Although the northern root-knot nematode (Meloidogyne hapla) is the most prevalent plant-parasitic roundworm species in Washington vineyards, not much is known about how to effectively manage the pest. But Katherine East, a WSU post-doctoral researcher in horticulture, has zeroed in on the nematode’s life cycle as a potential key to unlocking a comprehensive management plan.
This could be good news for wine grape growers who have long been bedeviled by the microscopic roundworm, and who have struggled to even detect early signs of infestation.
Root-knot nematodes have been linked to an array of vineyard maladies like overall vine decline and replant disorders, according to East. Replanting problems in particular could have statewide implications, and sooner rather than later. “The Washington wine grape industry will soon be facing a period of intensive replanting, as older vineyards become less productive and alternative varieties are wanted by winemakers,” East noted.
Because the northern root-knot nematode is present in 60% of the state’s surveyed vineyards, growers are vulnerable to its impacts, potentially creating increased management costs. But that’s where East’s research—studying the nematode’s life cycle—factors in. “Understanding the developmental dynamics of the northern root-knot nematode,” East reported, “can improve the timing of diagnostic sampling and nematicide applications.”
While research has been done on timing and application, the data isn’t particularly helpful to growers in Washington. “Current diagnostic sample timing and nematicide application in grapes are based primarily on information from California,” East added. That’s a big deal, it turns out. The species there—M. incognita, M. javanica, and M. arenaria—are considered tropical species, and differ significantly from Washington’s temperate M. hapla in their activity at different temperatures, East noted, “including reproduction, life cycle, and overwintering capability of its life stages.” East further added that “it’s not possible to directly draw management concepts like application timing from these tropical species to the northern root-knot nematode in Washington.”
For her study, East sampled three vineyards from March 2015 to March 2017 to determine developmental dynamics of the nematode by measuring second-stage juveniles in soil, eggs and adult females in roots, and fine root tips. East found that juvenile populations declined after March 1st, reaching their lowest density in early July and began to increase in early August through the fall. The number of females per root tip did not vary throughout the year.
East’s study, which was recently published in Plant Disease, suggests that her model can be used for sampling as a way to determine whether or not population densities of the nematode are at a critical threshold. Based on her findings, East recommends that growers wanting to manage the northern root-knot nematode time their nematicide applications for the fall. “That is likely the best timing.” However, as her study also indicates, “further research is necessary to support any conclusions of nematicide timing.”
This research was funded by Washington State University, Auction of Washington Wines, and all Washington State grape growers and wineries through the Washington Wine Commission.