Plastic Mulches Improved Plant Growth and Suppressed Weeds in Late Summer-planted Floricane-fruiting Raspberry

Abstract

Planting floricane-fruiting red raspberry (Rubus ideaus L.) propagated through tissue culture (TC) is becoming increasingly popular in the Pacific Northwest. However, there is a challenge associated with their establishment compared with traditional planting materials (dormant roots and canes), especially regarding weed management due to their sensitivity to herbicides. In addition, there has been an increased interest in late summer planting compared with traditional spring planting because growers find improved establishment in late summer planting. Although polyethylene (PE) and biodegradable plastic mulches (BDMs) have demonstrated excellent weed control and increased plant growth and yield in spring-planted TC raspberry, their impacts in late summer plantings are still unknown. The overall objective of this study was to investigate whether PE mulch and BDMs have similar effects on weed management and raspberry growth and yield in late summer plantings as in spring plantings. One PE mulch, four BDMs (BASF 0.5, BASF 0.6, Novamont 0.5, and Novamont 0.6), and a bare ground (BG) control were evaluated in a commercial ‘WakeHaven’ raspberry field planted in Aug. 2017. Mulch performance [percent soil exposure (PSE)], mulch mechanical properties (elongation and breaking force), soil temperature and moisture, plant growth, fruit yield and quality, and weed suppression were measured from 2017 to 2019. Average PSE was 1.4% and 2.0% to 15.0% by Dec. 2017 in the PE and BDM treatments, respectively. PE mulch generally had greater elongation and breaking force than BDMs. All BDMs were removed by Mar. 2018 because of the damage caused by on-farm activities and strong winds. Although average primocane height was greater for plants grown with PE mulch compared with all the other treatments except BASF 0.5 in Sept. 2018, there was no difference in yield between PE and the BG treatments, potentially because of cold damage on the buds in PE plots. There were no weeds in any of the mulched treatments in Sept. and Oct. 2017 and in PE mulch in Sept. 2018. In contrast, the BG plots had 51, 51, and 266 weeds/m2, respectively, and required handweeding and herbicide applications. In addition, early season application of herbicides to suppress primocane emergence was not required in the PE plots. Overall, PE mulch could be a viable tool for growers planting raspberry in late summer. The suitability of BDMs with similar thicknesses and formulations as used in this experiment is uncertain for late summer plantings because of the damage caused by on-farm activities and strong winds.