Root Health Update

Evan Johnson, a University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) plant pathologist at the Citrus Research and Education Center, updates efforts to help citrus tree roots cope with HLB.

He starts by noting that around 10 years ago he and former UF/IFAS researcher Jim Graham discovered “that HLB causes severe damage to the root system.” They hoped to find a management solution that would allow root health to recover, but those attempts “unfortunately failed,” he says. The root damage caused by HLB inhibits the tree’s ability to uptake water and nutrients.

To cope with the root loss, many Florida citrus growers have drastically altered their fertilization practices. Before HLB, many growers applied three fertilizer applications per year. “We really have to modify that” with fewer and lower fertilizer applications via fertigation, Johnson says. Growers and researchers call that new fertilization approach “spoon feeding.” Johnson adds that spoon feeding results in less fertilizer being wasted as it passes through the root zone unused.

Similarly, many growers are applying smaller but more frequent doses of irrigation than they did before HLB hit Florida in 2005. Johnson says that practice results in the same amount of water being applied over a month and “actually does improve the health of the tree.”

Johnson reports that in some groves managed by proactive growers, root mass is increasing. “We’re not sure of the exact cause,” he says. “We’re hoping to, in the next few years, figure out what factor it is” that causes the root mass increase.

Johnson also reports that he was surprised how well tree health and yield recovered after Hurricane Irma walloped the Florida citrus industry in September 2017. He says he and other researchers are now looking at the cost benefit of phytophthora management. “We know that some of the products have lost some of their efficacy,” he says. “And we don’t know why that is.”

This interview with Johnson is featured in the January episode of the All In For Citrus podcast, a joint project of UF/IFAS and AgNet Media. Listen to the full podcast here.