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Planning the great response to a micro pest

One of the terms tossed about during last week’s discussion of the discovery of phylloxera in Colorado vineyards was “symptomless carrier.” Which means (in this case) a grape vine may have phylloxera (which is the tiny bug that kills vines by attacking their roots) but shows no sign of the infestation.


Phylloxera aphids on a vine root. Photo – Australia Department of Food and Agriculture

I know, that’s not the preferred medical definition but give it up, these guys are grape growers, not doctors. Except, that is, for one or two, who offered this definition – A symptom is something only you know is there. A sign is something other people can notice.

Whether you use symptom or sign, the concern is the same: you might have an aphid-infested grape vine and not know it until it and its neighbors start to wither.

And with phylloxera, that physical manifestation is just the tip of the aphid iceberg because by then the bugs have spread.

First the worst news: “The rule of thumb is, once you find phylloxera, the vineyard is doomed,” intoned Bob Hammon, entomologist at the CSU Extension Service, during the packed-house phylloxera seminar Monday at the 2017 VinCo Conference.

And as of this writing there have been four vineyards in the Grand Valley positively identified to be phylloxera positive. Only one has been publicized.

“There’s no doubt in my mind it’s far more widespread,” Hammon said.

The bug will kill (most of) your vines but not all at once, Hammon and other experts warned.

It may take the phylloxera aphid a decade to move through your vines, which gives the grower time to save his livelihood, if not those specific vines.

While there are exceptions to every case, phylloxera kills vinifera vines, not the native American grapes that developed alongside the bug and have some resistance.

There are some sites in Europe (and here), which first noticed phylloxera in the 1860s after American grapevine cuttings spread it there, that haven’t been affected in the 150 or so years the rest of that continent has been tearing up and replanting vineyards.

Getting rid of own-rooted vines, especially vinifera vines, and using grafted rootstock is one and probably the surest way to combat phylloxera.

It’s expensive, adding about $2.50 to the cost of a vine. Plus, you could leave the vineyard fallow for a year and then wait another 3 years for a crop.

And you still must be careful about not spreading the bug around by carrying infected soil on your boots or tractors or other machines.

Also, grafted rootstock need protection against the harsh winters we get in Western Colorado.

Those aphid-resistant American grapes? Most of them don’t make good wines, or at least not wines demanded by most consumers.

Using vinifera vines grafted to resistant rootstock allows growers to produce the grapes winemakers want.

“No region has even succeeded in keeping it from spreading,” said Nancy Janes of Whitewater Hill Vineyards and Winery. “You can slow it down a lot but nobody has succeeded in stopping it.”

It comes down to managing the bug once it appears.

If you’re a big grower like Bruce Talbott, whose company manages upwards of 40 vineyards across the valley and consults on another 20 or so, your decision is rooted in economics.

If a phylloxera is found in their vineyards, “our response probably will be we assume everything we farm has got phylloxera and we will spray it with Movento,” a systemic insecticide against sucking pests, Talbott told the VinCo seminar.

“If it costs $100 an acres, it costs us $100 an acre,” he said. “That’s a lot cheaper than the other things.”

If you’re smaller, it’s still economics. Is it cheaper to pull your vines, wait and then re-plant or do you go into another crop, like peaches?

“Unless we get Napa-like prices, grapes will never replace peaches as a cash crop,” offered Talbott. But growing grapes allows him the latitude of keeping his Mexico-based crews working for six months or more.

For small-acreage growers, “the better approach is if it’s in here now, I better work at replacing a third or quarter of my vineyard,” said state viticulturist Horst Caspari of the CSU Research Center. “That way I stay in the production and not go (without a crop) for two or three years.”

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