Weed control practices in New Zealand pipfruit orchards: a thesis presented in partial fulfilment of the requirement for the degree of Master of Horticultural Science at Massey University

Abstract

A survey of 77 growers, mainly in Hawkes Bay and Nelson, was undertaken during the summer of 1989/90. Personal interviews were conducted on each property. All growers were found to use herbicides for weed control, and all but one established herbicide strips with mown grass between. The major herbicide application period was spring. Three-quarters of growers relied on four herbicide formulations, amitrole, glyphosate, simazine and terbuthylazine/terbumeton. Of the residual herbicides used, 70% were triazines. Grower knowledge about herbicides was found to be lacking. Grass species from the sub-family Paniceae were found to be the most problematic weeds, along with mallows, black nightshade, Californian thistle, tall willow herb and docks. These weeds were not adequately controlled by current weed control practices. Off-label use and herbicide damage to crop trees was noted. Growers were found to be applying herbicides through a wide array of equipment, through fan and off-centre nozzles with one to four nozzles on each boom. Only 37% of sprayers were calibrated at least annually. During the survey 41 sprayers were calibrated, with only 17% being correct within ± 5% of intended application rate. Of those sprayers with errors over ±5% two-thirds were underapplying at mean error of 37%, and one-third were overapplying at a mean error of 18.1%. Spray distribution patterns were found to be unacceptably uneven across the herbicide strip in most cases. Over 40% of growers were not able to relate the actual amount of herbicide used to a target application rate per hectare. A lack of training in both chemical use for weed control and sprayer calibration was apparent, and 80% of growers saw a need for a field manual. ADDITIONAL KEYWORDS New Zealand; pipfruit; weed control practices; herbicide use; sprayer calibration; accuracy of application; portable spray patternator.