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CPMG02 2012 Florida Citrus Pest Management Guide: Management Options for Nonbearing Groves and Fresh or Processed Fruit1L.L. Stelinski, J.H. Graham, R.P. Muraro and R.A. Morris2 1. This document is CPMG02, one of a series of the Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date December 1995. Revised February 2012. Reviewed February 2012. Visit the EDIS website at http://edis.ifas.u.edu 2. L.L. S telinski, assistant professor, Entomology and Nematology Department; J.H. Graham, professor, Soil and Water Science Department; R.P. Muraro, professor, and R.A. Morris, associate Extension scientist, Food and Resource Economics Department; Citrus REC, Lake Alfred, Florida; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or aliations. U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A&M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy, Interim DeanCitrus growers must maximize prots by maximizing fruit production and optimizing expenditures to remain competitive during these challenging economic times. Basic horticultural inputs to maximizing production include the optimization of fertilization, irrigation, weed control, and pest management of various foliar and soil pests. A fundamental working assumption to maximizing grower prots is that the cost of any input should be matched by an increased return of greater value. While expenditures for scouting and tree removal to control the spread of greening may not be matched by an increased return of greater value in the same or the coming season, these activities are of critical importance to help ensure long-term viability. Florida citrus is marketed either for the fresh market (50% grapefruit and specialty varieties, 5% round oranges) or processed market. Prior to the identication of citrus greening disease in Florida in 2005, the pest management strategies employed by growers producing fruit destined for these dierent markets could dier considerably; therefore, management expenditures diered as well. is is particularly true when comparing healthy, mature round orange groves with healthy mature grapefruit and specialty fresh fruit varieties. Simply put, it is not necessary to achieve fresh market fruit quality in a processing fruit production operation, as external cosmetics play virtually no role in processors acceptance of fruit for processing. Given that the prot margin for processing fruit is usually less than that for fresh market production, the inputs, including pest management, have been adjusted proportionally in order to realize the maximum prot potential. However, in the era of citrus greening and canker, management inputs for eective control of Asian citrus psyllid and citrus leafminer will likely need to increase for both fresh market and processing oranges. e Asian citrus psyllid is a true vector of citrus greening, while the citrus leafminer facilitates the spread of canker by injuring leaves. Curtailing disease spread will in large part depend on eective suppression of both pests. In the production of fresh market fruit, a high level of control of external blemishes is needed to achieve maximum protability. A greater input of pesticides and a higher level of monitoring can be economically justied to achieve this end. e approaches dier, however, with dierent varieties of citrus. With most round oranges, the value of fresh fruit is oen marginally dierent from processing fruit. Also, fungal and canker disease problems are less severe on oranges than on some other types of citrus. us, with additional fungicide and miticide application to control melanose and a high level of control of rust mites, oranges can be marketed fresh. If pest or windscar damage
2 occurs early in the season, the grove can be switched to a processing program without suering severe economic loss. Grapefruit, navel oranges, tangerines, and tangerine hybrids have high values as fresh fruit and relatively low value for processing. Depending on the variety, specialty fruit are also more severely aected by diseases such as canker, scab, melanose, Alternaria brown spot, and greasy spot rind blotch than are round orange cultivars. ey must be monitored very closely, and timely applications must be made to control rust mites and fruit blemishing canker and fungal diseases. If a high degree of control is not achieved and the fruit must be processed, the producer will almost always experience a net loss. White grapefruit can be grown protably for processing, but such groves must be designated at the beginning of the season and the inputs reduced correspondingly. In the production of fruit for processing, yields and internal quality must be maintained with minimal input. Although irrigation, fertilizer, and weed control should not be reduced, less control of foliar diseases and arthropod pests such as citrus rust mite may be justied. However, todays management of processing fruit will require input for eective suppression of Asian citrus psyllid and citrus leafminer to mitigate spread of citrus greening and canker, respectively. When the protection of foliage and fruit are the key objective, only a few diseases and pests are of primary importancenamely, canker on fruit, greasy spot fungus on foliage, and citrus rust mite on fruit. High mite populations over time can lead to reduced fruit size and productivity. Other pests and diseases that threaten tree vigor and subsequent productivity, notably nematodes, root weevils, and Phytophthora root rot, should be monitored and controlled when population levels dictate. In most cases, there is no way to predict on a seasonal basis the incidence and severity of pests and diseases. However, based on grove history and some