Plastic mulches improved plant growth and suppressed weeds in late summer-planted floricane raspberrry

Authors: ZHANG, H - Washington State University; GHIMIRE, S - University Of Connecticut; BENEDICT, C - Washington State University; Zasada, Inga; LIU, H - Washington State University; DEVETTER, L - Washington State University; MILES, C - Washington State University

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2020
Publication Date: 3/9/2020
Citation: Zhang, H., Ghimire, S., Benedict, C., Zasada, I.A., Liu, H., Devetter, L., Miles, C. 2020. Plastic mulches improved plant growth and suppressed weeds in late summer-planted floricane raspberrry. HortScience. 55(4):565-572. https://doi.org/10.21273/HORTSCI14734-19.
DOI: https://doi.org/10.21273/HORTSCI14734-19

Interpretive Summary: Red raspberry production is an important component of the rural economy in northwestern Washington. This research was conducted to determine the effects of nondegradable and biodegradable plastic mulches on weed suppression, soil temperature and plant productivity compared to the industry standard of bare ground without mulch in a late summer raspberry planting. Results indicate that biodegradable mulches can not withstand farm activities, such as tillage, shortly after application resulting in rips and ultimately destruction of the mulch in winter. Soil temperature was higher under nondegradable mulch compared to bare ground. Nondegradable mulch also resulted in greater weed suppression than bare ground. Despite increased soil temperature and weed control under nondegradable mulch, there was not a corresponding increase in raspberry yield over that of plants gown in bare ground. These findings will help guide growers and researchers in designing production practices that reduce the impact of weeds and improve raspberry productivity.

Technical Abstract: Planting floricane red raspberry (Rubus ideaus L.) propagated through tissue culture (TC) is becoming increasingly popular in the Pacific Northwest. Recently, there has been an increased interest in late summer planting compared to 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, the impacts of plastic mulches in late summer plantings are still unknown. The overall objective of this study was to investigate whether PE mulch and BDMs will 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 in 2017, 2018, and 2019. Average PSE was 1.4% and 2-15% by Dec. 2017 in the PE and BDM treatments, respectively. PE mulch generally had greater elongation and breaking force than BDMs. BDMs were damaged by farm activities shortly after mulch application and rips were enlarged by winds in the winter. As a result, all BDMs were removed by Mar. 2018. Soil temperature and moisture were usually higher under mulches compared to the BG control. While average primocane height was greater for plants grown with PE mulch compared to all the other treatments except BASF 0.5 in Sept. 2018, there was no yield difference between PE and the BG treatments. There were no weeds in any of the mulched treatments in Sept. and Oct. 2017 and in PE mulch in Sept. 2018, whereas the BG plots had 51, 51, and 266 weeds/m2, respectively. Overall, PE mulch could be a viable tool for growers planting raspberry in late summer.