Research bolsters foliar nutrients’ role in citrus greening management

10/07/2011 01:32:00 PM
Vicky Boyd

The trees already have significant regrowth and appear to be responding well to the nutritional program, Willis says.

“We’re trying to do everything we can to avoid having resets because that is a costly proposition,” Boyd says.

Both he and Willis say one of the keys is to include a strong psyllid management program with the other cultural practices.

Nutrient recommendations

Based on the results of the original trial, Rouse says he recommends a balanced program that includes both ground- and foliar-applied nutrients.

And at least one of the micronutrients should be in the phosphite form, such as zinc phosphite or manganese phosphite, which enhances fruit yield.

“At this point, we don’t see the benefit from the SARs. It doesn’t mean they’re not doing something, but we don’t see they’re doing anything for greening,” he says.

Salicylic acid, sometimes called an SAR-inducing material, is actually a growth regulator that releases buds from dormancy, Rouse says. It may benefit recovering trees by promoting more leaves.

Typically, the macronutrients—nitrogen, phosphorus and potassium—are soil applied whereas the micronutrients tend to be foliar applied.

Rouse also cites Liebig’s law, which states that plant growth is limited by the scarcest resource. If one micronutrient is in short supply, it will affect the tree even if all of the other micronutrients are adequate.

‘Evidence that something is working’

Last fall, Ron Brlansky, a plant pathology professor at the Citrus Research and Education Center in Lake Alfred, collected leaf samples from trees in citrus grower Maury Boyd’s Orange Hammock grove.

Brlansky also collected leaf samples from trees in Bob Rouse’s trials that received Boyd’s nutrient mix without systemic acquired resistance-inducing materials and from untreated trees.

Brlansky stained them, so the vascular tissue had more contrast, and viewed them under a conventional light microscope.

The phloem—the nutrient-carrying vascular tissue within the plant—from the trees receiving the Boyd cocktail wasn’t nearly as plugged and appeared to have new phloem being produced compared with untreated trees.

Boyd, who has championed his nutritional cocktail as an interim way to stay in business, says he was surprised by Brlansky’s findings.

“To me, this is the first evidence that something is working,” Boyd says.

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Manahar Kadariya    
Nepal  |  December, 16, 2011 at 11:43 AM

I also stressed to support this result. here we are doing a trial on 10 different groves for rejuvenation of more than 50 percent declined trees. But we do not have any resources for lab testing of these trees for greening. But most of the plant showed the typical symptoms of greening. Can i go further with farmers to disseminate technology ?

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