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POSTERS: Chemical control

Tractor speed and concentration of active ingredient affect the incidence and severity of scab on peach fruit
Clive Bock - USDA ARS, Southeastern Fruit and Tree Nut Research Laboratory. Chunxian Chen- USDA-ARS-Southeastern Fruit and Tree Nut Research Lab, Michael Hotchkiss- USDA-ARS-Southeastern Fruit and Tree Nut Research Laboratory, Phillip Brannen- University of Georgia, Glen C. Rains- University of Georgia

Peach scab (caused by Venturia carpophila) lesions on fruit result in market downgrade and monetary losses. Regular fungicide applications are required to reduce infection. Total spray volume, as affected by tractor speed at constant rate of active ingredient (a.i.) was investigated as a variable affecting scab control. In 2015 and 2016, trees were sprayed with fungicide at petal fall and shuck split, followed by cover sprays at 7-10 day intervals until harvest. Speeds were 3.2, 4.8 and 6.4 kph (spraying 1403, 935 and 702 L/ha, respectively). All speeds (different spray volumes, but equal a.i. ha) 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 61.9, 59.4 and 38.2%, and 65.1, 52.4 and 39.5% of fruit scabbed, respectively. Lesions per fruit (LPF) were reduced in 2015 from 12.3 and 20.0 LPF at 3.2 and 4.8 kph to 7.4 LPF at 6.4 kph. In 2016 there were 43.0, 14.7 and 32.8 LPF at 3.2, 4.8 and 6.4 kph, respectively. LPF did not differ between speeds of 6.4 kph and 3.2 or 4.8 kph, but LPF was lower at 4.8 compared to 3.2 kph. Spray date and speed affected spray coverage, with least coverage at 6.4 kph in July when the canopy was full. There was a negative linear relationship between speed and spray coverage. However, concentration of a.i. in low volume early-season sprays may provide some benefit, even though reduced coverage results at higher speeds.