266 Percival and Haynes: The Influence of Calcium Sprays to Reduce Fungicide Table 2. Selected calcium foliar sprays compared for the control of apple scab (Venturia inaequalis) on apple cv. Crown Gold as measured by leaf and fruit scab severity, chlorophyll fluorescence (Fv/Fm values), leaf chlorophyll content (SPAD values), and leaf Ca content. Data from 2007. Treatment Control Silwett Calcium chloride Calcium sulfate Calcium nitrate Calcium nitrate borate Calcium hydroxide Calcium metalosate Calcium amino acid complex Penconazole DF LSD Significance of Ca (P value) z y Values mean of 8 trees. Values mean of 8 trees, 10 leaves per tree. Asterisk (*) indicates value significantly different from controls according to Least Significant Difference (LSD) at P < 0.05. ns = not significant different from control value. sprays at four times during the growing season, significantly (P < 0.05) reduced apple scab severity of leaves and fruit at harvest maturity (September) from an average of 3.50 and 2.85 (2006) and 4.00 and 3.00 (2007), to 2.4 and 1.98 (2006), and 2.14 and 2.26 (2007) respectively, when averaged across all seven cal- cium treatments compared to the noncalcium control treatment A difference in the magnitude of scab severity reductions be- tween calcium products was recorded. In both the 2006 and 2007 trials, only apple trees treated with calcium chloride and calcium hydroxide had significantly (P < 0.05) less leaves and fruit with scab compared to untreated control trees (Table 1; Table 2). This indicates that out of all the seven commercially available calcium products tested, calcium chloride and calcium hydroxide pro- vided greatest protection against apple scab on both leaves and fruit. Maximal reductions in scab severity of leaves and fruit in both the 2006 and 2007 trials was, however, achieved by apply- ing sprays of the commercially recommended synthetic fungicide penconazole. In this instance, leaf and fruit severity was reduced by 51% and 65% in the 2006 trial, and by 54% and 67% in the 2007 trial, respectively (Table 1; Table 2). In both the 2006 and 2007 trials, applications of calcium and penconazole increased chlorophyll fluorescence Fv/Fm values in comparison with non- calcium treated controls indicating higher leaf photosynthetic ac- tivity in calcium and penconazole treated trees (Table 1; Table 2). In only three instances, however, were these increases significant, application of penconazole, calcium chloride (2006 and 2007) and calcium sulfate (2006 only). Likewise in both the 2006 and 2007 trials applications of calcium and penconazole increased chlorophyll content SPAD values compared with noncalcium treated controls indicating less damage to the leaf chlorophyll molecule at the cessation of the growing season (Table 1; Table 2). Mostly, this increase was statistically significant at P < 0.05, indicating that resistance to infection had been enhanced. In all cases, applications of calcium, irrespective of form, significantly ©2009 International Society of Arboriculture (P < 0.05) increased calcium concentration within leaf tissue by ca. 11%–25% in the 2006 trial (Table 1) and 12%–23% in the 2007 trial (Table 2) when averaged across all calcium treat- ments. Application of the synthetic fungicide penconazole had no significant effect on leaf calcium content (Table 1; Table 2). Relationship Between Foliar Calcium Content and Scab Severity There was no clear relationship between leaf calcium content and the degree of apple scab susceptibility. For reasons of clarity, data for five of the twelve species tested are shown in Figure 1. In this instance, percent variation accounted for recorded was 4% that was not significant; P = 0.179. Such a response reflects that recorded for all twelve species (percent variation accounted for recorded = 7%, P = 0.166, data not shown), and in Figure 1 where highest leaf calcium content (1.4%–1.9% dry weight) was record- ed in foliar tissue derived from M. ‘Cox’s Orange Pippin’ yet scab susceptibility ranged from 3–5 on a scab severity scale indicative of a scab sensitive species. Contrary to this lowest leaf calcium content (1%–1.3% dry weight) was recorded in foliar tissue de- rived from M. ‘Red Jade’, yet scab susceptibility ranged from 1–3 on a scab severity scale indicative of a scab resilient species. DISCUSSION Increased concerns regarding the over reliance of fungicides for pathogen control, coupled with development of pathogen insensitivity, increased legislative restriction regarding fun- gicide use and greater public awareness of the potential envi- ronmental impact of synthetic pesticides has meant consid- erable research has been aimed at developing nonfungicidal approaches to pathogen control (Akbudak et al. 2006; Walters 2006; Hagan and Akridge 2007; Percival and Haynes 2008). The primary aim of this study was to determine whether appli- Leaf necrosisz 4.00 3.88ns 1.63* 2.25* 2.62* 2.25* 1.88* 2.25* 2.13* 1.45* 79 0.722 <0.001 Fruit necrosisz 3.00 2.88ns 1.25* 3.12ns 2.25* 2.50ns 1.88* 2.38* 2.50ns 1.00* 79 0.556 <0.001 Fv/Fmy 0.715 0.702ns 0.807* 0.780ns 0.783ns 0.788ns 0.791ns 0.785ns 0.779ns 0.805* 79 0.091 0.004 SPADy 11.69 13.85ns 19.00* 16.45* 15.76* 14.79* 18.00* 12.69ns 16.18* 21.30* 79 2.708 <0.001 Leaf Ca contentz 1.21 1.24ns 1.45* 1.36* 1.50* 1.43* 1.51* 1.39* 1.57* 1.26ns 79 0.146 <0.001
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