Citrus Research Charges Forward

After serving as the director of the UF/IFAS Citrus Research and Education Center for a number years, Dr. Harold Browning left the citrus industry for brief time in 2009. But, the longtime researcher was never really away as he was consulting on a number of citrus projects in the meantime. Recently, Browning has returned officially in his new role as chief operating officer of the Citrus Research and Development Foundation (CRDF). Florida Grower caught up with Browning to get an update on CRDF’s activities.


Q: How many projects are currently being funded by CRDF? And, what range do they cover?

Citrus Research Charges ForwardBrowning: During the current fiscal year, CRDF is contracting approximately 130 research projects. With a specific focus on solutions to new citrus diseases, the majority of the research is invested in HLB, encompassing exploratory to near-term solutions related to the bacterial pathogen, the Asian citrus psyllid vector, and the citrus tree as it responds to infection and onset of symptoms. Secondarily, CRDF is sponsoring a number of research projects focused on citrus canker management strategies. Included in this area are projects aimed at better management of citrus leafminer, an insect which complicates spread and infection by canker bacteria. Finally, we also are supporting a few projects on other emerging diseases, including citrus black spot and citrus leprosis, the latter being a disease that currently is not in Florida. In addition to the projects in our current portfolio, we are receiving the full proposals for CATP11, this year’s call for new proposals. A significant number of proposals were invited from the pre-proposal process, and these will be subjected to peer scientific review, with those results provided to the Research Management Committee of CRDF, so that the grower-driven discussion and decisions on new projects to support can be made in early 2012. Again, the emphasis with these project proposals is on HLB and canker.

Can you name a few research areas that are showing results/promise?

Browning: The background work leading to creation of the Citrus Health Management Areas (CHMAs) has been important, as we realize that psyllid control is vital in managing HLB. This work continues, and the continuous progress being made is integrated into psyllid management programs. Intermediate-range research on the psyllid is being expanded on to develop alternatives to increased use of pesticides to control the vector, while at the same time research is focused on best use of pesticidal tools. Young groves are a primary target for improved psyllid management.

Efforts to better understand the HLB-causing bacteria and how disease is initiated and spread continues to be hampered by peculiarities of the bacterial/disease life cycle and our inability to culture the organism. However, approaches to work through these difficulties are being taken, and incremental understanding of the bacteria, plant infection, and residence of the bacteria within psyllids is progressing.

On the citrus production front, research continues to map and understand the infection process and particularly how trees responds to HLB and canker infection. Projects are focused on better detection of the pathogen that would allow researchers to track the movement of the causal agent Candidatus Liberibacter asiaticus in the plant, as well as to identify early infection. The genetics arena is busy, with scientists taking advantage of the availability of the citrus genome map to look at plant responses to infection, the plants defense systems and how they are interacting with invading HLB bacteria. These interactions ultimately are expressed through development of symptoms.

On a more practical front, a lot of effort is currently being invested in understanding rootstock and scion susceptibility to HLB and canker, and to manipulate the plants to encourage greater tolerance to the diseases.

Finally, there is a segment of research focused not on the diseases, but rather on how future citrus plantings can be designed to be more successful in the presence of HLB, canker, and other stresses. This is a multidisciplinary approach, and most importantly, directly involves growers who are interested in evaluating production system options. Several trial plantings are in place or are being planned, and a wide range of new scenarios are being incorporated, from higher density plantings, to novel irrigation/fertigation strategies, to rootstock/scion combinations.

There has been a lot of interest in foliar nutrition. There was a perception by some that this area was not getting funded by CRDF, but if I understand correctly, there are projects being funded in this area. Can you give some brief detail here?

Browning: The role of nutrition in tree health and response to stresses, including diseases, has a long history in citriculture and considerable work has been conducted over time under Florida conditions. The re-emergence of interest in improved nutrition, particularly with emphasis on use of foliar application to supply micro- and macro- nutrients should be no surprise. The difficulty with regard to HLB is that we know so little about how disease progresses in infected trees, and what conditions might counter this infection, that conducting research to answer specific questions about nutritional impacts on disease development is very difficult. At the same time, growers are seeking management strategies as alternatives to tree removal, and have expanded on former nutritional regimens to overcome the symptoms of HLB. CRDF is funding research on several fronts, including supporting a data-collection approach to better understand and describe the outcomes of application of foliar and soil nutrients as a response to HLB. Some of this work is in its 3rd year, while new projects are being initiated. We are concerned that this approach is viewed as an alternative to other management approaches to HLB, especially aggresive psyllid control, and have supported the extension efforts to keep growers appraised of what is happening in this arena. A one-day workshop this fall allowed scientists and growers who are active in this area to share information and to debate the basis for and outcomes associated with additional nutritional applications to infected groves. With grower trials expanding and more research being conducted, we hope to better advise growers on the potential benefits and risks of adopting this approach, and most importantly, to determine which specific components of the nutritional programs are most beneficial to make this strategy more economical and sustainable.

If growers want to learn more about these projects and even give feedback on the process, what should they do?

Browning: There are a number of outlets for information on research that is being supported by CRDF on behalf of the industry. Our website ( provides access to the lists of currently funded research in CRDF, as well as projects that are being funded by the California Citrus Research Board and the Texas Citrus Producer’s Board. In addition to current funded project lists, you can view progress reports for every project, provided quarterly for CRDF-funded work. Go the Grower tab on the webpage to find this information. There also is a place to submit comments or questions and the answers will be posted for all to read.

By far, the best way for readers to keep appraised of research progress in HLB and canker is to participate in the many citrus grower meetings scheduled throughout the year. While it is CRDF that is coordinating industry funding to support the research, the best updates are provided by the researchers themselves and the IFAS Extension team who is keeping the industry appraised of progress. State-wide grower meetings and institutes, regional grower meetings, and extension meetings and field days are widely publicized. I encourage growers to learn first-hand from those who are working with support from CRDF to develop and deliver solutions.