A number of privet species (Ligustrum spp.) that are important to the nursery and landscape industry have escaped cultivation and become invasive or weedy in the United States and other countries. Induced tetraploids in these species may produce new selections or cultivars with reduced or eliminated invasive potential. Applying drops of semisolid agar containing 0.1% to 0.3% colchicine and 0.2% dimethyl sulfoxide (DMSO) to newly emerged seedlings of japanese privet (Ligustrum japonicum Thunb.) resulted in 15.6% to 22.6% tetraploid induction. The nuclear DNA content of tetraploids was 5.31 pg/2C, 101.9% higher than that of diploids. Compared with diploid plants, tetraploids were more compact, with an average of 31.0% shorter plant height and 33.1% smaller canopy width. Tetraploids had 29.2% thicker internodes, and their leaves were 39.5% larger and 33.8% thicker, resulting in 42.1% to 24.1% greater fresh or dry leaf weights (per leaf) in tetraploids compared with diploids. Without indole-3-butyric acid (IBA) treatment, cuttings from tetraploids showed 28% lower rooting than diploids. IBA treatments improved the rooting of tetraploid cuttings, resulting in 65% rooting success. These results indicate that tetraploids can be readily induced in japanese privet and induced tetraploids show significant changes in plant growth and size, shoot growth, leaf morphology, and rooting of cuttings. The modified tetraploid induction method and the induced tetraploids are expected to be useful for producing new selections or cultivars with reduced invasive potential in japanese and other privets.
Mohammed I. Fetouh, Abdul Kareem, Gary W. Knox, Sandra B. Wilson and Zhanao Deng
Sandra B. Wilson, Gary W. Knox, Keona L. Nolan and James Aldrich
Chinese privet (Ligustrum sinense) and glossy privet (L. lucidum) have been classified as Category I invasives in Florida. The closely related japanese privet (L. japonicum) has escaped cultivation but is not considered a problem species in Florida. Plant growth, visual quality, flowering, and fruiting were assessed for the resident species (wild-type form) and selected cultivars of chinese privet, glossy privet, and japanese privet planted in northern and southern Florida for 132 weeks. Visual quality varied by site, month, and cultivar. With the exception of ‘Swift Creek’ chinese privet (which did not survive in southern Florida), all cultivars survived the study. All plants fruited in northern Florida. In southern Florida, fruiting was less abundant and not observed for ‘Jack Frost’ japanese privet, ‘Rotundifolium’ japanese privet, ‘Swift Creek’ chinese privet, ‘Suwannee River’ hybrid privet, and glossy privet within 132 weeks. In northern and southern Florida, the growth index rate was lower for ‘Lake Tresca’ japanese privet, ‘Rotundifolium’ japanese privet, and ‘Suwannee River’ hybrid privet than other cultivars. There was a significant interaction between temperature and species for seed germination. Germination in incubators set with a 12-hour photoperiod ranged from 51% to 78.5% for chinese privet, japanese privet, and glossy privet among temperatures, with the exception of glossy privet at 35/25 °C, where only 2.0% of seeds germinated. Germination in complete darkness ranged from 39.5% to 80.5% for chinese privet and glossy privet among temperatures, with the exception of glossy privet at 35/25 °C, where only 0.5% of seeds germinated.
Kimberly A. Moore, Amy L. Shober, Gitta S. Hasing, Christine L. Wiese, Geoffrey C. Denny and Gary W. Knox
Recent research suggested that the nitrogen (N) fertilizer rates needed to maintain high-quality landscape plants was lower than rates needed to grow the largest size plants. Our objective was to evaluate the effect of N fertilizer rate on the aesthetic quality of various landscape-grown annual and perennials species. Nineteen cool-season annuals, 20 warm-season annuals, and 4 perennials were planted into raised beds containing subsoil fill material in a completely randomized design in west-central Florida (U.S. Department of Agriculture hardiness zone 9b). Plants were fertilized every 12 weeks with polymer coated, slow-release N (42N–0P–0K) fertilizer at annual N rate of 3, 5, or 7 lb/1000 ft2 (annuals) or 1, 3, or 5 lb/1000 ft2 (perennials). Plants were rated for aesthetic quality every 6 weeks for a period of 18 weeks (annuals) or 54 weeks (perennials). For most species, quality ratings of plants fertilized with 3 lb/1000 ft2 of N per year (annuals) or 1 lb/1000 ft2 of N per year (perennials) were not significantly lower than plants receiving higher rates of N annually. Previously reported N fertilizer recommendations for central Florida of 2 to 4 lb/1000 ft2 per year should be adequate for maintaining acceptable quality landscape-grown annual and herbaceous perennial plant species.
