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- Author or Editor: Joyce Latimer x
Broccoli (Brassica oleracea L. Group Italica cv. Green Duke) seedlings were subjected to brushing with a piece of cardboard (40 strokes/min, 1 min twice daily), wind (7 m·s-1 for 5 min twice daily) or drought (visible wilt for 2 hours daily) treatments. Plant response to treatment was affected by seasonal or environmental conditions. All conditioning treatments reduced leaf dry weight and area, stem dry weight and length, and the total shoot and root dry weights in an experiment conducted in Sept. 1986 (Fall 1986). However, in experiments conducted the following year, broccoli transplants treated in March (Spring 1987) showed little response to the treatments, while transplants treated in August (Fall 1987) showed only a moderate response. In Fall 1986 and 1987, brushing improved field establishment as measured by the rate of shoot dry weight gain over the period of field establishment. Yield of the primary head of broccoli transplants treated in either Spring or Fall 1987 was not affected by the conditioning treatments. Brushing may provide an effective alternative to drought or plant growth retardants in conditioning broccoli transplants prior to field planting.
`Jupiter' or `Marengo' pepper (Capsicum annuum L.) seedlings maintained under 0%, 30%, 50%, or 80% shade in a greenhouse were brushed 80 strokes twice daily beginning at the cotyledonary, first true leaf, or second true leaf stage. Averaged across shade environments, brushing reduced `Jupiter' and `Marengo' stem length 25% to 36% and 6% to 28%, respectively. However, the percentage of plants exhibiting mechanical damage by brushing ranged from 86% to 93% and 48% to 90% for `Jupiter' and `Marengo', respectively. Transplant quality tended to decrease as brushing was delayed. When brushing of `Marengo' was reduced to 40 strokes twice daily in 1992, plant growth reduction decreased, but the percent damage was about the same. The damage severity, however, was reduced as indicated by higher plant-quality ratings. Pepper plant damage was excessive for the small amount of growth regulation provided by brushing.
Various spray rates of paclobutrazol, 5000 ppm daminozide, 200 ppm ancymidol, or drought imposition (visible wilt symptoms for up to 2 hours daily) were applied to three bedding plant species to determine effects on growth in the greenhouse and the subsequent growth and performance of treated plants in the landscape. Seedlings of Zinnia efegans Jacq. `Peter Pan Scarlet' responded to all growth retardants (paclobutrazol at 40 and 90 ppm) and the drought treatment in the greenhouse. However, zinnias treated with paclobutrazol or ancymidol still exhibited reductions in plant height 5 and 7 weeks after transplanting to the landscape, and in plant quality (subjective rating of plant appearance with emphasis on flower cover) at 5 weeks after transplanting. Daminozide or drought controlled zinnia growth in the greenhouse but had no carry-over effect in the landscape. Stem elongation of Impatiens wallerana Hook `Accent Red' seedlings was moderately controlled by 20 ppm paclobutrazol in the greenhouse. There were no other treatment effects in the greenhouse. Paclobutrazol (20 ppm) reduced final plant height and quality (7 weeks postplanting). Treatment with daminozide or drought reduced plant width and quality after 5 and 7 weeks in the landscape. Ancymidol had no effect on landscape performance of impatiens. Shoot dry weight gain and stem elongation of Tagetes erects L. `Papaya Crush' seedlings were reduced by ancymidol or 40 ppm paclobutrazol in the greenhouse. Shoot dry weight gain of marigold seedlings was inhibited during the first week of landscape establishment by prior treatment with daminozide, ancymidol, or drought. Final plant height and width in the landscape were not affected by any treatment; however, 40 ppm paclobutrazol, daminozide, or ancymidol decreased final plant quality. Chemical names used: α -cyclopropylα -(4-methoxyphenyl) -5-pyrimidinemethanol (ancymidol); butanedioic acid mono(2,2-dimethylhydrazide) (daminozide); β -[(4-chlorophenyl) methyl] - β - (1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).
