Arboriculture & Urban Forestry 40(4): July 2014 gen severity caused by several fungi and bacteria (Percival et al. 2009). Pertinent examples include enhanced resistance against soſt rot of potato caused by Erwinia carotovora subsp. amylovora (Bain et al. 1996), Phoma exigua (gangrene), and Fusarium solani (dry rot) (Olsson 1998), Botrytis cinerea of apple (Conway et al. 1991) and sweet cherries (Ippolito et al. 2005), and brown rot of peach caused by Monilinia fructicola (Elmer et al. 2006). Calcium is also known to directly affect some fruit pathogens by interfering with spore germination, germ tube elon- gation, and fungal cell wall thickness (Miceli et al. 1999; Chardonnet et al. 2000). The synthesis of plant protectant phytoalexin and phenolics substances has been reported to increase as a result of calcium application (Miceli et al. 1999; Glenn et al. 2001). Importantly, calcium phosphite provided a greater degree of scab control compared to the currently used potassium phosphite, although fruit yields were lower. Application of potassium phosphite and calcium phosphite together may improve the level of scab control and fruit yield. Calcium sprays provide other benefits to the fruit industry, such as enhanced fruit firmness and delayed ripening (Marschner 2012), as well as influencing other important com- mercial factors, such as aroma (Ortiz et al. 2011). Zinc is a component of a number of carbamate (zineb, metiram, propineb) and thiadiazole fungi- cides used for plant pathogen control of agricultural crops—including wheat, barley, and potato—while zinc pyrithione is a widely used active ingredient in antifungal shampoos and soaps for human medical purposes (Reeder et al. 2011). Zinc oxide nanopar- ticles, zinc sulphate, and zinc perchlorate have also been shown to demonstrate antifungal properties (He et al. 2011; Savi et al. 2013). However these fun- gicides display differing modes of action on plant pathogens with in general the anion (carmomate, triazole) being of greater effect than the zinc cation. The zinc cation may, however, contribute indirectly to disease resistance via increased plant nutrition (Marschner 2012) and fruit quality (Zhang et al. 2013). CONCLUSIONS Results of this study show that a range of commer- cially available phosphite formulations exist and provide higher degrees of control against the patho- gen apple scab compared to potassium phosphite. Further evaluation against other pathogenic fungi 241 and bacteria is warranted as, at least in the UK, phosphite formulations are classified as fertilizers or natural plant protection products and are not subject to the stringent government regulations regarding their registration and use compared to conven- tional synthetic fungicides. In urban environments where apple trees are planted for aesthetic purposes rather than for fruit production, phosphites may compliment conventional fungicide treatments, re- duce their usage, or completely replace them where small amounts of scab are acceptable (Percival and Noviss 2010). Currently, the most widely used (potassium phosphite) performed poorly against the criteria assessed in this study, and is oſten the worst performing phosphite in terms of scab control. Replacement of potassium phosphite with differing phosphite formulations may be warranted for scab plant protection purposes. Acknowledgments. The authors thank Miss Emma Schaffert for her help in conducting this experiment. LITERATURE CITED Aikpokpodion, P.E., L. Lajide, and A.F. Aiyesanmi. 2010. Heavy metals contamination in fungicide treated cocoa plantations in Cross River State, Nigeria. American-Eurasian Journal of Agri- cultural and Environmental Sciences 8(3):268–274. Bain, R.A., and P. Millard, and M.C.M. Perombelon. 1996. The resistance of potato plants to Erwinia carotovora subsp. atroseptica in relation to their calcium and magnesium content. Potato Research 39(1):185–193. Bevan, J., and S. Knight. 2001. Organic Apple Production: Pest and Disease Management. Emmerson Press, Kenilworth, UK. 36 pp. Borkow, G., and J. Gabbay. 2009. Copper, an ancient remedy returning to fight microbial, fungal, and viral infections. Current Chemical Biology 3(3):272–278. Butt, D.J., A.A.J Swait, and J.D. Robinson. 1990. Evaluation of fungicides against apple powdery mildew and scab. Tests of agrochemicals and cultivars 11. Annals of Applied Biology Supplement 116:34–35. Chardonnet, C.O., C.E. Sams, R.N. Trigiano, and W.S. Conway. 2000. Variability of three isolates of Botrytis cinerea affects the inhibitory effects of calcium on this fungus. Phytopathology 90:769–774. Conway, W.S., C.E. Sams, J.A. Abbott, and B.D. Bruton. 1991. Postharvest calcium treatment of apple fruit to provide broad- spectrum protection against postharvest pathogens. Plant Disease 75:620–622. Currie, H.A, and C.C. Perry. 2007. Silica in plants: Biological, bio- chemical, and chemical studies. Annals of Botany 100(7):1383– 1389. Doggett, S. L., M. J. Geary, D. Lilly, and R.C. Russell. 2008. The efficacy of diatomaceous earth against the common bed bug, Cimex lectularius. A report for Mount Sylvia Diatomite. ©2014 International Society of Arboriculture
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