Efficacy of agricultural oil and fungicide combinations as a late dormant treatment for control of peach scab in Alabama, 2016

Authors: SIKORA, EDWARD - Auburn University; PITTS, JAMES - Auburn University; BRANNEN, PHILLIP - University Of Georgia; Bock, Clive; Hotchkiss, Michael - Mike; GOTTILA, T - University Of Georgia

Submitted to: Plant Disease Management Reports
Publication Type: Other
Publication Acceptance Date: 2/15/2017
Publication Date: 3/1/2017
Citation: Sikora, E.J., Pitts, J., Brannen, P.M., Bock, C.H., Hotchkiss, M.W., Gottila, T. 2017. Efficacy of agricultural oil and fungicide combinations as a late dormant treatment for control of peach scab in Alabama, 2016. Plant Disease Management Reports. 11:STF002.

Interpretive Summary: Fungicides were evaluated for control of scab in a mid-ripening peach experimental block (‘Ruston Red’) located at the Chilton Area Research and Extension Center in Clanton, AL. Chemical formulations were applied with an airblast sprayer and included a non-treated control and a standard fungicidal spray program from petal fall through cover sprays (Bravo [chlorothalonil] at petal fall and shuck split with sulfur cover sprays). For remaining treatments, the shuck split application was removed. Because shuck split is the critical period for scab infection previous fungicide applications (late dormant or petal fall) must have significant and persistent activity for disease incidence and severity to be greatly reduced compared to the standard fungicide program. Treatments included a Bravo application at petal fall with sulfur cover sprays; Bravo + oil at late dormant, Bravo at petal fall with sulfur cover sprays; Abound (azoxystrobin) at late dormant, Bravo at petal fall with sulfur cover sprays; and Abound + Bravo + oil at late dormant, Bravo at petal fall with sulfur cover sprays. Scab incidence (percent infected fruit) and severity (lesions per fruit) were recorded. Disease levels were relatively low, and the chemical standard fungicide spray program did not significantly reduce disease incidence or severity. However, the spray programs with a high rate of Bravo + oil and with Abound + Bravo + oil provided a significant reduction in incidence and severity, respectively, of scab compared to the untreated control. This trial supports the notion that dormant season oil application may benefit scab control in peach orchards in the Southeast. However, further research is necessary to more definitively determine the efficacy of fungicides + oil in the suppression of peach scab.

Technical Abstract: Fungicides were evaluated for control of scab in a mid-ripening peach experimental block (‘Ruston Red’) located at the Chilton Area Research and Extension Center in Clanton, AL. Chemical formulations were applied with an airblast sprayer (112.5 gal/A spray volume). Treatment regimens included a non-treated control and a standard fungicidal spray program from petal fall through cover sprays (Bravo [chlorothalonil] at petal fall and shuck split with sulfur cover sprays). For remaining treatments, the shuck split application was removed; shuck split is the critical period for scab infection, so unless previous fungicide applications (late dormant or petal fall) have significant and persistent activity, disease incidence and severity would be greatly increased over the standard fungicide program. Remaining treatment regimens included a Bravo application at petal fall with sulfur cover sprays; Bravo + oil at late dormant, Bravo at petal fall with sulfur cover sprays; Abound (azoxystrobin) at late dormant, Bravo at petal fall with sulfur cover sprays; and Abound + Bravo + oil at late dormant, Bravo at petal fall with sulfur cover sprays. Four replications of each treatment were applied to a randomized complete block design, with each plot consisting of four trees; the center two trees in each plot were utilized for scab ratings. An unsprayed guard row was left between each treatment row. The test orchard was maintained following cultural management practices commonly used in the Southeast. At full maturity, ~50 fruit were harvested on each of two dates (5 and 8 Jul) and data was pooled from each plot for scab assessments. Scab incidence (percent infected fruit) and severity (lesions per fruit) were recorded. Disease levels were relatively low, and the chemical standard fungicide spray program did not significantly reduce disease incidence or severity. However, the spray programs with a high rate of Bravo + oil and with Abound + Bravo + oil provided a significant reduction in incidence and severity, respectively, of scab compared to the untreated control. Previous trials conducted on almonds in California between 2011 and 2014 concluded that a single late-dormant application of Bravo, when applied with oil, effectively suppressed scab. This trial supports the notion that this benefit may also translate to peach orchards in the Southeast, given that Bravo in combination with oil provided peach scab suppression. However, further research is necessary to more definitively determine the efficacy of fungicides + oil in the suppression of peach scab.