Efficacy of Thiophanate-Methyl (Topsin M) on Reduction of Canker Development in Prune, Almond and Avocado Orchards in California

After the turn of the 20th 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 multi-year and multi-location field experiments to determine the efficacy of fungicide thiophanate-methyl (Topsin M^TM) 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 the efficacy included canker severity, canker length, incidence of shoots, trunks or tree crotches showing canker symptoms, as well as 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.