Yesterday, I attended a citrus pest management field day at Rancho Guejito put on by the University of California. The focus was on the disease Huanglongbing (HLB) and ants. I’ve attended many similar lectures and research updates on these topics over the past decade, but this one was different. For one, it was meant for citrus farmers instead of gardeners. But most importantly, the tone of the speakers had changed.
I thought you might enjoy and benefit from my relating just a few highlights.
“I’m an epidemiologist . . . but personally, I’d be more worried about water than HLB if I were growing citrus in California,” said Neil McRoberts, Associate Professor of Plant Pathology at UC Davis. This was the first change in tone that I’d heard from a UC researcher on this subject in ten years.
Until yesterday, all I had heard from them or the California Department of Food and Agriculture was the impending doom, the total destruction that HLB was soon going to cause to all of California’s citrus trees. (Their public service announcement is titled, “What if California Citrus Disappeared?”)
Why the optimism (about HLB, not water) from McRoberts?
Pause. Do you know what HLB is? It’s a disease said to be caused by bacteria and which ultimately kills citrus trees. There’s no known cure. HLB has been found in some citrus trees in Southern California in a few locations. (You can learn more about it at the Citrus Threat website.)
HLB has caused a lot of damage to citrus trees in Florida. When it was first detected in a tree in California in 2012, it was feared that it would spread and cause similar damage. It has not.
“I’m more optimistic now than five years ago,” said McRoberts. “Definitely more than ten years ago.”
Why the optimism? He’s learned that the bacteria (Candidatus Liberibacter asiaticus, or CLas for short) that is believed to cause the disease as well as the insect that carries the disease from tree to tree find it harder to live in California than in Florida. McRoberts said that he can see after ten years of observation and testing that both the bacteria and the insect are not proliferating here as they do in Florida, and he thinks it’s mainly due to climate. California’s colder winters and hotter summers slow down the reproduction of the insects and sometimes kill them.
Asian citrus psyllid (ACP)
The insect that carries the bacteria from tree to tree is called the Asian citrus psyllid or ACP for short. (In the photo above, some ACP are on the leaves of a citrus tree in my yard.) It is the great enemy, for it vectors the disease-causing bacteria. I remember attending a lecture back in 2018 where a UC researcher recommended regularly spraying all citrus trees with insecticides to kill ACP or else putting them under a net structure to exclude the insects.
But Mark Hoddle, Entomology and Extension Specialist at UC Riverside, presented at yesterday’s field day about his work on “biocontrol.” That means he tried to find other insects that might eat the ACP. He travelled to Pakistan and brought back a wasp that ate ACP there. He released those wasps, called Tamarixia radiata, here in California in 2011.
He found that the wasps did eat the ACP (directly and through parasitizing them): success. But more recently he has found that other insects that we already have here in California also eat ACP. Hoverflies and lacewings eat many ACP, he found. Specifically, it is the larval forms of these insects that eat the nymph forms of the ACP, and they do so at night.
“Natural enemies have killed more ACP than any other control measures!” said Hoddle. By control measures, he’s referring to spraying pesticides, among other things.
How to have these natural enemies working near your citrus trees? “Put out some flowers and they will come,” he said. He’s found that allysum is an especially attractive flower for hoverflies. (I’ll add that I’ve found that cilantro is loved by hoverflies.)
See photos and read details about the biocontrol of ACP in Hoddle’s recent article for the Topics in Subtropics newsletter, “Natural enemies have significantly suppressed Asian citrus psyllid populations in
Hoverflies and lacewings and Tamarixia wasps have a hard time eating ACP however, if there are a lot of ants around. Specifically, we’re talking about Argentine ants, the little black ones that invade your house in the summer and your garden too. They are said to have arrived in California from Argentina around 1907, and they have a special relationship with ACP and other insects that feed on citrus leaves such as mealybugs (photos and details here).
Ivan Milosavljevic, a Project Scientist in the Hoddle Laboratory at UC Riverside, presented at the field day about ant control and the ants’ relationship with ACP. The ACP suck the sap from citrus leaves, which is sweet. They don’t digest all the sweet sap so they poop some out. This sugary excretion is called honeydew, and it is food for the ants. The ants eat the honeydew, and they also protect the ACP. They’re protecting their food.
