Srđan G. Aćimović

Spatial and temporal distribution of trunk-injected imidacloprid in apple tree canopies.

BACKGROUND Pesticide use in orchards creates drift-driven pesticide losses which contaminate the environment. Trunk injection of pesticides as a target-precise delivery system could greatly reduce pesticide losses. However, pesticide efficiency after trunk injection is associated with the underinvestigated spatial and temporal distribution of the pesticide within the tree crown. This study quantified the spatial and temporal distribution of trunk-injected imidacloprid within apple crowns after trunk injection using one, two, four or eight injection ports per tree. RESULTS The spatial uniformity of imidacloprid distribution in apple crowns significantly increased with more injection ports. Four ports allowed uniform spatial distribution of imidacloprid in the crown. Uniform and non-uniform spatial distributions were established early and lasted throughout the experiment. The temporal distribution of imidacloprid was significantly non-uniform. Upper and lower crown positions did not significantly differ in compound concentration. Crown concentration patterns indicated that imidacloprid transport in the trunk occurred through radial diffusion and vertical uptake with a spiral pattern. CONCLUSION By showing where and when a trunk-injected compound is distributed in the apple tree canopy, this study addresses a key knowledge gap in terms of explaining the efficiency of the compound in the crown. These findings allow the improvement of target-precise pesticide delivery for more sustainable tree-based agriculture.

Seasonal and Cross-Seasonal Timing of Fungicide Trunk Injections in Apple Trees to Optimize Management of Apple Scab

To optimize the number and timing of trunk injections for season-long control of apple scab (Venturia inaequalis), we evaluated 1 to 2 and 4 seasonal and cross-seasonal injections of potassium phosphites and synthetic fungicides and quantified residues in leaves and fruit. Phosphites accumulated in the canopy at the highest concentrations, aligned well in time with scab suppression, and gave better leaf scab control of 41.8 to 73.5% than propiconazole (16.9 to 51.5%) or cyprodinil + difenoconazole (5.4 to 17.4%). More injections of phosphites controlled leaf scab better than fewer (23.7% versus 48.2%), and more fungicide injections resulted in 21.9 to 51.1% better leaf scab control than fewer. Leaf scab control with phosphites was only 3.2 to 13.9% better with 4 cross-seasonal compared with 4 seasonal injections, while 1 to 2 seasonal compared with 1 to 2 cross-seasonal injections improved scab control only for 4.2 to 22.1%. On shoots, injected phosphites provided comparable or for 4.4 to 10.5% and 22.3 to 41.4% better scab control than spray standards. On fruit, injected phosphites slightly improved control compared with sprayed phosphites or the sprayed fungicide standard (33.4 to 40.8%). Two seasonal injections of phosphites controlled shoot scab 5.7% better than 9 spray applications. Five sprays of cyprodinil + difenoconazole controlled scab better than their injections. Fruit residues of phosphites reached 2.8 ppm and declined in all treatments except in 2 seasonal injections and phosphite sprays. Cyprodinil and difenoconazole fruit residues reached 0.02 and 0.07 ppm and declined sharply toward the end of the season. These were far below the United States, Codex, and EU MRL-s of 1, 0.8, and 0.5 ppm for difenoconazole, and 1.7, 2, and 1 ppm for cyprodinil, respectively.

HIGH MAGNITUDE OF FIRE BLIGHT SYMPTOM DEVELOPMENT AND CANKER FORMATION FROM JULY ONWARDS ON TWO APPLE CULTIVARS UNDER SEVERE NATURAL INFECTIONS

SUMMARY Fire blight (Erwinia amylovora) causes blossom and shoot blight ultimately forming cankers on woody tissues. The magnitude of late season symptom development has not been reported on apple in natural infections. Quantitative and qualitative changes of fire blight symptoms were monitored from July 2007 to April 2008 on cultivars Idared and Golden Delicious in northern Serbia with Idared displaying the highest number of symptoms. In July, shoot blight dominated with 67-88% necrotic shoot tips and completely necrotic shoots. Early blight led to formation of 7-18% cankers of determinate type. Between mid-July and end of September, the number of cankers increased from 65 to 80% on both cultivars. New cankers were of indeterminate type, suitable for pathogen overwintering. Cankers originated from extensive late season pathogen stem invasion from previously diseased shoots. Necrosis size on both cultivars increased significantly between July and September. Increases in canker number and necrosis size indicate a high level of renewed pathogen activity late in the season and its ‘preparation’ for overwintering. Poor winter pruning in one orchard resulted in considerable number of symptom units which constituted potential infection sources. The high magnitude of late season symptom changes, detected under severe natural infections, shows that the pathogen is vigorously active within previously formed symptoms and that pathogenesis continues clandestinely. The results underline the importance of the often neglected part of late season fire blight development for pathogen survival and enforce the requirement for eradication of cankers as primary sources of inoculum for the next season.