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Gary E. Murray, Kenneth C. Sanderson, and J. C. Williams

Abstract

Various rates of ancymidol granular incorporated, granular broadcast, soil drench, and foliar spray treatments were tested on 7 breeding plant species. Generally, treatment of media affected plant height more than foliar sprays. Media treatments reduced height linearly, with increasing rates reducing plant height. Effects were similar for Salvia splendens F. Sellow ex Roem. & Schultz and Pelargonium × hortorum L.H. Bailey plants. Height of Targetes erecta L. plants was controlled most effectively by 311 to 622 mg a.i. m−3 drenches or granular incorporated. Begonia semperflorens - cultorum Hort., and Antirrhinum majus L. plant height was best controlled with granular incorporated ancymidol at rates of 155 to 622 mg a.i. and 311 to 1243 mg a.i. m−3, respectively. Germination of Tagetes and Pelargonium seed was unaffected by granular incorporated ancymidol at 78 to 311 mg a.i. m−3. Chemical names used: a-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol).

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Jennifer L. Boatright and J. M. Zajicek

Hydrogel (Hydrosource™, Western Polyacrylamide, Inc.) was incorporated into 102 cm × 122 cm landscape beds at 25, 50, 75, or 100 lbs per 1000 sq ft. Weed barrier and 2 cm of pine bark mulch were added to the top of each bed. Controls consisted of 1) no hydrogel with weed barrier and mulch and 2) no hydrogel with mulch but no weed barrier. Each treatment was replicated four times with ten plants of petunia, marigold, and vinca planted per bed, for a total of forty plants of each species per treatment. Flower number of vinca and petunia increased with hydrogel incorporation, 75 lbs of hydrogel having the greatest number of flowers. Petunia also had higher visual ratings with increased hydrogel rates. Soil temperatures directly under the mulch and 10 cm below the mulch, at 1400 hr, were 49C and 40C respectively for controls, compared to 42C and 36C for beds with hydrogel.

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Martin Meeks, H. Brent Pemberton, Lurline Marsh, and Garry V. McDonald

The effect of UV-B fluorescent lamp light on seedling elongation was investigated using three species: marigold (Tagetes sp.), cucumber (Cucumis sativa), and tomato (Lycopersicon esculentum). Seedlings were exposed to light supplied from two unshielded and unfiltered 40-watt UV-B fluorescent lamps. In two experiments, seedlings were placed a distance of 45 cm below the light for varying lengths of time, while seedlings were placed 60 cm below the light in a third experiment. For marigold, seedlings were shorter when germinated under the UV-B lamp than when germinated under natural light in a glasshouse. Two hours of exposure just after glasshouse germination (cotyledons unfolded) was effective in reducing height of cucumber seedlings, whereas 6 hours was required to significantly reduce the height of tomato seedlings. Treatments were still effective when the last measurements were taken 12 to 14 days after germination. Exposure of seedlings to UV-B lamp light provides a possible alternative means of preventing excessive seedling elongation instead of relying on chemical plant growth regulators.

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Seenivasan Natarajan, Jeff S. Kuehny, and James E. Board

One of the greatest impediments to production of marketable ornamental herbaceous plants in southern U.S. is high temperature stress. Exposure of plants to sub-lethal temperature (heat preconditioning) before sustained heat stress helps some plants to tolerate subsequent heat stress a phenomenon often referred as acquired thermotolerance. The objective of this research was to examine various morphological, physiological and anatomical responses of `Vista red' (heat tolerant) and `Sizzler red'(heat sensitive) cultivars of Salvia splendens to heat preconditioning (HC) and subsequent heat stress treatments (challenging temperatures, CT). Cultivars of Salvia were subjected to short duration HC of 35 °C for 3 hours every third day until 5 weeks after germination and subsequent exposure to two CT treatments 30/23 °C and 35/28 °C (D/N) cycles in growth chambers for the next five weeks. Plant growth, marketable quality, stomatal conductance and net photosynthesis declined for Sizzler Red without HC treatment. Compared with nonpreconditioned plants, heat preconditioned Sizzler Red had 38.28% higher root dry weight, 95% greater leaf thickness, 50% higher marketable quality at 35/28 °C heat stress condition. Heat preconditioning helped both Vista Red and Sizzler to survive in both the heat stress treatments. Vista Red had greater heat tolerant traits than Sizzler Red, these traits exacerbated with heat preconditioning treatment. The results demonstrated that heat preconditioning enhanced heat tolerance in cultivars of Salvia, which could be related to maintenance of dense plant growth with shorter internodes, thicker stems, greater stomatal conductance, extensive root growth that compensated the transpirational water loss and overall cooling of plants.

