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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

A study was conducted with Magnolia grandiflora `St. Mary' to evaluate the effects of a pot-in-pot production system compared to a conventional aboveground production system and containers treated with or without copper hydroxide (Spin Out™). At 4 and 12 months after beginning the study, plants grown pot-in-pot were taller than plants in the conventional system. Stem diameters of plants grown pot-in-pot were also larger at 12 months. Production system influenced root dry weight in the outer 50% of the container, total root dry weight, percent root dry weight in the inner 50% of the container, percent root dry weight in the outer 50% of the container, and total biomass. Production system had no effect on shoot dry weight. Treatment with copper hydroxide had no effect on root or shoot growth. Production system and copper treatment influenced degree of root coverage. Plants grown pot-in-pot had higher rates of Ps and gs with increased Ci levels compared to plants above-ground. Production system had no effect on calculated transpiration rates.

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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

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

Carolina laurel cherry (Prunus caroliniana) is native to the U.S. southeastern coastal plain from North Carolina westward to eastern Texas. The species has been planted extensively in the southeast as an ornamental tree or hedge. Unfortunately, carolina laurel cherry naturalizes readily and is now found in a variety of habitats, both natural and disturbed. Flowering occurs in the late winter/early spring before new leaves emerge and fruit ripens in the fall/winter. Fruit is eaten by migratory birds and seed is dispersed. Seedlings readily germinate in the understory of forests and landscapes in the spring. As there are a limited number of cultivars available, selections with improved form and sterility are needed for the landscape trade. In 2008, seed was collected and treated with Cobalt-60 gamma irradiation at rates ranging from 0 to 150 Gy. The lethal dose killing 50% of the seedlings (LD50) was between 50 and 100 Gy. Three sterile plants were selected in 2012 from the M1 (first generation of mutagen-treated seedlings) population totaling 62 seedlings. M2 (second-generation seedlings from M1 parents) seed was collected Fall 2012, and 1509 seedlings were grown to flowering size in containers. In 2014–15, 120 seedlings that showed no fruit production were planted in the field in Watkinsville, GA, for further evaluation. Ratings on field-grown plants in Dec. 2017 and 2018 showed that 73% and 78% of the plants, respectively, produced no fruit, whereas the remaining plants had minimal to heavy fruit set. Because carolina laurel cherry is andromonoecious, production of male and bisexual flowers was evaluated on 17 selections in 2018. Of 500 flowers evaluated per selection, the number of male flowers per plant ranged from 22 to 415 (4.4% to 83%). The number of racemes with all-male flowers on each selection ranged from 1 to 32. There were no significant correlations between the number of male flowers or number of all-male flowered racemes per plant and production of fruit. Approximately 5% of M2 seedlings remain seedless after 6 years of growth.

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John M. Ruter

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John M. Ruter

Mouse ear disorder on container-grown river birch (Betulanigra L.) is a national problem caused by a deficiency of nickel. Symptomatic plants have leaves which are small, wrinkled, darker green, cupped, and have necrotic margins. Research showed that mouse ear could be cured by applications of nickel sulfate (Ruter, 2004). Further research was needed to determine optimal rates of application for sprays and drenches and to determine if phytotoxicity occurs at high rates. A study was initiated at a nursery in South Georgia on 25 June 2003, using river birch in their second growing season in #15 containers. Plants were selected for uniformity of mouse ear disorder. Treatments included a control, urea (0.24 g·L-1) + surfactant (1.0 mL·L-1), 250, 500, 750, and 1000 mg·L-1 nickel sulfate sprays, and substrate drenches applied at 150 and 300 mg of Ni/pot. After 30 days, all plants treated with nickel sulfate had 100% normal growth, except the 150 mg of Ni/pot drench, which had 79% of the canopy showing normal growth. No phytotoxicity was noted. Plants receiving foliar sprays had a 66% to 72% increase in leaf area, a 64% to 68% increase in leaf dry mass, a 31% to 44% increase in stem length, and a 9% to 17% increase in specific leaf area compared to nontreated plants. Drench treatments increased leaf area up to 62%, leaf dry mass to 55% and stem length up to 29% over control plants. Nickel in the foliage of nontreated plants was 2.3 mg·kg-1. For the spray treatments, foliar Ni ranged from 5.5 mg·kg-1 for the 250 mg·L-1 treatment to 9.3 mg·kg-1 for the 1000 mg·L-1 treatment. Though plants at the high rate of drench treatment resumed normal growth, foliar Ni levels were not different from control plants. In general, if plants were treated with Ni, then foliar B, Fe, and Zn decreased.