What's a little pesticide among neighbors? For Florida citrus growers, it could mean saving their trees that are under attack from the virulent citrus greening bacterium threatening to destroy the state's $10.7 billion industry.
Entomologist Michael Rogers, director of the University of Florida's Citrus Research and Education Center, is telling growers that one of the best approaches to managing citrus greening is to control the insect that spreads this disease. And the best way to do that is by coordinating their pesticide applications with their neighbors.
That's because the Asian citrus psyllid, the bug that carries citrus greening, could simply hide out in a grove not being sprayed until the pesticide wore off in the treated areas. In the rainy season, the pesticides can be depleted in as few as two days.
"For a pest like this that's so mobile, if you get growers that are adjacent to cooperate, you get better psyllid control and yields are higher, said Rogers.
Rogers created the Citrus Health Management Areas – CHMAs (pronounced ‘chee-mahs' by growers) - which are groupings of groves within an area in which growers coordinate the timing of their pesticide applications. Simultaneous treatment of groves improves pest control and ultimately reduces the number of pesticide applications needed to manage the psyllids.
What began as seven CHMAs in 2007 has grown into 52 statewide, as growers have recognized the value of coordinated treatments. As part of the CHMA program, 6,0000 one-square-mile blocks of citrus are surveyed for psyllids every three weeks by 89 scouts from the Florida Department of Agriculture and Consumer Services' Division of Plant Industries and the United State Department of Agriculture's Animal Plant Health Inspection Service. The survey results are housed on the CREC's website to aide growers in planning their next coordinated sprays.
The trees in areas with higher numbers of psyllids are under greater pressure to contract the disease or have increased numbers of diseased trees. Once an area with high psyllid pressure is identified, corrective spraying can take place.
The data show that growers who coordinate sometimes see no psyllids in their testing blocks, while growers who don't coordinate can find hundreds per block. While the blocks are not labeled by owner online, the local growers know who is not participating and put pressure on them.
While the goal of the CHMA program is to help manage the spread of citrus greening disease, a recent study presented at the 2015 Citrus Expo in Ft. Myers indicated that CHMAs can have a positive economic benefit for participating growers.
Ariel Singerman, a citrus economist at the CREC, reported that in a case study analysis during the 2013-14 harvest season, fruit yields were, on average, 145 boxes higher per acre in a CHMA with more grower participation - with one box containing about 90 pounds of oranges. In the CHMA with higher yields, the economic benefit was, on average, $1,218 per acre more compared to a CHMA with lower yields.
Citrus greening bacterium first enters the tree via the psyllid, which sucks on leaf sap and leaves behind greening bacteria. The bacteria then move through the tree via the phloem – the veins of the tree. The disease starves the tree of nutrients, damages its roots and the tree produces fruits that are green and misshapen, unsuitable for sale as fresh fruit or, for the most part, juice. Most infected trees eventually die and the disease has already affected millions of citrus trees in North America. It has recently been found twice in California.
Citrus greening was first detected in Florida in 2005. Between 2004 and 2011, the Florida commercial citrus acreage and the number of trees decreased by 28 percent, with greening one of the major reasons for this loss, along with real-estate development.
Although current methods to control the spread of citrus greening are limited to the removal and destruction of infected trees and the use of insecticides to control psyllid populations, UF/IFAS researchers are working to defeat it on a number of fronts, including trying to eradicate the psyllid, breeding citrus rootstock that shows better greening resistance, and testing anti-microbial therapies that could be used on trees.
James Tansey oversees the CHMA project for the Southwest Florida Research and Education Center, carefully mapping the areas from Hendry to Lee counties and beyond.
"There's an overall trend of depression of psyllid populations and that's mainly due to the CHMA captains, Tansey said, praising the volunteers who oversee spraying in their respective blocks.
Steve Farr is an area captain in Highlands County and vice president of the grove division for Ben Hill Griffin, Inc., one of the largest citrus growers in the state. He agrees that whenever there is coordinated spraying of pesticides, there are fewer psyllids.
"I liken it to spraying for mosquitoes – you don't just spray your yard, he said. "You spray the whole area. And aerial applications are more effective than ground applications.
To see the CHMA website, go to http://www.flchmas.org/Default.aspx.