Effect of Entomopathogenic Nematodes and Trichoderma harzianum on the Strawberry Black Root Rot Pathogens Pratylenchus penetrans and Rhizoctonia fragariae

Abstract

The effects of inundative releases of entomopathogenic Steinernema carpocapsae and S. feltiae infective juveniles and applications of the biological control fungus Trichoderma harzianum T-22 (RootShield) on Pratylenchus penetrans and strawberry black root rot caused by Rhizoctonia fragariae were determined in field microplots and small plots. Entomopathogenic nematodes were applied as a soil drench at rates of 7.4 or 14.8 billion per ha in May or August for 3 years. RootShield was applied as crown dips at planting or later as a soil drench. There were no differences in P. penetrans from plants drenched with water alone or with S. carpocapsae or S. feltiae nematodes, averaged over rates and timing. The nematode species applied and the rate or timing of application had no effect on lesion nematodes. Our results suggest that P. penetrans exposure to living or heat-killed S. feltiae and associated bacteria resulted in temporary lack of motility. A progressively increasing proportion of P. penetrans became active again and, after 8 days, had infected tomato roots in similar numbers to unexposed P. penetrans. In laboratory assays and field plots or microplots, S. carpocapsae and S. feltiae did not permanently affect P. penetrans in tomato or strawberry.