UCANR entomologist Houston Wilson, Ph.D. on state of the art thinking about integrated pest management, which starts in part, from biodiversity research he conducted with growers in Napa and Sonoma

Now based in the Central Valley, UCANR entomologist Houston Wilson, Ph.D. started his career counting leafhoppers at Quintessa

This is part 2 of an organic winegrowing field day held July 15 at Quintessa sponsored by the Napa Valley Grapegrowers as part of their July organic education series.

See Part 1 of this field day here.

Entomologists Are Widening Their Lenses

While entomologists look at the world of insects, these days they don’t look at bugs alone-they look at ecosystems. And it’s helping viticulturists learn how to understand pests and manage wine grape vines more effectively.

“The landscape context really tends to mediate how effective on-farm practices can be,” speaker Houston Wilson said.

That was the message the UCANR scientist highlighted for those attending the Napa Valley Grapegrowers’ Organic Field Day held at Quintessa. And he should know, because he was part of one of the landmark viticulture agroecology studies that set out to study cover crops but wound up discovering a bigger picture truth about landscapes and biodiversity.

That study, ultimately published in 2017, started first at Quintessa, Wilson recalled. As a student at U.C. Berkeley, he was lucky enough to study under some of the most esteemed agricultural entomologists in biocontrol, including those pictured below.

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In 2008, Wilson (left) with the powerhouse of U.C. Berkeley’s ag entomologists–Kent Daane, Robert Van Steenwyk, Miguel Altieri and Nicholas Mills. Note: I first met Houston around 2015 when he was a T.A. in Miguel Altieri’s agroecology class at U.C. Berkeley, (which I audited). .

Wilson was deeply involved in one of the first big studies in Napa and Sonoma that showed how leafhopper populations were and were not affected by various farming practices. While initially designed to study the impact of carefully selected cover crop mixes grown in vineyard middles, the 2017 landmark study entitled “Landscape diversity and crop vigor outweigh influence of local diversification on biological control of a vineyard pest” found that the biodiversity around sites was a more important factor in leafhopper populations than a set of selected cover crops and even pointed to one native plant as an important host for beneficials.

A Bit of Backgound

U. C. Berkeley has played a pivotal role in pioneering biocontrol, starting with Robert van den Bosch, whose seminal book Biological Control was first published in 1973, just 11 years after Rachel Carson’s Silent Spring, and followed up by his more influential and popular book The Pesticide Conspiracy (1978). It was the dawn of integrated pest management or IPM, as farmers were struggling to find a way to stop or reduce the use of toxic agrochemicals after their negative impacts became more widely known.

Miguel Altieri, Founder of the Field of Agroecology

Altieri holds the mantle as the founder of agroecology, writing the first text on it, Agroecology: The Science of Sustainable Agriculture in 1987.

He went on to become a celebrated expert working with the Pope, King Charles and United Nations, as well as countless other groups.

He has widely championed mixed agriculture for small farmers in Latin America.

Summing up the field of agroecology, Altieri has written, “Each ecological disease is viewed as an independent problem rather than what it really is–a symptom of a poorly designed and poorly functioning system.”

Today the term agroecology has become more and more fashionable in wine. The Coturri family at Winery Sixteen 600 used the term on a wine label recently. Retiring Opus One winemaker [now emeritus] Michael Silacci now calls himself an “agro-enologist,” on his LinkedIn page.

Return to Quintessa

Wilson is now a UC Cooperative Extension specialist in the Department of Entomology at UC Riverside where his title is Associate Cooperative Extension Specialist, Orchard/Vineyard Entomology. He is currently stationed at Kearney Agricultural Research and Extension Center in Parlier in southern San Joaquin County.

But his career in entomology began in Napa when he told Altieri that he was interested in agroecology. Chilean born Altieri, connected to the Chilean founders of Quintessa, Agustin Huneeus Sr. (former CEO of Concha y Toro) and Valeria Huneeus, was working a bit in viticulture. Altieri sent Wilson off to count leafhoppers at the Rutherford estate.

“One of the first projects I ever worked on in commercial agriculture–not at the U.C. Berkeley university farm–was here at Quintessa,” he said. That was in 2007.

“I was some 20 year old kid down there counting these leafhoppers, and what we did at that time eventually evolved into my PhD dissertation. It was to look at diversifying vineyards to enhance biological control of leafhoppers, and Quintessa [farming biodynamically] was experimenting with that at the time.”

The 280 acre Quintessa site has 140 acres of vines, lots of native oaks and varied soils and sites.

From Micro to Macro View

After the team worked at Quintessa for a summer, the study grew, involving a bigger group of growers who were putting in hedgerows and insectaries and playing around with summer flowering cover crops. “Caleb Mosley [who was in attendance at the field day] was part of that,” he said. Today Mosley is currently the executive director of the Napa Valley Grapegrowers.

