Arboriculture & Urban Forestry 46(5): September 2020 effects, i.e., reductions in leaf chlorophyll content or fruit yield. Applications are discrete with no spray drift, an important consideration when applying plant protection agents to trees located in densely popu- lated urban landscapes. CONCLUSIONS In conclusion, results of this study provide evidence that potassium phosphite, salicylic acid derivative, harpin protein, and liquid chitosan possess efficacy against apple and pear scab when applied as root drenches, and so could potentially play a role as an alternative and/or supplementary method of manage- ment under field conditions, providing at least 3 or more drenches are applied preventatively during April to June. LITERATURE CITED Aćimović SG, VanWoerkom AH, Garavaglia T, Vandervoort C, Sundin GW, Wise JC. 2016. Seasonal and cross-seasonal timing of fungicide trunk injections in apple trees to optimize management of apple scab. Plant Disease. 100:1606-1616. Agostini JP, Bushong PM, Timmer LW. 2003. Glasshouse eval- uation of products that induce host resistance for control of scab, melanose, and Alternaria brown spot of citrus. Plant Disease. 87:69-75. Akbudak N, Tezcan H, Akbudak B, Seniz V. 2006. Effect of harpin protein on plant growth parameters, leaf chlorophyll, leaf colour and percentage rotten fruit of pepper plants inoculated with Botrytis cinerea. Scientia Horticulturae. 109:107-112. Akinsanmi OA, Drenth A. 2013. Phosphite and metalaxyl reju- venate macadamia trees in decline caused by Phytophthora cinnamomi. Crop Protection. 53:29-36. Anand A, Srinivasa RU, Ryu CM, Allen SN, Kang L, Tang Y, Mysore KS. 2008. Salicylic acid and systemic acquired 367 Table 7. Curative treatment. Comparison of selected IR agents applied as root drenches for the control of Venturia inaequalis and V. pirina on mean fruit yield of apple (Malus cv. Crown Gold) and pear (Pyrus communis ‘Williams Bon Chrétien’), respectively. Treatment Water (control) HP HP HP HP PP PP PP PP SA SA SA SA Chitosan Chitosan Chitosan Chitosan Penconazole Penconazole Penconazole Penconazole Treatment (T) No applications (NA) T*NA HP = harpin protein; PP = potassium phosphite; SA = salicylic acid. + = root drench/spray applied; - = no root drench/spray. z Mean of six randomised complete blocks with a single tree per block. Lower case letters indicate significant differences between means for each evaluation date by Tukey’s honest significance test (P = 0.05). 19 June - + + + + + + + + + + + + + + + + + + + + Time and number of applications 10 July - 31 July - - + + + - + + + - + + + - + + + - + + + - - + + - - + + - - + + - - + + - - + + Yield/tree (kg) 18 August - - - - + - - - + - - - + - - - + - - - + Applez 6.0abc 5.8abc 6.3abcd 6.2abcd 7.1bcd 5.4a 5.5a 5.4a 6.1abc 5.8abc 6.1abcd 6.6abcd 6.8abcd 5.7ab 6.2abcd 6.6abcd 6.6abcd 6.2abcd 6.3abcd 7.2cd 7.5d 0.030 0.001 0.323 Pearz 6.0abc 5.8abc 6.1abc 6.6abcd 5.9abc 5.8abc 6.4abcd 6.6abcd 6.9bcde 5.3abc 6.4abcd 7.2cde 6.8bcde 6.0abc 5.7ab 6.0abc 6.4abcd 5.9abc 6.3abcd 8.0e 7.7de 0.050 0.050 0.128 ©2020 International Society of Arboriculture
September 2020
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