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Home , Citrus, Citrus production, Orange (fruit), Tangerine, The Citrus Industry

Factors affecting production and quality By Mongi Zekri resources between vegetative and itrus production and reproductive growth is one of the quality are influenced by reasons that citrus fruit grown Cmany factors, including in tropical climates tend to have climatic conditions and produc- lower TSS than that grown in tion practices. subtropical climates. In subtropical climates, the CLIMATE temperature usually falls below 70°F for several months dur- Within fairly broad parame- ing winter. This period of cool ters of adequate soil and rea- temperatures causes growth to sonably good cultural and cease and citrus to become protection practices, climate is dormant for about three months. the most important component of The cool temperatures during the climate-soil-culture com- this dormant period promote plex causing differences in fruit Figure 1. The HLB disease tetrahedron floral induction. When warm quality among commercial citrus spring temperatures, among production areas. other things, stimulate the There is considerable di- resumption of vegetative growth, versity among citrus induced grow and produce in their response to climate, . especially as regarding market In tropical climates, there quality of the fruit. For example, is no period of cold temperature navel develops its best to induce dormancy. However, eating and eye appeal qualities with periods of less than ample in a Mediterranean-type climate soil moisture (drought stress), with cool, wet winters and hot, flushes of bloom and vegetative tive growth will reduce the resources dry summers. In wet, tropical growth normally follow these drought available to developing fruit, resulting regions, navel fruit tends to be large periods. in fruit with lower total soluble solids with poorly colored rinds and low It is well documented that vegeta- (TSS). A period of dormancy, during TSS and acid in the . tive and reproductive fruit growth which there is little or no vegetative Unlike navel, most culti- compete for available resources, such growth, reduces this competition for vars develop optimum internal quality as () and resources and results in fruit with in warm climates with little winter . Flushes of heavy vegeta- increased TSS. The competition for chilling. is adapted to a broad range of climates, produc- ing excellent to acceptable fruit qual- ity in most of the world’s important citrus regions. What will tomorrow bring? Some — but not all — of these climate-induced differences can be Be prepared. overcome with cultural practices. For example, there is no known cultural practice that allows (a Medi- terranean climate) to produce low- acid, thin- grapefruit similar to the world’s top-quality grapefruit grown in (a humid, subtropical climate). Worldwide climate has a significant Protect your investment with crop effect on citrus yield, growth, fruit from Farm Credit. quality and economic returns. In growing regions where the average Deadlines: Fruit-April 1, 2011; temperatures remain high all Trees-May 1, 2011 (tropical climates), fruit peel chloro- phyll does not degrade and oranges and remain green, whereas This institution is an equal opportunity provider and employer. in cool-winter subtropical climates, oranges and tangerines develop more 866.824.5626 FarmCreditFlorida.com intense orange peel color and greater

6 CITRUS INDUSTRY • December 2011 eye-appeal at maturity. ing, and reduce preharvest fruit drop. Naphthalene acetic acid (NAA) is In lowland tropical areas, due to Gibberellic acid (GA) is recom- used to thin fruit when excessive set high respiration rates at warm tem- mended for citrus hybrids that are occurs. Thinning heavily cropping peratures, fruit mature quickly and do weakly parthenocarpic and without trees with NAA increases fruit size. not have sufficient time to accumulate sufficient cross- to improve The greatest thinning response to NAA high TSS, and acidity declines rapidly fruit set. Applied from full bloom to has been shown to occur when applica- so that the soluble solids/acid ratio two-thirds petal fall, GA can effective- tions are made when the average fruit increases sharply, and the fruit quickly ly set and produce an excellent crop diameter is about 1/2 inch, which typi- become insipid and dry. TSS in fruit of seedless Robinson, Nova, Orlando, cally occurs from six to eight weeks accumulate most slowly in cool coastal Minneola or other self-incompatible post bloom. Thinning of and areas. Maximum levels of TSS are usu- mandarin hybrids. Application of GA Sunburst tangerines with NAA was ally attained in the mid-tropics and in to citrus fruit approaching maturity found to increase fruit size, aver- humid subtropical regions with warm enhances peel firmness and delays age fruit weight and percent packout winters. Total acid (TA) levels are peel senescence. through improved fruit appearance. generally greatest in semiarid or arid Application of GA in the fall often subtropical and coastal climates and increases juice extraction from sweet / decline more slowly as fruit mature, oranges. It is likely that GA enhances The most important determinant of compared with other climates. De- juice extraction efficiency because fruit production and quality under the crease in TA is primarily a function of increased peel firmness provides better grower’s control is cultivar selection. temperature (heat unit accumulation) mechanical support for fruit within Under comparable conditions, Hamlin and the rapid respiration of organic extraction cups. orange always has poorer juice color acids at those higher temperatures. Applied in winter during floral and lower TSS than Midsweet or induction to cultivars that routinely Valencia orange. On the other hand, GROWTH REGULATORS heavily but set poor such Hamlin produces higher, more con- Application of growth regula- as Navel, Ambersweet and Ortanique, sistent yields per acre than any other tors (PGRs) can provide significant GA reduces flowering and often results sweet orange cultivar. Worldwide, economic advantages to citrus growers in increased fruit set. A combina- Valencia produces premium quality when used in appropriate situations. tion of GA and 2,4-D has been used fruit with excellent internal quality, Depending on cultivar and timing, in many fresh fruit-growing regions high sugars, superior and deep PGRs may improve fruit set, increase to enhance peel strength and extend color at maturity. fruit size by reducing cropload, extend the harvest seasons for grapefruit and Besides cultivar, many of the horti- the harvest season by delaying rind ag- sweet oranges. cultural characteristics of cultivars are

