Citrus Greening: Florida Battles On

Florida is approaching an unhappy milestone: its five-year anniversary of fighting citrus greening disease. In those years, greening has spread to all citrus producing counties in the state, forcing growers to ramp up spraying and other efforts to stop the spread of the currently incurable disease. This is on top of the industry’s battle against citrus canker, which was detected again in 1995 after previously being declared eradicated.

Background
Citrus greening—more frequently called Huanglongbing (HLB) disease in the research community—is caused by a bacterium spread by an insect called the Asian citrus psyllid. Apart from its role in spreading HLB, the psyllid damages citrus trees in its own right. A psyllid injects a toxin into the leaf on which it feeds, and this toxin in turn damages the leaf’s internal system, causing the tip to fall off and the leaf to twist as it grows. One nymph feeding for a day on a leaf permanently damages that leaf. Although psyllid nymphs can feed only on new leaf growth, adult psyllids can feed on mature leaves as well, allowing the population to thrive year-round. Psyllids were first discovered in Florida in 1998, although at that time they were not carrying the bacteria that cause HLB disease.

Psyllids pick up HLB disease from infected trees and carry it to other trees. HLB disease was first detected in Florida in 2005, and since then it has spread rapidly. A citrus tree infected with HLB has leaves with uneven yellow blotches due to the tree’s reduced ability to produce chlorophyll. The tree’s fruit is small, lopsided, and unevenly colored, with up to half of the fruit remaining green. The juice is bitter. Citrus trees, which normally live for over 50 years, die about five years after being infected with HLB. Symptoms of the disease, however, may not appear for one to two years after infection, which means the psyllids can carry the disease to many more trees before a grower may detect HLB’s presence.

Control
There is currently no cure for HLB disease, so growers must try to reduce the presence of the psyllid population through pesticide spraying and aggressive removal any trees showing symptoms of the disease.

The Florida Department of Citrus is funding the Citrus Research and Development Foundation (CRDF) to oversee HLB research efforts. Given the significant increase in pesticide spraying necessary to fight the spread of the psyllids, the impact that spraying has on the population of beneficial native insects, and the negative publicity that follows from concerned neighbors, a priority of CRDF is to reduce spraying as much as possible. Researchers have discovered that concentrated spraying on overwintering psyllids can significantly reduce the population that will reproduce come spring without causing as much damage to the beneficial insect population. Psyllids tend to be less active during winter months (easier to catch, in other words), and beneficial insects are in their dormant cycles and less vulnerable to spraying.

Infected trees must be removed, destroyed, and replaced with disease-free stock.

Economic Impact
The Florida citrus industry is in a state of flux following several years of poor returns and four hurricanes hitting the crops in 2004 and 2005. These setbacks, combined with the negative repercussions of citrus diseases and dangerously low nursery stocks, place the industry in serious jeopardy.

Florida ’s nurseries have been devastated by disease. Approximately 4.3 million trees were lost to citrus canker—over 60 percent of all nursery stock. New nurseries have been established in northern Florida and are enclosed and environmentally controlled. This add s significant cost to replacement trees (resets).

Normally, Florida needs 2 to 3 percent of its trees replaced. Given the condition of the nurseries, growers continue to face shortages of resets. And without new trees, the expected harvest each year will decline.

To alleviate the situation, USDA in October 2009 relaxed its quarantine on Florida citrus from groves showing symptoms of canker. Now, as long as the fruit is disinfected by approved methods, the fruit can be shipped to all states, even those with citrus industries such as California.

But HLB disease’s ever-increasing destruction of citrus trees is forcing Florida’s citrus industry to search for a cure or at least more effective controls before the disease destroys not only Florida’s citrus industry but also those of Brazil and Mexico. California is also on high alert because the psyllid has been discovered in southern citrus producing counties, and several shipments of HLB-tainted produce have been stopped at the border already.

To fund this effort, prices for finished goods will necessarily be higher. This is a fight for the industry’s life. We hope they win.

Please contact us for more information.

McKEANY-FLAVELL COMPANY, INC.