One of the many questions the growers had was how to attract beneficials with cover crops.

“Could we plant in the fall flowering plants in the row middles that over the spring and summer would bloom and provide some sort of habitat for beneficial insects that would then go on to control leafhoppers?” he said.

Said Wilson, “How you best manage these farms in an ecological way is really site specific–there’s principles of agroecology and how to approach your farming…

If you want to expand that ‘organism idea’, it’s not just all the biophysical things and how they’re interacting on your farm. It’s how they’re interacting across the entire landscape, this whole valley, and how they’re functioning over time,” he said.

The Leafhopper Pest’s Biggest Predator: Tiny Parasitoids

Vineyard managers have to manage leafhopper populations, which can decimate a crop of wine grapes.

One ally in their arsenal is tiny wasps like Anagrus species (fairyflies) that inject their eggs directly into leafhopper eggs. To quote from the U.C. IPM website, “The developing wasp larva consumes the contents, turning the translucent leafhopper egg brown or red before emerging.”

How can vineyard managers encourage these tiny wasps in their vines?

“When we first started this project, the best known overwintering habitat for the parasitoids [that feed on leafhoppers] was blackberries,” Houston said.

But one species alone was not the totality of the site.

“You’re not just managing leafhoppers," he said. ‘You’re managing 10 different things. How do you develop practices that work well for all of these competing demands?”

The group ultimately developed a group of cover crops with the growers–they were the lead experimenters at that point, Houston said. The questions were not just what species to select, but, “how to sow them? When to sow them? How to keep them from spreading and going to seed under the under the vine rows?” he said.

The group came up with a cover crop program focused on purple tansy, bishop’s flower, wild carrot and more.

“Those three flowers were ones you could put in the fall, and they would bloom in succession and as each one peaked at its bloom, you’d go in and mow it, and then the next species would come up, and it would keep it from spreading.

“We saw a lot of beneficials come to those plants, and so we set up this large replicated experiment to compare plots with and without this flowering summer flowering cover crop program over a two-year period, and we had vineyards in Napa, Sonoma, and all these different kinds of locations.”

The Surprising Results | Not What They Originally Thought They Would Be

“What we saw was that a lot of beneficials showed up on those flowers, but it didn’t really translate into increased beneficials in the canopy itself.

“There were major differences in biocontrol of leafhoppers between the different sites, not necessarily the plots at those sites.

“What it turned out to be is that certain vineyards had higher early season populations of these parasitoids, and that led to higher parasitism early in the season, and that led to lower leafhopper populations at the end of the year. And it just had to do with where they were located. If you think about the need for overwintering sites of this parasitoid, it starts to make sense.

“What defined these better sites is that they had more natural habitat around them (and we hadn’t done anything about the composition of the habitat).”

“The best sites just had more natural and semi-natural habitat within half a kilometer of the site. And the more of that you had, the more parasitoids you had, and the lower leafhopper populations you had,” he said.

Eye Opening Moment: Coyote Brush

“What we did at that point was to go out and basically sample every plant we could. There’s 70 or 75 different species or genera that we were able to collect around the North Coast over a two-year period.

“We found a number of different plants that harbored these parasitoids, but far and above, coyote bush was the number one plant.

“You have some of it planted down there [at Quintessa], and that for us was a very eye-opening moment. There’s coyote bush all over the place here, and it’s a native plant in California.

“When I brought this up with growers, some folks were like, ‘Man, I just cleared all that off my hillside or off the road cut’ or whatever. But it was an alternative plant that doesn’t harbor sharpshooters, it doesn’t harbor Pierce’s disease, but it is an effective overwintering habitat for this parasitoid. And so that was cool–the story kind of goes like this [in one direction], and then suddenly we find this landscape thing, and there’s this other overwintering habitat, and that was a good ending.”

The Trail Doesn’t End There

“There’s all sorts of questions that still remain about how much of this coyote bush do you put in your vineyard relative to the number of acres you have, and how far do they go from it, and all sorts of stuff like that. But this is kind of how science goes.”

Then the project ended.

"I got my PhD, and that year red blotch showed up, and we also had Virginia creeper leafhopper show up in Mendocino and Lake County, and it was like, stop all that, focus on this, and off we go.”

“But at the end of, I think one of our final presentations with the group which was about 30 different operations…was that what we discovered was pretty cool.

“More questions arose: what do those plants do for vine mealybug or sharpshooters? We didn’t study any of that. It’s so difficult in some of these systems where you’re doing all these multi-layered practices to scientifically isolate certain variables and try to tease apart these things,” he said.

The New Bottom Line: Collaborative, Region Wide Projects Matter Most

Wilson said scientists today are more excited about broader projects that involve larger landscape studies.

“As an ag entomologist, area-wide IPM is how you do IPM now,” he said.

