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  • Author or Editor: James Ferguson x
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Cover crops, cultivation, flaming, soil solarization, and mulching are commonly used for weed control in organic production systems. However, several new herbicides, approved by the Organic Materials Review Institute (OMRI), are recommended as contact, non-selective, post-emergence herbicides for annual grasses and broadleaf weeds. Citric acid (Alldown), clove oil (Matran 2), thyme/clove oil (XPRESS) were compared with glyphosate (Roundup Pro), a systemic broad spectrum herbicide, at three sites in southern and north central Florida during September and October, 2003. Treatments varied at each site but included glyphosate (5% a.i. applied to runoff) organic herbicides at recommended rates (undiluted citrus acid at 61 L·ha-1; 10% clove oil at 76 L·ha-1; 10% clove oil/thyme oil at 76 L·ha-1) and at twice recommended concentrations and application rates. Grasses and broadleaf weed species were different at each site but included Alexander grass, bahia grass, Bermudagrass, carpetweed, crabgrass, hairy indigo, lambs quarters, Florida pusley, goatweed, nutsedge, pigweed, shrubby primrose willow, broadleaf signalgrass, southern sandbur, spurge, torpedograss, and citrus rootstock seedlings. Weed control with the organic herbicides at all three sites at recommended and at higher concentrations and rates was inconsistent, ranging from 10% to 40%, compared with 100% control with glyphosate. Labels for the organic herbicides generally specify application to actively growing weeds less than 10 cm tall, emphasizing their use as early season herbicides. Fall applications to larger weeds, some within the specified maturity and size range and others taller and producing seed, could partially explain poor weed control.

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Citrus rootstock improvement has relied historically on clonal selections chosen from traditional field trials and from cold-hardy scion improvement programs. Although the impact of traditional plant breeding programs on citrus rootstock improvement has been limited because of biological impediments and lack of understanding of citrus genetics, newly developed techniques on the cellular and molecular level have provided new opportunities for progress.

Although trends in citrus rootstocks can be monitored through Budwood Registration data, official statistics are generally not available on rootstocks in bearing groves. Traditional screening programs include initial testing for resistance to fungal and viral diseases, nematode susceptibility, and nursery performance followed by evaluation as a budded tree. Rootstock trials underway include hybrids of `Ruby' orange/trifoliate orange, sweet orange/trifoliate orange, pummelo/trifoliate orange, and `Changsha' mandarin/trifoliate orange.

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Shredded and chipped wood mulches are used for weed suppression in perennial fruit crops, in urban landscapes, and occasionally in vegetable crops. Wood chip mulches with weed-suppressing allelochemicals may be more effective for weed control, especially under sustainable and organic production systems, than mulches without such properties. The objective of this study was to test for the presence of water-soluble allelochemicals in wood chips derived from tree species, often found in wood resource recovery operations in the southeastern US. Presence of allelochemicals in water eluates of woodchips and leaves was evaluated in a lettuce bioassay. Eluates of wood chips from red maple (Acer rubrum L.), swamp chestnut oak (Quercus michauxii Nutt.), red cedar (Juniperus silicicola L.H. Bailey), neem (Azadirachta indica A. Juss.), and magnolia (Magnolia grandiflora L.) highly inhibited germinating lettuce seeds, as assessed by inhibition of hypocotyl and radicle growth. The effects of wood chip eluates from these five species were more than that found for eluates from wood chips of black walnut (Juglans nigra L.,) a species previously identified to have weed-suppressing allelochemicals. Tests on red cedar, red maple, and neem showed that water-soluble allelochemicals were present not only in the wood but also in the leaves. In greenhouse trials, red cedar wood chip mulch significantly inhibited the growth of florida beggarweed (Desmodium tortuosum DC.), compared to the gravel-mulched and no-mulch controls.

