New detection and management practices for brown rot of peach in California

Brown rot caused by Monilinia fructicola or M. laxa is a major pre- and postharvest disease of stone fruit in California. Research was conducted to develop several components of an integrated pest management program: 1) early detection of disease using molecular techniques; 2) preharvest fungicide applications for postharvest decay control; and 3) postharvest fungicide treatments for postharvest disease management. Using a species-specific primer for M. fructicola that was developed from the ribosomal internal transcribed spacer I region and a genus-specific primer that was developed from a RAPD fragment, the fungus could be detected after PCR amplifications 72 h after inoculation that included a 10-h initial wetness period or 24 h after inoculation that included a 6-h initial wetness period, respectively. Thus, the presence of the fungus in fruit tissue was confirmed when no visual symptoms were present. In our preharvest fungicide applications for postharvest decay control, fruit treated with tebuconazole (Elite 45WP) or cyprodinil (Vangard 75WG) 8 and 1 or 14 and 7 days before harvest were harvested and postharvest washed and waxed. These fungicide treatments were effective for postharvest brown rot control on spray- or wound-inoculated fruit. Only cyprodinil, however, was highly effective in reducing gray mold decay. New fungicides were also evaluated as postharvest treatments in laboratory and experimental packingline studies. In wound-protection studies with nectarine or peach fruit, fludioxonil, fenhexamid, and tebuconazole were highly effective against brown rot. Decay incidence values generally were near zero. For gray mold, only fludioxonil (Scholar 50WP) and fenhexamid (Elevate 50WG) gave excellent control. These latter two fungicides are classified as "reduced-risk" by the US-EPA and represent two new postharvest treatments for stone fruit crops in the United States to replace the canceled iprodione (Rovral 50WP) and other fungicides.