In Ontario, flue-cured tobacco (Nicotiana tabacum L.) growers routinely fumigate their soils to control root-lesion nematodes (Pratylenchus penetrans Cobb). Studies suggest that planting pearl millet (Pennisetum glaucum L.) as a rotation crop may control the nematodes; winter rye (Secale cereale L.), the crop commonly grown in rotation with tobacco, is susceptible to the nematodes. In 2002, plots of forage millet (var. CFPM 101), grain millet (var. CGPMH-1) and winter rye were established at three sites and in 2003, tobacco was grown at these sites in non-fumigated plots where the rotation crops grew, except for a winter rye/fumigation treatment. The goal was to evaluate P. penetrans populations and tobacco yield and quality in the millet rotations relative to the traditional rye-fumigation system. In 2002, initial P. penetrans populations assessed in the spring were similar for all treatments; however, the final populations and consequently the ratios of final populations/initial populations (Pf/Pi) consistently differed among treatments. The Pf/Pi ratios ranged from 0.07 to 0.79 for forage millet, from 0.18 to 0.94 for grain millet and from 2.33 to 21.65 for rye. In 2003, P. penetrans populations in tobacco plots previously cropped to either type of millet were comparable with those detected in fumigated winter rye plots. Compared with tobacco following rye without fumigation, tobacco yield was 14 to 51% higher following rye with fumigation, 19 to 70% higher following forage millet and 18 to 65% higher following grain millet. Grade index was unaffected. Results indicate that pearl millet offers an alternative to fumigants for the suppression of P. penetrans population and provides equivalent gross returns. Key words: Pennisetum glaucum, rotation crop, Nicotiana tabacum
The root-lesion nematodes found in uncultivated soils, mainly in natural grasslands in Japan