresistancetosingle-siteProvysolforthemanagementof becomeangular,restrictedbypri- modeofactionfungicidesusedinearlyblighthavebeenconducted maryleafveinsthatextendfromitscontrol.TheQoIfungicidesince 2018 (Figs. 1 and 2). The appli-the leaflet midrib. Early blight startsQuadris (azoxystrobin) was regis- cationofProvysolhasbeencom-inthelowercanopywhereleavesteredforuseonpotatoesinanpared to other premium fungicides aresenescingandmovesintotheemergencyuseregistrationlateinincludingSDHIfungicidesLuna uppercanopyastheseasonpro- the 1998 growing season in NorthTranquility, Miravis Prime, the gresses. A. solani also infects tubers,Dakota,Minnesota,NebraskaandAPfungicideScalaandtheDMI resulting in dark, sunken lesions.WisconsinandtheproductwasfungicideRevusTop.Inalltrials fullyregisteredin1999.Reducedreportedhere,allfungicidetreat-In our region, the use of premium,efficacyofthisfungicidewasments resulted in significantly high-single-sitemodeofactionfungi- observedasearlyas2000.Today,erdiseasecontrolwhencompared cidesinrotationwithprotectant,over 95% of A. solani isolates carryto the non-treated control. multi-sitemodesofactionfungi- the mutation responsible for resist-cides chlorothalonil and mancozebance to QoI fungicides registered onIn 2018, the first year Provysol was hasbeenshowntoincreaseyield.potatoes. evaluated in North Dakota, compar-For premium control of early blightisonsweremadeamongseason-intheregion,NDSUrecommendsA similar story can be told for SDHIlong applications of Provysol, Luna two fungicide applications prior tofungicides.TheSDHIfungicideTranquilityandourrecommended row closure, including one applica- Endura(boscalid)wasregisteredgrowerstandardprogram.Wedo tion of a quinone outside inhibitorin2005andreducedefficacywasnot recommend multiple sequential (QoI; FRAC 11) fungicide for blackdetected as early as 2009. Resistanceapplications of any single-site mode 10 POTATO GROWER MARCH 2022'