Bock Clive H, Cottrell Ted E, Hotchkiss Mike W, Wood Bruce W
USDA-ARS-SEFTNRL, 21 Dunbar Road, Byron, GA 31008, USA.
Plant Dis. 2013 May;97(5):626-634. doi: 10.1094/PDIS-05-12-0453-RE.
Pecan scab (Fusicladium effusum) is a destructive disease of pecan in the southeastern United States. This study was conducted to investigate the vertical distribution of scab in tall pecan trees (14 to 16 m tall) in three experiments in 2010 and 2011. Although 2010 had average rainfall, a factor that drives scab epidemics, 2011 was a very dry year with a consequently low scab severity. A total of eight trees were included in each experiment, four were nontreated controls, and four were sprayed using a ground-based air-blast sprayer. Trees were assessed for foliar and fruit scab at 0-5.0, 5.0-7.5, 7.5-10.0, 10.0-12.5, and 12.5-15.0 m. Mixed model analysis showed main effects of height, fungicide treatment, and heighttreatment interactions in all three experiments, although on foliage the effects were less consistent (P value = 0.003-0.8), perhaps due to delayed fungicide applications early in the season. However, fruit of nontreated trees had more severe scab low in the canopy compared to fungicide-treated trees, with a consistent heighttreatment interaction (P value = <0.0001-0.04). Most often the severity of scab in the upper canopy was similar in trees on fungicide-treated and nontreated trees, suggesting that fungicide had less impact at heights ≥10.0 m compared to <10.0 m in the canopy. There was a consistent reduction in scab severity on foliage and on immature fruit in August due to fungicide treatment at heights ≤10.0 m. Above 10.0 m, the effect was inconsistent, but late in the season (October), the fungicide-treated trees showed lower scab severity throughout the canopy. A metallic tracer study using cerium (Ce) showed an exponential relationship between quantities of Ce recovered and sample height in the canopy, with the quantity of Ce at ≥10 m being statistically equal to background levels. The relationship between scab severity on fruit and sample height in the canopy of nontreated trees was most often described by a negative linear function, but there was no discernible relationship on fungicide-treated trees, as the severity of scab in the lower canopy was most often similar to that in the upper canopy. Gradients in fungicide coverage and scab severity have ramifications for scab management options and potentially for the development of fungicide resistance in F. effusum.
山核桃疮痂病（Fusicladium effusum）是美国东南部山核桃的一种毁灭性病害。本研究旨在调查2010年和2011年三个试验中高大山核桃树（高14至16米）中山核桃疮痂病的垂直分布情况。2010年降雨量平均，降雨是引发疮痂病流行的一个因素，而2011年是非常干旱的一年，因此疮痂病严重程度较低。每个试验共纳入8棵树，4棵为未处理对照树，4棵使用地面风送喷雾器进行喷洒。在0 - 5.0米、5.0 - 7.5米、7.5 - 10.0米、10.0 - 12.5米和12.5 - 15.0米处对树木的叶片和果实疮痂病情况进行评估。混合模型分析表明，在所有三个试验中，高度、杀菌剂处理以及高度处理交互作用均有显著影响，不过在叶片上的影响不太一致（P值 = 0.003 - 0.8），这可能是由于季节早期杀菌剂施用延迟所致。然而，与经杀菌剂处理的树木相比，未处理树木的果实疮痂病在树冠下部更为严重，存在一致的高度处理交互作用（P值 = <0.0001 - 0.04）。大多数情况下，经杀菌剂处理和未处理树木树冠上部的疮痂病严重程度相似，这表明与树冠中低于10.0米处相比，杀菌剂在高度≥10.0米处的影响较小。由于在高度≤10.0米处进行了杀菌剂处理，8月份叶片和未成熟果实上的疮痂病严重程度持续降低。在10.0米以上，效果不一致，但在季节后期（10月），经杀菌剂处理的树木整个树冠的疮痂病严重程度较低。一项使用铈（Ce）的金属示踪剂研究表明，树冠中回收的Ce量与样品高度之间呈指数关系，在≥10米处的Ce量在统计学上与背景水平相当。未处理树木果实上的疮痂病严重程度与树冠中样品高度之间的关系通常用负线性函数描述，但在经杀菌剂处理的树木上没有明显关系，因为树冠下部的疮痂病严重程度通常与上部相似。杀菌剂覆盖梯度和疮痂病严重程度对疮痂病管理方案有影响，也可能对F. effusum中杀菌剂抗性的发展有影响。