CITRUS INDUSTRY • December 2011 7 fast-growing, vigor- cal stages of expansion, bloom, ous such fruit set and fruit enlargement. as rough , Proper irrigation increases fruit , size and weight, juice content and soluble solids: acid ratio. Soluble and . How- solids per acre may increase due to ever, these rootstocks yield increase. However, soluble solids impart high vigor to per box and acid contents are reduced. the scion and induce Through its tendency to stimulate high yield. vegetative growth, irrigation in the fruit from trees grown dry fall and winter may reduce soluble on vigorous rootstocks solids in the fruit. Decline in total acid tend to be puffy, hold levels can also be aggravated by exces- poorly on the and sive irrigation. have high incidence of Citrus trees require a good water granulation. management system and a balanced Cultivars on slower- nutrition program formulated to pro- growing rootstocks vide specific needs for maintenance generally do not pro- and for expected yield and fruit quality duce vigorous vegeta- performance. Adequately watered and tive growth, but tend nourished trees grow stronger, have to produce small- to better tolerance to pests and stresses, medium-size fruit yield more consistently and produce with smooth peel tex- good quality fruit. On the other hand, ture and good quality excessive or deficient levels of water or fruit with high TSS fertilizer will result in low fruit yield and acid content in the and oversize fruit with poor quality juice. This latter group and diluted soluble solids content. influenced by the rootstock, including of rootstocks includes The most important nutrients tree vigor and size, and fruit yield, and some of its hybrids ( and influencing fruit quality are nitrogen, size, maturity date and quality. One citrumelos). Sweet oranges budded and . However, of the best-known examples is the on Carrizo have been among when any other is deficient or small fruit size of Valencia budded on the most profitable combinations over in excess, fruit yield and quality are Cleopatra mandarin (Cleo) rootstock. the long term in Florida. Planted negatively altered. Nitrogen (N) in- Cleo is well suited for use with Temple on the right soils, trees on Swingle creases juice content, TSS per box and orange, tangerines and tangerine are very productive at high- per acre, and acid content. However, hybrids. Sweet orange and grapefruit density plantings. excessive N can induce excess vigor cultivars on Cleo generally produce and promote a vegetative rather than a small fruit and are not precocious, IRRIGATION AND NUTRITION flowering tree, and can result in lower thus Cleo is not commonly used for Although citrus trees develop large- yields with lower TSS per acre. In these varieties. Low yield associated ly in response to their genetic endow- contrast, low N levels promote exten- with Cleo rootstock is the result of ment and the climate, good production sive flowering, but fruit set and yields poor fruit set and size, and fruit split- practices can have favorable influences are poor. ting. Scions on Cleo are most produc- on fruit production and quality. Cultur- Phosphorus reduces acid content, tive on heavier soils. al practices that attempt to cope with which increases soluble solids: acid ra- Larger fruit with thicker, rougher climatic or weather problems include tio. Potassium (K) increases fruit pro- peel and lower concentrations of TSS irrigation and nutrition. Irrigation is duction, fruit size, green fruit and peel and acid in the juice are generally of particular importance during the thickness. Foliar spray of potassium associated with cultivars budded on spring, which coincides with the criti- nitrate or monopotassium phosphate in the spring often increases fruit size of tangerine and grapefruit, and fruit size and total pound solids of Valen- cia orange. Foliar application (six to eight weeks before bloom) of urea can increase flowering and fruit set. SUNLIGHT AND PRUNING Even though citrus trees can toler- arcadia citrus enterprises, inc. ate shade and still flower and fruit, Over 30 in maximum flowering occurs when trees are grown in full sun and light Brian Bartholomew penetration through the canopy is Mobile (863) 990-0800 • Office (239) 368-2128 maximized. Therefore, pruning — including topping and hedging — to P.O. Box 1289 Fort Myers, Florida 33902 avoid crowding is extremely important

