EFFECT OF NITROGEN FORM AND APPLICATION METHOD ON INCIDENCE AND SEVERITY OF PHYTOPHTHORA CROWN AND ROOT-ROT OF APPLE-TREES

The effect of ammonium nitrate broadcast as a soil or through irrigati on, urea applied as a foliar spray, and monoammonium phosphate applied as a planting hole treatment on the incidence of Phytophthora crown a nd root rot of apple trees was determined under orchard conditions in the Okanagan Valley of British Columbia, Canada. Results from the eigh t year study showed that ammonium nitrate applied as a single dose in spring at 240 g tree(-1) year(-1), as a split dose at 120 g tree(-1) e ach in spring and early autumn, and in irrigation water (fertigation) at 7.5 g tree(-1) wk(-1) for 10 wk year(-1) significantly increased Ph ytophthora crown and root rot of Macspur on MM106 rootstock. There was no significant difference in P. cactorum infection between the unfert ilized control and treatments with urea applied as a foliar spray at 1 .0 kg 100 l(-1) of water in spring and early autumn, and monoammonium phosphate applied as a planting hole treatment at 1 g l(-1) of soil at planting time.