| The two most important pathogens of apple Erwinia amylovora (fire blight) and Venturia inaequalis (apple scab) require pesticide sprays for control. This leads to accumulating side effects such as disease resistance, contamination of environment, elevated fungicide residues in fruit, and increased health risks to consumers and workers. While sprays are effective for disease control, need for increasing the sustainability of apple production by reducing pesticide use in the environment incited our research on delivering pesticides via trunk injection. This method delivers the compound into the canopy via tree xylem and could increase the efficiency in disease control. To find out how, where and when injected compounds distribute in the apple tree, thus affecting the efficiency in pest control, we injected imidacloprid through 1, 2, 4, or 8 injection ports per tree. By quantifying leaf residues we demonstrated variable spatial distribution of imidacloprid in the canopy. Spatial uniformity of distribution increased with more injection ports and 4 ports provided uniform distribution. To demonstrate the efficiency of injected compounds in fire blight and apple scab control we injected apple trees with antibiotics, plant resistance inducers, and fungicides. Antibiotics, potassium phosphites (PJ) and acibenzolar-S-methyl (ASM) provided weak control of blossom and shoot blight while oxytetracycline was the most efficient. ASM and PJ significantly expressed PR-1, 2, and 8 protein genes showing resistance activation in apple leaves (SAR) which suppressed the pathogen. Four injections of PJ in spring controlled leaf apple scab for 2 seasons, similar to 2 seasons of standard sprays. To optimize injections for apple scab control we evaluated 1-2 and 4 cross-seasonal and 1-2 seasonal injections of PJ and fungicides. PJ provided better scab control than propiconazole, cyprodinil and difenoconazole and showed better or equal and more persistent scab control with fewer injections than sprays. Control varied among canopy organs due to different transpiration, with best scab control on shoots, fruit, and then spurs. Good scab control is provided by 2-3 spring injections. Residues of synthetic fungicides in fruit were always below the residue tolerances. Fall injection did not improve apple scab control. To get temporally uniform imidacloprid distribution in the crown, best results were achieved by injection dose delivery at 4 times, 14 days apart. Injection method comparison showed that drill-based injection of the liquid imidacloprid formulation provided the highest residue concentration in the canopy when compared to other injection methods. Comparison of 7 trunk injection devices showed that drill-based devices did not provide higher residue concentration of cyprodinil and difenoconazole in apple leaf canopy when compared to needle-insertion device Bite, while Wedgle was similar. All the injection devices allowed similar apple scab control with fungicides. When monitoring the rate of trunk injection port healing in apple trees, we found that port closure with callus lasted for 1-1.3 and >2 years depending on the port size and type. Port closure was faster on the ports with smaller diameters. Around all injection port types, bark cracking due to frost events was higher in vertical direction of the trunk. The visible port depth declined faster on port from 11/64" drill bit and on lenticular injection port from double-edge blade, versus the port from 3/8" drill bit. When the port from 3/8" drill bit was sealed with an Arborplug, visible and covered port depths significantly increased in time due to callus formation on the top and laterally, around the plug. Overall, trunk injection of injection formulated pesticides could be a viable option for disease control in apples with minimal impact of injection ports on the tree. |
