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Florida's avocado industry faces major threat from fungal disease

by Christina DiMartino | August 05, 2009
Samples taken from an avocado tree in Florida in late July confirmed that the tree has laurel wilt, a fungal disease that is carried and spread by the ambrosia beetle. The state now finds itself in yet another battle to save a valuable commercial crop.

"The beetle was discovered in Martin and Okeechobee counties in the spring, so it has been on our radar," said Adrian Hunsburger, entomologist and urban horticulture agent for the University of Florida, Miami-Dade County Extension, in Homestead, FL. "We are ramping up efforts to get word to homeowners who have avocado trees in their yards. The commercial avocado industry in the state is on alert, and they have all known information at their disposal."

According to the Florida Department of Agriculture & Consumer Services, approximately 60,000 homes in south Florida have at least one avocado tree in their backyard.

Unfortunately, all the information in the world won't help avocado grove owners stop or slow down the insect and the fungus it carries, at least not until there is a scientific research breakthrough. There is no known deterrent for either killing the beetle or correcting the fungus once it is inside a tree. The first discovery of the ambrosia beetle in the United States was in South Carolina in 2004. Native to Asia, it is believed to have arrived on shipping pallets or other imported wood materials.

Brooks Tropicals LLC, headquartered in Homestead, FL, is a leading producer of Florida avocados that are marketed under the "SlimCado" brand. The company is closely tuned in to the insect's activity, but it wasn't until November 2008 that the fungus damage to trees in the laurel family became known.

"News reached us that Redbay trees, which are in the same family as avocado trees, had laurel wilt," said Mary Ostlund, marketing director for Brooks Tropicals. "We stayed on alert, but there was minimal initial concern for south Florida's avocado groves because the beetle migrates only about 20 miles a year. We thought it would take decades to reach us, so it's apparent that it had some transportation help, probably on firewood, wood pallets or live plant materials."

The beetle carries laurel wilt in its mouth, deposits it in trees and uses the fungus to feed its young. The disease does its damage quickly, suffocating the tree's vascular system by blocking nutrients and moisture from the soil. The initial visual signs of the disease are browning leaves at the tree's crown. "This is an insect that moves inside the tree's wood, so it is much more complicated to control," said Ms. Hunsburger. "Pesticides and fungicides cannot be used on edible crops, so we are researching other options."

As soon as Brooks Tropicals realized the impact laurel wilt could have on avocado trees, it went to work with the University of Florida and Miami and Dade counties to secure research funds.

"We were able to get $1.9 million through the university," said Ms. Ostlund. "Research began in earnest early this year. The disease will not affect the 2010 Florida avocado crop, but it certainly has the potential to cause serious damage in the future."

International free and fair trade has caused tremendous change in the landscape of the produce industry. But like all things, it has its upside as well as its downside. It may not be possible to prevent imported diseases like laurel wilt, citrus canker and greening, or damaging insects such as fruit flies, weevils, worms and maggots, from infiltrating the nation's produce crops. Companies like Brooks Tropicals are left to measure and weigh every possible solution to the dilemma.

"Green-skin avocados such as the 'SlimCado' grow well only under certain environmental conditions," said Ms. Ostlund. "This variety can grow in the Dominican Republic, but avocados are fragile in nature. They have to be grown, harvested, packed and shipped under a rigid set of conditions.

"Disease and insect spread is a global economic problem," Ms. Ostlund continued. "Our pallets are insect-proof, but in some industries this is not a criterion for shipping pallets. If you bring a pallet in from - you name a country - it can potentially be carrying an insect."

Ms. Ostlund added that one reason Brooks Tropicals produces its papayas in Belize is that the country has the Mediterranean fruit fly under control.