2019 ASHS Annual Conference

In the Pacific Northwest, dormant roots and canes of floricane red raspberry (Rubus ideaus) are traditionally planted in the spring on raised beds. Weed management is achieved through a combination of herbicide applications and hand weeding. However, with the increasing popularity of tissue culture (TC) transplants, there is a challenge associated with their establishment compared to traditional planting materials, especially in regards to weed management. There also has been an increased interest in late summer planting because growers find improved establishment relative to traditional spring planting. Our previous research has shown polyethylene (PE) and biodegradable plastic mulches (BDMs) provide excellent weed control while increasing plant growth and yield in spring-planted TC raspberry. While impacts of plastic mulches in late summer plantings are unknown, there is a concern that mulch may increase populations of root lesion nematode (Pratylenchus penetrans; RLN), an important plant-parasitic nematode for raspberry. The overall objective of this study was to investigate whether the benefits of PE and BDMs observed in spring-planted raspberry extend to late summer 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 ‘WakeTMHaven’ raspberry field planted in Aug. 2017 in northwest Washington. Mulch performance [as percent soil exposure (PSE)], weed suppression, plant growth, and soil temperature and moisture were measured in 2017 and 2018. Despite a lack of statistical difference, average PSE was 1.4% and 2-15% by Dec. 2017 in the PE and BDM treatments, respectively. Mulch damage observed in 2017 was mainly caused by farm equipment. Mulch continued to be damaged from seven wind events with speeds over 35 km/h from Jan. to Mar. 2018. Damage was most extensive to the BDM plots and therefore all BDMs were removed by Mar. There were no weeds in any of the mulched treatments in Sept. and Oct. 2017, whereas the BG plots had 51 weeds per m2. Average primocane height was greater in the PE mulch treatment compared to all the other treatments except BASF 0.5 in Sept. 2018. RLN populations in soil and roots in Sept. 2018 were low and not different between the treatments. PE mulch could be a management tool for growers planting raspberry in late summer. However, the viability of BDMs for late summer plantings is uncertain due to the damage caused by on-farm activities that were worsened by strong winds.