8 CITRUS INDUSTRY • December 2011 for optimum flowering. The amount of fruit that is set has a very signifi- cant effect on fruit quality. There is a Outlook for Florida Citrus positive correlation between the num- ber of fruit per tree and fruit quality. Remains Positive When the number of fruit per tree is By Bob Norberg low, the peel texture, shape of fruit Deputy Executive Director , Research and Operations and often fruit color are poor. Quality he Florida Department of Citrus (FDOC) provides growers with up-to-date of individual fruit varies significantly, resources to make informed business decisions. In addition to a variety of even on the same tree. Heavily shaded T monthly reports including economic indicators, sales trends, pro- fruit borne on the interior of the cessed products statistics, imports and exports and fresh citrus shipments, the canopy have less TSS than fruit on FDOC compiles an annual Florida Citrus Outlook with supply, demand and price the exterior of the canopy. Insufficient projections to help growers plan for the upcoming season. light contributes to reduced TSS con- Dr. Mark Brown, senior economist, utilizes information from the USDA Oc- centration of interior fruit nourished tober 2011 citrus crop estimate to calculate potential scenarios for the 2011-2012 by heavily shaded . season. Once again, the numbers predict that Florida citrus will continue to be a sustainable, vibrant industry and a key economic contributor to the state. It is well established that shoots This season, both Florida and orange juice production levels are pro- with fruit do not flower the follow- jected to increase, by 6 percent and 31 percent, respectively. Combined Florida- ing year. A heavy fruit crop tends to Brazil orange juice production is expected to be up about 22 percent, but these deplete carbohydrates and results in increases are offset by relatively large declines in the beginning inventories for the a small crop and increased vegetative 2011-2012 season. As a result, the aggregate Florida-Brazil orange juice avail- growth the following year. Pruning ability (new production plus beginning inventory) is projected to increase by 5.5 after a heavy crop additionally stimu- percent from last year. lates vegetative growth and reduces Much of the increase in Brazil’s production, however, is expected to be used to fruit yield the following year. Pruning rebuild inventories in Brazil. Therefore, the aggregate Florida-Brazil orange juice after a light crop and before an ex- availability for the market may be similar to or decline from last year’s level. Over- pected heavy crop can increase fruit all, orange juice availability and movement levels in 2011-2012 support relatively size and help reduce alternate bear- strong pricing. Retail orange juice sales and U.S. orange juice consumption in ing. Pruning or topping and hedging 2011-2012 are estimated to decline by about 3 percent from last year due to lower availability and higher prices. usually increase fruit size and packout This season’s Florida grapefruit crop is expected to be slightly larger than last of fresh-market fruit by reducing crop year. Domestic fresh grapefruit shipments are projected to increase moderately load, thus increasing net cash returns due to an estimated 19 percent decrease in grapefruit production. to growers. availability is expected to be down from last season as a result of a reduction in the beginning inventory level. Grapefruit juice movement is CONCLUSION projected to be down from last year due to lower availability and higher prices. The improvement in citrus fruit Overall, the grapefruit juice supply and demand situation supports relatively high production and quality that a grower grapefruit prices. can achieve through choice of scion/ Total on-tree revenue for oranges, grapefruit and specialty citrus is projected to rootstock combinations, good irriga- be $1.38 million, up 20.5 percent from last season, and the second highest total tion management, balanced nutrition in history. and proper pruning may easily be In spite of challenging economic conditions, the ongoing viability of the overwhelmed by pests, diseases and Florida citrus industry remains strong. There are currently 71 million citrus trees other injuries. Excessive leaf loss in commercial production, and the industry continues to contribute approximately $9 billion to the state economy. will noticeably reduce flowering the FDOC will continue to help grow the market for the Florida citrus industry to following spring and subsequent fruit ensure its sustainability for future generations, as well as its important contribu- production. The primary causes of tions to Florida’s agriculture and economy. leaf loss are freeze, tropical storm The complete Florida Citrus Outlook report is posted on FDOCGrower.com injury, and water stress problems at https://fdocgrower.box.net/shared/2n5zfo2cur. Please join me in thanking Dr. including drought stress and flooding Brown for 28 years of dedicated service to the citrus industry and wishing him injuries, mites, greasy spot, well in his retirement. You can expect a seamless transition as Dr. Matt Salois and pesticide toxicities. Excessive leaf joins FDOC as director of Economic and Market Research. loss in the fall and in early winter is Please feel free to contact me at 863-537-3957 or [email protected] the worst thing that can happen to cit- if you have any questions. rus trees. It will reduce accumulation The mission of the Florida Department of Citrus is to grow the market of carbohydrates affecting flowering, for the Florida citrus industry to enhance the economic well-being fruit set and fruit yield. Therefore, of the Florida citrus grower, citrus industry and the state of Florida. good practices in citrus groves should For more information, visit www.FDOCGrower.com be adapted to minimize negative plant physiological stresses, improve tree health and performance, and enhance citrus trees to produce high yield of good fruit quality.

Mongi Zekri is a multi-county citrus Column sponsored by the Florida Department of Citrus Extension agent based in LaBelle. P.O. Box 9010, Bartow, FL 33831-9010

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