Volume 2, Issue 1 March 2005
Spring Citrus Meeting
Thursday, April 14, 2005
Tulare County Ag Bldg
4437 S Laspina, Tulare, CA
8:00 Registration
8:30 Regulated Deficit Irrigation Progress Report
Dr. David Goldhamer, UC Water Management Specialist
Kearney Research & Extension Center
9:00 Status of a Pheromone Trap for Citrus Peelminer
Dr. Beth Grafton-Cardwell. UC IPM Specialist
Kearney Research Extension Center
9:30 Mandarin Cultural Management
Dr. Thomas Chao, UC Subtropical Specialist
UC Riverside
10:00 Economic Impact of Citrus Tristeza on Navel Orange
Louis Whitendale, Superintendent
Lindcove Research Extension Center (Retired)
One (1) hour of continuing education credit has been requested
Citrus Notes • March 2005 • Page 3
Citrus Notes • March 2005 • Page 3
Citrus Notes • March 2005 • Page 3
Nitrogen Management
An efficient nitrogen management program should involve consideration of the results of leaf analysis, production and fruit quality records, as well as fertilization records including material, rate, timing and method of application. To assist in management decisions regarding nitrogen use results from recent research in navel oranges in Tulare County by Drs. Lund and Arpaia are included. In the study nitrogen was applied in increasing amounts and at various times by foliar application, introduced into the irrigation system or in a combination of foliar and fertigation applications. Foliar treatments were as follows: one time only at late May; two applications, one late winter and one late May; four times-late winter, prebloom, late May and 30 days following the late May application. Soil treatments (injected into the low volume irrigation system) were: one application in late winter; two applications-late winter and early summer; continuous application –applied in every irrigation from late winter through summer. Samples were taken of soil solution moving below the root zone. Fruit yield, size and quality were evaluated. Results of the trial demonstrated an increase in yield with increasing amounts of applied nitrogen up to 1 to 1 ½ lbs. of actual nitrogen per tree per year. This effect was demonstrated regardless of the method of application. The rates of actual nitrogen applied varied with the various treatments from 0-2.1/4 lbs. Soil applications (fertigation) resulted in the highest nitrate nitrogen leaving the rootzone in the soil solution with foliar applications resulting in the least and combination treatments of foliar and soil resulting in intermediate levels of nitrate in the leachate.
When nitrogen was applied in a single irrigation versus application in split or applied in each irrigation, the single application always resulted in the highest nitrate in the soil solution leaving the rootzone. Among the various rates in the fertigation treatment, the higher the rate the higher the nitrate leaving the rootzone.
Canopy Management Considerations
In considering a pruning program for an orchard a critical consideration would be the impact of pruning on yield and fruit size. A recently completed research study by Craig Kallsen CE Kern County addressed the impact of topping and interior pruning. Thirty-five year old Frost Nucellar navel trees 20 feet in height, planted on a 20 x 22 spacing received one of three topping treatments-no topping, topped to 16 feet and topped to 14 feet. Three levels of interior pruning were also evaluated-no interior pruning(2000-2002), deadbrush removal only(2000-2002) and severe interior pruning where major scaffold branches were removed(2000) followed by deadbrush removal only(2001-2002). The study was begun in March 2000 and the last harvest was January 2004. The overall objective of the study was to evaluate the effect of topping and interior pruning on yield, fruit size and fruit grade. The results demonstrated no difference in yield (lbs. of fruit per tree) among the three topping treatments either annually or cumulatively. There was no difference in number of fruit per tree in sizes 72-48 among the three topping treatments. There was a significant difference in yield and fruit size from the interior pruning treatments. Severe interior pruning resulted in a significant reduction in yield (number of fruit per tree) and significant reduction in number of fruit sized 72-48. Regardless of pruning intensity or weather a constant linear relationship seemed to exist between numbers of fruit and number of large fruit. Conditions that promote numbers of fruit allow for production of larger fruit. Large fruit may result from severe interior pruning, but there are too few of them. The trees that received no interior pruning produced equal or greater yields, fruit of equal or greater size and grade.
Rind Quality
Loss in rind quality has resulted from the effects of the freeze, and continuing periods of rain and foggy weather. Episodes of ice formation on the peel result in tissue damage that eventually may be invaded by secondary pathogens. Limb rub, and puncture wounds are often the sites of colonization as well. As an example, colonization by Penicillium (green and blue mold) of these sites has been of frequent occurrence in citrus orchards this winter. Many of these affected fruit drop prematurely avoiding harvesting costs of affected fruit. Cool, wet weather is conducive to reproduction of several weak pathogens that are commonly found in citrus. Tear staining or anthracnose results from the colonization of one such fungus (Colletotrichum); as spores of the pathogen move with films of water down the surface of the rind a streaking or tear staining is produced. Rind tissue weakened during cold episodes can be invaded by Septoria, a bacterial invader, which often results in minute dark brown or black pits which may coalesce into pits of much larger size. There are cultural operations which are helpful in reducing the incidence of these rind conditions. Careful harvest and transport operations that minimize abrasion of the rind and clipper cuts, dumping harvested fruit from excessive heights into bins, jostling of fruit during transport are all helpful. Removal of deadbrush is also helpful in reducing the opportunity for fruit abrasion during windy conditions, allowing for better coverage during spray operations, and removal of sites where much of the pathogen resides.
Citrus Notes • March 2005 • Page 3
Citrus Notes • March 2005 • Page 3
Neil O’Connell
Farm Advisor
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