A major challenge in controlling zebra chip disease of potatoes is our inability to predict which potato fields are likely to be colonized by potato psyllid, the vector of the pathogen that causes zebra chip. Adding to this challenge is substantial variability in psyllid pressure among fields and years. Annual psyllid trap catches across the region can range from a few hundred to tens of thousands. The current difficulty in predicting which potato fields are at risk to be colonized by psyllids is due to not knowing the source of those colonists. Because potato is unavailable to psyllids for much of the year, colonization of potato fields must be due to movement by psyllids from other habitats and host plants. Potato psyllids are typically found on a few annual and perennial weeds related to potato in the plant family Solanaceae plus some members of the Convolvulaceae. Plant species in Washington State potentially include very common annuals such as hairy nightshade, a known weed pest in Washington row crops, as well as a number of uncommon annuals such as Jimsonweed and buffalo bur. Perennial species such as matrimony vine and bittersweet nightshade are found throughout Washington State, often growing in large patches. In addition to supporting summer populations of psyllids, some of these perennial species are now known to be important overwintering hosts for potato psyllid (Horton et al. 2014, 2015). For most potential psyllid hosts in Washington State, we have little or no information about suitability to the psyllid (Horton et al. 2015) and whether some species are more suitable than others, and we therefore struggle to predict which species are likely sources of psyllids moving into potatoes. We have even less information about whether these non-crop species are also reservoirs of the zebra chip pathogen and thus are potential sources of infective psyllids. Without this knowledge, growers struggle to predict whether stands of weedy Solanaceae near their fields might be sources of infective psyllids.
To read this full report, click on the attached PDF file from the Northwest Potato Research Consortium.