Non-Chemical Alternatives for Weed Control in Containerized Plants

Weeds are a serious problem in nursery for container production, because air, nutrient and water are limited by the container volume. Chemical weeding is the main method to control weeds in nurseries but problems as proper calibration, herbicide run-off, need for multiple applications and product cost must be taken into account. The aim of this work was to investigate the degradation time and cost of some environmental-friendly materials used to control weeds in three widely used container-grown shrubs (Photinia xfraseri 'Red Robin', Prunus laurocerasus 'Rotundifolia', Thuja plicata 'Atrovirens'). 120 plants per species were potted into 3 L containers. Four non-chemical mulching materials were used: 1) coconut fibre discs; 2) vegetal and synthetic fibre discs; 3) viscose fibre discs; 4) a mineral grain mixture without chemical additives (Gerval (R)). The effectiveness of these materials was compared with a chemical control (oxadiazon) and with a hand weeding control. Weeds in container were counted and removed every 45 days during two growing seasons (2006 and 2007). Plant height and biomass were recorded at the beginning and at the end of the trial. Vegetal/synthetic fibre discs allowed a weed control as good as the chemical in all the species tested. Due to its short duration this material was replaced at the beginning of the second growing season. Coconut discs and Gerval (R) assured a satisfying weed control. No differences between these treatments and vegetal/synthetic fibre discs were found. These materials were applied at the beginning of the experiment and were not replaced in the second year. Serious damages to the root flare were caused by Gerval (R). The viscose fibre discs did not allow a satisfying weed control, because of their quick degradation, and they had to be replaced during the trial. No significant differences in plant height and biomass production were found among treatments. Total cost of weed control (including installation) in the two years of the trial was 0.19 (sic)/pot for coconut discs and 0.20 (sic)/pot for vegetal/synthetic fibre discs. Chemical control allowed weed control with half of the cost, but this value does not take into account chemical externalities and a possible rise of resistances in weeds. Costs of Gerval (R), viscose fibre discs and manual weed removal did not give a result acceptable for nursery production.