Although demand for organic produce continues to increase in the mid-Atlantic, few apple (Malus ×domestica Borkh.) growers in the region have adopted organic management practices due to the considerable disease, insect, and weed pressure, as well as the lack of effective crop load management tools. In this study, lime sulfur (LS) and Regalia® (R) were applied in different sequences (i.e., LS/LS, LS/R, R/R, and R/LS), each in a mixture with JMS Stylet-Oil, to chemically thin apple flowers in an organically managed ‘Honeycrisp’/‘MM.111’ orchard. There was also a nontreated control, a “grower standard” control (LS at 11 mm fruitlet diameter), and a hand-thinned control. The treatments were evaluated for their ability to reduce crop load, as well as to control powdery mildew [Podosphaera leucotricha (Ellis & Everh.) E. S. Salmon], cedar apple rust (Gymnosporangium juniperi-virginiana Schwein.), and quince rust (Gymnosporangium clavipes Cooke & Peck). All treatments reduced crop load compared with the nontreated control, and after the first application of LS or R, the number of fertilized king blooms was reduced and fertilization was prevented in all side blooms. All bloom thinning treatments had more fruit peel russet than the control and russet was more severe when LS was one of the applications. Bloom thinning applications of LS and R did not reduce powdery mildew leaf infection compared with the nontreated control. Cedar apple rust incidence was reduced by all bloom thinning treatments, though some lesions were detected in all treatments. There were minimal quince rust infections in any of the treatments, including the nontreated control. These results suggest that when LS and/or Regalia® are mixed with JMS Stylet-Oil and applied as bloom thinners, they can reduce crop load, and, as a secondary benefit, they can also decrease cedar apple rust incidence from infections that occur during bloom.
Funding support was provided by a U.S. Department of Agriculture-Specialty Crop Block Grant administered by the Virginia Department of Agriculture and Consumer Services, Virginia Agricultural Experiment Station, and Virginia Tech’s Department of Horticulture.
We thank Sierra Athey, Matt Borden, David Carbaugh, Allen Cochran II, Scott Kilmer, Abby Kowalski, Taylor Mackintosh, Jared Repass, William Royston, Jr., Ashley Thompson, and Jim Warren for their assistance with this experiment.
Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the authors and does not imply its approval to the exclusion of other products or vendors that also may be suitable.
HalbrendtN.O.TravisJ.W.JarjourB.2010Evaluation of organic fungicide programs for apple scab powdery mildew and cedar apple rust 2009. Plant Dis. Mgt. Rpt. 4:PF011. Online publication. doi: 10.1094/PDMR04
HergerG.KlingaufF.MangoldD.PommerE.H.SchererM.1988Efficacy of extracts of Reynoutria sachalinensis (F. Schmidt) Nakai (Polygonaceae) against fungal diseases, especially powdery mildews (in German)Nachrichtenblatt des Deutschen Pflanzenschutzdienstes (Braunschweig)405660
Herger,G.Klingauf,F.Mangold,D.Pommer,E.H.Scherer,M.1988Efficacy of extracts of Reynoutria sachalinensis (F. Schmidt) Nakai (Polygonaceae) against fungal diseases, especially powdery mildews (in German)405660)| false
HyreR.A.1939The effect of sulfur sprays on the photosynthesis and transpiration of apple leaves. N.Y. Agr. Expt. Sta. Mem. 222
Konstantinidou-DoltsinisS.SchmittA.1998Impact of treatment with plant extracts from Reynoutria sachalinensis (F. Schmidt) Nakai on disease severity of powdery mildew and yield in cucumber under Greek conditionsCrop Prot.17649656
Konstantinidou-Doltsinis,S.Schmitt,A.1998Impact of treatment with plant extracts from Reynoutria sachalinensis (F. Schmidt) Nakai on disease severity of powdery mildew and yield in cucumber under Greek conditions17649656)| false
Konstantinidou-DoltsinisS.MarkellouE.KasselakiA.M.FanourakiM.N.KoumakiC.M.SchmittA.Liopa-TsakalidisA.MalathrakisN.E.2006Efficacy of Milsana®, a formulated plant extract from Reynoutria sachalinensis, against powdery mildew of tomato (Leveillula taurica)BioControl51375392
Konstantinidou-Doltsinis,S.Markellou,E.Kasselaki,A.M.Fanouraki,M.N.Koumaki,C.M.Schmitt,A.Liopa-Tsakalidis,A.Malathrakis,N.E.2006Efficacy of Milsana®, a formulated plant extract from Reynoutria sachalinensis, against powdery mildew of tomato (Leveillula taurica)51375392)| false
YoderK.S.CochranA.E.IIRoystonW.S.JrKilmerS.W.2006Broad-spectrum disease management by certified organic and home fruit fungicides 2005. F&N Tests 61:PF019. 31 Aug. 2016. <http://www.plantmanagementnetwork.org/pub/trial/fntests/reports/2006/PF019.pdf>.
YoderK.S.PeckG.M.CombsL.D.ByersR.E.2013Using a pollen tube growth model to improve apple bloom thinning for organic productionActa Hort.1001207214
Yoder,K.S.Peck,G.M.Combs,L.D.Byers,R.E.2013Using a pollen tube growth model to improve apple bloom thinning for organic production1001207214)| false
YoderK.S.CochranA.E.IIRoystonW.S.JrKilmerS.W.2015After-infection control of quince rust on Red Delicious and Golden Delicious apples 2014. Plant Disease Mgt. Rpt 9:PF015. 31 Aug. 2016. <http://www.plantmanagementnetwork.org/pub/trial/PDMR/reports/2015/PF015.pdf>.