Weed management practices for organic production of trailing blackberry. I. Plant growth and early fruit production

Authors: HARKINS, RENEE - Oregon State University; STRIK, BERNADINE - Oregon State University; Bryla, David

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2013
Publication Date: 9/1/2013
Citation: Harkins, R.H., Strik, B.C., Bryla, D.R. 2013. Weed management practices for organic production of trailing blackberry. I. Plant growth and early fruit production. HortScience. 48(9):1139-1144.

Interpretive Summary: A long-term field study is being conducted to evaluate management practices for organic production of processing blackberries. The objective of the present study was to evaluate the effects of three different organic weed management strategies, including weed mat, hand weeding, and no weeding, on growth and early production of trailing blackberry. Plants in each treatment were irrigated by drip and fertilized using certified organic liquid fish products. Two popular cultivars, ‘Marion’ and ‘Black Diamond’, were included in the study. Both are predominantly harvested by machine for high-value processed markets and together account for greater than 75% of the 7,200 acres of blackberries produced in Oregon in 2012. So far, the results of the study indicate that weed control is beneficial during establishment of trailing blackberry and can be done successfully in organic plantings using hand-weeding or weed mat. Of the two, weed mat led to the highest yield and net returns in the study and required less than a half-hour of labor per acre for weed control each year. Both ‘Black Diamond’ and ‘Marion’ appeared well-suited to organic production in the present study. The study will continue for at least 3 more years to determine sustainability of each practice.

Technical Abstract: Weed management practices were evaluated in a new field of trailing blackberry established in western Oregon. The field was planted in May 2010 and certified organic in May 2012. Treatments included two cultivars, ‘Marion’ and ‘Black Diamond’, grown in 1) non-weeded plots, where weeds were cut to the ground just prior to harvest, 2) hand-weeded plots, hoed two to three times per year, and 3) weed mat plots, covered with black landscape fabric. Each treatment was fertilized with fish emulsion and irrigated by drip. Weeds increased from 2010 through 2012 in both non-weeded and hand-weeded plots and required 38 and 90 h of labor per hectare to remove the weeds in the latter treatment in 2011 and 2012, respectively. Weeds in weed mat plots, in comparison, were confined primarily to the planting holes in the fabric and required only 1 h of labor per hectare for weed removal each year. Blackberry growth, in terms of number and dry weight of the primocanes, was similar among treatments during the first year after planting but differed with cultivar and weed management the following season. In 2011, ‘Black Diamond’ produced shorter but an average of three more primocanes per plant than ‘Marion’, while plants in hand-weeded and weed mat plots produced nearly twice as many primocanes as non-weeded plots. Hence, when fruit were produced on floricanes (the previous year’s primocanes) for the first time in 2012, ‘Black Diamond’ had 15% more yield than ‘Marion’, and weed control increased yield by 67% with hand-weeding and 100% with weed mat, on average. ‘Black Diamond’ and weed control also produced larger berries with a greater water content but a lower soluble solids concentration. So far, of the three practices studied, weed mat was best suited to organic production of blackberries. The initial cost of the weed mat was far less than the cost of hand-weeding during the first 3 years following planting, and after only one season of fruit production, the yield benefit of weed mat provided enough profit to warrant its use over no weeding or hand weeding.