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James J. Ferguson, Elizabeth Lamb and Mickie Swisher

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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Laura Guazzelli, Frederick S. Davies and James J. Ferguson

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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James J. Ferguson, Fedro S. Zazueta and Juan I. Valiente

Fungal diseases have their greatest impact on citrus in Florida by reducing tree vigor, fruit yield, and quality. Given the complex etiology of these diseases, this software was developed to facilitate diagnosis of symptoms and to explain the dynamics of Alternaria brown spot of mandarins, greasy spot, melanose, Phytophthora brown rot, post-bloom fruit drop, and sour orange scab. CITPATH includes a diagnostic key to identify symptoms of the major fungal diseases of citrus foliage and fruit in Florida and a hypertext program containing a description and graphic display of symptoms, maps of geographic occurrence, diagrams of disease development, and management strategies. Users can also consult a list of citrus cultivars susceptible to specific diseases and a reciprocal list of diseases affecting specific cultivars. Chemical control methods are discussed briefly with reference to the current Florida Citrus Spray Guide, a hardcopy of which is included with the software purchase. Developed for commercial growers, county extension programs, citrus horticulture classes, and master gardeners, this software is available on CD-ROM disks containing other citrus databases and as a separate disk for MS-DOS-based computers.

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James J. Ferguson, Fedro S. Zaueta and Juan I. Valiente

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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Laura Guazzelli, Frederick S. Davies and James J. Ferguson

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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Jose Linares, Johannes Scholberg, Kenneth Boote, Carlene A. Chase, James J. Ferguson and Robert McSorley

Citrus is one of the most important crops in Florida. During the past decade, increased international competition and urban development, diseases, and more stringent environmental regulations have greatly affected the citrus industry. Citrus growers transitioning to organic production may benefit from premium prices, but they also face many challenges, including development of effective weed management strategies. Cover crops (CC) may constitute an environmentally sound alternative for improved weed management in organic systems. Two field experiments were conducted at Citra in north central Florida from 2002 to 2005, to evaluate the effectiveness of annual and perennial CC to suppress weeds in organic citrus groves. To quantify and compare the effectiveness of CC to suppress weed growth, a new weed suppression assessment tool, the cover crop/weed index (CCWI), was developed using the ratio of biomass accumulation of CC and weeds. Annual summer CC accumulated more biomass in comparison with winter CC. Sunnhemp (Crotalaria juncea L.), hairy indigo (Indigofera hirsuta L.), cowpea (Vigna unguiculata L. Walp.), and alyceclover (Alysicarpus vaginalis L.) all provided excellent weed suppression, which was superior to tillage fallow. Single-species winter CC did not always perform consistently well. Use of winter CC mixtures resulted in more consistent overall CC performance, greater dry matter production, and more effective weed suppression than single species of CC. Initial perennial peanut (PP) growth was slow, and summer planting of PP (Arachis glabrata Benth.) was determined to be the most effective date in terms of weed suppression, which was improved gradually over time, but all planting dates resulted in slow initial growth compared with annual CC. For both PP and annual CC, weed biomass typically was inversely related to CC dry weight accumulation resulting from competition for resources. The CCWI was a suitable tool to quantify CC performance in terms of weed suppression.

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Louise Ferguson, Hesham Gawad, G. Steven Sibbett, Mark Freeman and James J. Hatakeda

A stepwise multiple regression analysis, using payment by processors as the dependent variable (Y) and numerous physical and chemical characteristics as the independent variables (X), demonstrated that the primary factor determining `Manzanillo' olive (Olea europaea L.) value at harvest was size. Optimal crop value correlated strongly with the combined percentage of standard, medium, large, and extra-large olives; R' values were 0.93***, 0.93***, and 0.42 (ns) in 1984, 1985, and 1986, respectively. As the harvest season progressed, increased percentages of olives within these size classifications, not weight increases of individual olives within the size categories, produced the increase in value. Individual olives within size categories maintained the same weight through the harvest season, regardless of tree crop load. The best criterion for predicting optimal harvest time “is the total percentage of standard, medium, large, and extra-large olives.

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Michael B. Thomas, Jonathan H. Crane, James J. Ferguson, Howard W. Beck and Joseph W. Noling

The TFRUIT·Xpert and CIT·Xpert computerbased diagnostic programs can quickly assist commercial producers, extension agents, and homeowners in the diagnosis of diseases, insect pest problems and physiological disorders. The CIT·Xpert system focuses on citrus (Citrus spp.), whereas the TFRUIT·Xpert system focuses on avocado (Persea americana Mill.), carambola (Averrhoa carambola L.), lychee (Litchi chinensis Sonn.), mango (Mangifera indica L.), papaya (Carica papaya L.), and `Tahiti' lime (Citrus latifolia Tan.). The systems were developed in cooperation with research and extension specialists with expertise in the area of diagnosing diseases, disorders, and pest problems of citrus and tropical fruit. The systems' methodology reproduces the diagnostic reasoning process of these experts. Reviews of extension and research literature and 35-mm color slide images were completed to obtain representative information and slide images illustrative of diseases, disorders, and pest problems specific to Florida. The diagnostic programs operate under Microsoft-Windows. Full-screen color images are linked to symptoms (87 for CIT·Xpert and 167 for TFRUIT·Xpert) of diseases, disorders, and insect pest problems of citrus and tropical fruit, respectively. Users can also refer to summary documents and retrieve management information from the Univ. of Florida's Institute of Food and Agricultural Sciences extension publications through hypertext links. The programs are available separately on CD-ROM and each contains over 150 digital color images of symptoms.

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Laura Guazzelli, Frederick S. Davies, James J. Ferguson and William S. Castle

Two experiments were conducted with container-grown `Hamlin' orange trees [Citrus sinensis (L.) Osb.] on `Swingle' citrumelo [C. paradisi Macf. × Poncirus trifoliata (L.) Raf.] rootstock to study the effects of N rate on plant growth in the nursery. Treatments consisted of 12, 50, 100, or 200 mg N/liter per tree applied once a week by drip irrigation. Commercial media was used and soil water content was maintained at container capacity. In Expt. 1, fertilization at 200 mg·liter−1 resulted in greater scion growth, trunk diameter, and total leaf dry weight compared to the other rates. In Expt. 2, fertilization at 100 and 200 mg·liter−1 resulted in greater scion growth,” trunk diameter, and leaf and stem dry weights compared to lower rates, but no differences were observed between the two highest rates. Trees that received 12 and 50 mg·liter−1 were stunted and leaves were chlorotic. Therefore, the optimum calculated N rate for `Hamlin' nursery trees on `Swingle' citrumelo rootstock, based on critical level analysis, is 155 to 165 mg·liter-1.

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Chad E. Finn and John R. Clark