Crop rotation effects on Pratylenchus neglectus populations in the root zone of irrigated potatoes in southern Alberta

Abstract

Root-lesion nematodes (Pratylenchus spp.) are important pests of potato (Solanum tuberosum L.), particularly in sandy soils and in the presence of Verticillium dahliae. We assessed the effects of crop rotation and soil management practices (reduced tillage, cover crops and composted manure applications) on population densities of P. neglectus on potato in a sandy loam soil in southern Alberta. Crops in rotation included potato (P), dry bean (DB, Phaseolus vulgaris L.), wheat (W, Triticum aestivum L.), sugar beet (SB, Beta vulgaris L.), oats (O, Avena sativa L.) and timothy (T, Phleum pratense L.). The rotations included ‘conventional’ and ‘conservation’ versions of 3-year (DB-W-P) and 4-year (W-SB-DB-P) rotations, as well as 5-year (W-SB-W-DB-P) and 6-year (O/T-T-T-SB-DB-P) rotations. Conservation practices included autumn cover crops and incorporation of compost as a substitute for inorganic fertilizer. Population densities of P. neglectus in the potato phase of each rotation were assessed in autumn of 2006 and 2007, and at the beginning, middle and end of 2008, 2009 and 2010 growing seasons. Pratylenchus neglectus populations were affected by rotation length but not soil management practices; population densities in the 3-year rotations were larger than in most other rotations at most sample dates. Potato yields in the 3-year conventional rotation were consistently lower than in longer rotations. In the 3-year rotation, potato was preceded by wheat, which is known to be a good host for P. neglectus. We speculate that greater population build-up on wheat in the year before potato, rather than rotation length or crop diversity per se, was the cause of the larger population densities in the 3-year rotations than in longer rotations.