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John M. Ruter

A study was conducted with Prunus × incamp `Okame' to evaluate the effects of a pot-in-pot production system compared to a conventional above-ground system and cyclic irrigation on plant growth and water loss. Plants were grown in #7 (26-L) containers with a 8:1 pinebark:sand (v/v) substrate. Cyclic irrigation provided the same total volume of water, but was applied one, three, or four times per day. Final plant height and stem diameter, shoot and root dry weight, total biomass, and root:shoot ratio were all increased for plants grown pot-in-pot compared to above-ground. Multiple irrigation cycles increased stem diameter, shoot dry weight, and total biomass, compared to a single irrigation application. Multiple irrigation cycles decreased the root:shoot ratio. Evapotranspiration was influenced by production system, irrigation, and date. Amount of water lost as leachate was influenced by irrigation and date. Cyclic irrigation resulted in a two-fold decrease in leachate volume. Soluble salts and nitrate-nitrogen in the leachate were influenced by an interaction between production system, irrigation, and date.

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John M. Ruter

Loropetalum chinensevar.rubrum, Chinese fringe-flower, was introduced into the United States in 1989 and quickly became on of the most popular plants in the nursery trade. Growth abnormalities (little-leaf disorder) became a problem on container-grown plants in pine bark substrates during the late 1990s. Symptoms are as follows: darkening of older growth, shortening of internodes, upward cupping of leaves, crinkling of new growth, particularly the distal part of the leaf, decrease in leaf size. In severe cases leaf necrosis occurs along with stem elongation, thus branches appear to be elongating without new leaves. Petioles become very short. Branchlets may also be reflexed or drooping. In Florida, an eriophyid mite has been touted as the causal agent for the disorder. On plants sampled from Georgia nurseries, eriophyid mites have never been detected. `Ruby' consistently has the problem, while it has also been noted on `Sizzling Pink' and `Suzanne'. Plants in the ground do not express the problem. There may be an element present in native soil that is not supplied in sufficient quantity in organic substrates. Foliage from a commercial nursery was sampled for micronutrients concentrations. Initial data indicated that copper, zinc, and nickel were low and could be causing the problem. In May 2005, a study was initiated at a commercial nursery in Grady County, Ga. Copper and zinc sulfate, along with nickel lignonsulfonate, was applied as foliar sprays to symptomatic plants of `Suzanne' growing in #5 containers. Within two weeks after treatment, plants sprayed with copper sulfate resumed normal growth. Control plants, or plants treated with zinc or nickel did not resume normal growth. A second study was initiated in June to evaluate different rates of copper sulfate and Kocide, a copper fungicide. Medium to high rates of copper sulfate and the high label rate of Kocide were effective. The plants in this study had severe symptoms and required repeat applications of copper. Further research is needed on appropriate formulations of copper, rates of application, and rates of incorporation into pine bark substrates to eliminate the problem.

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John M. Ruter

Temperatures producing heat damage in leaves of Ilex ×meserveae S.Y. Hu `Blue Prince' and Ilex rugosa × cornuta Lindl. & Paxt. `Mesdob' (China Boy) were evaluated using electrolyte leakage and chlorophyll fluorescence techniques. Whole leaves were exposed to temperatures from 30 to 65C for 30 minutes to determine critical midpoint heat-killing temperatures (TJ using electrolyte leakage techniques. The Tm for `Blue Prince' and `Mesdob' was 52.4 ± 0.lC and 53.8 ± 0.lC, respectively. Dark-adapted leaves were heated for 30 minutes in darkness at temperatures between 30 and 57C before chlorophyll fluorescence was measured. Initial (F0) and peak fluorescence measurements were higher at 54 and 55C for `Mesdob' than for `Blue Prince'. Cultivar had no effect on variable fluorescence (F,). Based on the Fv: Fo ratio, `Mesdob' was estimated to have a higher optimal plant growth temperature than `Blue Prince'. The physiologic data support the hypothesis that I. cornuta as a parent conferred heat tolerance to the interspecific hybrid in this study.

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John M. Ruter

Granular and liquid formulations of paclobutrazol were tested to evaluate the growth and flowering response of butterfly bush (Buddleia davidii Franch. 'Dubonnet'). At the rates tested (5, 10, 20, and 40 mg ai·pot–1), the granular formulation reduced the growth index, plant height, shoot dry weight, total plant biomass, number of panicles and panicle length to a greater degree than the liquid formulation applied as a drench. Both formulations reduced total plant biomass and increased the root:shoot ratio compared to the control. All rates of the granular formulation above 5 mg ai · pot–1 produced non-marketable plants. Since no phytotoxicity was observed with any treatment, the application of paclobutrazol to control the growth of butterfly-bush may be useful if the correct formulation and rate of application are chosen.

