Carrots are susceptible to the world's number-one pest

Root knot nematodes, when sufficient numbers are present, cause swellings against the main root or swellings further away

- Bill Kerr

Eelworm (nematodes) are considered the world’s most serious pest. These worms are microscopic but in some cases can just be seen by the naked eye, especially the females of some species when full of eggs. There are a number of genera and species, and a huge amount of cultivated crops are susceptible to at least one species.

Root knot nematodes (Meloidogyne spp.) are endoparasites, which means they enter into the root of the host as compared to ectoparasites that attack the root externally.

Whereas in most crops a small or moderate population in the soil may cause negligible to moderate yield loss, this is not so in the case of carrots, where even a low eelworm population can cause serious damage. If a nematode enters the root when the carrot is still young, it will cause the carrot to fork or worse, causing the root to be a cull.