EXPERIMENTS ON CHEMICAL CONTROL OF DAMPING-OFF IN PINUS RESINOSA AIT.
Results from a series of greenhouse and nursery experiments on the relative control of damping-off in red pine, afforded by a wide range of chemicals, brought out the following points: (1) Semesan solutions in concentrations of 1:100 to 1:150 applied as soil treatment gave consistently the best control in both greenhouse and nursery. (2) Red copper oxide suspension in concentrations of 1:250 to 1:500 applied as a soil treatment was also effective, particularly in the greenhouse. (3) Red copper oxide and zinc oxide dusts used as seed treatments gave effective control under greenhouse conditions. (4) In the greenhouse, combinations of seed and soil treatments failed to prove more effective than treatments applied separately, while under certain nursery conditions the combined treatments were significantly less effective. (5) Fungicides as a group generally proved more effective than acidifying agents such as sulphuric acid and aluminium sulphate. It appeared that the acidifying agents gave good control in seasons of normal rainfall, but were more or less ineffective in dry seasons, when relatively large quantities of slightly alkaline irrigation water were applied, or in wet seasons, when excessive percolation occurred. (6) Seedlings from two-year–old red pine seed of somewhat reduced vitality proved to be much more susceptible than those from one-year–old seed.White spruce was used in some of the preliminary experiments and proved to be much less susceptible than red pine, although very similar in response to the various treatments.