Recipient Organization
UNIVERSITY OF FLORIDA
G022 MCCARTY HALL
GAINESVILLE,FL 32611
Performing Department
(N/A)
Non Technical Summary
Hurricane Ian hit most citrus groves in Florida with high windspeeds and flooded many. Dropped fruit and lost foliage from the canopies were immediately apparent, but previous experience suggests that recovery will lag, with continued leaf and fruit drop over the coming months. Field measurements suggest that branch strain probably induced hydraulic failure, and rootzone flooding will also limit water uptake from the soil. Grower practices that are expected to improve recovery, but the impacts have not been tested in this context, and growers need timely information to improve recovery, as well as recommendations to plan production systems that are more resilient to future storms. These practices include particle films, individual protective covers, and irrigation to reduce stress, and gibberellic acid to enhance new leaf production, as well as grove layout and windbreaks to reduce damage from future storms. Therefore, we aim to assess and inform growers of post-hurricane recovery strategies to improve the resilience of the citrus production industry in hurricane-prone regions. Specifically, we will:1. Communicate regularly with citrus growers to inform them of the status of citrus tree recovery and the efficacy of mitigation practices.2. Assess tree health response to damage and recovery from the impacts of high winds and flooding caused by Hurricane Ian across the gradient of impact intensity.3. Assess the effects of horticultural practices to enhance recovery and mitigate damage.Achieving our objectives will make the Florida citrus industry more severe-weather resilient, and contribute knowledge to similar impacts in other crops and regions.
Animal Health Component
100%
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Goals / Objectives
Goal: Assess and inform growers of post-hurricane recovery strategies to improve the resilience of the citrus production industry in hurricane-prone regions.Specific Objectives:Communicate regularly with citrus growers to inform them of the status of citrus tree recovery and the efficacy of mitigation practices.Assess tree health response to damage and recovery from the impacts of high winds and flooding caused by Hurricane Ian across the gradient of impact intensity.Assess the effects of horticultural practices to enhance recovery and mitigate damage.
Project Methods
Survey of impacts and recoveryUp-to-date communication with growersWe have already begun to develop a list of collaborating growers who will receive regular, direct communications. In addition to direct communications, an e-mail list has been produced and each month a report will be sent to inform growers of how tree recovery has progressed and any results of specific practices that have been observed. In addition to the report blog updates (www.treephysiologylab.org), social media posts, articles in Citrus Industry Magazine, and discussions on the All in for Citrus podcast will make the information widely available to all growers and stakeholders.Assess tree health response to damage and recoverySelection of grovesWe will continue to identify willing grower collaborators. Currently six grower groups (individuals or cooperative companies), offering multiple locations each, are already involved and can provide letters of support if needed. These sites cover a swath of the impacted area and experienced winds ranging from 75-130 mph. We will expand this to include 20-30 growers total, depending on availability, including groves the experienced only tropical-storm-force winds (<75 mph). Selection of sites will focus on sampling a broad range across the gradient of conditions experienced in groves across Florida. We are surveying the growers to assess the storm conditions including flooding of the groves as well as practices that may impact recover, including questions related to mineral nutrition, pruning, plant growth regulators (eg. GA), and yield history.Different varieties have been observed to have undergone different impacts depending on their fruit maturity stage. Thus, we will select groves including 'Hamlin' sweet orange (Citrus x sinensis), 'Valencia' sweet orange (C. x sinensis), 'Star Ruby' grapefruit (C. x paradisi), and 'Sugar Belle' mandarin (C. reticulata) hybrid. Hamlin, an early maturing variety, was much closer to harvest and much more fruit drop has been observed in the immediate aftermath of the storm than in Valencia trees which mature 3-4 months later. Grapefruits have intermediate ripening time between the two varieties, but with much larger fruit. Meanwhile more defoliation has been observed in Sugar Belle than in other varieties. These varieties will be sampled in all areas in which they are available.In each grove selected, three groups of three trees each will be labeled along a transect parallel to the prevailing winds (Figure 2). One group facing the prevailing storm winds in that location. Wind direction is different in each area and in some location shifted