Abstract
Summary The root-lesion nematode, Pratylenchus penetrans, causes growth reduction in glasshouse-grown lettuce and is mainly controlled by chemical soil disinfestation. Integrated management strategies require more knowledge about the population dynamics and damage threshold densities. We monitored the population during 2.5 years in a commercial glasshouse by sampling soil in the same four 1 m2 spots at 0-30 cm and 30-60 cm depth. The grower grew lettuce in rotation with leek, applied 1,3-dichloropropene in summer and left the field fallow during winter. Growing leek reduced the nematode population slightly but chemical soil disinfestation lowered the numbers drastically, although 41% of the nematodes in the deeper layer survived. Black fallow resulted in a slight increase of the population, probably due to hatching. Two pot experiments with ten densities of P. penetrans were conducted to estimate the damage threshold for a summer and autumn cultivar (‘Cosmopolia’ and ‘Brighton’, respectively). The thresholds for lettuce weight were 669 and 3834 P. penetrans (100 ml soil)−1 in summer and autumn, respectively, but with considerable variability in estimated parameters. The thresholds for root damage were much lower: 204 and 48 P. penetrans (100 ml soil)−1. Nematode numbers did not increase on lettuce in the pot tests (maximum multiplication rate was 0.40) but increased slightly in the commercial setting. These results show that populations of P. penetrans build up slowly when butterhead lettuce is rotated with leek and fallow, but chemical soil disinfestation is required to avoid numbers resulting in root damage.
Highlights
These results show that populations of P. penetrans build up slowly when butterhead lettuce is rotated with leek and fallow, but chemical soil disinfestation is required to avoid numbers resulting in root damage
After removal of the plastic, 3 weeks after the nematicide treatment, P. penetrans was absent in the 0-30 cm layer and only 7 P. penetrans (100 ml soil)−1 were found in the 30-60 cm layer, a population decrease of 59%
To obtain more insight into the factors influencing the dynamics of a P. penetrans population in a commercial lettuce glasshouse, nematode population dynamics were monitored during a 2.5 year period
Summary
To set up integrated pest management strategies, knowledge about the population dynamics and the damage threshold of P. penetrans for lettuce is required. Olthof & Potter (1973) noticed damage by P. penetrans on field-grown lettuce at 6000 P. penetrans (kg soil)−1, they did not define a threshold density. The knowledge of this threshold is important to provide good management advice for lettuce growers. The damage threshold was estimated by growing lettuce in pots in the glasshouse and recording lettuce growth parameters over a wide range of P. penetrans population densities. The obtained knowledge will contribute to the set-up of integrated pest management tools and the reduction of chemical soil disinfestation
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