The outer layers of scales of the infected bulbs are split allowing the inner layers to bulge through. When the splits extend into the root region, leaf-like shoots often grow out where roots normally grow. Although strains of the bulb and stem nematode that infect carrots have not been confirmed in Ontario, growers should become familiar with the damage symptoms. Young carrot seedlings develop distorted leaves and by harvest time, infected crowns become spongy and crumbly making mechanical harvesting difficult. The symptoms often resemble those caused by Aster Yellows.
Infected carrots are also more prone to infection from crown rot fungi and soft rot bacteria.
The nematodes travel in the film of water covering the surface of stem and leaves. In onions the nematodes will move down inside the leaf sheath until they reach the bulb and feed between onion scales. They prefer moist muck soil and are less likely to cause damage during hot, dry seasons. However, irrigation can encourage the invasion of susceptible crops during drought periods. The nematodes can spread through irrigation water, infected bulbs or seed, and on contaminated equipment.