A 10-year field experiment was conducted on 20-year-old apple trees (Malus domestica Borkh.) inoculated with Phytophthora cactorum (Leb. & Cohn) Schroet. to study the influence of the scion cultivar on rootstock susceptibility. The rootstock MM.111 was less susceptible to P. cactorum than M.7 when `Golden Delicious' was the scion, but there were no differences when `Delicious', `Haroldred Delicious', or `McIntosh' were the scions. Similarly, the rootstock M.26 was less susceptible than M.7 when `McIntosh' was the scion, but there were no differences when `Delicious', `Haroldred Delicious', or `Golden Delicious' were the scions. These results suggest that the influence of scions on rootstock susceptibility to P. cactorum crown rot is variable.
The effects of various nonfumigant planting-hole treatments on growth and yield of apple (Malus domestics Borkh.) trees were measured during the first 3 years after planting. Eight orchards diagnosed as having a replant problem were monitored. First-year shoot growth, the number of blossoms in the second year (inmost orchards), and first-year trunk cross-sectional area increment (TCAI) in 50% of test orchards were increased by monoammonium phosphate (MAP) fertilizer+ peat, MAP+ mancozeb, or MAP + peat + a bacterial antagonist. By the end of year 3, TCAI generally was not affected by treatments, but treatments resulted in more blossoms by the third season in two of seven orchards that blossomed in the second season. Cumulative yield after 3 years increased significantly in only three orchards, with the best treatment, MAP+ peat, resulting in cost recovery in only one orchard. Inadequate K or Cu nutrition may have reduced growth in some of the orchards, which were characterized by a wide range in yields, independent of planting-hole treatment.
Apple seedling height after 7 weeks of growth in greenhouse pots was compared with total first year shoot growth of `McIntosh' or `Delicious' apple trees [Malus domestica (Borkh.)] on M.26 rootstock for eight orchards and five soil treatments. The apple trees were replanted in old orchard sites with the same treatments applied in the planting hole as were tested in the greenhouse. The pot test successfully predicted treatments that increased first year shoot growth in 23 of 30 opportunities. However, a less precise relationship (R2 = 0.38) existed between total first year shoot growth (Y) of `Summerland Red McIntosh' on M.26 rootstock and seedling height (X).