Amy L. Shober, Kimberly A. Moore, Gitta S. Hasing, Christine Wiese, Geoffrey C. Denny and Gary W. Knox
Research supporting recommendations for fertilizer needs of landscape-grown vines and groundcovers is lacking. The objectives of our study were to (1) evaluate the quality response of selected vine and groundcover species to nitrogen (N) fertilization at five rates and (2) validate the recommended N fertilizer rates (from the initial evaluation) by monitoring quality of additional landscape-grown vine and groundcover species. Three vine species and two groundcover species were planted in west-central Florida into raised beds containing subsoil fill material in a completely randomized design. Plants were fertilized every 6 weeks with a controlled release fertilizer (20N–0P–0K–23S) at an annual N rate of 0, 2, 4, 6, or 12 lb/1000 ft2. Plant aesthetic quality (0–5 scale) was assessed every 6 weeks for 30 weeks after planting. Although quality of some species increased significantly as N rate increased, all plants supplied with at least 4 lb/1000 ft2 per year N fertilizer had acceptable quality ratings of 3 or better. Screening of three additional vines and four additional groundcovers fertilized with controlled release fertilizer (42N–0P–0K) at an annual N rate of 3, 5, or 7 lb/1000 ft2 confirmed that fertilization with 2 to 4 lb/1000 ft2 per year should be adequate to maintain acceptable vines and groundcovers grown in the landscape in west-central Florida.
Matthew R. Chappell, Sarah A. White, Amy F. Fulcher, Anthony V. LeBude, Gary W. Knox and Jean-Jacques B. Dubois
In 2014, the Southern Nursery Integrated Pest Management (SNIPM) Working Group published both print and electronic versions of IPM for Shrubs in Southeastern U.S. Nursery Production: Volume I. Five hundred print books (of 3000 copies) were distributed to commercial ornamental growers and extension educators in return for their participation in a follow-up survey. The survey was administered to determine the value of book contents, savings that growers realized from using the book, perceived value of the book had users been asked to pay for it, and demographic information. The survey response rate was 46.2%, with respondents from 18 states. Of 243 respondents, 194 (79.8%) had used the book. Entomology information was most used and most useful, followed by plant pathology, weed science, and cultural information. Collective savings attributed to book use totaled $408,832/year for the 194 nurseries that used the book. Applying the use rate (79.8%) identified in this survey, this represents $5.62 million in savings per year for the 3000 printed books, of which 2394 are estimated to have been used. Savings varied by the type and size of operation. Larger operations had greater savings per year. Container growers saved $44.15/acre and field growers $28.37/acre. The price that growers were willing to pay for the book also varied by operation type and size. Extension educators and growers were willing to pay an average of $41.20, with an additional $0.063/acre for container growers and $0.126/acre for field growers. Return on investment for the U.S. Department of Agriculture grant funding for the project was $187.60 per dollar of funding. This survey demonstrates that collaborative efforts can produce high-value deliverables with significant regional and/or national impact.
Amy L. Shober, Kimberly A. Moore, Nancy G. West, Christine Wiese, Gitta Hasing, Geoffrey Denny and Gary W. Knox
Despite inconsistent reports of nitrogen (N) fertilization response on growth of landscape-grown woody ornamentals, broad N fertilization recommendations exist in the literature. The objective of this research was to evaluate the growth and quality response of three landscape-grown woody shrub species to N fertilizer. Three ornamental shrub species, ‘Alba’ indian hawthorn (Raphiolepis indica), sweet viburnum (Viburnum odoratissimum), and ‘RADrazz’ (Knock Out™) rose (Rosa) were transplanted into field soils in central Florida (U.S. Department of Agriculture hardiness zone 9a). Controlled-release N fertilizer was applied at an annual N rate of 0, 2, 4, 6, and 12 lb/1000 ft2 for 100 weeks. Plant size index measurements, SPAD readings (a measure of greenness), and visual quality ratings were completed every month through 52 weeks after planting (WAP) and then every 3 months through 100 WAP. Plant tissue total Kjeldahl N (TKN) concentrations and shoot biomass were measured at 100 WAP. Results of regression analysis indicated little to no plant response (size index, biomass, SPAD) to N fertilizer rate. Shrub quality was acceptable for all species through 76 WAP regardless of the N fertilization rate. However, quality of rose and sweet viburnum fertilized with N at the low rates (<2 lb/1000 ft2) was less than acceptable (<3 out of 5) after 76 WAP. Results suggest that posttransplant applications of fertilizer may not increase plant growth, but that low-to-moderate levels of N fertilization (2 to 4 lb/1000 ft2 per year) may help plant maintain quality postestablishment.
