Brassicaceous seed meal, root removal, and chemical fumigation vary in their effects on soil quality parameters and Pratylenchus penetrans in a replanted floricane raspberry production system

Abstract

A decline in red raspberry (Rubus idaeus) crop longevity has been partially attributed to parasitism by the plant-parasitic nematode Pratylenchus penetrans. Soil fumigation with 1,3-dichloropropene (1,3-D) and chloropicrin is the most common management practice for P. penetrans in this production system, but the effects are variable and there are strict regulations regarding application; alternatives are needed. A three-year study was conducted in a replanted commercial red raspberry field with a history of P. penetrans to evaluate brassicaceous seed meal (BSM) soil amendment combined with root inoculum removal (RR) as preplant alternatives to traditional soil fumigation with 1,3-D and chloropicrin. Additionally, the fumigant metam sodium at full and half rates with root removal was evaluated. Treatments were applied once prior to planting and included: BSM at 3.4 t ha−1 with RR, full rate metam sodium (692 L ha−1; Max Fum) with RR, half rate metam sodium with RR (Min Fum), and full rate metam sodium without RR (Max Fum–RR; control). Data collected included: P. penetrans population dynamics in soil and raspberry roots, microbial (bacterial and fungal) communities in soil, raspberry vegetative growth, estimated yield, and fruit total soluble solids (TSS) concentration. Population densities of P. penetrans in soil and roots were significantly higher in BSM (983–4801 P. penetrans g−1 of root) than in Max Fum and Max Fum–RR (32–802 and 40–1509 P. penetrans g−1 of root, respectively) during the first two years of the study. By the end of the study there were no differences in P. penetrans population densities among the treatments. Root removal did not affect P. penetrans densities as there were no significant differences between Max Fum and Max Fum–RR. Min Fum was more effective than BSM at reducing P. penetrans population densities, but not as effective as Max Fum or Max Fum-RR. The only difference among treatments regarding the soil microbial community was observed in the first spring after treatment application, when BSM had a soil bacterial community that differed from the other treatments; this difference did not persist into the next sampling date. The most noticeable differences in bacterial and fungal soil communities were due to season, not treatment. There were no significant differences in raspberry vegetative growth the first summer after planting. Yield or TSS did not differ in the second and third summer after planting. The current data show that Min Fum, BSM amended to soil at this experimental rate, and root removal are not effective in reducing P. penetrans population densities, but yield and fruit quality are not compromised under the conditions of the experiment.