Anson: Predators target Napa Valley vineyard pests

Jane Anson reports on the war being waged between Napa Valley winemakers and vineyard pests.

Napa Valley vineyard pests: a lesson from literature?

Do you know the children’s story The King, the Mice and the Cheese? The one about a King who loves cheese, but ends up being over-run by mice who want to eat it too?

For anyone who didn’t have the book as a child, I’ll just give you a brief run-down. Cats are brought in to chase away the mice, but then the palace is over-run by cats, so dogs are brought in to chase away the cats… and so on through the animal kingdom until the palace is full of rampaging elephants, and the only thing that elephants are scared of is… mice. So back the mice come, but this time they learn table manners, eat their cheese with a knife and fork, and everyone lives together happily.

Well, I think we need to send a copy of that book to Spring Mountain Vineyards in Napa. They have pretty much the most effective natural pest-busting system that I have seen, and it’s all based on finding natural predators at each point of the food chain.

Read also: Animals eating wine grapes – five most wanted

Napa Valley and the wilderness

Napa lends itself to this approach perfectly. Every time I leave, it’s the sense of wildness that I take with me. Last time I was there I got obsessed by companies sending out trained falcons and hawks to scare away small birds who like to eat ripe grapes off the vines at harvest time.

This time it was the ground-level wildlife that fascinated me – mountain lions, foxes, possums, deer, raccoons, wild turkeys, rattlesnakes, feral cats… It meant that this time, instead of Aviation Predators, I was calling up Beneficial Insectary in the Central Valley, and Whiskers, Tails and Ferals in the city of Napa.

Napa County is only 9% vines

I guess the cost of land here, the glitz of the auctions and the invasion of hedge-fund money can make you forget that Napa Valley is just 9% vines. Those vines, and a further 80% of Napa County, are under permanent or high levels of protection from development, and around 10% of the county is entirely set aside as national conservation sites.

Spring Mountain is a perfect example of how this wildness lurks around every corner in Napa. It rises just a few hundred metres from the chic central street of St Helena, home to Dean & Deluca, Press restaurant, Model bakery, and a string of other upmarket stores. But up on the mountain you find wild open spaces, volcanic soils and 31 mountain-fruit vineyards such as Cain, Paloma, Stony Hill, Lüscher-Ballard and Spring Mountain itself – the largest land owner in the AVA with 845 acres (342ha).

Showing an instinctive knack for his audience, vineyard manager Ron Rosenbrand tells me that makes Spring Mountain Vineyards the same size as Central Park, split into 135 different plots that range from 1.3 acres to 5.1 acres (2ha). We head off to explore in a small off-road buggy, and it’s not hard to believe that only 20% of the land is vines, with a full 620 acres (251ha) given over to wild land with native trees such as oak, madrone, pine, fir and redwoods.

Rosenbrand is the son of Theo Rosenbrand, legendary winemaker at Beaulieu and Sterling Vineyards. He managed the vineyards for Charles Krug and V. Sattui before arriving at Spring Mountain in 2003 to get to grips with an entirely different set of challenges.

‘At Charles Krug, most of the 1,200 acres (486ha) of fruit grew on the valley floor. If we had an insect issue [during that period], we just got the chemicals out and treated it, but when I got here the owner set me the task of converting to entirely organic viticulture.’

Great in theory – but that meant finding alternatives to fighting two of the most pressing issues that had just started to appear in the vineyards; Pierce’s disease and leaf-roll virus.

These are widespread problems caused by different bug infestations that pose a huge threat to production levels. Programmes to fight them are mandated from above through spraying of chemical insecticides (just like flavesence dorée in France, where non application of treatments has got various organic producers into trouble over the past few years).

‘When we were mandated to start treatments in 2003, I complied for a few years but could see that it wasn’t working,’ said Rosenbrand. ‘So I went to the Napa Valley Agricultural Commission in 2005 and asked for special permission to start an insect trial as a way to control the mealy bugs that are the cause of leaf-roll and delayed ripening.

‘An entymologist, Dr Monica Cooper at UC Berkeley, agreed to monitor the trial, and we released a range of beneficial insects into the vineyards.’

When they first stopped applying the chemicals, the mealy bug population exploded, Rosenbrand tells me. ‘There were a few sleepless nights, be we were committed.

‘In the end, we had great success with a parasitic wasp called anagyrus. It lays its eggs in the body of the mealy bug, and when its young hatch, they eat the mealy bug from the inside out, killing it along the way’.

Like a Jeff Goldblum film

It might sound like the plot of a Jeff Goldblum film, but it worked. It also clearly got them fired up about the benefits of natural selection; in 2006 they turned their attention to the glassy winged sharpshooter that is a vector for Pierce’s disease. Luckily this too has a natural predator, and it’s a rather more attractive one that the parasitic wasp that lurks in wait for the poor old mealy bug.

‘I had read that bluebirds enjoyed sharpshooters as part of their diet, so we started off building 50 bluebird houses among the vines, and monitored the numbers,’ says Rosenbrand.

‘We knew there is a direct link, because we found remains of sharpshooters in the birds’ droppings. Today we are up to 1,000 birdhouses, and we keep on building them. It has pretty much entirely solved the problem.’

These tactics have since spread further across the Valley, and Spring Mountain received the 2010 Innovators Award for its commitment to using alternatives to chemicals, one of only 100 such awards given since 1994 across a range of businesses. As of today, no insecticides or herbicides have been used for seven years.

Back to the king and the mice

Rosenbrand is telling me this as we head back down the mountain, stopping to admire one of the oldest Cabernet Sauvignon plots. And here is where I started thinking about the King and his mice problem.

One of the signs of organic winemaking is the long grass that grows everywhere between the rows. It turns out that here on Spring Mountain that long grass leads to another problem; namely voles. They get to hide from falcons in the long grass, and while there start to wrap, or girdle, themselves tightly around the vine trunk and then gnaw their way through it, killing the vine.

This is where Whiskers, Tails and Ferals come in. It’s an animal rescue centre that collects wild cats from homes and neighbourhoods and rents them to vineyards. And, you guessed it, Spring Mountain is an enthusiastic recipient, hosting around 25 feral cats that successfully control the vole problem.

‘These are all natural predators that live in this area,’ Rosenbrand assures me, ‘we have just intensified their numbers.’ I look at him and smile, hoping that the feral cats are going to mind their table manners.