It helps us understand why rates are given in different ways if we consider the history of fruit growing and fruit spraying. Looking at the history helps us to see how pesticide rate recommendations have come about.
In the early decades of this century, apple trees were large and widely spaced within the orchard; horticulturalists still refer to large trees as standard trees. The old sprayers were handgun type sprayers that thoroughly covered the trees with the spray mix until drops began to drip from the leaves, which is what we call "to the point of runoff."
To treat large standard apple trees to the point of runoff, the
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| Figure 1. Hand-held application |
For crops other than apple, the same principle applies but with different volumes. For peach, plum, and cherry, 300 gallons per acre is the standard dilute volume. For strawberries, brambles, blueberries, and grapes, 200 gallons per acre is the standard dilute volume.
Two major factors have changed since the old days. First, modern sprayers can adequately cover an acre of large trees with much less than 400 gallons per acre because coverage to the point of runoff is not needed for control of most arthropod pests and diseases. Second, few orchards now have large standard trees that take 400 gallons of spray mix per acre to treat to the point of runoff. Most commercial orchards now use dwarfing rootstocks. Dwarf or semidwarf trees are much smaller and more closely spaced than the old standard trees, and it takes less water to cover the dwarf or semidwarf trees.
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