HOMESTEAD, Fla. — There is no shortage of interest or appetite for guacamole. When you consider the endless variety of recipes for dishes and dips that you can dig into, coupled with an annual designation of September 16 as National Guacamole Day, you might consider chanting “Viva la Guac.”
Sadly, the guacamole needs some help these days. A team of researchers at University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) have been at ground zero of a pest problem that is endangering the sustainability of guacamole’s key ingredient in South Florida– the avocado.
Laurel wilt disease (LWD) is an invasive, lethal disease in the southeastern United States spread by a fungus transmitted by the ambrosia beetle. The disease wilts and then browns tree leaves, killing entire trees in only a few weeks. Since 2003, it has killed millions of native forest trees and has impacted commercial avocado production in South Florida, said Jonathan Crane, a UF/IFAS professor of horticultural sciences and Extension tropical fruit specialist stationed at UF/IFAS Tropical Research and Education Center (TREC) in Homestead.
Given the destructive nature of this disease, there have been major concerns over the future of the Florida avocado industry, which provides an annual economic impact of nearly $100 million (USD), adds Edward “Gilly” Evans, a UF/IFAS professor of food and resource economics and director of TREC. Since 2012, the disease has been directly and indirectly responsible for the death and destruction of more than 120,000 trees which is the equivalent loss of about 16.5 million pounds of potential guacamole.
There are more than 500 registered commercial avocado producers operating on about 6,250 acres with the bulk (close to 99%) of the production occurring in Miami-Dade County (USDA, 2007). The industry is valued at $21 million with an economic impact of $100 million. Roughly 65 percent of the crop is sold outside of the state.
Regardless, help is on the way.
The IFAS Tropical research and Education Center, which celebrates its 90th anniversary this year, has been at the forefront of the research to find pest management and eradication methods for the disease. An area wide management program centered on early detection and destruction of affected tress has slowed down the spread of the disease as research continues.
Research results indicate that the benefits of the program far exceed the costs. The program has played a significant role in minimizing the rate of spread, thus providing time for scientists working around the clock to continue their effort towards developing a more cost-effective treatment, added Evans.
“A cost benefit analysis shows that our modeling of the disease spread at that time and indicates that in a ‘do nothing situation,’ meaning if growers did not adopt some aspects of our recommendation in about five years, the industry would become nonexistent,” he said.
In the meantime, UF/IFAS scientists at TREC and throughout the state are committed to developing ongoing integrated pest management practices to protect the valuable commercial crop industry that is valued at $100 million a year to producers who are mostly in Miami Dade County.
Daniel Carrillo, assistant professor of entomology and nematology and his biological scientist, Rita Duncan, conducted work at TREC for avocado growers that compares an integrated pest management system involving common chemical pesticides and entomopathogenic fungus, or Beauveria bassiana. Entomopathogenic fungi infect and kill only insects, and so pose no harmful threat to humans, non-insect wildlife, or plants. The fungus not only kills the ambrosia beetles that carry the disease-causing pathogen, but also inhibit the pest’s ability to bore into the wood where it can spread the plant pathogen.
Another new tactic to manage healthy and productive avocado trees involves growers maintaining healthier soils and even considering adjusting the pH in their groves. Because the fungus that causes laurel wilt is halophilic, it shows a dramatic decrease in growth at high pH values, and this could help in reducing persistence of the pathogen in soils, although effects on beetle-vectored transmission are likely to be minimal.
Florida has a rich history with the Guacamole’s main ingredient. The Florida avocado industry is the state’s third-largest fruit industry behind citrus and blueberry. The first varieties in the United States date back to Florida in the 1800s as reported in a UF/IFAS Electronic Data Information Source (EDIS) publication.
“When we think of diseases that we have yet to find a cure for, we have learned that steps are taken to manage the disease. We continue to learn more about the pathogen each day and are drawing closer to a solution,” said Evans. “While as scientists we are not happy with the fact that we have yet come up with a cure for the LWD, the truth is that without our recommendations and research that we do have, the Florida Avocado Industry would be history”
Little known Florida facts about guac’s main ingredient
- The first recorded importation of the avocado into Florida was in 1833.” Henry Perrine is credited with introducing the avocado to Florida in 1833. (California wasn’t introduced to the fruit until 1856). It is believed that this was the first domestic avocado planting in the US. The effort of growers in Miami Dade led to the establishment of University of Florida/IFAS Tropical Research and Education Center (TREC), then called the Sub-Tropical Experiment Station in 1929. It made way for scientists at UF to conduct research that would enhance and solve agricultural challenges related to production problems of tropical crops like avocadoes, mangoes, and citrus.
- The first avocado planting at UF/IFAS Tropical Research and Education Center was 10 seedling trees in 1932. From that time on, additional seedlings, seedling selections, and cultivars were planted at TREC. This continues to the present, currently the Center has about 78 avocado cultivars in its collection.
- In Florida, there are over 600 varieties of avocados while worldwide there are more than 2,000 cultivars.
- Avocado fruit do not ripen on the tree, they must be picked when mature (horticulturaly mature i.e., able to ripen off the tree) and then allowed to ripen. Commercially, fruit are picked when horticulturaly mature, then washed, sorted, packed, and stored at cool temperatures, shipped, then bought at the market. Fruit bought at the market should be placed at room temperature to ripen, then refrigerated. Placing your avocados in a paper bag with a ripening banana or apple will help to speed the ripening of the avocado because bananas and apples emit ethylene—the natural plant hormone that induces ripening.
- The United States (US) is the tenth largest producer of avocados worldwide, following Mexico, Dominican Republic, Peru, Indonesia, Colombia, Brazil, Kenya, Venezuela, and Chile (FAOSTAT, 2018). Total US production for 2017 was about 133 thousand tons valued at about $392 million. There are two main commercial avocado regions in the US, namely southern Florida and southern California. While production in California is based largely on the Guatemalan and Mexican races of avocados, the Hass variety, production in Florida is based primarily on the West Indies varieties. Florida is the only area of the continental US where West Indian and Guatemalan-West Indian cultivars can be grown commercially; thus, to a certain extent, the two regions complement each other.