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John M. Ruter

Membrane thermostability of `Needlepoint' Chinese holly (Ilex cornuta Lindl. & Paxt.), `Albo-marginata' English holly (Ilex aquifolium L.), and `Nellie R. Stevens', an Ilex aquifolium × Ilex cornuta hybrid, was determined by measuring electrolyte leakage in excised leaves and roots. The critical midpoint heat-killing temperature (T,) after a 30-min exposure was 54.4 ± 0.4C for `Nellie R. Stevens' leaves and was ≈ lC higher than that for Chinese (52.9 ± 0.3C) or English holly (52.9 ± 0.4C). The Tm for English holly roots (53.9 ±_ 1.5C) was higher than that for either `Nellie R. Stevens' (51.7 ± 0.3C) or Chinese holly (50.1 ± 0.3C). The results of this study suggest that English holly and `Nellie R. Stevens' leaves and roots can withstand direct heat injury equal to or greater than that of Chinese holly.

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John M. Ruter

The long-term effects of paclobutrazol applied to container-grown `Mojave' pyracantha (Pyracantha ×) and `San Jose' juniper (Juniperus chinensis L.) were investigated. Paclobutrazol was applied as a drench to container-grown (2.8 liter) plants at the rates of 0, 5, 10, 20, and 40 mg a.i./pot in June 1991, and plants were transplanted to the field in Feb. 1992. Pyracantha plant height, shoot and root dry weight, and total biomass (shoot dry weight + root dry weight) decreased quadratically as rate of paclobutrazol increased during nursery production. Paclobutrazol had no effect on plant height or shoot dry weight of Juniperus, although width indices were reduced. Ratings for root quality for Juniperus in containers increased as rate of paclobutrazol increased. After 9 months in the landscape, paclobutrazol still influenced plant height, width, and shoot dry weight for Pyracantha but had no effect on Juniperus. As rate of application increased, fruit retention on Pyracantha increased. Paclobutrazol applied as a container medium drench at 5 mg a.i./pot was excessive during nursery production of Pyracantha and Juniperus. Chemical name used: [(2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-yl)penten-3-ol] (paclobutrazol).

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John M. Ruter

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John M. Ruter

A study was conducted with Lagerstroemia indica x fauriei `Acom a' to evaluate methods for reducing rooting-out problems in a PIP production system. The products tested were Biobarrier™, a geotextile fabric impregnated with trifluralin; Root Control'” fabric bag material; and Spin Out™, a commercial formulation of copper hydroxide (7.1%) in latex paint. Biobarrier™ reduced plant height, shoot dry weight, percent root dry weight outside of the planted container and total biomass compared to the non-treated control. For the control, 7.1% of the total root dry weight was found between the holder pot and planted container compared to 0.2% for the Biobarrier™ treatment. When the holder pot and planted container or the planted container and Root Control™ fabric were both treated with Spin Out™, plant height and shoot dry weight were reduced. Spin Out™ reduced root circling on the sidewalls of the planted containers but not on the bottom of the containers. All treatments except the control reduced rooting-out to a degree that allowed for the manual harvesting of the planted container from the holder pot after seven months in the field.

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John M. Ruter

Decline of certain container-grown ornamental species during the hottest months of summer is a common problem for nurserymen in the southeastern United States. When roots are killed due to high root-zone temperatures and growth ceases, production of plant hormones also decreases. A study was conducted with Early Harvest PGR (Griffin LLC, Valdosta, Ga.), which contains cytokinins, gibberellic acid, and indole butyric acid, to determine if this product would improve the growth of five ornamental species that typically decline during the summer in south Georgia nurseries. The species used were Cotoneaster dammeri Schneid. `Coral Beauty', Cotoneaster salicifolius Franch. `Green Carpet', Spiraea japonica L. `Shirobana', Thuja occidentalis L. `Little Giant', and Weigela florida (Bunge) A. DC. `Minuet'. The treatments (control, 1.5 and 3.0 mL Early Harvest PGR/1125 mL water) were applied every 2 weeks from mid-June until mid-Sept. 1999 as a foliar drench. Treatment of both Cotoneaster species and the Thuja with Early Harvest PGR resulted in little influence on plant growth. While growth indices did not increase, shoot dry mass of Spiraea and Weigela increased 17% and 26%, respectively, when treated with Early Harvest PGR at the medium rate. Plant quality ratings for Spiraea increased when the 1.5-mL rate of Early Harvest PGR was applied. A rate of 3.0 mL of Early Harvest PGR on Spiraea decreased shoot and root dry mass, total biomass, root ratings, and final plant quality. Root ratings and plant quality were highest for Weigela grown with the 1.5-mL Early Harvest PGR treatment. These results indicate that treatment of woody ornamentals with Early Harvest PGR for positive results is both species- and rate-dependent.