Gitta Shurberg, Amy L. Shober, Christine Wiese, Geoffrey Denny, Gary W. Knox, Kimberly A. Moore and Mihai C. Giurcanu
Current nitrogen (N) fertilizer recommendations for landscape-grown ornamentals are based on limited research. The objective of this research was to evaluate plant response of selected warm- and cool-season annuals to N fertilizer applied at five rates in the landscape. Three warm-season annual species [‘Profusion Cherry’ zinnia (Zinnia elegans ×angustifolia), ‘Cora White’ vinca (Catharanthus roseus), and ‘Golden Globe’ melampodium (Melampodium divaricatum)] and three cool-season annual species [‘Telstar Crimson’ dianthus (Dianthus chinensis), ‘Delta Pure Violet’ pansy (Viola wittrockiana), and ‘Montego Yellow’ snapdragon (Antirrhinum majus)] were transplanted into raised beds containing subsoil fill in U.S. Department of Agriculture (USDA) hardiness zone 9a. Slow-release N fertilizer was applied over an 18-week period at an annual N rate of 0, 2, 4, 6, and 12 lb/1000 ft2. Trials were replicated a second year. Plant size index (SI), tissue chlorophyll (SPAD), and plant quality were determined every 6 weeks. Shoot biomass and tissue total Kjeldahl N (TKN) were determined at 18 weeks. Regression analysis indicated that all species required N inputs at annual rates exceeding 8 lb/1000 ft2 to achieve maximum size, shoot biomass, or SPAD. However, acceptable quality plants were produced at much lower N rates. We suggest application of N fertilizer at a rate of 4 to 6 lb/1000 ft2 per year to landscape-grown annuals to maintain acceptable plant quality and growth. We expect fertilization at lower rates (based on aesthetics) can reduce the amount of fertilizer applied and the potential for nutrient losses in runoff or leachate. Future research should address N fertilization needs in higher fertility soils as well as the response of other plant species.
Gitta Shurberg, Amy L. Shober, Christine Wiese, Geoffrey Denny, Gary W. Knox, Kimberly A. Moore and Mihai C. Giurcanu
There is limited research regarding proper fertilization rates and timing for landscape-grown herbaceous perennials. Most current nitrogen (N) fertilizer recommendations for landscape-grown perennials are based on rates for woody landscape plants or on rates for greenhouse-grown perennials. In addition, most fertilizer guidelines are defined to achieve peak growth, which may not be the best indicator of desirable plant quality. Basing fertilizer input rates on plant quality levels rather than maximum growth may result in a lower fertilizer application rate and a reduction in excess fertilizer available for leaching. The objective of this research was to evaluate the response of landscape-grown herbaceous perennials to N fertilizer applied at five rates. Five herbaceous perennials [bush daisy (Gamolepis chrysanthemoides), ‘New Gold’ lantana (Lantana ×hybrid), ‘Mystic Spires’ salvia (Salvia longispicata ×farinacea), ‘Evergreen Giant’ liriope (Liriope muscari), and ‘White Christmas’ caladium (Caladium bicolor)] were transplanted into raised landscape beds containing subsoil fill in U.S. Department of Agriculture (USDA) hardiness zone 9a. Controlled-release N fertilizer was applied at an annual N rate of 0, 2, 4, 6, and 12 lb/1000 ft2 for 96 weeks. Plant size index (SI), tissue chlorophyll, and plant quality were measured every 6 weeks for 96 weeks. Flower cover was determined every 6 weeks from 42 to 96 weeks. Shoot biomass and tissue total Kjeldahl N (TKN) were measured at 96 weeks after planting (WAP). Regression analyses suggested that some species required in excess of 12 lb/1000 ft2 N to reach maximum size, chlorophyll content, and shoot biomass. However, plants exhibited quality ratings of good to excellent at annual N rates of 2 to 4 lb/1000 ft2 N per year. We suggest that these low to moderate levels of N fertilization (2 to 4 lb/1000 ft2 N per year) will provide sufficient N to produce acceptable size and quality herbaceous perennials in the landscape.