Impact of Pratylenchus penetrans on Established Red Raspberry Productivity.

The plant-parasitic nematode Pratylenchus penetrans is a major constraint to the production of red raspberry. To determine whether several popular raspberry cultivars in Washington State differ in susceptibility to P. penetrans and whether post-plant nematicides treatments are warranted, five independent, multiyear trials were conducted. Trials in existing plantings of 'Cascade Bounty', 'Chemainus', 'Meeker' (two trials), and 'Saanich' raspberry were established in northwest Washington. Treated plots were protected from P. penetrans by applying nematicides over a 3-year period, while nontreated plots received no nematicides. P. penetrans population densities in soil and root samples were assessed spring and fall of each year. In addition, impact of P. penetrans on raspberry yield, fruit composition, cane production, and root biomass was measured several times in each cultivar during the 3-year study. P. penetrans root population densities in nematicide-treated plots were consistently lower than those in nontreated plots at all the samplings. There were few consistent treatment differences in fine root biomass, the preferred feeding sites for P. penetrans. However, a complete root system sampling of one of the cultivars did show greater fine root biomass in treated plants compared with nontreated plants. When differences were observed aboveground, treated plants yielded less than corresponding nontreated plants, indicating that the nematicides may have been phytotoxic to some of the cultivars. This study suggests that post-plant nematicide applications are of limited benefit because, at least during the 3-year time period of this study, there were few observable benefits of protecting these raspberry cultivars from P. penetrans.