by Thomas Grandperrin
Published on November 15, 2020
This article was initially published on the Wine Industry Network.
Grape growers are facing increased threats from invasive insect pests. The issue with those non-native species is that there are often no naturally occuring enemies capable of controlling them and new Integrated Pest Management (IPM) protocols might take years to be developed, forcing growers to rely on broad-spectrum insecticides until more ecologically friendly alternatives are available.
A notable example of an invasive pest affecting California vineyards is the vine mealybug, which is a major pest of grape vines not only because of the damage they can cause to the fruit but also for the viruses they transmit, such as the grape leafroll-associated virus.
Vine mealybug infestation on a grape cluster
To discuss the latest knowledge on these topics, I reached out to Kent Daane, an entomologist and cooperative extension specialist at the University of California, Berkeley. Kent has led several research projects on vine mealybugs and the development of ecologically-based insect pest management systems in vineyards and other perennial crops, such as almonds, pistachios, grapes, and stone fruit.
During our conversation, we discussed the need to manage insecticides as part of an IPM program, the biological control agents being used in vineyards, and the use of cover crops for promoting vine health.
From IPM to biocontrol: the need to manage insecticides
According to Kent, all vineyard managers or Pest Control Advisors (PCAs) in California are practicing IPM to some extent, and comments that, “There’s not a PCA or farmer that I talk with that isn’t practicing IPM, although their view sometimes will be a little bit more towards conventional insecticides where others might be a little bit more towards sustainable practices.”
When we talk about the use of biocontrol and beneficial insects for instance, practices can differ greatly. However, due to the fear of pesticide residues and increased regulations and restrictions in agriculture, the trend is turning towards chemical pesticide alternatives, such as biocontrol and mating disruption.
While many new insecticides are compatible with IPM and biocontrol programs, some still widely used products might affect the population of naturally occurring natural enemies and ruin the effort of augmented releases if not properly coordinated, resulting in wasted time and money. Insecticides also have some limitations when it comes to controlling pests like mealybugs due to their cryptic behaviour (hiding under the trunk bark) and protective waxy coatings.
Some novel, narrow range insecticides are very effective against mealybugs, but, while less harmful than the organophosphates previously used, they can still affect natural enemies such as predatory mite populations. Because of this, Kent explains that the first step to start implementing beneficial insect releases is to manage the insecticides being used. If this is done properly, even conventional growers can benefit from the help of released natural enemies.
“Growers need to look at the insecticide they’re using and try to use materials that work well with beneficial insects. The UC IPM program is a good source to find this information, but you can also find it on numerous websites where they just have got a red, yellow, green color coding for the different insecticides, red meaning it’s harmful on beneficial insects and green meaning it’s soft on beneficials.”
Transitioning from a more conventional pest management program to a IPM program more oriented towards biocontrol takes some time and knowledge.
“As a grower, you can’t put on a pyrethroid or M-Pede insecticidal soap week after week and then release natural enemies and still expect to have the augmentation program work well.”
So how should vineyard managers get started?
“Start by scouting your field and seeing what kind of pest populations and beneficials you’ve got naturally”, suggests Kent,“then work with a PCA knowledgeable about natural enemies and ask him for help to move to a softer program.”
This way, for example, a grower who needs to control worm pests in the fruit clusters can move from broad-spectrum organophosphate insecticides to a more selective Bacillus thuringiensis (Bt) microbial insecticide.
By controlling the pesticides being used, growers should start to see the population of generalist natural enemies increase and be able to start releasing some specialist predators or parasitoids.
The beneficial biological control agents used in vineyards
To fight mealybugs in vineyards, Kent has a few recommendations for growers. “Release Cryptolaemus (also known as the mealybug destroyer) and Anagyrus pseudococci as soon as you can start seeing the mealybugs move, so around April and May”.
On the left: Anagyrus next to a mealybug. On the right: a Cryptolaemus larvae
Unfortunately, Anagyrus supply can be scarce in California and some growers don’t get them until August and September.
Releases of parasitoids can still be done around harvest time, as Anagyrus overwinters pretty well throughout most of California. But Kent explains that “if you have a real problem at the end of the season, you can’t count on Anagyrus to provide control in three weeks. It’s not an inundated program, it’s an inoculated program. You can’t buy enough to control an outbreak of vine mealybug. So you should do it year after year after year as an inoculate release program.”
Kent shared another point grape growers need to be aware of. “The Anagyrus that have overwintered in the vineyard naturally start to emerge a bit late in the season, around May. So you start off with really low parasitism and they don’t do very well against the vine mealybug underneath the bark.”