“For us it’s been really important to try to build more collaborative projects where we have someone looking at how do birds and owls respond to this? How do weeds respond to this practice? How do the insects respond? And that’s more the type of work that I’ve been able to develop in the past 10 years.”

He cited Matthew Johnson’s project at Cal Poly Humboldt (with numerous western bluebird boxes on sites in Napa) and Danny Karp at U.C. Davis who are studying song birds and their response to proximity to natural habitat and nest boxes. Both are featured in the video below.

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Of special interest to Wilson, those scientists are studying what the birds eat–specific insects.

“We’ve been able to take fecal samples and run it through molecular methods that can tell us what insects we’re finding, DNA from there,” he said.

“We’ve found that the birds eat vine mealybugs, they eat leafhoppers, like they also eat lacewings.

You’re trying to manage an ecosystem that is not evolved to make sure you can produce wine. The birds are just trying to get food. They eat the good bugs, eat the bad bugs, and so it’s difficult. But it’s important to think of it in this way,” Wilson said.

“There’s more to come, and results will be out soon,” he said.

Wilson said insects of interest in his field boil down to two categories.

“With biological control, you have two types of insects.

“You have these generalist predators like spiders and lacewings and ladybugs, and then you have parasitoids. Well, the generalists-they’re general. They eat a bunch of different stuff. Some of it you want them to eat. Some of it you don’t. Sometimes they eat each other–like a spider and a lacewing. Parasitoids can have really hyper specific host ranges.

“Anagrus is pretty specific… it’s got the leafhoppers, but then it also has this alternative host.

“There’s other parasitoids that are known to attack 60 different types of insects. So, when you think about these insectary plantings, like which beneficial insects are showing up, and which ones do I need to control the pest I’m trying to control, and do they show up at the right time of year that aligns with the phenology of this insect or with the timing when my crop is vulnerable to damage from that insect, and how far do they move from these plants? There are a ton of unknown questions.

“Those are all very approachable questions, but each one is a huge study of its own, and you need a bunch of people to look at these things.”

“Coming back to the coyote brush…that would be one of the next steps for me if we were to resume that work.

“How much coyote brush is enough? Every 10 rows, or do I put it around the border? We don’t know.”

Because Anagrus are so lightweight, studying them is a little more challenging, Wilson said.

“Rather than flying, it’s more like they’re swimming through the air,” he said. 'They’re so tiny. They’re one of the five smallest known parasitoids on planet earth, which has made them a total joy to work with. They look like a little thing with pepper–not a peppercorn, like a piece of pepper you put on your food–bouncing around in a vial.

“So how does wind affect their dispersal? And if you have a ton of insectaries or a bunch of vineyard and a little insectary–this is where the questions about landscape ecology come in.”

“What I was saying earlier about the surrounding landscape, more and more what we’ve seen in these type of studies–not just in vineyards and not just in California, but globally–is that the landscape context really tends to mediate how effective these on-farm practices can be.”

Population size and habitat size are other factors, making tracking the tiny parasitoids and their impacts elusive.

“If you don’t have enough habitat at a larger scale, you don’t have a metapopulation–a regional population of these beneficial insects–to draw into your farm. And so, if you’re in a huge monoculture and you put flowers in 10 acres, nothing might show up because there’s nothing in the area.

“In other cases, if you have so much habitat, and you add flowers, you may not see a difference because there’s so much just already coming in,” he said.

Landscapes Are Diverse | Biocontrol Results Can Vary Widely

Looking at the broader landscape of biocontrol, biodiversity, agroecological studies, scientists have found mixed results.

“There’s been some synthesis of these studies over the past 50 years, and when you diversify in agriculture in a cropping system, whether it’s for pollinators or weed control or biocontrol or whatever–a third of the time it works, a third of the time it doesn’t work, a third of the time maybe it kind of worked.

“So it’s not necessarily the absolute solution. But it’s an important principle to think about as a root cause. For example, mating disruption is awesome. We need more of that, and you can’t do that in house. Sprayable beneficial insects–those are really cool. And the sterile insect technique,” he said.

A Final and Very Practical Tip | QA Your Purchased Insects

Wilson cautioned that growers purchasing insects should do quality checks on their purchased insect shipments.

“Quality control is a major issue,” he said. “They’re living organisms, and so we always recommend to anybody who’s applying beneficial insects from an insectary to do a quality control check when you get them. We’ve had shipments with high variability. This isn’t to criticize these ancestries,” he said, adding that bugs can be damaged in the shipping process.

Next in the series of NVGG organic field days, Ground Cover Management at Opus One, featuring Kimberlee Marinelli of Opus One, Dave Kaplow of Petaluma based Eco-Management, and native plant specialist Selena Vengco for a field-based discussion exploring how thoughtful ground cover management can support soil health.

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