The nation’s avocado supply is at risk. An invasive species has brought a fungus to Florida that has the potential to wipe out the avocado industry in that state and beyond. Increasing Human Potential recently talked with Dr. DeEtta Mills at Florida International University to learn how researchers are preparing to use UAS – and dogs – to stop the spread of laurel wilt in its tracks.
Could you explain what laurel wilt is and how it impacts avocado groves?
Dr. DeEtta Mills: Laurel wilt is a disease of laurel trees, including the avocado, which is caused by a fungus. The fungus is carried by an invasive beetle that came into the US in 2002 on untreated wooden packing material. The beetle bores into the laurel trees and actually plants and farms the fungus for food for itself and its brood of new beetles. These beetles then carry the fungus with them wherever they go in specialized sacs near the mouth, thus inoculating any tree they bore into for a nesting gallery. The tree’s response to the ‘invasion’ is to try to wall off the invaders. Since the fungus is established in the xylem, the vascular system, the tree produces compounds that plug up the vessels (similar to plaques in our blood vessels). Since these vessels are necessary to carry water and nutrients from the roots to all parts of the tree, the tree succumbs to its own response when it plugs up too many of the vessels.
The first outwardly signs of the disease that are visible are usually the leaves in the crown of the tree wilting because they are not receiving water and nutrients. Only one beetle boring into a tree is enough to cause the disease and the eventual death of the tree in 4-8 weeks. Since avocado trees are members of the family of laurel trees, the beetle is attracted to them as well as the wild swamp bays and other members of the tree family.
Left unchecked, what would it do to the nation’s avocado supply?
The disease has impacted millions of wild laurels along the southeast coastline of the United States already and now that most of the wild laurels are dead, the beetle has jumped over into the avocado groves in southern Florida. Over 1% of the avocado trees in southern Florida have been killed by this disease so far and the spread has not been contained to date. Left unchecked, it has the potential to wipe out the avocado industry – the 2nd largest fruit industry in Florida – in the state.
The disease and beetle have been found as far west as Mississippi since its introduction and, if the spread is not stopped, it could impact the avocado industry in California – approximately 10 times the economic impact of the southern Florida industry – and move into Mexico, the largest producer of avocados in North America – 100 times the value of what the southern Florida industry produces.
Florida International University and the University of Florida have teamed up in the battle against the laurel wilt. Can you tell us about your research?
The University of Florida has been at the forefront of this fight since it was discovered. Florida International University has now joined the fight by providing a method to try to detect the disease before the visible signs are apparent — early detection to contain the spread. We are doing that using canines and UAS. The canines have been trained on the ‘scent’ of the disease, just as you would train them on explosives or drugs…imprinting and scent association. They are rewarded with their favorite toy when they indicate a positive alert — to them it is all about getting to play with their favorite toy!
The UAS will come into play, once we have an exemption to fly, by first flying over the 7,400 acres of groves and pinpointing areas of apparent infection and/or trees that are stressed. Stress can be something other than the laurel wilt disease, such as lightning strikes, poor irrigation, other disease, fruit load before harvest, etc.
We will use multi-spectral camera platforms to take images that can later be processed and can possibly identify changes in spectral output. Due to changes in chlorophyll content because of stress, as the tree puts energy towards fighting the disease, it produces fewer chloroplasts, thus less chlorophyll. That subtle color change can be picked up and, using imaging processing software, can distinguish stressed trees from healthy ones. That can be used to focus the deployment of the canines into suspect hot spots and not have to deploy them to every grove.
The canines have been successful to date in identifying non-symptomatic trees that have been verified as being infected either by using DNA tests for the presence of the fungus or seeing visible signs several weeks later of wilt. The goal is to be able to identify the newly infected trees so we can remove that infected tree before (a) the fungus moves through the roots to the adjacent trees (i.e., root grafting) and (b) newly hatched beetles with the fungus in their specialized sacs move out of the natal tree and they find new trees to infect.
Could you describe how dogs work together with the UAS? What is the process when you test a grove?
The process would be to fly the UAS with the cameras, take images and then through processing identify stressed trees. Once the hot spot has been identified, the canines can be deployed and will only alert on trees that have the disease, not on trees that are stressed for other reasons mentioned above.
Since the current sanitation of diseased groves is to remove the visibly infected tree plus two rings of trees around it (due to root grafting and fungal infection spreading to neighboring trees), if early detection of non-symptomatic trees is possible, then that one tree can be removed and the surrounding trees immediately infused with a fungicide that will suppress the growth of the fungus and not leave any toxic residue in the fruit. Thus, earlier detection saves trees and helps contain the spread of the disease via root grafting.
How did the unlikely pairing of UAS and dogs come about?
Two of my colleagues and I were talking about the news of the new disease one day. We all have different areas of expertise, (mine is microbiology, Dr. Ken Furton is olfaction and canine olfaction in particular, and Dr. Jennifer Gebelein has expertise in remote sensing and image processing. Since UAS were in the news and had been used on a project that Dr Gebelein was associated with in Costa Rica, we wanted to combine these three fields of expertise into an early detection program that could help contain the spread of the disease.
How have UAS helped in your efforts to stop the laurel wilt from spreading to healthy avocado trees?
To date, we haven’t been able to use the UAS as the Section 333 exemption request has not been approved, but once it is, it will dramatically increase the acreage that we can cover with monitoring, spectral analyses, and more precise deployment of the canines.
What benefits does the UAS have over other technologies in doing this work?
To date, some work on spectral imaging has been done with helicopters. The UAS, however, would be less expensive to deploy, allow for more flights per month (e.g., weekly versus the monthly flights by helicopters) and overall [is safer for] pilots. Some of these groves are located under power lines, etc. so the UAS is a better safety option than helicopters. Plus, we need to be between 50-150 feet above the groves to get meaningful spectral images and that is not safe or in some cases possible with the helicopter.
Do you have any exciting plans for using UAS in future research?
I think the use of UAS will expand and simplify agricultural monitoring for diseases and will be a major tool in containing of agricultural diseases and invasive species once they have spread into the U.S. environment.
As UAS technology continues to develop, do you foresee it being used by researchers in the future?
Most definitely! I have several colleagues that are working in remote areas of the Everglades, and other field sites, that would benefit tremendously with the use of UAS in research. And as I mentioned before, this is a huge tool for agriculture, whether it is flying across huge wheat fields to find disease or areas that are not receiving adequate irrigation, to being able to inventory huge nurseries and even monitor those nurseries for diseases and pests before they are shipped across the US or abroad. The UAS will be an indispensable tool for so many different projects.