If you cannot purchase Anagyrus early in the season, one option could be to focus on the release of Cryptolaemus and spray narrow range insecticides to control the vine mealybug population until Anagyrus emerge.
While relying entirely on biocontrol and cultural practices to control pests can be more expensive in the short term, Kent confirms that it can be done in accordance with the principles of economic pest management decision making, and that augmentation releases can be easily budgeted into a pest management program. “I’ve got a vineyard here on station where we haven’t put an insecticide on it in 15 years. There’s vine mealybugs there, but it’s not a major issue.”
Cover crops can bring some great benefits to the vineyard health
Kent has done several research projects on the benefits of cover crops in vineyards with two postdoctoral researchers. He studied the use of barley, vetch, and clovers with Michael Costello, and more recently the use of phacelia, buckwheat and sweet alyssum with Houston Wilson.
Phacelia and sweet alyssum cover crop in a vineyard (Credit: Dr. Houston Wilson, University of California, Riverside)
While he encourages grape growers to use ground covers, he recommends that they do it mindfully. “Think about their positive impact on vineyard health first. If you get a benefit on the natural enemies, that’s a bonus”.
He thinks that “there’s a misplaced confidence in conservation efforts for bio-control of mealybugs because people will plant these insectary ground covers with the idea that they’re going to add nectar pollen. If you’ve got vine mealybug, you’ve already got a lot of honeydew. So you’ve got what the natural enemy, the parasite, needs to live longer. Now they feed on the mealybugs honeydew and that’s been better than any of the ground covers I’ve seen!”
From his years of experience, he has also observed that some growers will put a lot of time and energy in planting ground covers and then spray some broad-spectrum insecticides. Even insecticidal soaps approved for use in organic agriculture can kill natural enemies. Due to this only too frequent occurrence, he feels strongly that the most important conservation effort that can be made is being conscientious about the type of insecticides that are applied.
Poor vine health and nutrition balance creates favorable conditions for many pests. Kent’s studies suggest that although ground covers in vineyards had a positive impact lowering leafhopper populations, it was as much due to their ability to improve the vine vigor balance as it was from improving extra floral resources.
He also explains that if ground covers have a benefit for natural enemies, it’s because they increase the generalist predators such as green lacewings and ladybird beetles. Those are useful in a vineyard but, unfortunately, most of the natural enemies of mealybugs, Anagyrus and the mealybugs destroyer being the most commonly used, are specialists and cover crops are of little use to support their populations.
So what should growers use cover crops for?
“I always say use ground covers when you want to think about the overall vineyard health from the soil up. They can help to increase or reduce vine vigor and improve water penetration”.
Different cover crops are used for different purposes. For example, planting a grass will suck out some of the nitrogen when vines have too much growth. For the opposite effect, planting a legume can act as an organic fertilizer for vines with poor vigor. If the vineyard soil has poor water penetration, planting something with long roots is recommended.
PCA are the best partners to help implement alternative pest control techniques
In general, Kent is impressed with the knowledge of pest control advisors in California, especially groups like the Association of Applied IPM Ecologists as well what he sees at the California Association of Pest Control advisors (CAPCA) meetings. He says that for PCAs and growers, leaning more towards biocontrol instead of spray comes down to one thing in particular -their risk tolerance. He comments that “some pest control advisors have a low tolerance for risk and that gives them a quick trigger on pesticides.”
So the adoption of alternative pest management techniques such as biocontrol and mating disruption starts with the growers expressing to their PCA their goals of limiting insecticide use.
He elaborates on the topic, “The IPM practitioner then walks them through the process of removing these insecticides and seeing how it goes. If more pests are seen, he would ask the grower if they are comfortable with it. If they are, then more pesticides can be removed and the grower can start doing some augmentation releases and add some ground covers. If the grower feels like moving forward, they can even take the decision to go organic.”
Kent feels that the process of going from conventional pesticides practices to a more sustainable IPM program is a continuum, and it depends largely on the farmers, their risk assessment and level of comfort with the presence of insects. After that, it’s up to the IPM practitioner to walk down that pathway with them.
To conclude our conversation, Kent shares his thoughts on how new technology could help vineyard managers and PCAs to implement a successful and cost-effective IPM strategy. “Drone and satellite imagery are already used to find vines with leafroll disease before we can see them with naked eyes. It would be great if pest populations could be detected the same way, allowing us to perform augmented releases of natural enemies with a drone in the area of the vineyard where the pest pressure is higher.”
Do you have experience with the implementation of augmented biological control or conservation techniques to manage invasive pests in vineyards? Reach out to us, we’d love to hear your story and write about it!
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