Citrus Pests – Your Questions Answered by Dr. Monique Rivera

In the following video on citrus pests, I visited Dr. Monique Rivera, a University of California entomologist to get answers to reader and viewer questions on citrus pests including Asian citrus psyllids and Argentine ants. Our discussion included both Asian citrus psyllid treatment to reduce the spread of HLB and also ant control for citrus trees. We discussed the Argentine ant in California and how to kill ants with a liquid ant bait. We also discussed a case of liquid ant bait not working and how to use liquid ant bait more effectively.

Below you will find the resources mentioned in the video as well as a transcript.

Resources

CDFA hotline: 1-800-491-1899

Citrus pest control products mentioned in the above video
University of California Agriculture and Natural Resources
UCANR HLB Locator Web application
UCANR Insectary Plants
UC Cooperative Extension
UC Master Gardener Program
University of California Integrated Pest Management

Citrus Pests – Transcript

Asian Citrus Psyllid Treatment and Control – Pesticides

Question: What synthetic or organic pesticides can be used to control Asian citrus psyllids?

Answer: For the homeowner this is a really complex question, in the sense that, first, you need to figure out if you have psyllids. So, your treatment plan is really going to be dictated by your specific context in your yard. So if you have a psyllid population that just can't quit, using organic tools is not going to be effective. Even the synthetic tools that are available to homeowners are not ideal. However, if you want to input your time and effort into controlling the psyllids, I think ideally if you have a high population you would go with the synthetic formulas. And that's because you can apply them and then you have approximately three months of control. Either way, you should be tracking your population. So, now having a citrus tree is not just some casual thing where you can have the tree, pick the fruit off of it; it's managing it so that you don't become the so-called Typhoid Mary. You don't want to be the person that has HLB. One, because you're encouraging the spread of it by having that source of it, and then secondarily because that tree, if you're in California, is going to legally be removed by the CDFA. So, in terms of actual recommendations, though, for the synthetic we've been recommending the Bayer Advanced Fruit and Citrus, that's a soil drench product, that's a systemic, that's going to give you that three months of control. If you choose to do organic, what that takes is a level of vigilance that I don't think people are really prepared to undertake. So, it's going to mean a constant vigilance of your ACP population and at peak population times you might be applying the insecticidal soap or oil two to three times a week.

Question: So then would it be better if people spent their energy controlling the ants?

Answer: Depends on what your psyllid population looks like. So, if you have a significant and persistent psyllid population and you're near an HLB area, basically if you're in Southern California, no, you should really focus on controlling the psyllid itself. In any case, you know, if you have an established population there I don't think that controlling the ants is going to give you that much benefit. It's just going to allow your natural enemies and parasitoids access to the population. The focus should always be primarily on the psyllids.

Repelling Asian Citrus Psyllids

Question: Is there some way to repel Asian citrus psyllids?

Answer: So, in terms of a chemical repellent, no, but you can have a physical repellent. It's a barrier but it's also a repellent. So, kaolin clay or the product called Surround. This can be applied to the tree and it makes it visually unappealing to the psyllids and it also makes it not palatable, they're not going to want to use that leaf material.

Physical Barrier for Asian Citrus Psyllids

Question: Can I use a physical barrier to keep psyllids away from the citrus trees?

Answer: So, it really depends on where you're trying to get your psyllids away from and what it is. So, it's context dependent. If you have one tree in your yard, something like the Surround Kaolin Clay is going to be the best physical barrier to repel them. But if you have, say a small orchard, putting up a treeline or a fence that's tall can help prevent psyllids from migrating into your area. The real goal should be to not have them establish there. Sometimes that's dependent on your neighbors, so in every instance a physical barrier isn't going to work. So, for each different situation, you're going to have to curate your response plan.

Attracting Predators to Kill Asian Citrus Psyllids

Question: Are there any plants that I could put in my garden to attract predators that will kill Asian citrus psyllids?

Answer: Anything that's flowering will provide an additional resource for predators to also operate on. So, basically predators, like humans, want a variety. They're not going to move in just for psyllids; they want a high population of insects that they can use as food. Usually flower resources are going to attract more insects in general because there are insects that will go in there and consume the pollen as an extra food source. If you Google insectory plants it should come up with, potentially different species of plants that could be used in different areas.

Question: So, you don't have anything specific?

Answer: No. Because that's going to vary greatly by what region you're in. I would suggest always going with native plants because native plants are going to have a more close relationship with the insect population where you live.

Question: So native flowering plants?

Answer: Yeah, that would be perfect. Perfect way to say that.

What to do if Asian Citrus Psyllids and Huanglongbing are Discovered

Question: Where can homeowners find information on what to do if Asian citrus psyllids or Huanglongbing are found in their yards?

Answer: UCANR provides all this information online and there's actually two things that can be accessed. So, one is this online web app where you can type in your address and find out how close you are to the nearest HLB find, that kind of provides some context for how urgent you need to be about controlling your psyllids in order to keep your tree. Secondarily there are homeowner options and recommendations that are provided there on that website.

Controlling Argentine Ants on Citrus Trees

Question: Why is it important to control Argentine ants on citrus trees?

Answer: It's important to control Argentine ants on citrus trees because they're mutualists with honeydew producing insects and Asian citrus psyllid does produce honeydew, so what happens is that the ant will come in and collect the honeydew and it will lay a trail down, so that all of the colony will follow that trail and know that this is a resource for them, this is a food source. So what happens is that while tending them and removing this honeydew, which is food for them, they'll also protect the psyllids. So, that protection means defending off biological control agents like Tamarixia wasps or discouraging predators from feeding on Asian citrus psyllids.

