University of Florida Institute of Food and Agricultural Sciences researcher Jude Grosser discusses small experiments that indicated manganese and boron can help citrus trees cope with HLB.
In a greenhouse experiment from a few years ago, HLB-infected sweet orange trees were overdosed with micronutrients and secondary nutrients. “It looked like … manganese had the biggest effect on growth of the feeder roots. We got bigger and more robust root systems with an overdose of manganese. And boron also looked interesting, not quite as much as manganese.”
In a later field test, manganese and boron were used together and separately on HLB-infected trees. “We found that the overdose of manganese at three times the normal level is actually showing to be therapeutic,” he says, emphasizing that “it’s a very small experiment.” He reports that after two years, seven out of 12 trees in the experiment apparently had no active HLB infection and had increased yields.
“It looks like a little bit of extra boron is very helpful against HLB, but there’s a line where you can’t go too far,” Grosser says. He says four times normal manganese and two times normal boron “seems to be a good target.” He notes that his experiment was a small one on rough lemon rootstock only, so he doesn’t know what target doses might be for other rootstocks or rootstock/scion combinations.
“The growers that are experimenting with constant supplies of the micronutrients are getting excellent results,” Grosser adds. “Manganese is certainly one of the key micronutrients for dealing with the disease.”
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