Evaluation of the Tree-Row-Volume Concept with Density Adjustments in Relation to Spray Deposits in Apple Orchards. T. B. Sutton, North Carolina State University, Raleigh 27695. C. R. Unrath, North Carolina State University, Raleigh 27695. Plant Dis. 68:480-484. Accepted for publication 21 February 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-480.

The tree-row-volume concept (TRV) was evaluated as a method for determining the amount of pesticide or growth regulator to apply per hectare in apple orchards. TRV is based on the assumption that the volume of foliage per hectare in an orchard can be used as a guide for determining the spray-dosage volume per hectare. An adjustment for canopy density was proposed and evaluated. Three pruning levels (light, moderate, and heavy) were established in five orchards of different sizes ranging from 11,720 to 69,520 m³/ha TRV. TRV and density adjustments resulted in similar deposits on trees over pruning levels within orchard size classes. Deposit was not as consistent among trees in different size classes. Deposit on the smallest trees was significantly less than on larger trees in other orchard blocks. This may have been due to blow-off of deposit by wind from the sprayer fan. Differences in deposit among trees in other orchards may have resulted from differences in tree structure or from the use of different numbers of nozzles and different disc and core combinations to achieve the proper TRV water volume per hectare. Drift from adjacent rows was shown to contribute significantly to deposit in orchards with small trees. A survey of growers indicated that about 50% were using less fungicide than the TRV rate and 50% were using more.

Keyword(s): Malus domestica.