Abstract
After the turn of the twentieth century and the change in cultural practices to achieve high production, canker diseases of stone fruits and nut crops, caused by various fungal pathogen species, have become major problems, significantly impacting tree growth and fruit production in California. This study involved multiyear and multilocation field experiments to determine the efficacy of fungicide thiophanate-methyl (Topsin M) on reduction of canker development in prune, almond, and avocado orchards. Treatments mainly included applications of Topsin M on pruning wounds and on main trunks and crotches of young trees. Different measurements to determine efficacy included canker severity, canker length, incidence of shoots, trunks or tree crotches showing canker symptoms, and the proportion of samples showing changes in canker situation before and after treatments. The overall results demonstrated that, with one exception, Topsin M significantly reduced canker development compared with the untreated control for all the experiments in all the three tree crops. The study strongly confirms the efficacy of thiophanate-methyl applications in these three tree crops to reduce risk of canker development and its usefulness in designing canker control strategies.