VIEW ARTICLE

Relationship Between Population Densities of Meloidogyne hapla and Crop Losses in Summer-Maturing Vegetables in Ontario. T. H. A. Olthof, Nematologist, Research Station, Research Branch, Canada Department of Agriculture, Vineland Station, Ontario; J. W. Potter, Nematologist, Research Station, Research Branch, Canada Department of Agriculture, Vineland Station, Ontario. Phytopathology 62:981-986. Accepted for publication 1 March 1972. DOI: 10.1094/Phyto-62-981.

Five vegetable crops were grown in 20-cm-diam clay-tile microplots infested with 0, 666, 2,000, 6,000, or 18,000 northern root knot nematodes (Meloidogyne hapla) per kg of soil. At a nematode population density of 18,000, yields of cabbage and cauliflower were reduced by 9% and 24%, respectively, and cauliflower curd maturity was delayed by 3 days. The weight of marketable lettuce heads was inversely correlated with nematode populations, with a maximum decrease of 46% at the 18,000 density. The number and weight of marketable potatoes and onions decreased with increased nematode populations, whereas the number and weight of culls increased. Commercial losses for these crops were 46% and 64%, respectively, at the highest nematode density. Soil nematode populations under onions and potatoes at harvest were considerably larger than those under cabbage, cauliflower, or lettuce.