Weed survey of lowbush blueberry fields in Saguenay–Lac-Saint-Jean, Québec, following eight years of herbicide application

Abstract

A weed survey was conducted in 1995 and 1996 in eight lowbush blueberry (Vaccinium angustifolium Ait.) producer sites of the Saguenay–Lac-Saint-Jean region to measure the impact of repeated herbicide applications on weed frequency and percent cover. A previous survey (1981–1983), done in the same area before the widespread use of herbicides by the producers, had shown an impact of weed abundance on blueberry productivity. Weed frequency decreased from 1981–1983 to 1995–1996. Some species have apparently disappeared and all showed a reduction in abundance, suggesting that tolerance to herbicides or shifts to herbicide tolerant species has not occurred in this region. Weed cover decreased from over 65% to 10% in surveyed blueberry producer sites, and their presence no longer affects blueberry productivity. However, herbicide use is associated with an increase in percent bare ground, which now accounts for an average of 38% of lot surfaces. Blueberry plants do not seem to be able to quickly colonise bare weeded sites. In plots weeded manually, blueberry shoots did not increase in cover after 2 yr. Herbicide applications are still needed to maintain the weed populations at low levels, but we now have to stimulate the colonisation of bare patches by blueberry plants. Key words: Vaccinium angustifolium, glyphosate, hexazinone, weed control, weed frequency, blueberry productivity