One of the many benefits of living in Santa Barbara County is the ability to grow citrus trees in your backyard.

There is nothing like making fresh-squeezed orange juice (or a margarita for that matter) with homegrown citrus.

Now citrus growers can use a common ornamental flower — the alyssum — to help keep their citrus trees safe from a devastating citrus disease, Huanglongbing (HLB), which is getting worryingly close to Santa Barbara County.

How can a pretty, small flower help prevent a devastating disease? It’s a bit of a long story so let’s start from the beginning.

What Is HLB?

All citrus growers, both backyard and commercial, in Southern California are dealing with a threat to their beloved trees from HLB.

The intruder is a bacterial infection of citrus trees and, once a tree is infected, fruit quality and yield will deteriorate, and most trees will die within a few years.

There is no cure. It is one of the most — if not the — most destructive citrus diseases in the world.

The Florida citrus industry has been decimated by HLB. In the last 20 years, Florida citrus production has declined from nearly 300 million boxes in the 2003-2004 season to under 20 million boxes in the 2022-2023 season.

The Agriculture Department’s Animal and Plant Health Inspection Service estimated in 2022 that HLB has reduced Florida citrus production by 75% and more than doubled production costs.

Last year, HLB was detected in residential citrus trees in Ventura County, which is a concern for all Santa Barbara County citrus growers — particularly us commercial growers.

Since the first detection last year, 73 citrus trees (all residential trees) have tested positive for HLB in Ventura County.

Once a tree tests positive, the State of California will remove the tree right down to the roots. Boom. Gone.

The state will also begin an intensive twofold program of pesticide treatment and HLB testing of citrus trees of properties neighboring the positive HLB find.

How Does HLB Spread?

HLB is transmitted from tree to tree through the vector of the Asian Citrus Psyllid, or ACP. The ACP is a tiny insect about the size of an aphid.

If we can effectively control the populations of ACP in our area, we can hopefully prevent the spread of HLB.

Within the last six or seven years, many of you backyard citrus growers would have had the experience of getting a letter in the mail or a knock on the door from the California Department of Food of Agriculture requesting permission to treat your citrus trees with pesticides to keep ACP at bay in the community.

The backyard treatment program was stopped in 2023. Now funds have been redirected toward detection of HLB-positive trees and growing and releasing a predatory wasp (tamarixia radiata) as a biological control.

Not to worry, the tamarixia wasp cannot sting you.

The CDFA has been releasing tamarixia regularly in residential areas around Santa Barbara County since 2021 to help control ACP.

Since the program started, CDFA’s data suggests ACP numbers have been declining in areas where tamarixia have been released on a regular basis.

Hoverfly to the Rescue

Researchers at UC Riverside wanted to get a better understanding of the effectiveness of tamarixia in controlling ACP in the field. They set up several very sensitive cameras focused on citrus trees to capture the tamarixia in action.

What the UCR researchers found shocked them in a good way. The research team found that tamarixia were indeed targeting the ACP, but they also found that more than 60% of the ACP predation was being done by a native insect: the hoverfly. Or, to be more accurate, the larvae of the hoverfly.

It turns out that the hoverfly larvae were by far the most prolific biocontrol for the ACP.

Alyssum and hoverflies

The UCR researchers found that adult hoverflies do not have a lot of food sources in citrus orchards so hoverfly populations in citrus orchards tend to be low without intervention.

As a result, the UCR team began looking at ways to attract hoverfly populations into citrus orchards. They found that flowering plants like alyssum, buckwheat and even California poppies attract adult hoverflies.

But if you had to pick one, adult hoverfly populations were highest when alyssum was present and, through experiments, UCR researchers found the presence of alyssum near citrus significantly increases mortality of ACP nymphs by hoverfly larvae.

Calling All Citrus Growers

As a South Coast commercial lemon grower, the presence of HLB only 40-50 miles away as the hawk flies keeps me up at night.

When commercial citrus growers scout for ACP, they normally find the highest populations of ACP where the commercial citrus groves border residential areas. So, controlling ACP in backyard citrus trees is pretty important to the overall ACP management strategy. 

Santa Barbara County — and the Goleta Valley, in particular — has a long and proud history of citrus growing.

The first commercial lemon groves were planted by my great-great grandfather, Sherman Stow, in 1875 at La Patera Ranch.

In honor of the Goleta Valley’s lemon heritage, the Santa Barbara South Coast Chamber of Commerce still holds the Goleta Lemon Festival each September.

For my part, I want to do as much as possible to prevent HLB from moving in Santa Barbara County and our lemon groves at La Patera Ranch.

Friends with backyard citrus trees often ask me, “What can I do to prevent ACP on my trees?”

Well, you can plant alyssum. It appears to be the most effective way to attract the ACP’s No. 1 enemy, the hoverfly.

You are not only protecting your ability to make homemade margaritas for years to come, but you are also helping out us local lemon growers in Santa Barbara County.

How You Can Help

Other tips for managing ACP in your backyard trees:

• Manage ant populations, especially near your backyard citrus trees. Argentine ants feed on the white honey dew that ACP nymphs excrete. Ants attack any potential natural predators to the ACP nymphs so they can keep up their honey dew diet. Controlling ant populations helps ACP’s natural enemies do their job.
• Regularly scout for ACP. ACP like to lay their eggs on the new, tender flush (new leaves and shoots) of citrus trees. Look for the little orange eggs or little orange nymphs on the new leaves and shoots. Adults are a bit harder to find.
• Spray trees if you detect ACP. Garden centers sell organic and inorganic pesticide sprays especially designed for citrus trees. Look for pesticides that are especially designed for controlling ACP.