Exotic beetles threaten Florida crops

Exotic beetles threaten Florida crops

DECEMBER 4, 2008 - Small, invasive beetles that kill trees in the laurel family -- including avocados -- are heading closer to South Florida. An Asian beetle half the size of a rice grain is spreading a fungus fatal to avocados and red bay trees and is working its way south, toward 6,500 acres of commercial avocado in south Florida.

Most of the state's commercial avocado groves -- a $12.7 million industry -- are in Miami-Dade and are so far untouched by the fungus.

University of Florida researchers told the Miami-Dade County Commission Tuesday they needed funding to find a way to eradicate the insects and disease before they reach commercial groves. The beetles have spread as far south as Okeechobee County.

Most of the state's commercial avocado groves -- a $12.7 million industry -- are in Miami-Dade and are so far untouched by the fungus, as is the national avocado collection at the USDA Subtropical Horticulture Research Station in Coral Gables. But scientists already know the damage it can do because it has killed many red bay trees -- a close relative of the avocado -- as it creeps south from Savannah, Ga., where it was discovered in 2002.

Backyard avocados in Jacksonville have been infested and killed, said Bud Mayfield, an entomologist with the Florida Division of Forestry in Gainesville. Researchers have deliberately infected small avocados in tests and found them susceptible as well, although susceptibility may vary from variety to variety. There are 56 varieties of avocado grown in the state.

Reports of dying red bay trees started turning up in 2003 and 2004. Red bay is native to coastal forests throughout the southeast, and the fungus now is killing most of the large mature trees in Georgia, South Carolina and north Florida.

The fungal disease spread by the beetles is called laurel wilt. It attacks the laurel family, which has about 100 species, including the avocado and red bay. It plugs up the trees' plumbing so that the leaves wilt, turn reddish and then brown as the trees die.

The beetles are hard to control, Mayfield said, because they spend most of their life cycle inside trees. Wilt diseases like this one are equally difficult to control.

Sassafras trees in North Florida also are susceptible. In South Florida, laurel relatives include the native lancewood and licaria.

Jason Smith and graduate students at UF's School of Forest Resources and Conservation are trying to find natural resistance to the disease in red bay populations. Mayfield also has worked on injecting fungicides into red bay trees, but that may not be an option for growers.