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Dharmalingam S. Pitchay, James L. Gibson, C. Ray Campbell, Paul V. Nelson, and Brian E. Whipker

The margin of error in pinpointing the difference in deficiency symptoms between calcium and boron is high. Several experiments were conducted in the greenhouse to induce as well as to differentiate the exact foliar and root symptoms of Ca and B. The experiments were conducted with modified Hoagland nutrient solutions. The treatments were with or without Ca or B salts for inducing total deficiency symptoms. Symptoms were expressed on the upper part including the growing point of the plant. In absence of Ca, marigold and zinnia plant heights were reduced by 58% and 37%, respectively, from the control. However, the reduction in height was only in the 27% and 25% range for B deficiency. Ca deficiency was noted as a blackened region on the leaf blade (early stage symptoms) which progressed into necrotic spots on the newly formed leaves. Severe necrosis, was observed on the growing point with advanced Ca deficiency. B deficiency results in a leathery and gray color in zinnia, needle like and narrow leaflets in marigold. The leaf blades were brittle in all B deficient species. B deficient plants roots were stiff and leathery and lateral roots possessed black nodule like endings at the tips. The Ca deficient roots expressed less side branching and at the advanced stage the roots were shorter and fewer with severe necrotic symptoms. The above initial and advanced deficiency symptoms appeared earlier in treatments without Ca than B. Images of Ca and B deficiency symptoms, as well as tissue concentration values will be presented.

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Douglas A. Cox

`First Lady' marigold (Tagetes erecta L.) and `Selenia' New Guinea impatiens (NGI; Impatiens sp. hyb.) were grown in solution culture for 60 days. At 10-day intervals, plants received low N for 10 days (marigold) or 20 days (NGI). Low-N treatment was 5% and 10% of the control, respectively, for marigold and NGI. After each low-N period, FW of treated and control plants was measured and N uptake by the controls was determined by solution depletion. Nitrogen uptake by marigold reached a peak 40 days after planting, and then decreased somewhat during the final 20 days of the experiment. In contrast, N uptake by NGI increased gradually after planting, reaching its highest level at the end of the experiment (60 days). Low-N periods 10 to 20 and 20 to 30 days after planting reduced the FW of marigold about 35% vs. control. FW reductions resulting from earlier or later low-N periods were much smaller or did not occur. Reductions in NGI FW resulted from low-N periods 20 to 40, 30 to 50, and 50 to 60 days after planting. While short periods of low N reduced the growth of both species, these reductions were desirable and not excessive, and no foliar symptoms of N deficiency were apparent at any time. Results of these experiments have implications for efficient fertilizer use and growth suppression using short periods of low nutrition.

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JinSheng Huang and Paul V. Nelson

It is desirable to have a large root mass and compact shoot in the final stage of plug seedling production. Marigold `Discovery Orange' was grown for six weeks from sowing in a hydroponic system. Hoagland's all nitrate solution was used at 0.25X for the first three weeks and 0.5X for the final three weeks. P was applied continuously in the control and was eliminated for the first one or three weeks in the two stress treatments. Weekly mot and shoot dry weights indicated: a.) P stress caused an increase in root/shoot ratio with roots larger than in the control plants and b.) restoration of P after a P stress resulted in a rapid shift of root/shoot ratio back to the control level with final root and shoot weights less than in the control plants. A continuous marginal P stress or a stress near the end of seedling production is suggested. Tomato `Marglobe' was grown for five weeks and impatiens `Super Elfin White' for six weeks in a 3 sphagnum peat moss: 1 perlite substrate in 288 cell plug trays. Fertilizer was applied at every third watering at a zero leaching percentage. The control nutrient ratio (mM) was 5.4 NH4+ NO3: 0.5 PO4: 1.6 K while the low P treatments contained 0.15, 0.1, and 0.05 mM PO4 throughout the experiment. The root/shoot dry weight ratios increased in the low P treatments. Tomato plants at 0.15 and 0.1 mM P and impatiens plants at 0.15 mM P had larger roots than the control plants. A continuous stress at 0.15 mM PO4 appears promising.

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Chi Won Lee, Gye-Soon Jeong, and Byoung-Ryong Jeong

Toxicity symptom of micronutrients copper, magnesium and zinc were investigated for geranium, marigold, vinca and zinnia. Plants were grown in peat-lite mix in 11 cm plastic pots and watered with nutrient solutions containing 0.05, 0.5, 1, 5, 10 mM concentrations of Cu2+, Mg2+ and Zn2+. In most species, the concentrations of these micronutrients higher than 5 mM greatly reduced plant growth and induced stem and foliar toxicity symptoms. Toxic levels of Cu2+ and Zn2+ reduced plant and leaf sizes without producing leaf spots in all species tested. Toxicity symptom of Mn2+ were characterized by numerous chlorotic or brown leaf spots. Visual leaf toxicity symptoms of these 3 micronutrients in each species are illustrated.

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Joyce G. Latimer and Ronald D. Oetting

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).

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Jonathan M. Frantz, James C. Locke, Dharmalingam S. Pitchay, and Charles R. Krause

We thank Tera McDowell, Sarah Lancianese, Stephen Ohene-Larbi, Douglas Sturtz, and Leona Horst for their technical assistance throughout the studies, the Paul Ecke Ranch, Ball Seed Co., and GreenCircle Greenhouses for donating plant material