Fungicides, to be effective, must be properly applied. There are two important factors never to be neglected. They may be designated as timeliness and thoroughness.
Having determined on the proper kind of fungicide and the correct strength to be used in the case in hand, the question of the time of application comes up for consideration. Timeliness in making the application is the key to success in the control of diseases with fungicides. The stage of the development of the host must be the primary consideration; the tree, not the calendar, must be the guide. For example, the time to spray apple-trees to protect from scab is determined by the stage of development of the blossoms or fruit; first application, just before the blossoms open when the central blossom shows color and after the individual blossom-buds in the cluster have separated (Fig. 124). Second application, just after the petals fall (when two-thirds off) (Fig. 125), and so on. One must watch the trees closely and act promptly when they are just right for application. Seasons differ, varieties differ, and these facts must be taken into consideration. Next to the stage of the development of the host, as determining the time to spray, comes the weather. Spray just before rains, not after them. Remember that the fungus usually reaches the leaf or the fruit and produces infection during the rain, not before nor after. Get the fungicide on ahead of the rain and thus ahead of the fungus. Watch the weather maps and the developing blossoms. It will be more profitable in some cases to spray a little before the host is in just the right condition in order to get in ahead of a rain - period. Long, rainy, cloudy periods are the dangerous ones. Heavy showers followed by rapid clearing seldom afford conditions favorable to serious infection by orchard fungi.
The period for effective applications of fungicides, in practically all cases, is a brief one; at most a few days, more often only a day or two. This means that equipment, labor and materials necessary to cover the trees in a short time must be provided. The continuous running of one sprayer in a large orchard throughout the season is largely a loss of time and money. Fungicides to be effective must be applied at just the right time.
Thoroughness is second only to timeliness as a factor in determining the success of spraying or dusting operations. Since fungicides are applied to protect, every part of the susceptible surface must be covered. In spraying this cannot be done rapidly. Dusting can be done in much less time. Spraying will be much more thorough if done against, rather than with, the wind. Use a nozzle set at an angle of 60° on a ten-to fourteen-foot pole with a pressure of 175-200 pounds behind it. The spray should be fine and the nozzle should be moved along carefully and intelligently over every limb and branch. Where trees are fifteen feet or more in height, spraying should be done from a tower, and where the trees are very large, a man on the ground with a trailer will be necessary to cover the low - hanging limbs and lower inner branches. In spraying against the wind hold the nozzle at such a distance from the limb to be sprayed that the spray will come just where the wind breaks the force of the spray. Where spraying is done with the wind a second application after the wind changes is necessary. This is usually too late to be effective and requires double the time and material. Dusting is done with the wind, but here the light particles floating slowly through the branches settle and coat every part. Dusting is to be done at the same times that spraying should be done. However, since it can be done much more rapidly, the grower may often be able to make a timely application of dust which would not be possible with spray.
Fig. 125. - Apple blossoms in proper stage for the first application of a fungicide.
Fig. 126. - Apple blossoms in proper stage for the second application of a fungicide.
(Departments of Entomology and Plant Pathology.) The control of insect pests and plant diseases. Cornell Univ. Agr. Exp. Sta. Bul.
283: 463 - 500. Revised June, 1915. Blodgett, F. M. Experiments in the dusting and spraying of apples.
Cornell Univ. Agr. Exp. Sta. Bul. 340: 145 - 179. 1914. Reddick, D., and Crosby, C. R. Further experiments in the dusting and spraying of apples. Cornell Univ. Agr. Exp. Sta. Bul. 354:
49-96. 1915. Reddick, D., and Crosby, C. R. Dusting and spraying experiments with apples. Cornell Univ. Agr. Exp. Sta. Bul. 369: 305 - 356.
1916. Parrott, P. J., and Schoene, W. J. Experiments with home-made concentrated lime sulfur mixtures. New York (Geneva) Agr.
Exp. Sta. Bul. 330: 449-484. 1910. Van Slyke, L. L., and others. Chemical investigations of best conditions for making the lime sulfur wash. New York (Geneva)
Agr. Exp. Sta. Bul. 329: 403 - 149. 1910. Hedrick, U. P. Bordeaux injury. New York (Geneva) Agr. Exp.
Sta. Bul. 287: 103-189. 1907. Wallace, E., Blodgett, F. M., and Hesler, L. R. Studies of the fungicidal value of lime sulfur preparations. Cornell Univ. Agr. Exp.
Sta. Bul. 290: 163-207. 1911. Wallace, Errett. Lime sulfur as a summer spray. Cornell Univ. Agr.
Exp. Sta. Bul. 288: 101-137. 1910. Butler, O. Notes on the preparation of bordeaux mixture. New Hampshire Agr. Exp. Sta. Circ. 15: 1-10. 1914. Brooks, Chas. Fungicides in the apple orchard. New Hampshire Agr. Exp. Sta. Bul. 161: 1-16. 1912. Morse, W. J. Six years of experimental apple spraying at Highmoor Farm. Maine Agr. Exp. Sta. Bul. 249: 79-96. 1916. Waite, M. B. Experiments on the apple with some new and little known fungicides. U. S. Agr. Dept. Pl. Ind. Bur. Circ. 58: 1 - 19.
1910. Lutman, B. F. The covering power of the precipitation membranes of bordeaux mixture. Phytopath. 2: 32 - 41. 1912.
Fairckild, D. G. Bordeaux mixture as a fungicide. U. S. Agr. Dept.
Veg. Path. Div. Bul. 6: 1 - 55. 1894. Swingle, W. T. Bordeaux mixture, its chemistry, physical properties, and toxic effects on fungi and algae. U. S. Agr. Dept. Veg. Phys.
and Path. Div. Bul. 9: 1-37. 1896. Butler, 0. Bordeaux mixture I. Physico-chemical studies. Phytopath. 4: 125-180. 1914. Scott, W. M. Self-boiled lime sulfur as a promising fungicide. U. S.
Agr. Dept. Pl. Ind. Bur. Circ. 1: 1-18. 1908. Scott, W. M. Lime sulfur mixture for the summer spraying of orchards. U. S. Agr. Dept. Pl. Ind. Bur. Circ. 27: 1-17. 1909. Scott, W. M. The substitution of lime sulfur preparations for bordeaux mixture in the treatment of apple diseases. U. S. Agr.
Dept. Pl. Ind. Bur. Circ. 54: 1 - 15. 1910. Crandall, C. S. Bordeaux mixture. Illinois Agr. Exp. Sta. Bul. 135:
199-296. 1909. Crandall, C. S. Spraying apples. Relative merits of liquid and dust applications. Illinois Agr. Exp. Sta. Bul. 106: 205-242. 1906. Fulmer, H. L., and Caesar, L. Lime sulfur wash. Ontario Agr.
Coll. Bul. 177: 1-64. 1909. Safro, V. I. An investigation of lime sulfur injury, its causes and prevention. Oregon Agr. Exp. Sta. Research Bul. 2: 1-32. 1913. Stewart, J. P. Concentrated lime sulfur spray. Pennsylvania Agr.
Exp. Sta. Bul. 115: 1-23. 1912. Stewart, J. P. Preparation and use of concentrated lime sulfur.
Pennsylvania Agr. Exp. Sta. Bul. 99: 1 - 13. 1910.