How to Get Rid of Ants on Citrus Trees

Question: How can I get rid of ants on my citrus tree?

Answer: Ants are pretty hard to get rid of. I know you have some experience with this. And anybody who's ever tried, it's hard. Especially with the Argentine ant because they're basically a super colony. So, what happens is that they're not going to be aggressive with nearby colonies, they all almost work together as one. So, the best thing to do to control ants is to try to control ants in your entire yard, because if you have ants at all, they're going to work together and find that citrus tree right? I don't think there's really a lot of effective tools on the market but you can try some cool stuff in your back yard. Tanglefoot is really the thing everybody recommends, but like any treatment that's not a chemical control it takes a lot of maintenance. So, you apply it and you have to make sure that, you know, say the ants didn't build a bridge over the sticky Tanglefoot, and now they're walking over some stick and defeating the whole purpose of it. So, it's going to take a lot of back yard experimentation until we have actually a good bait that will truly work.

Question: So you think Tanglefoot is the best for homeowners?

Answer: For protecting the tree specifically? Yeah.

It takes care of it right away.

Yeah, and I think it prevents them from trailing onto the tree. Where the bait station, I mean, that's good if they're going there and actually dying. But you have to make sure that bait is the most attractive thing in the yard. So, if there's anything else that's more attractive, they're going to still be streaming to the aphids on your roses. And if that's more attractive than the bait station then.

Question: So that's why they say to do it in March, right?

Answer: Yeah, so you want to get ahead of the seasonal things that are happening that are their food sources.

Organic Ant Baits

Question: I want to be strictly organic, can I use ant bait?

Answer: I think so. I think if you're using a boric acid based ant bait and it's not near what you're producing, which it doesn't necessarily have to be. Yeah. I don't understand why that would fall outside of organic.

Question: What are some good ant baits?

Answer: I really think boric acid based ant baits are probably the best option.

Approach for Large vs. Small Ant Infestation

Question: What would be the different approach for if you have just a few ants or if you have a huge infestation?

Answer: If you have a few ants, you could use one of those small bait stations that you would use in your house just to see how many you're capturing. If you have a ton of ants then you're going to want to start stacking techniques. So, you want your Tanglefoot and your bait station in that case.

How Many Bait Stations Needed to Control Ants

Question: Should I place a bait station next to every citrus tree, which could become expensive, or can I just put them in intervals in the yard?

Answer: I would definitely go with intervals. I don't think that you need bait stations next to every tree. However, I would look to see where the ants are trailing. So, if you have drip in your back yard, the ants love to walk along that drip, it gives them a structure, Argentine ants, anyway, it gives them a structure to follow. Putting your bait station next to where the ants are actually walking and accessing the trees is going to be ideal. Interval-wise you're just going to have to play around with that. I would start at whatever the edge is, and do maybe two or three depending on how many trees, maybe every third or fourth tree. But just play around and see what gives you the best control when it comes to placing bait stations.

How to Get Ants to Go to a Bait Station

Question: Someone deployed bait stations in the fall of 2017 and couldn't get the ants to go to the bait station. How can they get the ants to go to the bait station?

Answer: Like I said, the bait station is really context dependent. It's really about knowing what's going on. So, if you put out bait stations and you are not finding ants going to it, well, first of all, did you have ants in the first place? And how many of them did you have? Because they might be in your yard doing something completely different, or they may not be attracted to that particular bait station. So, that's why I think it's best to stack your techniques. So if you're putting the bait station out in order to control ants on citrus, well, combine that with a back-up where you can also have Tanglefoot. So, that will specifically protect the citrus tree. But, unless you really know your yard, and you know, oh, this rose bush over here always has aphids and I have scale on this bush over here. You never know what the ants are truly capitalizing on. So you would need to do some pretty intensive investigative research in your back yard to figure out what it is they are going to. But, the main takeaway is that if they're not going to the bait station, there's something else more attractive in your yard.

Question: So then let's say you're struggling to, like this person was trying to bait them in the fall, so then if they baited in the springtime before there are other attractive sources, would that be a more effective way?

Answer: Yeah, I think that's one way to address it. The thing is is, like I said, it's always gonna be context dependent and one of the most fun things that you can do is these little mini experiments in your back yard and say “Okay, didn't work in the fall, “well, we'll try again in the spring. “This time we'll combine it with Tanglefoot.” Maybe send a sample of your ants off to be identified. So, you want to know if it's the Argentine ant. That's going to be the most intensive of any ant species because they have huge numbers and no inter-colony aggression.

Scientific Research on Reducing the Spread of HLB

Question:  There's been so much research into ways to stop or slow the spread of Huanglongbing, for example dogs that can smell the bacteria and detect it early, ways to modify this psyllid by traditional breeding or other techniques so that it doesn't spread the disease. Is the solution close at hand?

Answer: I would say no, the solution is not close at hand, and the reason I say no is because despite the massive amount of research going on, any product or tool that's developed, I think most of them would need to go through a regulatory component. Even with the dogs, we still don't have the data generated to fully certify that that process is something that can be depended on. That's in the pipeline, like we know that the research for that is going to come through. But on the other hand, let's say, a grower could hire the dogs and have them smell out their fields, right? But from a regulatory side of that, just as an example, you know, the state might not use those dogs in order to retrieve, to pull infected trees out of people's yards. So, that's an example for that tool. But let's say you have a genetically modified psyllid or a genetically modified tree, that, you know, while that may become available, the regulatory hurdles to get that to market, whether that's the commercial market or the home-owner market is going to be an uphill battle. So, I think to call any of that close at hand would be giving you a false positive hope.

Funding

This article was funded by a grant from California’s Citrus Research Board.

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