HLB: What We Know Today

Tom Kirschner

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This fall will mark eight years since HLB was officially confirmed in Florida. It brought with it a sea change in an industry that had grown citrus in much the same way for decades. While the scientific community takes on the huge challenge of finding solutions to HLB, growers have adapted and revamped their production systems to survive. It has been a difficult and costly process, but they have no choice.
“It used to be that we were really busy in the spring and summer, and then we were able to take it a little easier in the fall and winter,” says Tom Kirschner, director of grove operations for Cooperative Groves, which are spread across Southwest Florida. “It is much more like growing a row crop these days. You have to be in the grove every day of the year, making decisions about psyllids and tree health.
“Growers can’t just sit back and wait for science to solve HLB, because that might not ever happen. We’ve learned a lot from UF/IFAS, USDA, and other growers, so we need to put that knowledge to work in the groves and use every available tool we have if we are going to get through this.”

Poor Psyllid Control = No Program

While a great deal of attention has been placed on foliar nutrition’s role in tree health, growers have learned any HLB mitigation program starts with psyllid control. “My main focus used to be the horticulture of growing citrus, but now that has shifted more toward managing psyllids and mitigating HLB,” says Kirschner. “If you are not effectively managing psyllids, you are not even going to have a grove to worry about.”

Kirschner has a zero tolerance policy for psyllids in the groves he manages. “The most important thing we’ve learned since HLB came on the scene is the level of psyllid control necessary is much higher than we ever would have imagined,” he says. “We have a threshold of zero for psyllids. If you want to be successful, you can’t have them in your groves, especially now that there is so much HLB inoculum out there.”

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Kirschner’s spray program has evolved from three sprays in 2006 (plus Temik, before it exited the market) to 12 applications per season in 2013. This past season included four ground applications and eight aerial applications. In addition to those applications, perimeter sprays around groves were made to protect the edges. He notes their approach has been successful in keeping psyllids out of groves.

Protecting Young Trees

Florida has oriented itself around resetting trees to replenish those going out of production. Putting in new trees and protecting them from HLB in their vulnerable years is critical to maintaining the state’s fresh and processed infrastructure.
Kirschner has employed an aggressive tree replacement program in all groves he oversees. “We have been successful with our resets and know we can get them to age three or four with very low infection rates,” he says.
“We’ve lost far more young trees to freezes than to HLB in the past few years.”

The foundation of young tree protection is the use of neonicotinoids for psyllid control like in many groves across the state. Where Kirschner’s program might differ is he reserves all his neonicotinoid applications for young tree protection.
“We save all of our neonicotinoids for usage in soil drench applications on the resets,” he says. “We don’t make foliar applications of neonicotinoids on mature trees. Being that we are a reset-oriented operation, we can’t risk the loss of neonicotinoids to resistance.”

Kirschner also recommends growers consider some of the newer rootstocks when putting in resets. New resets in their groves are going in on US812, US802, US897, C35, and X639 rootstocks.

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“We are trying to use rootstocks that have improved horticultural traits,” he says. “The ‘US’ rootstock numbers are good; and the better they handle different stresses in the grove, the better they will help trees in HLB environments.
“The challenge will be getting these young trees from four to five years old up to eight and 10 years old,” says Kirschner. “Until we get in a hedge row situation where we can manage flushes a little better, those are the vulnerable years where we really only have foliar psyllid control as an option.”

Enhancing Citrus Tree Health

HLB symptoms on citrus

Probably the biggest area of in-the-grove innovation since HLB came onto the scene has been the development of nutritional “cocktails” to boost tree health. Kirschner is blunt in his assessment of nutritional therapy.“The nutrition programs pay for themselves and are necessary in groves regardless of whether you are removing infected trees or not,” he says. “I believe these nutrition programs are having a positive effect on both infected and non-infected trees. Some groves respond differently to these programs for any number of factors. But, I definitely believe they are helping to mitigate the effects of HLB.”

Dr. Bob Rouse, a citrus horticulturist with UF/IFAS, has the only long-term research trial testing the ability of nutritional therapies to mitigate the effects of HLB. He says the proliferation of programs based on growers’ own experimentation is remarkable. “There are more than a dozen commercially suggested nutritional programs for HLB available by venders and being suggested by fertilizer companies,” says Rouse. “In addition, there are an infinite number of nutritional programs being used by individual growers who are using their own developed nutrition mixes. This would include foliar and ground fertilizer programs as they complement each other and both are needed.”

Growers React And Evolve

Florida Grower has featured the nutritional programs of many growers since HLB’s spread. Maury Boyd was on the forefront of nutritional therapy and his program is a model for many. Since Boyd’s program was featured in 2009, we asked him how his program has been modified.“We have had to deal with blight, HLB, and canker in our groves,” says Boyd. “We are learning more about friendly bacteria and its uses. We introduced applying nickel and have shifted more to calcium nitrate in our nutrition program. We have increased the rate of boron. We feed the trees from
both directions — the roots and foliage.”

Steve Farr, director of grove operations for Ben Hill Griffin, was featured in 2010 for the operation’s approach in managing HLB. “We are using more ultra-low-volume and aerial sprays to control the psyllid and making more efforts to work with neighbors to control the psyllid in regional applications,” he says. “We have not changed our foliar nutritionals a whole lot, but have gone to more liquid fertilizers and more frequent injections.”

A Tale Of Three Groves

Addressing Area Issues

Another observation growers are making is that groves react differently in terms of HLB’s spread and how that spread is managed. This only reinforces the idea that growers must be flexible and able to react quickly in managing the disease. Kirschner notes the progress of three groves he manages to illustrate the point. The CPI, Cooperative Three, and Ranch One groves are located in Hendry, Lee, and Collier counties respectively. The most successful grove has been CPI, with a cumulative HLB infection rate of 12% over six years.

Kirschner credits very early psyllid control, a large grove, and inoculum removal in CPI’s ability to maintain its low infection rate. The Ranch One grove also continues to remove infected trees, but cumulative infection rates are higher at 24% after seven years.

In the Cooperative Three grove (60% grapefruit), infected tree removal is not practiced, but aggressive psyllid control remains, along with nutritional therapies. It is this grove that has seen the largest yield bump (11%) due to enhanced nutrition and tree care.

Ranch One has seen a 9% decrease in production, but that was with 21% tree removal due to HLB and blight. CPI has seen a 10% decrease with 12% removal of trees. These groves, too, follow aggressive psyllid control and nutrition protocols. Kirschner cautions not to take the decrease in production as a mark against inoculum removal.
“CPI always has been a gem of a grove and highly productive,” he says. “We’ve added the enhanced nutrition program, but we have not seen the bump in yields. That is because these trees were already highly productive, so you get to a point of no return on fertilizer. I do think the nutrition is helping CPI absorb the losses of tree removal better than without it.
“The Cooperative Three grove where we did see yield bump has traditionally not been as productive even before HLB, so it had the most to gain from nutrition programs and overall better care.”

With all three groves, Kirschner says the bottom line dictates their actions. “The good news is economically the groves are all doing very well,” he says. “At the end of the day, that is what matters, but we depend on good prices to afford all this intensive management.”

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