Seeds of marigold (Tagetes erects L. `Janie') were sown in flats of three cell sizes (inverted pyramids, Todd 080A, 100A, or 175; volume 7, 24, or 44 cm3, respectively) or in flats of different root cell configurations [Todd 100A, Grow-Tech (GT) 200, or Growing Systems (GS) 135; shaped as inverted pyramid, cylinder, or cylinder with a bottom lip, respectively]. During 2 consecutive years, plants grown in Todd 080A trays had 60% less leaf area and shoot and root dry weights than plants grown in Todd 175 trays. Plants grown in Todd 100A trays had 30% less leaf area and shoot and root dry weights than plants grown in the larger volume tray. Stem length was less affected by container size. The rate of shoot dry weight gain during the 3 weeks after transplanting in the field was greater in plants from the smaller containers (Todd 080A and Todd 100A) in 1987. Final height (7 weeks after planting) of plants from Todd 080A or Todd 100A flats was 12% and 7% less, respectively, than those of plants grown in Todd 175 flats, while final plant quality was reduced 34% and 21%, respectively, in plants from these flats in 1987. Similar, but smaller, effects were recorded in 1988. Container type had little effect on plant growth in the greenhouse and no effect on growth in the landscape. The maximum quality rating in the landscape, awarded to plants from Todd 100A flats, was 12% greater than that of plants from GT 200 flats in 1987 and 5% and 9% greater than plants from GT 200 and GS 135 flats, respectively, in 1988. Final plant performance of marigold seedlings was reduced more by root restriction or transplant size than previously reported with vegetable species.
Since chemical growth retardants are no longer labelled for use on vegetable transplants, mechanical conditioning provides an alternative method of controlling excessive stem elongation under greenhouse conditions. Mechanical conditioning includes brushing or shaking treatments that physically impact or displace the plant and generally reduce plant growth, increase stem and petiole strength, and improve overall plant quality. The resulting transplants have less breakage during postharvest handling, may be more stress tolerant, and are faster to establish in the field. However, only minor effects on crop yield have been identified. Brushing reduced broccoli transplant size, but improved shoot dry weight gain during field establishment but had no effect on head yield. Brushing is a labor intensive practice for large-scale operations. Current attempts to mechanize brushing require that the plants are uniform in height and treatment tolerant. Additional research in non-contact treatments like shaking or vibration of benches is necessary. The effects of the treatments on stress tolerance and predisposition to disease need to be clarified.
`Floradade' tomato (Lycopersicon esculentum Mill.) transplants treated with foliar sprays of paclobutrazol at 0, 14, 30, 60, or 90 ppm exhibited reductions in stem length, leaf area, and plant dry weight in a cubic response pattern. Gibberellic acid (GA) drenches, at 10, 100, or 250 ppm, increased stem length, leaf area, and plant dry weight. Daminozide (2500 or 5000 ppm) sprays reduced leaf area and dry weight, but 5000 ppm had no effect on stem length. Abscisic acid drenches, at 275, 660, or 1320 ppm, did not affect final plant size. In subsequent experiments to produce transplants for field evaluation, plants treated with paclobutrazol sprays at 90 (1987) and 14 or 60 ppm (1988) had smaller leaf area, stem length, and shoot dry weight than untreated plants. In 1987,90 ppm paclobutrazol reduced stem shear strength, while 2500 ppm daminozide increased stem strength relative to controls. In 1988, 2500 ppm daminozide increased transplant growth while 660 ppm abscisic acid had no effect. Paclobutrazol (14 ppm) and drought improved field establishment of transplants as measured by shoot dry weight gain after field planting. In 1988, total fruit yield was reduced by 60 ppm paclobutrazol and GA. Although fruit size was unaffected by treatments, fruit number was reduced by GA. Chemical names used: butanedioic acid mono (2,2-dimethylhydrazide) (daminozide); B-[(4-chlorophenyl)methyl]-α -(1,1-dimethylethyl) -N-1,2,4-triazole-1-ethanol (paclobutrazol).
