Rotations to manage the quarantine root-knot nematode Meloidogyne chitwoodi in open field grown vegetables

Within Flanders, Belgium open-air vegetable cultivation is a very important economic activity, both for fresh consumption and for industry. Problems with nematodes in the cultivation of outdoor vegetables have increased significantly in recent years. The increasing problems can partly be explained by the sharp decrease in chemical soil disinfection, more intensive use of machinery and the ill-considered use of green cover instead of black fallow in the rotations. Using a good crop rotation scheme with resistant cover crops, can lead to a lower nematode population build up for a subsequent cash crop. In 2018 field trials where set up on two naturally M. chitwoodi infested fields where three population densities of M. chitwoodi were established using marigolds for low density, maize for intermediate density and Italian ryegrass for high density. In three consecutive years (2019-2021) the population of M. chitwoodi and other plant-parasitic nematodes was monitored under different crop rotations including vegetables and cover crops. The initial and final population of nematodes was determined through intensive soil sampling before sowing/planting and after harvesting. Vegetables such as black salsify (1 cultivar) pea (2 cultivars), spinach (1 cultivar), leek (4 cultivars), carrot (2 cultivars), celeriac (1 cultivar) and bean (2 cultivar) were sown/planted in order to determine their susceptibility to M. chitwoodi. Crop yield was also determined during harvest across the three different population densities. Some of the tested vegetable crops were susceptible to M. chitwoodi damage, such as black salsify, leek and peas, while others such as beans were not affected, even at high M. chitwoodi population densities.. The susceptibility of the crops was cultivar dependent. Field rotations with black fallow and certain cover crops were able to reduce the M. chitwoodi population densities. Japanese oat (Pratex), Yellow mustard (Chacha), Italian ryegrass (Meroa) and Fodder radish (Dacapo, Contra and Teranova) were able to reduce M. chitwoodi numbers but this was depending on initial population densities. Other cover crops such as Rye (Dukato) increased the field population density confirming the results from our pot experiments. Based on our results future crop rotation strategies can be developed that control M. chitwoodi and allow competitive vegetable production.
Key words: Plant-parasitic nematodes, cover crops, yield, population density