Effect of Plant Age and Longidorus africanus on the Growth of Lettuce and Carrot.

Needle nematodes, Longidorus africanus, were added to carrot and lettuce seedlings in a range of inoculum levels and at various times after seeding. The effects of inoculum density and delayed inoculation on plant growth were analyzed according to Seinhorst's damage function. Growth of both lettuce and carrot was severely affected by L. africanus, but delaying nematode inoculation until 10 days after seeding significantly increased estimated minimum yields in both crop species. Tolerance levels of lettuce and carrot for L. africanus were approximately 10 times lower than those reported for other longidorid-crop associations. We conclude that methods aimed at avoiding immediate exposure of germinating seeds to L. africanus may significantly reduce crop damage.