Mechanical conditioning is an excellent means of regulating the growth of vegetable transplants and some ornamental bedding plants. It improves the stature, appearance, handling characteristics, and overall quality of treated plants. The application procedures reported for transplants have included wind, shaking, brushing, and more recently impedance; all of which result in physical displacement of the growing points. Brushing has been most commonly studied for mechanical conditioning in high density transplant production. Brushing reduces plant height, increases stem and petiole strength, improves insect resistance in the greenhouse, tends to improve stress tolerance and enhance stand establishment in the field, and has no effect on crop yield. Although growers using the technique have been very pleased with the quality of brushed vegetable transplants, widespread commercial application of brushing is limited by a lack of automation.
During greenhouse production in Spring 1995, conditioning treatments were applied to columbine (Aquilegia×hybrida Sims `McKana Giants'), New Guinea impatiens (Impatiens hawkeri Bull. `Antares'), marigold (Tagetes erecta L. `Little Devil Mix') and ageratum (Ageratum houstonianum Mill. `Blue Puffs') plants. Treatments included: mechanical conditioning (brushing 40 strokes twice daily); moisture stress conditioning (MSC) (wilting for ≈2 hours per day); undisturbed ebb-and-flow irrigation; overhead irrigation; high (500 mg·L-1 N) or low (50 mg·L-1 N) 3×/week N fertilizer regimes; daminozide (5000 mg·L-1); or paclobutrazol (30, 45, or 180 mg·L-1). One week after initiation of treatments, individual plants in separate greenhouses were inoculated with two adult green peach aphids (Myzus persicae Sulzer) or five two-spotted spider mites (Tetranychus urticae Koch). A natural infestation of western flower thrips (Frankliniella occidentalis Pergande) in the mite-inoculated greenhouse provided an additional insect treatment. Brushing was the only treatment that consistently reduced thrips and mite populations. Aphid populations were lower on low-N than on high-N plants, but thrips and mite populations were not consistently affected by plant fertilization. Moisture stress conditioning tended to increase aphid populations on New Guinea impatiens and marigold, but had little effect on spider mite or thrips populations. Ebb-and-flow irrigation reduced the mite population on ageratum relative to that on overhead irrigated (control) plants. Plant growth regulators did not consistently affect pest populations. Chemical names used: butane-dioic acid mono(2,2-dimethylhydrazide) (daminozide); β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-1-ethanol (paclobutrazol).
Increasing fertilizer levels may reduce production time but can lead to excessive growth of herbaceous perennials, requiring the application of plant growth regulators (PGRs). This study investigated the effects of ascending fertilizer rates in conjunction with two rates of uniconazole and a control. Rooted liners of Artemisia arborescens L. `Powis Castle', Artemisia vulgaris L. `Oriental Limelight, Astilbe chinensis (Maxim.) Franch. `Pumila', Filipendula rubra (Hill) Robinson `Venusta' and Perovskia atriplicifolia Benth. were potted with controlled-release fertilizer (15N-3.9P-10K) incorporated at 2.4, 4.72, and 7.11 kg·m-3. A single foliar spray application of uniconazole was applied two weeks after transplanting at a volume of 210 mL·m-3 and two rates from 15 to 60 mg·L-1 plus a control (species-dependent). Plant height and width were measured at 2,4,6, and 8 weeks after treatment (WAT). No interactions between fertilizer rate and uniconazole were observed. Main effects varied by species. The application of uniconazole controlled height and width of Artemisia `Oriental Limelight' and Astilbe for the duration of the experiment. Height, width, and dry weight of Artemisia `Oriental Limelight' increased with ascending fertilizer rates while Astilbe was not affected. Growth of Filipendula and Artemisia `Powis Castle' was unresponsive to uniconazole, though dry weight was reduced for both at the lowest fertilizer rate. Uniconazole provided height control of Perovskia, but the effect did not persist beyond 6 WAT. Ascending fertilizer rates increased Perovskia dry weight but not height.