Weed management strategies in long-term organic blueberry production systems - impact of mulch type and weed control methods on economics

Weed management was identified as one of the most challenging aspects of organic blueberry production by an advisory panel of growers. A long-term research trial was established in autumn 2006 to evaluate several components of organic production of northern highbush blueberry (Vaccinium coymbosum), including the use of three weed management strategies: sawdust mulch; yard debris compost topped with sawdust mulch (compost+sawdust); and a black, woven polyethylene ground cover (weed mat). Weeds were managed by hand pulling in sawdust and weed mat mulched plots, and a combination of hand pulling, propane flaming, and targeted applications of organically-approved herbicides to compost+sawdust plots. Mulches were replenished as needed. Treatments also included planting bed type, nitrogen fertilizer source and rate, and cultivar. Since these did not affect weed management costs, they are not discussed here. Weed management strategy affected establishment costs, weed presence, and weed control costs (herbicide application and labor required for hand weeding). Economic returns during establishment were negative for all mulch treatments (as is typical in blueberry), but losses were greatest for compost+sawdust due to increased weed presence and high weed management costs relative to other treatments. Costs were lowest for weed mat, where almost complete weed control was achieved. Weed presence increased as the planting aged and costs of weed management continued to increase with organic mulches whereas the weed mat had relatively low weed control costs throughout the product lifespan (5-7 years). The cumulative labor requirements to control weeds in the weed mat, sawdust, and compost+sawdust treatments were 270, 1085, and 1309 h ha^-1, respectively. Weed mat increased cumulative yield (years 2-8) 4% compared to the organic mulches. Even with the small increase in yield, weed mat was the most economical method of weed control, increasing net income 13 and 22% in 'Liberty' and 'Duke', respectively, compared to compost+sawdust mulch.