It was found that when many ants were on a citrus tree, less than 12% of the ACP would be eaten (parasitized) by Tamarixia wasps. But if the ant numbers were reduced, over 90% of the ACP would be eaten. In other words, get rid of the ants and the natural enemies will get rid of the ACP.
But how to get rid of the ants? I asked Milosavljevic if there are any natural enemies of Argentine ants. How convenient if we could bring in some insect or animal that feeds on ants, or maybe we already have one in California that we can promote. Alas, he didn’t know of any ant predators. We are left with only poisons at this time.
At present there are no effective, safe, and cheap poisons for Argentine ants that you can buy. I’ve used KM AntPro bait stations in my yard for a few years, as have the researchers at UCR in citrus groves throughout the state. The KM AntPro bait stations are effective, and they seem safe, but they are expensive. They also require a lot of maintenance.
So the UCR researchers have been developing their own ant control method using hydrogel beads. These beads are made of algae and are soaked in sucrose (for bait) and a little poison. The hydrogel beads have been very effective so far, they say, and it appears that only the ants are attracted to them so they seem safe, and they’re cheap to make as well. They even biodegrade right there on the soil under a tree.
See photos and read details about the hydrogel beads in Milosavljevic’s article in the recent Topics in Subtropics newsletter, “Synergizing IPM of Argentine ant and biocontrol of sap sucking pests with
biodegradable hydrogels, infra-red sensors, and cover crops in commercial citrus
I left the field day hopeful overall about ACP and HLB and grateful for the work of these researchers. Natural enemies can control ACP, and HLB is turning out to be far less dangerous in California compared to Florida in part because of our climate — although McRoberts noted that this news shouldn’t make us complacent.
I like the innovation of using hydrogel beads to kill ants too. I might even experiment with making some in my garage, as there are no companies yet making them available for purchase.
However, poisoning the ants isn’t totally satisfactory for me, even if the poison is effective, cheap, and appears to be safe. Pesticides always lead to resistance and the need for more and new pesticides, and often, safety problems appear over time.
Earlier this year, chlorpyrifos, the pesticide that was sprayed on fields of citrus trees to kill ants for dozens of years was banned. Chlorpyrifos had long been linked to brain damage in children, among other maladies. (See the EPA announcement on the chlorpyrifos ban here.)
Ants are problematic for our citrus trees, but I’m hoping to attend a field day in the future where UC researchers announce that they’ve found an even better way of dealing with them.
Thank you for your support of The Yard Posts so I can keep them coming and never run ads! Here’s how to SUPPORT
All of my Yard Posts are listed HERE
It seems more likely that the nymph forms would eat the larval forms of ACP.
My favorite nursery, Maddock in Fallbrook, stopped selling citrus entirely 9 months ago due to the encroachment of the HLB in Oceanside/Vista causing a quarantine. The Home Depot in Oceanside also destroyed all their Citrus stock. So while HLB may not be as prolific in SoCal as it is in Florida, it’s already impacting us here in SD County in a negative way. Quarantines are also helping slow the spread but I do sure hope we find good natural remedies like the folks at the Field Day discussed.
I have about 30 different citrus trees and I keep a close eye on them for any signs of HLB. It would suck big time to lose that part of my grove.
in my yard the fence swifts eat ants. it seems like the poisoned ants might harm or kill the lizards. do you see the lizards in your yard?
I have many lizards in my yard, but I’ve never seen them eat the Argentine ants. I’ll pay close attention to that.
Great post. You gave me another reason to spray down my citrus trees with water: help prevent HLB! When I see ants active or I see any soft bodied pests on my 4 trees, I form berm around each tree, set the nozzle to “flat” and blast the leaves trying to get underside and into tree. Then set nozzle to “shower” and fill berm with water. These steps disrupt the ants and knocks out the ants establishing/tending scale, white fly or mealy bugs. Additionally this gets the dust off leaves to improve photosynthesis. See ya, Robert
I mix dry detergent soap with grandulated sugar. no more ants around the house.
I use a product called “Tanglefoot” to control ants on my Citrus. I spread a band around the trunk. I also make sure that the ants don’t have any other means of getting on the trees by pruning any branches or leaves that may touch other plants or the ground. This works very good for me.
nice post, so many ants right now in our neck of the woods!
Greg, this is good news/bad news post that gave me hope and inspires me to renew my efforts to “feed” my ants. I mix borax, sweetener (honey, sugar, etc.) with water and put bait stations around the house, admittedly with barely noticeable effect. Inside, soapy water deters them as well as anything and I suspect using the same as a spray outside might drown them as well. Since misery loves company, I’m gratified to learn I’m not alone in my battle against the ants.
