260 Banks and Percival: Evaluation of Biostimulants on Leaf Blotch and Black Spot son (2004) and Sahain et al. (2007) demonstrated positive growth effects on plants following application of biostimulants. Reasons for these differences between authors were suggested by Barnes and Percival (2006), who identified that effects on growth can vary widely between tree species possibly as a result of i) the dif- fering active ingredient used in the formulation of a biostimulant, and ii) the concentration applied. They concluded that this would be disadvantageous to the tree care industry where products with universal applicability for a wide range of species are required. Possibly such a response exists with respect to disease control (i.e., biostmulants proved non-effective in this instance against Guignardia leaf blotch and black spot of roses, but may prove effective against other diseases not tested in this investigation). Likewise, many biostimulants are now marketed in combination with a range of biological propagules, such as mycorrhizae and/ or growth promoting bacteria. However, the viability of many of these propagules can be a highly influential factor in affecting the degree of disease tolerance achieved (Corkidi et al. 2004). For example, out of ten products tested by Corkidi et al. (2004), mycorrhizal colonization varied from 0% to 50% and only one of the products promoted greater mycorrhizal colonization in a soil-based medium. Similar results (i.e., lack of efficacy) were re- corded by Poincelot (1993), who evaluated the systemic inducing properties claim of biostimulants as a means of disease control. Consequently with the influx of biostimulants released into the amenity market, evaluating all of them independently is a time con- suming and labor-intensive process. Results of this study indicate that where independent scientific data are not available to support the pathogen control claims of the manufacturer, then using an unevaluated biostimulant for this purpose is not recommended. Acknowledgments. The authors are grate- ful for funding in part from the TREE FUND (Hyland Johns Grant). LITERATURE CITED Azcon-Aguilar, C., M.C. Jaizme-Vega, and C. Calvet. 2002. The Contri- bution of Arbuscular Mycorrhizal Fungi to the Control of Soil-Borne Plant Pathogens. p. 187–197. In: G. Gianinazzi, H. Schuepp, J.M. Barea, and K. Haselwandter (Eds.). Mycorrhizal Technology in Agri- culture: From Genes to Bioproducts. Birkhauser Verlag, Switzerland. Barnes, S., and G.C. Percival. 2006. Influence of Biostimulants and Wa- ter-Retaining Polymer Root Dips on Survival and Growth of Newly Transplanted Bare-Rooted Silver Birch and Rowan. Journal of Envi- ronmental Horticulture 24(3):173–179. Burr, T. J., M.N. Schroth, and T. Suslow. 1978. Increased potato yields by treatment of seedpieces with specific strains of Pseudomonas fluore- scens and P. putida. Phytopathology 68:1377–1383. Corkidi, L., E.B. Allen, D. Merhaut, M.F. Allen, J. Downer, J. Bohn, and M. Evans. 2004. Assessing the Infectivity of Commercial Mycorrhi- zal Inoculants in Plant Nursery Conditions. Journal of Environmental Horticulture 22(3):149–154. Ferrini, F., and F.P. Nicese. 2002. Response of English oak (Quercus robour L.) trees to biostimulants application in the urban environ- ment. Journal of Arboriculture 28(2):70–75. Kelting, M., J.R. Harris, J. Fanelli, B. Appleton, and A. Niemiea. 1997. Humate-based biostimulants do not consistently increase growth of container-grown Turkish hazelnut. Journal of Environmental Horti- culture 15(4):197–199. Marchant, R., M.R. Davey, J.A. Lucas, C.J. Lamb, R.A. Dixon, and J.B. Power. 1998. Expression of a chitinase tansgene in rose (Rosa hybrid L.) reduces development of black spot disease (Diplocarpon rosae Wolf). Molecular Breeding 4:187–194. Pastirčáková, K., M. Pastirčák, F. Celar, and H. Shin. 2009. Guignardia aesculi on species of Aesculus: New records from Europe and Asia. Mycotaxon 108:287–296. Percival, G.C. 2010. Effects of systemic inducing resistance and bios- timulant materials on apple scab using a detached leaf bioassay. Ar- boriculture & Urban Forestry 36(1):41–46. Percival, G.C., K. Noviss, and I Haynes. 2009. Field evaluation of sys- temic inducing resistance chemicals at different growth stages for the control of apple (Venturia inaequalis) and pear (V. pirina) scab. Crop Protection 28:629–633. Poincelot, R.P. 1993. The use of a commercial organic biostimulant for bedding plant production. Journal of Sustainable Agriculture 3(2):99–110. Sahain, M.F.M., E.Z.A. El Motty, M.H. El- Shiekh, and L.F. Hagagg. 2007. Effect of some biostimulant on growth and fruiting of Anna apple trees in newly reclaimed areas. Research Journal of Agriculture and Biological Science 3(5):422–429. Thalheimer, M., and N. Paoli. 2001. Effectiveness of Various Leaf-Ap- plied Biostimulants on Productivity and Fruit Quality of Apple. In- ternational Symposium on Foliar Nutrition of Perennial Fruit Plants. 594. ISHS Acta Horticulturae. Thompson, B.E. 2004. Five years of Irish Trials on Biostimulants – The Con- version of a Skeptic. USDA Forest Service Proceedings. RMRS-P-33. Tronsmo, A. 1991. Biological and integrated controls of Botrytis cinerea on apple with Trichoderma harzianum. Biological Control 1:59–62. Whipps, J.M. 2001. Microbial interactions and biocontrol in the rhizo- sphere. Journal of Experimental Botany 52:487–511. ©2012 International Society of Arboriculture
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