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  • Author or Editor: Annette Chandler x
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Common liverwort (Marchantia polymorpha L.) is an increasingly troublesome weed in containerized plant production. Postemergence applications were made to try to eradicate established stands of liverwort. Treatments consisted of sprays of quinoclamine at 1× and 2× rates and oxadiazon at the highest label rate, broadcast applications of sodium carbonate peroxyhydrate at 1x and 3x rates and four granular herbicides (flumioxazin, oxadiazon, oxyfluorfen + pendimethalin, and prodiamine) applied at label rates. The granular herbicides were applied both alone and with the sodium carbonate peroxyhydrate treatments. Herbicides were applied to common liverwort growing on an 80% aged pine bark: 20% Sphagnum peat-based soilless growing medium contained in 10-cm diameter plastic pots located in a double-poly covered greenhouse. At 2 weeks after treatment (WAT), control was best (93% to 100%) for both quinoclamine and the 3× peroxyhydrate treatments, intermediate (68% to 83%) for the 1× peroxyhydrate treatments, and not significant for any of the preemergence herbicides used alone. At 4 WAT, slight regrowth was evident in plots in which the treatments had an initial effect and the 1x peroxyhydrate + flumioxazin was as effective as the 3× peroxyhydrate and the 2× quinoclamine treatments. At 6 WAT, control was excellent in the 3× peroxyhydrate and 1× peroxyhydrate + flumioxazin treatments. Control was less, but still evident, in the quinoclamine and other 1× peroxyhydrate treated plots. While none of the treatments had completely eradicated common liverwort in all replications at 10 WAT, control was still excellent to good in many of the peroxyhydrate + preemergence herbicide-treated plots.

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Desiccation of containerized plants at retail outlets due to inadequate watering is a recurring problem. Water stress can decrease plant quality and survivability. Treatments that could reduce plant transpiration without lowering plant quality could be beneficial in maximizing the likelihood that plants would not become water stressed between waterings at retail outlets. Abscisic acid (ABA) is known to be involved in the regulation of stomatal aperatures, the major control mechanism for transpirational water loss. Containerized plants of four cultivars of hibiscus were thoroughly sprayed with S-ABA at concentrations of 0, 125, 250 or 500 mg·L–1. Plants were held under simulated retail conditions and were not watered until visible wilting occurred. Transpiration and pot weights were monitored over time. Transpiration rates and weight loss percentages were negatively correlated with S-ABA concentrations. Effects on transpiration rates lasted for at least 30 hours after treatment. For mean hours to wilt, there was interaction between S-ABA treatments and cultivars. For the most sensitive cultivar (`Double Apricot'), treatment with S-ABA at 500 mg·L–1 almost doubled the time to plant wilt (130 h) compared to the control treatment (72 hours). Hours to wilt was increased 24% for `Double Pink' treated at the highest rate. For `Double Red' and `Single Pink', hours to wilt was not affected by treatments. For some hibiscus, S-ABA treatments prior to placement of plants at retail outlets might decrease the chances that the plants would become severely water stressed.

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Organic mulch is commonly used in landscape planting beds to improve plant growth and reduce competition from weed species. Although many different mulch materials have been evaluated in landscape, forestry, or agricultural settings, there have been no previous reports concerning the maintenance costs associated with different mulch materials from a weed control perspective. Trials were conducted at two locations in Florida to estimate the annual maintenance costs associated with pine bark nuggets (bark derived from pine species not specified) and pine straw mulch [mix of longleaf pine (Pinus palustris) and slash pine (Pinus taeda) needles] with and without the use of a granular preemergence herbicide when maintained at similar depths in schilling’s holly (Ilex vomitoria ‘Schilling’s Dwarf’) shrub beds and asiatic jasmine (Trachelospermum asiaticum ‘Minima’) groundcover beds. Weed coverage and residual mulch depth were tracked over time, with maximum and minimum thresholds (20% and 2 inches, respectively) set as triggers for maintenance activities. Results showed that the addition of herbicide (trifluralin + isoxaben) had little to no impact on weeding frequency or time when plots were mulched, but did reduce hand weeding frequency and time compared with nontreated, nonmulched plots. Both mulch materials used alone reduced hand weeding frequency and time compared with herbicide-only treatments. Although results varied by bed type and location, pine bark generally provided greater weed control compared with pine straw and required fewer mulch additions and less mulch by volume. Results from this study suggests that using pine bark nuggets as mulch may result in lower maintenance costs and weed pressure compared with pine straw when both are applied and maintained at 2-inch depths.

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