Potato

This pest is is not known to be a vector and it is not vectored by any organism.

Laboratory methods that are acceptable for cyst extraction include sugar centrifugation, USDA cyst extractor, Fenwick can sieving, wet sieving, and elutriation.

Mature females and cysts are just visible to the naked eye and can be seen as minute white globes on the root surface.
As females mature and die, becoming cysts, they turn from white to brown. This can distinguish G. pallida from G. rostochiensis, which turns from white to yellow/gold and then brown (See Fig. 3 in the CAPS datasheet)

Infested fields may have patches of potatoes with poor growth, chlorosis, and wilting with poor top growth (see Fig. 2 in the CAPS datasheet). Affected plants suffer yield loss, and tubers are smaller.

Soil surveys conducted soon after harvest are preferred to take advantage of the soil mixing that occurs when potatoes are harvested. However, because eggs in cysts remain viable for many years, soil surveys can be conducted at any time of year following production of a potato crop.

Seed potato fields must be sampled using a full field grid survey. For each acre of surveyed field, a composite sample of at least 68 oz of soil, comprised of at least 100 sub-samples of approximately 0.68 oz of soil each, should be collected, to a depth of approximately 4 inches. Seed potato and commercial potato fields can be sampled either by mechanical sampling or hand sampling.

If soil sampling is unavailable, conduct visual inspection for G. pallida by searching in the field for patches of potatoes with poor growth, chlorosis, and wilting with poor top growth (see Fig. 2 in the CAPS datasheet) and sampling root tissues.

Surveys should target annual seed potato acreage, because seed potatoes pose the greatest risk of spreading G. pallida from one field to another. Seed potato field surveys also provide the necessary data to demonstrate to U.S. trading partners that potato-growing areas in the United States are free from G. pallida. Sampling may also be conducted by collecting dirt that is carried with potato tubers during harvest when they are transferred to storage.

Note: Soil sampling is the preferred survey method.

Symptoms occur in a spotty manner in the field, and the spots tend to elongate in the direction of cultivation due to spread of the nematode by machinery. Areas at the ends of rows where farm equipment turn around and parts of the field where potatoes are either loaded into machinery or onto trucks are especially likely to be infested.

Nematode extraction from soil samples has been described by EPPO (2013).

If tissue samples are collected for analysis, the root system should be gently removed from the soil with a shovel, so as not to dislodge the attached cysts (Mimee, 2024).

Morphological: Characteristics of second-stage juveniles, females, and cysts.

Molecular: There are USDA-validated conventional PCR and real-time PCR methods to detect G. pallida, G. rostochiensis, and G. tabacum. A validated work instruction for the real-time PCR method developed by Nakhla et al. (2010) is available.

Morphological characters and keys to differentiate between potato cyst nematode species can be found in various publications (See Baldwin and Mundo-Ocampo, 1991; Subbotin et al., 2010 in the References section).

Globodera pallida can be mistaken for G. rostochiensis, G. tabacum, and G. ellingtonae. However, G. tabacum primarily infests tobacco and is unlikely to be associated with potato. Globodera pallida, G. rostochiensis, and G. ellingtonae infect potato and have limited distributions in the United States. Globodera species can be differentiated using in-depth morphological or DNA-based analysis. Additionally, females of G. pallida change directly from white directly to brown as they mature and die, becoming cysts, whereas females of G. rostochiensis change from white to yellow/gold to brown.