Several plant parasitic nematodes are known to attack the root system of citrus plants, especially the citrus nematode, Tylenchulus semipenetrans. The burrowing nematode, Radopholus similis , causes a disease known as spreading decline and is a serious pest of citrus in other production areas. This nematode has been found in the Valley on ornamentals, but not in citrus orchards. Serious losses to the Texas industry could result should it ever become established in citrus groves. The citrus nematode occurs commonly in Valley citrus orchard soils.
Sour orange is rated as highly susceptible to nematode infection.
Of the common rootstocks with potential use in the Valley, only Swingle citrumelo is rated as highly tolerant to the citrus nematode. A microscopic view of a swollen female citrus nematode. Young trees also may be injured if planted in orchard sites where nematodes previously prevailed. Because the presence of the citrus nematode cannot be detected visually, positive diagnosis is based on external symptoms and laboratory examination of root and soil samples. The Texas Agricultural Extension Service operates a Plant Nematode Detection Laboratory at College Station where samples can be sent for analysis and recommendations.