When I spotted state agriculture agents on our street I knew something was wrong. It turns out that a specimen of the dreaded Asian citrus psylid showed up in our neighborhood. The Asian citrus psylid is not a problem in itself, but carries an incurable bacterial disease called huanglongbing (HLB). HLB, first reported in Asia in 1919, renders citrus fruit inedible and eventually kills the tree. Parts of Africa, Asia and South America are infected with HLB and in some regions of Brazil the disease is so bad that they’ve given up growing citrus altogether. HLB is in Florida and is adding to a nightmarish collection of other diseases afflicting citrus in the Sunshine State. Now California growers are panicking with the appearance of the psylid.
So far the psylids found in California do not carry HLB. However, according to an article in the Journal of Plant Pathology (pdf), HLB inevitably follows the citrus psylid within a few years. In several ways HLB resembles Pierce’s disease which has killed most of my grape vines and basically made growing table or wine grapes in Southern California impossible without copious pesticide application. Both diseases are bacterial and both are spread by phloem sucking insects. The pesticides used to control the Asian Citrus Psyllid and the Glassy Winged Sharpshooter (the insect that spreads Pierce’s disease) are also the same, and include a ground application of imidacloprid, marketed under the brand name Merit and manufactured by Bayer Environmental Science. State agricultural officials that I spoke with at an informational meeting on Wednesday in Echo Park hope that applications of imidacloprid and pyrethroids will slow the progress of the psylid and, “buy some time”, as they put it, to come up with a strategy to deal with the possible appearance of HLB. California agriculture officials hope that their proactive approach combined with lessons learned from missteps in psylid control in Florida and the rest of the world will slow the progress of the insect and minimize the damage of an emergence of HLB in California.
Compliance with the residential pesticide application program is voluntary. State agriculture officials will knock on the doors of residents in three areas in Los Angeles where the psylid has appeared to ask for permission for a foliar application of pyrethroid and a ground application of imidacloprid to any citrus trees a homeowner might own.
While I understand the gravity of the situation–we really are looking at the possible end of citrus in California if HLB gets a foothold–the use of imidacloprid gives me cause for concern. Imidaclopred is highly toxic to honey bees and has been banned in several European countries for its likely connection to colony collapse disorder. When I told an employee of the Department of Pesticide Regulation at the meeting on Wednesday that people in my neighborhood keep bees he paused and said, “you’ve got a problem.” Another official said to me that our bees (and presumably other pollinators in the neighborhood) will be sacrificed for the greater good of preserving the state’s citrus industry.
As with Pierce’s disease the best long term solution to this problem will be to breed trees resistant to HLB. This is easier said than done as, unlike Pierce’s disease and grapes, no HLB resistant citrus cultivars have been found. It may be that the only way to breed for resistance soon enough to head off the HLB will be through the development of transgenes with antimicrobial properties. This approach is already being funded by the USDA and the citrus industry.
As a backyard gardener and rabble rousing blogger, I could lose a lot of sleep pondering all the thorny questions this crisis brings up. Are there situations where genetic modification is warranted, or do antimicrobial transgenes pose unintended consequences? Will localized applications of imidacloprid kill our pollinators in significant numbers or will strategic applications head off more widespread use later on if nothing is done? What are my responsibilities as a backyard gardener to large scale growers? Do the benefits of international trade outweigh the inevitable appearance of invasive species? Should we close the downtown flower markets and produce distribution warehouses where state entomologists suspect the psylids might have come from?
Rather than try to answer the unanswerable, I’m going back to two of my favorite books books that don’t have anything to do with plants. Nassim Nicholas Taleb’s The Black Swan: The Impact of the Highly Improbable, a meditation on the logical fallacies of economists and Seneca’s Letters from a Stoic have all the strategic wisdom a gardener needs. Seneca would say, do what is in your power to do and don’t worry about what you can’t fix. Taleb would advice always maximizing upside potential while minimizing exposure to the downside. My unsentimental conclusion: don’t try to grow citrus. If I had a mature tree I’d leave it in place and rip it out at the first sign of HLB. Despite the state’s offer to replace any HLB infected tree with a free citrus tree I wouldn’t take them up on the offer. In our case we have three small, immature citrus trees that are already chewed up by citrus leafminers. I’m pondering pulling them up and replacing them with fruit trees unrelated to citrus. This follows our stoic, get tough policy in the garden. Planting a tree entails a considerable investment in time. It can take years to get fruit. Why not plant pomegranate instead and let other people worry about citrus diseases? If a pomegranate disease shows up, rip it up and plant something else. Following this approach will eliminate habitat for the psylid and negate the need for pesticides.
The first consideration with any domestic plant or animal should be choosing species with robust immune systems and then following that up with an objective selection process. This is an approach that mimics one of the fundamental laws of evolution: survival of the fittest. True, there is often a trade off between the flavor and yield of a fruit and strength of its natural defenses. Oranges are juicier and easier to peal than the spiny and seed filled fruit of the prickly pear cactus. But the long term odds of having a reliable supply of prickly pear fruit are a lot higher than a steady flow of orange juice. I may get a few spines in my fingers, but it will be the citrus farmers who will be losing sleep. As Seneca says, “If you shape your life according to nature, you will never be poor; if according to people’s opinions, you will never be rich.”
View a video on how to recognize Asian citrus psylids here.