within-season observations, you can reasonably assess the situation and look at available options. In the nal economic evaluation, net savings in pest management can be considered as prot to the extent that they do not cause loss through increased incidence of diseased trees, premature fruit drop, reduced fruit size, and lower internal quality. With most citrus pests, the pressure must be extremely high before economic damage levels on the processing fruit crop are experienced. us, there may be considerable latitude in taking measures to suppress certain pests. However, greening and canker management may necessitate more intense pest management than has been previously recommended for arthropod pest of citrus. Although close observations and pest monitoring, informed decision-making, and judicious pesticide application should reduce the level of input and associated costs in most seasons, psyllid and leafminer management remains a priority. Eliminating psyllid infestations in the winter months when naturally-occurring populations are low will be a good strategy for reducing the need for greater pesticide inputs during bloom and spring ush. Within a season, circumstances may dictate a decision change in marketing from fresh to processing and this decision may be based on many factors (Figure 1). One is that the composite of pest and disease pressures and environmental factors (wind) have produced fruit damage (e.g., windscar) such that packout will be so low that fruit must be marketed for processing. In this case, the grower should immediately change his IPM strategy for the remainder of the season to reduce costs. When the original marketing strategy is made prior to the beginning of the season, crop variety, local conditions, and pricing information are major factors in the Figure 1. Fruit marketing decision matrix for citrus production.
3 decision-making process. Clearly, the pre-season decision to seek processing markets aords the manager more latitude in modifying the pest management program. e decision towards processing may be determined by a multi-year contract (round oranges), may vary annually, or remain xed for a given block or grove. e grower may still elect to market fresh fruit from this grove if fruit condition, fruit contract and price warrant. Managing pests on nonbearing citrus trees (<4 yr old), either as a new planting or as resets to an existing grove, is essential to the subsequent development of a healthy, highly productive, mature grove. Young tree care diers somewhat from mature grove care, in that management expenditures should focus on maximizing the protection of rapidly produced foliage and roots; fruit is not a factor. erefore, a citrus growers goal should be to maximize the production of leaves and roots of young trees through the optimization of fertilization, irrigation, weed control, and management of various foliar and root pests. e various foliar and root pests, comprised of insects, mites, nematodes and diseases that infest nonbearing citrus trees dier widely in distribution and abundance compared to those found on mature trees. Dierences in tree size and canopy density alone result in changes in microclimate that will aect pest and natural enemy population dynamics and injury thresholds for various pests. Frequent leaf and root ushing patterns typical of young trees supply a copious, continuous source of food that stimulates rapid pest and pathogen development. Severe and repeated canker infection of new leaf ushes may induce defoliation and debilitate young trees. Foliar insects such as psyllids, aphids, citrus leafminer, orangedog larvae, grasshoppers, and the little leaf notcher weevil can severely injure new leaf ushes without appropriate control, while these same insects are incidental pests of mature trees. Currently, the Asian citrus psyllid and citrus leafminer are the arthropod pests of greatest concern for young, non-bearing trees because of the need for greening and canker management. Both pests require new ush for reproduction and development into the adult stage. Given that young trees continuously produce new ush season-long, population densitites of both pests can reach high densities if le uncontrolled. Furthermore, resets in mature groves can serve as the only breeding site and food source for psyllids and leafminers in the o-season when there is little to no ush on mature trees. us, new leaf ush should be intensely scouted and managed. Root pests, such as sting nematode and termites, are also important pests of nonbearing trees and require control in certain situations. By contrast, greasy spot, a major economic disease of mature trees, is of much less importance in nonbearing citrus groves. Rust mites and spider mites, important defoliators or fruit pests of mature trees, can be more injurious on nonbearing trees, particularly those trees with open canopy. Although judicious use of pesticides is highly recommended for young tree care, eective management of citrus greening and canker dictates eective suppression of psyllid and leafminer populations. Scouting should be intensied on young trees such that treatment applications for psyllid and leafminer are timed to prevent major outbreaks of these pests. Spot treatment is also encouraged when pests are localized within the grove. General predators, such as ladybeetles, can be quite numerous feeding on psyllids, aphids, leafminers, and other foliar pests. Avoiding treating groves where natural enemies are numerous may help improve biological control. Consulting your extension agent will help in choosing the most eective and selective pesticide for the occasion. Refer to other sections of this guide that address specic pests of citrus trees in more detail.