Assessing the Damage Potential of Root Lesion Nematodes on Red Raspberry Varieties

Washington State is the nation’s largest producer of red raspberries for processing.  The root lesion nematode, Pratylenchus penetrans, which feeds on fine roots, is a major constraint to the industry, shortening the productive lifetime of many plantings. Current management of P. penetrans relies upon preplant soil fumigation, but federal regulation of soil fumigants has made this practice increasingly more difficult and expensive for growers. In addition, few post-plant nematode management options exist. To guide the management this nematode in the future a better understanding of the damage potential of this nematode to raspberry needs to be determined. The objective of this project was to determine whether several popular raspberry varieties, ‘Meeker’, ‘Cascade Bounty’, ‘Saanich’, and ‘Cheminus’ differ in their susceptibility to P. penetrans. Field trials in established plantings of these varieties were established in northern Washington. Treated plots were sprayed with a combination of two nematicides oxamyl and fosthiazate, while non-treated plots received no nematicide. P. penetrans population densities in soil and root samples were assessed Spring and Fall 2011. P. penetrans populations in nematicides treated plots were consistently lower than those in non-treated plots at the fall sampling. In Summer 2011, yield of nematicide treated plots was not significantly higher than yield from non-treated plots in all trials. In December 2011, destructive plant samples were collected from one of the trials. Plants from nematicide treated plots had a greater amount of fine roots biomass (root diameter< 8 mm) than plants from non-treated treated plots (P < 0.05), while woody root biomass (> 8 mm) was not significantly different between nematicides treated and non-treated plots.