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Soil incorporation of poultry litter can damage roots of citrus trees grown on shallow soils in southern Florida. Using an alternative application method, young `Minneola' tangelo trees (Citrus reticulata Blanco × C. paradisi Macf.) on Cleopatra mandarin rootstock (C. reticulata Blanco) on bedded groves in southeast Florida were fertilized for 18 months after planting with surface-banded poultry litter (PL) overlaid with wood chips (WC). PL/WC was applied at 142, 284, and 425 kg·ha-1 N in two applications/year in one 0.6-m band within the dripline of trees planted at 278 trees/ha. Other treatments with different N rates included 220 kg·ha-1 N broadcast in the middle of the bed twice a year and 116 kg·ha-1 N as controlled release fertilizer applied within the dripline of trees in three applications per year. Eighteen months after planting, growth of trees receiving PL/WC treatments of 142, 284, and 425 kg·ha-1 N per year and 116 kg·ha-1 N per year was similar and greater than growth of trees receiving PL broadcast in grove middles at 220 kg·ha-1 N per year. Soil P, Ca, and Mg levels beneath the three banded PL/WC treatments were higher than in other treatments; in all treatments leaf N levels were optimum, but leaf P, K, Ca, Mg, and Fe levels were excessive. Banded PL/WC treatments applied at 142 kg·ha-1 N per year and even lower rates may be adequate for growth of young citrus trees, especially in terms of reducing excessive soil and leaf nutrient levels.

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Alternate bearing in pistachio (Pistacia vera L.) is correlated with crop load; a heavy crop on l-year-old wood appears to cause abscission of inflorescence buds on current wood. Defruiting heavily bearing trees before or during the period of nut growth stopped inflorescence bud loss. This relationship between crop and bud loss was affected by the fruiting status of neighboring shoots. Large defruited branches (> 5.5cm diameter). in fruiting trees had bud retention values (50% to 65%) equivalent to fully defruited control trees, but smaller branches showed reduced bud retention levels. Bud retention was increased 2- to 6-fold in small branches when neighboring branches were defruited. Nitrogen concentration of leaves in late August was positively correlated with the final bud retention percentage and inversely correlated with defruiting date.

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Wood chip mulches from southern redcedar (Juniperus silicicola) and southern magnolia (Magnolia grandiflora) were evaluated for their effectiveness in weed control in nursery containers. In greenhouse tests, southern redcedar and southern magnolia wood chip mulches significantly inhibited the germination of redroot pigweed (Amaranthus retroflexus) and large crabgrass (Digitaria sanguinalis). In a field trial, nursery containers with ‘Carolina Beauty’ crape myrtle plants (Lagerstroemia indica) were sown with large crabgrass and redroot pigweed seeds, mulched with southern redcedar or southern magnolia wood chips, and compared with plants without mulch and plants treated with a mixture of isoxaben and trifluralin (Snapshot). Wood chips from both southern redcedar and southern magnolia were as effective as a mixture of isoxaben and trifluralin in suppressing weed growth in nursery containers. The wood chip mulches had no inhibitory effect on the growth of crape myrtle plants. In a similar, longer-term field trial using containerized dogwood (Cornus florida) plants sown with large crabgrass and redroot pigweed, the southern redcedar wood chip mulch was most effective in weed suppression when used in combination with a low dose of the chemical herbicide.

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With funding to increase support for organic farming research at land grant universities, organic growers have collaborated with faculty and administrators to develop an undergraduate, interdisciplinary minor at the University of Florida. Required introductory courses focus on general concepts of organic and sustainable farming, alternative cropping systems, production programs, handling, and marketing issues. An advanced horticulture course requires intensive examination of certification procedures, farm plans, soil fertility, and crop management, all of which are integrated into a required field project. Extension faculty have also fostered development of this new curriculum by coordinating regional workshops and field days in collaboration with organic growers and by developing educational materials on organic certification and related issues.

