The citrus nematode—Tylenchulus semipenetrans—is known to be in the 14 counties of California where there are commercial plantings of citrus. The nematode is a parasitic pest that feeds on the roots of citrus trees. Its feeding decreases vigor and rate of tree growth and the yield and size of fruit. The nematode does not kill the trees but may reduce growth of young lemons and oranges by 40% to 60%.