Citrus producers are fighting HLB, a disease associated with the bacterium Candidatus Liberibacter asiaticus [CLas (Bové, 2006)]. The disease was detected in Florida in 2004, and since that time, citrus commercial acreage has decreased from 748,555 to 480,121 acres, and the total citrus production reduced from 291,800,000 to 94,205,000 85-lb boxes in 2015–16 season [U.S. Department of Agriculture (USDA, 2017)]. The 36% reduction of planted area and 68% drop in yield is causing major economic and social problems to the state of Florida. HLB disease affects 90% of Florida’s total citrus acreage and on average 80% trees in an individual citrus operation are infected with the pathogen, resulting in 41% yield loss (Singerman and Useche, 2016). Trees affected by HLB suffer from general canopy and root decline, yield reduction, and lopsided fruit that are not fit for sale on the fresh market. One characteristic of the disease is that yield losses precede visible foliar symptoms (Bassanezi et al., 2011), potentially indicating that fruit production is negatively affected before the disease is visually detected. Because the CLas bacterium is vectored by the ACP, insecticide applications aimed at reducing ACP populations and feeding activity typically constitute the main bulwark of HLB mitigation programs (Bassanezi et al., 2013; Hall et al., 2013; Stansly et al., 2014). The success of an insecticide ACP-management program is affected by the treated area, with greater efficacy usually achieved over larger swaths of land (Bassanezi et al., 2013). Coordinating insecticide applications over large acreages and among different farms adds another layer of complexity to an inefficient HLB-ACP control strategy.
Completely enclosed screen houses physically exclude the ACP and thus prevent inoculation and disease development. One of the main advantages of this system includes decrease in frequency of insecticide sprays to control psyllids. Ferrarezi et al. (2017) found no eggs, nymphs and adult ACP and no trees tested positive for CLas inside protective screen houses after 2 years of monitoring, where 75% of surveyed trees in the open-air plots tested positive for CLas during the same period. Thus, the use of screen houses offered a substantial level of protection against the establishment of HLB within a young grapefruit planting compared with management programs founded solely on insecticidal sprays. The system was developed at the University of Florida/Institute of Food and Agricultural Sciences (UF/IFAS) Indian River Research and Education Center in Fort Pierce, FL, and has been tested at the UF/IFAS Citrus Research and Education Center in Lake Alfred, FL. The economics of citrus under protective screens (CUPS) is being determined (Schumann and Singerman, 2016). To date, there are 50 acres of commercial CUPS with three growers in Florida and at least 150 acres more are planned (E.I. Pines and S.B. Callaham, personal communication).
If protected antipsyllid screen houses are to be used as a strategy by fresh citrus fruit producers to grow HLB-free trees, it must be demonstrated that young tree growth is not impeded by this potential cultivation method. Ferrarezi et al. (2017) reported that monthly rainfall was unaffected by the screen houses compared with open-air plots. Cumulative solar radiation and reference evapotranspiration (ETo) were reduced within the screen houses by 23% and 21%, respectively, compared with the open-air plots over 5 months of data collection. In Florida citrus production regions, rainfall amounts are typically the greatest from June to September (Parsons and Wheaton, 2000; USDA, 2014), with the rest of the year receiving little to no precipitation. Thus, the meteorological conditions inside the screen houses (no loss of rainfall, decreased solar radiation, and cumulative ETo) could offer a horticultural benefit to growing young citrus trees undercover by potentially increasing water-use efficiency (WUE).
Containerized production of young citrus trees could offer a novel approach to growing trees within a protected environment for fresh fruit product. A chief advantage of potted production, compared with conventionally growing trees in-ground, is its high degree of possible compartmentalization. For example, if a breach occurred and ACP detected, sprays would commence and the affected container-grown trees could be swiftly removed. Because CLas has a long incubation period before detection, the impact from a breach may not be detected for several years—which is a serious issue for the production system. Our hypothesis is antipsyllid screen houses and container-grown cultivation would allow rapid young plant growth, playing a role in developing new citrus production systems aiming a vector-free environment. One should note that the screen house itself cannot prevent disease development.
The current study investigated the use of antipsyllid screen houses on plant growth and physiological parameters of young ‘Ray Ruby’ grapefruit trees.
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