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Our objectives were to determine if leaf N concentration in citrus nursery trees affected subsequent growth responses to fertilization for the first 2 years after planting and how N fertilizer rate affected soil nitrate-N concentration. `Hamlin' orange [Citrus sinensis (L.) Osb.] trees on `Swingle' citrumelo rootstock [C. paradisi Macf. × P. trifoliata (L.) Raf.] were purchased from commercial nurseries and grown in the greenhouse at differing N rates. Three to five months later trees were separated into three groups (low, medium, high) based on leaf N concentration and planted in the field in Oct. 1992 (Expt. 1) or Apr. 1993 (Expt. 2). Trees were fertilized with granular material (8N–2.6P–6.6K) with N at 0 to 0.34 kg/tree yearly. Soil nitrate-N levels were also determined in Expt. 2. Preplant leaf N concentration in the nursery varied from 1.4% to 4.1% but had no effect on trunk diameter, height, shoot growth, and number or dry weight in year 1 (Expt. 1) or years 1 and 2 (Expt. 2) in the field. Similarly, N fertilizer rate had no effect on growth during year 1 in the field. However, trunk diameter increased with increasing N rate in year 2 and reached a maximum with N at 0.17 kg/tree yearly. Shoot number during the second growth flush in year 2 was much lower for nonfertilized vs. fertilized trees. Leaf N concentrations increased during the season for trees with initially low levels even for trees receiving low fertilizer rates. Soil nitrate-N levels were highest at the 0.34-kg rate, and lowest at the 0.11-kg rate. Nitrate-N levels decreased rapidly in the root zone within 2 to 3 weeks of fertilizing.

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Our objectives were to determine the effects of leaf N concentration in citrus nursery trees on subsequent growth responses to fertilization for the first 2 years after planting and the impact of N fertilizer rate on soil NO3-N concentration. `Hamlin' orange [Citrus sinensis (L.) Osb.] trees on `Swingle' citrumelo rootstock [C. paradisi Macf. × P. trifoliata (L.) Raf.] were purchased from commercial nurseries in Apr. 1992 (Expt. 1) and Jan. 1993 (Expt. 2) and were grown in the greenhouse at differing N rates. Five months later, trees for each experiment were separated into three groups (low, medium, and high) based on leaf N concentration and were planted in the field in Oct. 1992 (Expt. 1) or Apr. 1993 (Expt. 2). Trees were fertilized with granular material (8N-2.6P-6.6K-2Mg-0.2Mn-0.12Cu-0.27Zn-1.78Fe) with N at 0, 0.11, 0.17, 0.23, 0.28, or 0.34 kg/tree per year. Soil NO3-N levels were determined at 0- to 15- and 16- to 30-cm depths for the 0.11-, 0.23-, and 0.34-kg rates over the first two seasons in Expt. 2. Preplant leaf N concentration in the nursery varied from 1.4% (Expt. 1) to 4.1% (Expt. 2) but had no effect on trunk diameter, height, shoot growth and number, or dry weight in year 1 (Expt. 1) or years 1 and 2 (Expt. 2) in the field. Similarly, fertilizer rate in the field had no effect on growth during year 1 in the field. However, trunk diameter increased with increasing N rate in year 2 and reached a maximum with N at 0.17 kg/tree per year but decreased at higher rates. Shoot number during the second growth flush in year 2 was much lower for nonfertilized vs. fertilized trees at all rates, which had similar shoot numbers. Nevertheless, leaf N concentrations increased during the season for trees with initially low levels, even for trees receiving low fertilizer rates. This suggests translocation of N from other organs to leaves. Soil NO3-N levels were highest for the 0.34-kg rate and lowest at the 0.11-kg rate. Within 2 to 3 weeks of fertilizing, NO3-N levels decreased rapidly in the root zone.

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CITPATH, a computerized diagnostic key and information system, was developed to identify the major fungal diseases of citrus foliage and fruit in Florida. This software provides hypertext-linked descriptions and graphic displays of symptoms, maps of geographic occurrence, diagrams of disease development, and management strategies, with reference to chemical control methods detailed in the current Florida Citrus Pest Management Guide. Reciprocal lists of citrus cultivars susceptible to specific diseases and diseases affecting specific cultivars are included. Developed for commercial growers, county extension programs, citrus horticulture classes, and master gardeners, this software is available for MS-DOS-based computers and on CD-ROM disks containing other citrus databases.

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