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  • Author or Editor: Kenneth G. McCabe x
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Our objective was to quantify the efficacy of different plant growth regulator (PGR) substrate drenches on growth of lantana (Lantana camara) cultivars varying in growth habit. Rooted ‘Little Lucky Peach Glow’, ‘Lucky Peach’, and ‘Landmark Peach Sunrise’ lantana cuttings were individually planted into 4-inch-diameter containers filled with a commercial, soilless growing substrate. Fourteen days after planting, solutions containing 0 (control), 0.5, 1, 2, or 4 mg·L−1 ancymidol, flurprimidol, paclobutrazol, or uniconazole were applied to the surface of the growing substrate. Six weeks after applying PGR drenches, data were collected. The growth index (GI), an integrated measurement of plant size incorporating the height and widths of plants, was calculated. There was variation in the GI among the control plants, reflecting variation among cultivars within the species. In addition, we measured variation in activity among the different PGRs applied. Across the concentrations applied, ancymidol generally had the lowest activity across the four PGRs. For example, drenches containing 4 mg·L−1 ancymidol resulted in plants that were similar to plants treated with 0.5 to 1 mg·L−1 flurprimidol or uniconazole or 2 mg·L−1 paclobutrazol for ‘Lucky Peach’ lantana. Across all cultivars, flurprimidol and uniconazole had the greatest activity in suppressing plant height, width, and GI. Substrate drenches containing flurprimidol, paclobutrazol, or uniconazole are useful to control size of lantana produced in containers, though the recommended concentration depends on the active ingredient and the growth habit of cultivars being treated.

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Biocontainers made of coconut coir, paper, peat, wood, or other natural fibers are considered sustainable alternatives to containers made of petroleum-based plastics, but growers’ acceptance and use of fiber containers have been limited by their comparatively high cost, low strength and durability, and poor water-use efficiency (WUE). We hypothesized that coating fiber containers with biopolymers would improve their strength, durability, and WUE during plant production. We compared the effectiveness of fiber containers of coir, paper, and wood that were either uncoated or coated with one of four biopolymers [polyamide (PA), polylactic acid (PLA), polyurethane (PU), or tung oil (TO)], peat-fiber containers that were uncoated, and injection-molded containers made of petroleum-based plastic. Ease of coating was assessed, along with the cost and strength of containers, their effectiveness during greenhouse production of ‘Honeycomb’ marigold (Tagetes patula), ‘Autumn Bell’ pepper (Capisicum annuum), ‘Madness Red’ petunia (Petunia ×hybrida), ‘St. John’s Fire’ salvia (Salvia splendens), and ‘Rutgers’ tomato (Solanum lycopersicum), and their WUE during production of salvia and tomato. Castor oil-based PU was the least expensive biopolymer coating and was easy to apply as a water-based dispersion. The other biopolymers required a hazardous and costly organic solvent (e.g., chloroform). Coatings of PA, PLA, and PU increased container strength and durability, and improved WUE during plant production. Coated paper-fiber containers resisted horizontal compression better than petroleum-plastic containers. Greenhouse-grown plants in containers coated with PA, PLA, or PU were larger and rated healthier and of better quality than plants grown in uncoated or TO-coated fiber containers. Plants grown in paper- and coir-fiber containers coated with PA, PLA, or PU were similar in health and size to plants grown in petroleum-plastic containers. Two coatings of PU on paper-fiber containers resulted in WUE similar to that of petroleum-plastic containers for both 4- to 5-inch and gallon sizes. Coating fiber containers with biopolymers slowed, but did not halt, their degradation in soil, indicating that decomposition in soil may be a suitable end-of-life option for biopolymer-coated fiber containers. Our results support the hypothesis that coating fiber containers with biopolymers can improve their effectiveness for crop production, while maintaining an improvement in sustainability over petroleum plastic. Paper-fiber containers coated with PU showed particular promise and were similar in material cost and performance to containers made of petroleum-based plastic.

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The container-crops industry relies heavily on single-use plant containers made from petroleum-based plastics, most of which contribute to the solid waste stream in landfills. Plant containers made from biorenewable materials have potential to be more sustainable, but most commercially available biocontainers are either not durable enough for common production cycles or do not effectively biodegrade in soil after use. In 2012 and 2013, we evaluated 28 novel biocontainers (injection-molded prototypes) for their performance during plant production and their biodegradation in soil at two sites with dissimilar soil and climate in Iowa and Nevada, and we compared their performance to that of commercially available biocontainers. Prototype containers made of blends or composites of polylactic acid (PLA) or polyhydroxyalkanoates (PHA) performed well during crop production, and many showed an effective rate of biodegradation in soil. Their rates of biodegradation in Nevada were either similar or lower than they were in Iowa, but the highest rated containers were acceptable for use in both locations. Adding biobased fibers of distiller’s dried grains with solubles or corn stover to form composite materials improved biodegradation over that of the base polymers (PLA or PHA) and had little effect on container performance under greenhouse conditions. Many of the injection-molded prototypes performed as well as the petroleum control containers during crop production, yet biodegraded at similar or faster rates than commercially available fiber containers.

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