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- Author or Editor: D.P.H. Tucker x
- HortScience x
Abstract
Citrus trees to which glyphosate (N-phosphonomethylglycine) was intentionally applied at 1.7, 3.3 and 6.6 kg/ha exhibited varying degrees of toxicity depending on tree age, location on tree sprayed, tissue maturity, and application rate. Symptoms included defoliation, twig dieback, malformed regrowth and callus inhibition around wound areas sprayed with glyphosate. While translocation from sprayed limbs was minimal, it was quite marked in citrus seedlings.
Recent trends in increased nitrate contamination of groundwater in parts of Central Florida have prompted this study to evaluate the potential for reducing the rates of nitrate (N) fertilizer to citrus. `Pineapple' orange trees on Swingle citrumelo rootstock growing on Candler fine sand were selected for the study. Fertilizer blends were applied using N as: (1) soluble ammonium nitrate and calcium nitrate in 4 applications per year and (2) controlled-release sources (Meister, Osmocote, Escote in one application per year and IBDU and Neutralene in 2 applications per year). Nitrogen rates varied 18-154, 36-308, and 57-454 g/tree/year during the first, second and third year after planting, respectively. Tree growth and leaf mineral concentrations (during the first 3 years) and fruit size and juice quality (second and third years) were not adversely affected by application of reduced N rates. Fruit yield (third year) was lower in the trees which received ≤ 114 g N/tree/year than in those which received higher rates of N.
Abstract
The relative susceptibility of ‘Ruby’ grapefruit (Citrus paradisi Macf.) and ‘Valencia’ sweet orange [C. sinensis (L.) Osb.] nursery trees on 8 rootstocks to applications of 4 herbicides was evaluated. Significant differences in injury ratings were determined following application. The severity of tree foliage toxicity symptoms was independently related to each factor. Toxicity ratings were highest for bromacil-treated trees, while grapefruit trees on C. macrophylla Wester, and Cleopatra mandarin (C. reticulata Blano) rootstocks showed the greatest phytotoxicity.
Abstract
These experiments were designed to evaluate the seasonal efficacy of several preemergence herbicides in the production of container-grown citrus trees. Sweet orange [Citrus sinensis (L.) Osb. cv. Hamlin] nursery trees on Carrizo citrange [C. sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.] and on Milam (C. jambhiri Lush hybrid) rootstocks were potted in synthetic mix (1 sand : 1 peat: 1 wood shavings, by volume) and grove soil (Astatula fine sand) in 15-liter, black plastic containers. Treatments included high and low rates of the preemergent herbicides trifluralin, napropamide, oxyfluorfen, metolachlor, oryzalin, alachlor, and oxadiazon along with manually weeded and weedy checks. Initial herbicide treatments were applied in March 1981 and repeated 3 additional times at 90-day intervals. All herbicide treatments significantly reduced the total number and fresh weight of weeds. High rates were consistently more effective than low rates. No treatment resulted in any visual foliar phytotoxicity, although alachlor and metolachlor significantly reduced the root vigor of both Carrizo and Milam.
Abstract
Some drip irrigation systems installed in central and south Florida citrus groves have ceased to function properly because of filter and emitter clogging. The most serious clogging has been a slime formed by filamentous sulfur bacteria. The most abundant sulfur bacteria was Thiothrix nivea Robenhorst, a common inhabitant of warm mineral springs in Florida. The bacteria oxidize H2S to S and can clog small openings within a brief period of time. Beggiatoa sp., a sulfur bacteria, was also found in the slime although the organism occurred most frequently in emitter orifices.
Another serious clogging factor has been Fe deposits in the form of filamentous, gelatinous ochre. The Fe deposits were associated with iron bacteria. The sticky sludge adhered to filters, grooves, and orifices of emitters. Iron sulfide clogged filter screens and accumulated in the grooves of some emitters.
