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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.
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.
Membrane thermostability of Heritage river birch (Betula nigra L. Heritage) was measured by electrolyte leakage from excised roots of plants grown in pot-in-pot (PIP) and conventional aboveground production systems (CPS). The predicted critical midpoint temperature (Tm) for a 30-min exposure was 54.6 ± 0.2 °C for PIP and 56.2 ± 0.6 °C for CPS plants. Plants grown PIP had a steeper slope through the predicted Tm, suggesting a decreased tolerance to high root-zone temperatures in relation to plants grown aboveground. Since the root systems of Heritage river birch grown PIP are damaged at lower temperatures than plants grown aboveground, growers should prevent exposure of root systems to high temperatures during postproduction handling of plants grown PIP.
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.
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).
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.
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.
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.
A study was conducted to compare four different controlled-release fertilizers when used in conjunction with Tex-R Geodiscs on the growth of Ilex crenata Thunb. ex J.A. Murray `Compacta' in 3.8 L (#1) containers. The fertilizers used were Osmocote Plus Southern Formula (18N-3.9P-10K), Osmocote Plus Northern Formula (18N-3.9P-10K), Wilbro (15N-1.7P-7.5K), and Nutricote T-360 (17N-2.6P-6.6K) all applied at the rate of 1.8 kg N/m3. Geodisc treatments were: 1) no disc, 2) fertilizer placed on top of the disc, and 3) fertilizer placed beneath the disc. At 2 and 4 months after the initiation of the study, the growth indices for plants grown with both Osmocote Plus fertilizers were larger than for either of the other two fertilizers. After 7 months, final growth indices were greater for the Osmocote Plus and Wilbro treatments compared to Nutricote. Final leaf, stem, and root dry masses were all greater for the Osmocote Plus fertilizers compared to the other two, as was final plant quality. Plants with fertilizer placed on top of the disc were smaller compared to the no disc or beneath the disc treatments. Geodisc treatment had no influence on shoot dry mass or final plant quality. Data for leachate nutrient analysis and evapotranspiration will also be presented.