The effect of tractor speed and canopy position on fungicide spray deposition and peach scab incidence and severity

Authors: Bock, Clive; RAINS, GLEN - University Of Georgia; Hotchkiss, Michael - Mike; Chen, Chunxian; BRANNEN, PHIL - University Of Georgia

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2020
Publication Date: 6/2/2020
Citation: Bock, C.H., Rains, G.C., Hotchkiss, M.W., Chen, C., Brannen, P.M. 2020. The effect of tractor speed and canopy position on fungicide spray deposition and peach scab incidence and severity. Plant Disease. 104(7): 2014-2022. https://doi.org/10.1094/PDIS-11-18-1950-RE.
DOI: https://doi.org/10.1094/PDIS-11-18-1950-RE

Interpretive Summary: Peach scab is caused by the fungal pathogen, Venturia carpophila, and is an economically harmful disease of peach in the southeastern U.S. Lesions on the fruit results in downgrading of fruit, and thus value. Fungicides are required to reduce scab on fruit. Tractor speed was investigated as a variable affecting spray deposition and disease control in relation to volume applied. Speeds were 3.2, 4.8 and 6.4 kph resulting in 1403, 935 and 701 L ha-1, respectively, with the quantity of active ingredient (a.i.) kept constant per hectare. Deposition declined for all speeds with later spray dates between April and July. There was a negative linear relationship between tractor speed and spray coverage in 3 of 4 dates the experiment was repeated. All tractor speeds (volumes, equal a.i. per hectare) reduced incidence and severity of scab compared to the control. However, the number of lesions per fruit was not consistently affected. Concentration of a.i. in lower volume sprays applied at higher speed may provide some benefit in reducing incidence of scab, but there appeared to be less effect on severity.

Technical Abstract: Peach scab (caused by Venturia carpophila) is a damaging disease of peach in the southeastern U.S. Lesions on the fruit results in downgrading of fruit, and thus value. Fungicides are required to reduce scab on fruit. Tractor speed was investigated as a variable affecting spray deposition and disease control in relation to volume applied. In experiments in 2015 and 2016, trees were sprayed with fungicide to control scab at petal fall to 1% shuck split and at shuck split to 10% shuck off. Speeds were 3.2, 4.8 and 6.4 kph resulting in 1403, 935 and 701 L ha-1, respectively, with the quantity of active ingredient (a.i.) kept constant per hectare. Spray date and tractor speed affected spray coverage, with least coverage (3.6%) at 6.4 kph in July 2016 when the canopy was full (on Apr 7, 2016, deposition was 28.1, 20.7 and 11.8% at 3.2, 4.8 and 6.4 kph, respectively). Indeed, deposition declined for all speeds with later spray dates between April and July. There was a negative linear relationship between tractor speed and spray coverage in 3 of 4 dates the experiment was repeated. All tractor speeds (volumes, equal a.i. per hectare) reduced incidence and severity of scab compared to the control. Mean incidence at 3.2, 4.8 and 6.4 kph in 2015 and 2016 was 68.6, 59.2 and 38.3%, and 64.2, 53.0 and 40.4% of fruit scabbed, respectively. Effect of speed on lesion number per fruit depended on year: lesions per fruit were reduced in 2015 from 8.1 and 10.8 lesions per fruit at 3.2 and 4.8 kph to 3.6 lesions per fruit at 6.4 kph, but in 2016 the difference was not significant between tractor speeds of 6.4 kph and 3.2 or 4.8 kph, but was lower at 4.8 kph compared to 3.2 kph (11.2, 8.6 and 9.9 lesions per fruit at 3.2, 4.8 and 6.4 kph, respectively). Control trees had fewer lesions per fruit high in the canopy, but there was little effect of sample height in fungicide-treated trees. Concentration of a.i. in lower volume sprays applied at higher speed may provide some benefit in reducing incidence of scab, but there appeared to be less effect on severity.