Jan 22, 2020
Nematodes tough on Washington winegrapes

Four feet under the vineyard ground, and in the middle of the row far from the grapevines it loves to eat, dagger nematodes still are plentiful, researchers found.

Katherine East, a Michigan State University researcher, spoke in December at the Great Lakes Fruit, Vegetable & Farm Market EXPO in Grand Rapids, Michigan, about vineyard nematodes. East conducted the research while employed by Washington State University (WSU) with Michelle Moyer of WSU and Inga Zasada of the USDA Agricultural Research Service.

WSU researchers found vineyard nematodes were hard to kill or even control.

For grapes growers in eastern Washington, the area is very dry and dependent on irrigation, and the vinis vinifera is grown on its own roots.

“Access to land with water is very limited,” East said. “So as the wine industry started to expand really they ran out of room.”

The result is that growers are planting new vineyards on top of old vineyards. Nematodes are a major contributor to replant with new vineyards such as reduced yields, vineyard longevity, and other replant issues, East said. For grapes growers in Eastern Washington, northern root-knot nematodes and dagger nematodes are the most troublesome.

Northern root knot nematodes are the most prevalent.

“In a survey done in 2012, about 60% of vineyards that were surveyed had this nematode to some degree,” East said, and about half of the vineyards tested had nematode levels above the theoretical threshold for management. “There were a lot of questions as to, ‘What do we do about this pest out there?’” Existing research has focused mostly on other species of root-knot nematodes, so growers wanted a better look at what was troubling the industry.

The usual suspects

Northern root-knot nematodes invade root tips and eat cells that they infect. Not only do they take energy from the plant, but they also inhibit water and nutrient uptake by the vines. East said most products and techniques target the microorganisms in their juvenile stage before they’ve taken up residence in roots.

“That’s the stage that’s free-living, that’s the stage that has to find a root to reproduce or it’ll starve to death, which we would like,” she said.

Dagger nematodes are also a concern. Although they do very little damage to the vines themselves, they are a vector for viruses between plants such as tobacco ringspot and tomato ringspot.

East and her colleagues researched the location of the nematodes on the vineyard floor.

“We had an opportunity where there was a vineyard that was going through replant,” she said. Because the vineyard was being replanted anyway, the team had a chance to test underneath the vines and even in the middle of the vine rows, all the way down to a depth of four feet deep.

“There was some specialized equipment involved,” she said.

The study found that root-knot nematodes were located mostly within the top two feet of the ground, mostly hugging close to the rows of vine roots – almost none were in the middle of the vine rows. By contrast, dagger nematodes were throughout the soil, in the middle of the rows and to a depth of four feet.

Time targets

East and her colleagues also researched when the northern root-knot nematodes were in their juvenile stages.

“If you’re going to apply fumigant if you’re going to apply nematicide, you’ve (got to) know when to do it, and we didn’t even know what the life cycle looks like, for this particular nematode on grapes,” she said.

They found the nematode was going through about one life cycle per year, and the juveniles were declining in spring when they were either invading root tips or dying off.

“If you’re going to want to apply a fumigant, or apply a nematicide, or sample for nematodes, you wouldn’t want to do it in the summer, because you’d only see about 20 percent of maximum juveniles were you to sample at a more appropriate time,” East said. Fall is a better time.

Fuel for the fight

Fumigation and rootstock choice can play a big role in heading off replant issues.

Fumigation seemed to work well for dagger nematodes – knocking down the population for about four years. Root-knot nematodes were only reduced for about one year. East said nematicides didn’t seem to do very well in initial trials, perhaps due to timing.

“Timing and rate are going to be really, really important for any soil nematicide to be efficacious,” East said.

Washington growers don’t often use rootstocks – East said that WSU’s experimental planting may be the largest in the state. But she and her colleagues were able to confirm at least four readily-available rootstocks had resistance to northern root-knot nematodes.

So, a lot of a new vineyard’s success depends on choices made before planting.

“A lot of that’s going to depend on what species you have,” East said.

— Stephen Kloosterman, associate editor


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