Preliminary Studies of a Bird Damage Assessment Technique for Trellised Grapes

A mechanical sampling device was designed to locate grape bunches randomly. These bunches were visually assessed to determine the percent of bird damage. The sampling device consisted of a length of plastic pipe over which a plastic T joint was slid. A rope was attached to the T joint with three knots tied at equal spacings. The sliding T joint determined the horizontal location, and the knotted rope provided the vertical location. Trained scorers made visual assessments of the sample bunches. Three scorers practiced evaluating artificially damaged grape bunches, using a predetermined rating system. A repeatability test was used to determine whether the scorers were ready for field work. The scorers were tested again in the field with damaged grape bunches on the vine, before beginning actual damage assessment. This system allowed the assessment of large acreages at the rate of one vine per minute with two people and one vine per half minute with three people. The technique is adaptable to different varieties of table and wine grapes and is useful as a reference locator for repetitive evaluations of samples over a prolonged period.