Weed Control and Canopy Light Management in Blackberries

Weed control in blackberries (Rubus spp.) is a serious problem for organic producers and those who wish to reduce their reliance on herbicides.  At the southern limits of blackberry production, late season yields are reduced because of high day-time temperatures generated by solar irradiation and other environmental constraints.  In a field experiment using ‘Kiowa’ root cuttings established in 2008, weeds were controlled mechanically by hand and with an industrial grade laminated white plastic.  In spring 2009, plant volume and leaf area were improved by use of white plastic.  Early season flowering on 30 Mar. and the number of red fruits on 27 Apr. were increased by white plastic.  After the third harvest on 19 May, half of the weed control plots were tented with 40% shade cloth for the remaining 7 weekly harvests, resulting in improved cumulative yields from both white plastic weed control and shading.  Shade reduced ripe fruit temperatures by 3.4 C (P= 0.0002) regardless of weed control method.  The percentage of reflected light through the canopy was improved by white plastic and was not influenced by shading (P=0.001).  Air movement over the canopy (not replicated) was reduced 30% by shading.   White plastic alone improved the cumulative season yield by 86%, while shade alone increased season yield by 34%.  The combined use of white plastic and shade increased season total yield by 142% or 4.4 Mt / ha compared to current production practices (bare ground and no shading).  Late season average fruit weight, % SS, and berry juice yield (ml/g) were improved by shade application.