Shank Application of Chloropicrin as an Alternative to Methyl Bromide for Prunus Tree Replant

The poor growth of fruit trees that occurs after replanting in intensive agricultural systems has been termed “replant disease” or “replant disorder.” Fruit trees in a replant disorder site have reduced growth and produce leaves that are light green to yellow-green rather than dark green. Fruit production is delayed and yields are reduced. Numerous soilborne organisms have been implicated as potential causal agents of apple replant disease. Armillaria mellea has been associated with the occurrence of peach replant disease. Armillaria root disease is an important disease of fruit, nut, and vine crops. Reports of increased incidence of Armillaria root disease in peach have also recently come from Emilia Romagna in northern Italy. Nevertheless other microorganisms and abiotic factors including low or high soil pH, phytotoxins, unbalanced soil nutrition, heavy metal contamination, poor soil structure and drainage, and cold or drought stress have been considered affecting factors. Peach replant disease has primarily been controlled upon the use of biologically broad-spectrum soil fumigant such as methyl bromide or chloropicrin alone or combined with 1,3-dichloropropene. Since 2004 three field trials were organized in Emilia Romagna (Northern Italy) and aimed at evaluating the efficacy of treatments with chloropicrin (200-400-800 kg/ha) combined with 240 kg/ha of 1,3-dichloropene applied throughout shank injection against A. mellea and compared with non-treated plots. Trials were carried out in naturally and heavily infested fields. Fumigations were done in October 2004 and 2008. The assessments were focused at evaluating the plant development after transplanting, the incidence of the soilborne disease and the yield. Moreover collapsed plants were collected and brought to the laboratory to confirm the presence of Armillaria mellea. The data confirmed the positive effect of the soil fumigation on the plant development and on the yield. Moreover a significant reduction of plant collapses due by A. mellea infection was consistently recorded. No differences in term of efficacy were observed between 400 and 800 kg/ha, while 400 kg/ha performed better than 200 kg/ha in term of disease control, yield and plant development.