Bock Clive H, Hotchkiss Michael W, Cottrell Ted E, Wood Bruce W
Southeastern Fruit & Tree Nut Research Lab, United States Department of Agriculture-Agricultural Research Service, Byron, GA 31008.
Plant Dis. 2015 Jul;99(7):916-925. doi: 10.1094/PDIS-11-14-1154-RE. Epub 2015 May 22.
Pecan scab (caused by Fusicladium effusum) is the most damaging disease of pecan in the southeastern United States. Large air-blast sprayers for orchards are used to apply fungicide to control the disease but little quantitative information exists on the spray coverage achieved in the canopy of these trees. A series of experiments using water-sensitive spray cards to record spray coverage (percent area) at different heights and locations up to 15 m in the canopy of pecan trees showed a significantly greater percentage of card area covered at the lowest sample height when compared with the highest sample height. At the lowest height (5 m), spray coverage on individual cards ranged from 4.7 to 73.5% and, at the highest sample height (15 m), spray coverage ranged from 0.02 to 9.5%. In general, there was little significant difference in spray card coverage up to at least 10 m but, at 12.5 and 15 m, there was significantly less spray coverage compared with the coverage at 5 m. Regression analysis indicated a consistent linear relationship between sample height in the tree and the percent area covered. When spray cards were positioned at different heights without possible interference from pecan limbs and foliage, similar effects of sample height on spray coverage were noted. Wind speed measurements showed that air movement declined rapidly with distance from the sprayer fan. Whereas, at 2 m from the fan, wind speeds were approximately 26 m s, by 10 m, speeds had declined to 2 to 4 m s. At distances >12 m, wind speed was approaching ambient air movement of about 1 to 3 m s. Although aerial application resulted in numerically greater spray coverage at sample heights >10 m, it was not significant even though a weak linear relationship (R = 0.21 to 0.25) suggested an effect of height. Characterizing and understanding pesticide spray coverage in pecan will allow us to discern limits imposed by existing technology, and provide the basis for improving spray application methods (or tree management) for more efficacious disease control.
山核桃疮痂病（由扩散黑星菌引起）是美国东南部山核桃最具破坏性的病害。果园使用大型鼓风式喷雾器喷洒杀菌剂来控制该病，但关于这些树木树冠层喷雾覆盖情况的定量信息很少。一系列使用水敏性喷雾卡片记录山核桃树树冠层不同高度和位置（最高达15米）喷雾覆盖率（覆盖面积百分比）的实验表明，与最高采样高度相比，最低采样高度的卡片覆盖面积百分比显著更高。在最低高度（5米）时，单个卡片的喷雾覆盖率在4.7%至73.5%之间，而在最高采样高度（15米）时，喷雾覆盖率在0.02%至9.5%之间。一般来说，至少在10米高度范围内喷雾卡片覆盖率差异不大，但在12.5米和15米处，与5米处相比喷雾覆盖率显著降低。回归分析表明，树中的采样高度与覆盖面积百分比之间存在一致的线性关系。当喷雾卡片放置在不同高度且不受山核桃树枝条和树叶干扰时，也观察到采样高度对喷雾覆盖有类似影响。风速测量表明，空气流动随着离喷雾器风扇距离的增加而迅速下降。在离风扇2米处，风速约为26米/秒，到10米处，风速已降至2至4米/秒。在距离>12米处，风速接近约1至3米/秒的环境空气流动速度。尽管空中喷洒在采样高度>10米时喷雾覆盖率在数值上更高，但即使存在微弱的线性关系（R = 0.21至0.25）表明高度有影响，也不显著。了解和掌握山核桃农药喷雾覆盖情况将使我们能够识别现有技术的局限性，并为改进喷雾施药方法（或树木管理）以更有效地控制病害提供依据。