Timely post! I’ve had a lot of success with Terro ant bait. According to the label and website, it is made of sugar, water and borax which seems like it would not be toxic to humans. The only negative (if any) is that I need to keep replacing the little modules until all the ants are gone and also make sure that they aren’t in a place where any sprinkler or watering mechanism will send water inside and thus melt/dissolve the sugar/water/borax solution. Curious if anyone else on here uses this ant bait for their backyard garden.
For a couple of years have used the Terro liquid Borax baits in the house – I find the ants don’t go in, so I pour a few drops 2-3 places along their trails, then push many ants into the puddles. They drink up, bring lots of buddies, share it around back at the nest, and within 36 hrs there are no more ants, the colony is dead,and they have even carried away the dead ones.
I have used Terro the same way on trees, but it is more labor intensive, so for many yrs I have used fine powdered diatomaceous earth(Garden Safe Crawling Insect Killer). It is made from the “sediment of fossilized algae.. that were high in silica dioxide”, which is the active ingredient, which is micro-razor sharp, and cuts their body tissues – keep it away from eyes and lungs. I pour about 1/4 c around the base and trunk of the tree, and again, 36 hrs later, all gone; you can hose it into the earth, and then the area is safe for pets again.
Greg, looking forward to your comments on this stuff…
What kind of maintenance do the KM AntPro bait stations require? I’ve been considering them but they’re expensive and ants seem like a losing battle.
The KM AntPro bait stations need refilling from time to time — frequently in the summer. They also sometimes get cockeyed and leak so you need to check them for that.
If you have a small yard, you could probably reduce the ant population a lot with around five stations. I have eight stations spread out around a half acre of my yard and it isn’t anywhere near enough. I heard the UC guys say that they use at least 20 stations per acre in a citrus grove.
As always very interesting post. Thanks to your photo I can now see how small the ACP is and what to look for on mine citrus trees.
Argentine ants are big problem in my yard and i have to be vigilant especially for scales and aphids from early spring all the way to fall. I’m using formula 100/10/1 water, sugar and boric acid in the bait trays with cotton makeup pads that soak up the solution. I keep cleaning the trays every couple of days and shade the trays from the sun. So far i was only able to reduce the ant numbers but no complete elimination. Same results inside the house. Perhaps i might need to increase the boric acid to something like 1.2 to 1.5%
On a different note out of citrus psyllid scope.
I would like to purchase couple of avocado trees on clonal rootstock (Dusa) from Brokaw wholesale nursery. Their minimum order is 20 plants. If anyone would be interested to get included in the purchase and reserve trees please let me know.
I lost couple of avocado trees to Phytopthora Cinamomi root rot and cannot take chance on regular rootstock and lose the tree in a few years again even thought I have solarized soil from the infected beds.
Trees available are Lamb Hass, Reed, Fuerte, Bacon, Edranol. Some are on Toro canyon and Duke7 rootstock.
Great post Greg! Makes me much more hopeful. Argentine Ants are a never ending problem, though. 25 years ago, we used to broadcast the entire yard outside of our tiny rented house in Mira Mesa with diazinon and water it in. Smelled awful and I had to keep my kids and pets inside for at least a week. But it seemed to keep the ants away for about a year. But of course diazinon is no more.
Now we are in 4S Ranch on 1/4 acre. The worst ant invasion was in 2007 after we returned from a week-long evacuation due to the fires and the ants had invaded inside seeking shelter. There were 3-4 inch wide streams of marching soldiers in several areas (not an exaggeration). The worst was one trail that went up the wall along the stairs. It was bad enough that we hired an exterminator. But after 3 months of calling them out again and again, the ants were as bad as ever. What finally worked was buying a range of non-repellant products from an online diy pest control place, with different active ingredients. One was a spray for the foundation up to about 1 foot on the wall, plus various granular baits and gels. Fipronil, imidacloprid and abamectin were some of the actives. All applied outside. Over the spring and into summer, it got rid of >90% of the ants outside and I haven’t seen any inside in 15 years – without using any insecticide indoors. Now when we see them outside, we rotate the pesticide baits until the ant levels are tolerable. We must have some super species, though, because borax-based baits do absolutely nothing.