|Trees and their Management (IIRR, 1992, 195 p.)|
Species and varieties
Three species of citrus are commonly grown commercially. They are calamansi, mandarin orange and pomelo. Calamansi has no recognized horticultural varieties and, except for the variegated mutant, all trees belong to only one form.
Ladu, Szinkom and Ponkam are the leading mandarin orange varieties while Amoy Mantan, Sunwiluk and Siamese are the commercial pomelo varieties grown.
Almost all fruit nurseries specializing in citrus propagation produce shield-budded planting materials on calamandarin rootstocks.
Citrus is known to thrive well in both tropical and subtropical climates. Places with well-distributed rainfall are best although those with distinct wet and dry seasons are equally suitable, especially if irrigation can be provided during the dry season.
For best production, the soil should be deep, clay loam or sandy loam in texture for easy drainage, slightly acidic (pH 5.5-6.5) and rich in organic matter. Lands with flat to gently rolling terrain are preferrable although those with hilly terrain may also be utilized.
Flat to gently rolling lands are deep-plowed once and harrowed 2-3 times during the dry season well in advance of planting. These operations are dispensed with in hilly areas.
Plant at the onset of the rainy season. Set planting materials in previously prepared holes laid at the following planting distances: calamansi, 4-5 m; mandarin orange, 5-6 m and pomelo, 8-10 m. In hilly areas, adjust planting distances according to the slopes.
TRAINING AND PRUNING
Starting on the second year after planting, trim young citrus trees so that they have only a single trunk with 34 well-distributed primary branches. The main branches should originate at different points on the trunk from 30 to 60 cm above the ground. Remove all shoots on the trunk that sprout below 30 cm.
In subsequent years, prune regularly to remove all watersprouts as well as diseased and dead twigs.
Water the plants right after planting to effect immediate root contact with the soil. Irrigate regularly during the first dry season after planting.
Irrigation during the subsequent dry seasons can be dispensed with although it is most beneficial to the vegetative and reproductive processes of bearing trees.
Leaf nutrient standards as fertilization have been established for other citrus species (e.g., sweet orange, grapefruit) but not for calamansi, mandarin orange and pomelo.
In their absence, only a general fertilization guide can be made. Thus, for non-bearing trees, apply 100-200 9 ammonium sulfate (or 50-100 9 urea) per tree at the onset and towards the end of the rainy season. At the start of fruiting, apply 300 9 complete fertilizer (NPK) twice a year as indicated. Increase the rate as the trees grow bigger and yield increases. At the peak of production (10-15 years old), each tree should receive at least 2 kg per application.
Use organic fertilizers to reduce the requirements for inorganic fertilizers.
Apply the fertilizer either by broadcasting it or placing it in several shallow holes beneath the tree canopy.
CONTROL OF PESTS
Rind borers (especially in pomelo), green bugs and jumping lice are the most serious pests. Control rind borers by collecting and buming infested fruits and spraying the trees with an insecticide at the pre- and post-bloom stages at 12-14 days interval for four applications.
Control green bugs and jumping lice (the vector of leaf mottling disease) by regular application of an insecticide).
CONTROL OF DISEASES
Canker, footrot and leaf mottling are the most serious diseases. Control bacterial canker (on leaves and fruits) with sprays of a copper-based fungicide. Cut down and bum infected trees.
Avoid footrot by planting only on well-drained soils. Also avoid too-close planting, too-low budding and deep planting.
Avoid leaf mottling or greening disease by using diseasefree-planting materials and by controlling the jumping lice.
Harvest calamansi fruits when they have attained full size. At this stage, they are yellowish green in color and very juicy. Harvest mandarin oranges when they show color break and their juice turns subacid. Harvest pomelo when their skin turns yellowish and yields easily to finger pressure.