No significant difference in root or top weight of 25 citrus rootstock seedlings grown in the greenhouse for 15 months was attributable to infestation of the citrus nematode, Tylenchulus semipenetrans (Cobb). Many nematodes were found on the roots of most of the cultivars tested regardless of nematode biotype, with the exception of trifoliate orange and some hybrids where one parent was trifoliate orange.
Three-year-old seedlings of Cleopatra mandarin (Citrus reticulata Blanco) and Troyer citrang [Citrus sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf] were budded to ‘Valencia’ orange (Citrus sinensis (L.) Osbeck) at 5, 15, 30, 45, 60, and 90 cm above the ground level. Fruit yield was highest from trees budded at 15 cm height above the ground and tended to decrease as budding height increased. Nutrient concentrations in the leaves of trees were affected by the height of budding, but remained in an optimum range for maximum fruit production. The different rootstocks affected the nutrient concentrations in the leaves dramatically, but they still remained in an optimum range for maximum production of oranges.
Tree density (222-801 trees/ha) affected growth of roots in plantings of ‘Washington’ navel orange (Citrus sinensis (L.) Osbeck). Root spread, circumference, and root size were greater on wide spaced trees than on closely planted trees which had overlapping root systems. Roots of closely spaced trees were shorter in length and smaller in size.
Naphthaleneacetic acid (NAA) formulated as a sodium salt and as the ethyl ester applied in the spring of 1975 and 1976 to unpruned trunks of Pyracantha coccinea (Roem.) cv. Rosedale effectively controlled sprout growth. The 1% concentration of each formulation reduced growth 4 cm more than the 0.5% concentration. The control averaged 49 sprouts and treated plants ranged from 2 to 4 sprouts.
Three year old lemon trees [C. limon (L.) Burm f.] were selectively pruned to form a 3- to 4-scaffold branch structure for limb shaker harvesting. Yield was reduced 16 kg per tree and trunk circumference 10 cm above the bud union was reduced 5.3 cm per tree over a 6-year period. Training was completed with minimal production loss.
Trees of old-line ‘Atwood’ navel sweet orange [Citrus sinensis (L.) Osbeck] on Rubidoux trifoliate orange [Poncirus trifoliata (L.) Raf.] were planted in 1970 at 331 to 801 trees per ha to determine effects of tree spacing on growth, yield, production costs, and fruit quality. Growth measured as trunk circumference and hence fruit-bearing capacity per tree was inversely proportional to tree density but fruit yields per hectare increase with close spacing.
In 1961, trees of Frost Nucellar ‘Washington’ navel orange on Troyer Citrange rootstock were planted at eleven different spacings to determine the effect of tree spacing on growth, production, and fruit quality. Growth rate as measured by trunk circumference was proportional to decreasing tree density or increased spacing. The wider the spacing, the greater was the trunk circumference and the fruit-bearing capacity of the tree. Shading of skirt foliage, as closely planted trees began to crowd, caused the skirts to die and decreased production. Pruning to keep these trees from crowding reduced yield in proportion to the amount of foliage removed. Removal of alternate trees in the two most densely planted spacings, 9 ft. × 11 ft. and 11 ft. × 11 ft., reduced competition and allowed more light to reach the remaining trees. Skirt foliage regrew and yield per-tree and per-acre increased.
Fruit colored faster and was larger on the widely spaced trees, where less shading had occurred, than on closely spaced trees. Fruit quality analysis showed no difference in percent of juice, soluble solids, acid, or rag, or in peel and rind thickness.
The closest spacings, 9 ft. × 11 ft., 9 ft. × 15 ft. and 11 ft. × 11 ft., operated at a net loss for the first five years of production. Although per tree production was highest on the widest spacing, 22 ft. × 22 ft., net returns per acre on this spacing are still low because of the number of trees per acre. The 11 ft. × 22 ft. spacing with 180 trees per acre had the largest net income per acre.
High density planting of tree crops has the potential of increasing yield and income during the early years of an orchard’s life. Eleven different planting densities of citrus were studied over a 10-year period to determine the effect of tree spacing on yield, tree growth, root distribution, nutrition, and economic factors involved. Extremely close plantings soon crowded to the point where they were unmanageable and tree removal became necessary. Pruning was needed to maintain a workable orchard in more moderatley spaced plots.
Application of 1% ethyl ester of napthaleneacetic acid (NAA) in an aqueous or latex formulation to trunk and scaffold branches of pruned lemon trees [C. limon (L.) Burm.] did not affect yield during the season of application or during the year following application. Regrowth of trunk and limb sprouts was controlled for approximately 1 year.