Abstract
Four commercial formulations of 2,4-dichlorophenoxyacetic acid (2,4-D), including 3 oil-soluble amines and one low volatile ester were tested at 2 rates in plots of established budded citrus nursery stock. Five rootstocks budded to ‘Pineapple’ orange scions were evaluated for damage from spray applications to trunks. All amine salt formulations caused varying degrees of damage to the bark (below soil line) and root systems, with little or none from the ester. Rootstock sensitivity to 2,4-D formulations was highly significant with trifoliate orange (Poncirus trifoliata L.) and the hybrid ‘Carrizo’ citrange being most tolerant and rough lemon (Citrus jambhiri Lush.), ‘Cleopatra’ mandarin (Citrus reticulata Blanco), and sour orange (Citrus aurantium L.) least tolerant.
Evaluation ratings of cold injury following a freeze on December 24 & 25, 1989, showed differences among scion cultivars and rootstock. `Star Ruby' grapefruit (Citrus paradisi Macf.) and `Fallglo' citrus hybrid, a cross of Bower mandarin citrus hybrid × Temple tangor (C. temple Hort. ex Y. Tanaka) were the most severely damaged scion cultivars. `Rohde Red' valencia orange selection 472-11-43. [C. sinensis (L.) Osbeck]. was the least damaged scion cultivar. Scions budded to Cleopatra mandarin (C. reshni Hort. ex Tan.) and FL 80-18 citrumelo [C. paradisi × Poncirus trifoliata (L.) Raf.] rootstock were damaged more than on other rootstock. Scions budded to smooth flat seville (C. aurantium?) and P. trifoliata × Ridge pineapple sweet orange selection 1573-26 [C. sinensis (L.) Osbeck] had the least injury. Analysis comparing replications showed the greatest damage to be in the north side of the planting.
Abstract
Trees of ‘Bearss’ lemon [Gtrus limon (L.) Burm. f] in Florida produce numerous undesirable sprouts on scaffold limbs following severe pruning. Considerable time and expense is involved in removing these by hand. Several formulations containing naphthaleneacetic acid (NAA) singly and in combination with ethyl hydrogen 1-propylphosphonate (EHPP) were applied to determine if these sprouts could be satisfactorily controlled with chemicals. NAA by itself was effective and caused no abnormalities in new growth. The addition of EHPP increased sprout inhibition in some cases, but some leaf loss and distortion occurred.
`Hamlin' and `Valencia' oranges [Citrus sinensis (L.) Osb.], `Murcott' tangor (C. reticulata Blanco × C. sinensis), and `Redblush' grapefruit (C. paradisi Macf.) on 15 rootstock and own-rooted cuttings were planted at a 1.5 × 3.3-m spacing providing a density of 2020 trees/ha. Growth rate, productivity, and fruit quality varied among the scion and stock combinations. Combinations of moderate vigor and precocious fruiting performed better than very vigorous or dwarfing materials. Several freezes slowed canopy development and delayed production. Most trees had filled their allocated canopy space 7 years after planting. At that age, the orange trees yielded 23 to 75 t·ha-1. Scion and stock combinations with desirable vigor and fruiting characteristics were satisfactory in this high-density planting. However, there appears to be little advantage of high tree density under Florida conditions, and moderate densities of fewer than 1000 trees/ha may be preferable.
Abstract
Three applications granular formulations of herbicides were applied broadcast over a 7-month period to budded citrus trees growing in 7.6 liters (4-gal) containers with a soil mix containing equal parts of peat, bark, and sand. Materials and rates at each application were alachlor + simazine 4.48 + 2.24 and 8.96 + 2.24 kg/ha; oryzalin 5.60 and 11.20 kg/ha; trifluralin 5.60, 11.20 and 22.40 kg/ha; oxadiazon 4.48 and 8.96 kg/ha; napropamide 11.20 and 22.40 kg/ha; and alachlor 11.20, 22.40 and 44.80. Good to excellent weed control was obtained at all rates of all herbicides used with no phytotoxicity to citrus trees observed.