throughout the storm. A second group of three trees from the center of the grove, and a third group of trees will be sampled from the edge of the grove opposite that facing the prevailing storm winds. This will assess the range of direct wind intensity across each grove. Each tree will be observed once per month.Horticultural Measures.We will measure important horticultural variables. These will include, the number of fruits dropped month-to-month, final yield per tree, and canopy recovery. Ground under trees will be raked at each observation time and the dropped fruit will be counted and removed from under the tree to ensure that the following month's count will include exclusively newly dropped fruits. At harvest time the number of fruits remaining on each tree will be counted to calculate the proportion of fruit dropped. Canopy recovery will be measured monthly by measuring the height and width of the canopy using measuring sticks. Canopy density will be measured using an optical fish-eye-lens based instrument to measure leaf area index, a measure of leaf area per unit of ground area (LI-2200c, Plant Canopy Analyzer, Li-Cor Biosciences, Lincoln, NE). Canopy density is currently the most effective measure of plant health and is strongly correlated with yield (Tang, Chhajed, and Vashisth 2019). Production of new shoots will be noted for each of the limbs sampled for physiological sampling (below). Mature, fully expanded leaves will be sampled every 6 months and measured for weight. Then same same leaves will be quantified for starch accumulation, callose accumulation (which measures the plugging of phloem, a key symptom of HLB disease), oxidative stress, leaf carbohydratea, and mineral nutrient content (performed at the UF/IFAS Analytical Testing Lab) to assess tree health and nutritional status. For oxidative stress assessment different spectrophotometric assays applied will be lipid peroxidation, hydrogen peroxide, total antioxidant capacity, superoxide dismutase, catalase, and peroxidase.Physiological measures On each tree selected, 10 branches will be selected, five on the windward size and five on the leeward side, situated at angles of 15º, 40 º, 65 º, 90 º, 115º relative to a vertical transect, representing positions from the top to the bottom of the tree (Figure 3). The mechanical strain from winds will be assessed by measuring branch angles relative to the wind, and any limb breakage will be noted, though broken limbs will not be sampled. Roots will be sampled at six month intervals to assess impact of flooding. These will be performed using soil cores, which will be washed in a fine strainer and the roots will be scanned on a flatbed scanned and root length density quantified using WinRhizo software (Regent, Quebec, CA). Leaf photochemical function will be assessed using a portable chlorophyll fluorimeter to measure Fv/Fm a measure of photochemical oxidation, broadly characterized as a measure of stress (OS-30p+, Opti-Sciences Inc., Hudson, NH). Leaf hydraulic function assessed by measuring transpiration and stomatal conductance using a handheld porometer (LI-600, Li-Cor Biosciences, Lincoln, NE). HLB symptom status will be assessed by measuring stem carbohydrates at the end of the study using colorimetric assays. These measures will inform us of the degree to which internal function remains impaired or has begun to recover.Decision support systemThe information gathered in this grove-survey study will be used to model the impacts of windspeeds and flooding on grove health and on recovery time. This tool will be developed using linear or non-linear models as appropriate and will be made publicly available. This decision support tool can be used to further understand the medium-term economic and horticultural impacts of tropical storms.Assess effects of horticultural practices on damage and recoveryExisting replicated trials will be used to assess impacts of horticultural practices on hurricane damage and recovery. These include two trials of particles films, one including reflective mulch and individual protective covers (netting over individual trees), as well as four ongoing trials to evaluate the efficacy of GA in HLB-affected citrus and one trials evaluating GA and 2,4-D (synthetic auxin) effect alone and in-combination. Geographically, these trials are located from central Florida to southwest Florida, Polk City, Ft. Meade, Ona, and Arcadia. In these trials we already have pre hurricane data collected on untreated and GA-treated trees. In these studies the same horticultural and physiological variables described above will be measured in at least three replicates of each treatments. These results will also be compared with grower assessments of the same practices in their groves where available, though commercial grove observations may not be sufficient in number to draw conclusions from inferential statistics, which is our motivation for using existing replicated trials. This will enable us to make recommendations for horticultural practices to mitigate hurricane losses and hasten recovery of tree health.