Lilium longiflorum Thunb. cv. Ace grown without plant growth regulators and plants drenched with 0.5 mg a.i. ancymidol per pot following shoot emergence were compared to plants growing in a medium containing uniconazole-impregnated amendments. Uniconazole was applied at rates of 0.18, 0.018, and 0.0018 mg a.i. per pot using either impregnated rockwool (RW) or copolymer acrylamide acrylate (CA). Two other treatment groups received a uniconazole drench at potting (0.018 or 0.0018 mg a.i. per pot). Impregnated CA resulted in undesirably short lilies (i.e., plants <1.5 times the height of the pot) when 0.18 mg uniconazole per pot was incorporated into the medium; effective height control was obtained with CA at 0.018 mg/pot; no height control was observed at 0.0018 mg/pot. Similarly, final height of lilies grown in medium containing uniconazole-impregnated RW decreased as the rate of uniconazole increased. Pre-emergence potting medium drenches with uniconazole (0.018 and 0.0018 mg a.i. per pot) did not significantly affect lily growth and flowering. Ancymidol drench was less effective at retarding stem length and plant height than medium incorporation of 0.18 mg uniconazole. Flowering was not significantly affected by any treatment. Chemical names used: a-cyclopropyl-a-(4-methoxy-phenyl)-5-pyriimidine methanol(ancymidol);B-[(4-cyclophenyl)methyl]-a-(1,1-dimethylethyl)1 H-1,2,4-triazole-1-ethanol(paclobutrazol);(E)-(p-chloro-phenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol(uniconazole).
Richard J. McAvoy
Poinsettias, Euphorbia pulcherrima Willd. cvs Lilo and Diva Starlight, were exposed to either warm day-cool night or cool day-warm night greenhouse temperature regimes. Day time temperatures were imposed between 900 to 1600 HR. Within each temperature regime, poinsettias were grown single stem or pinched and drenched with either 0.04 or 0.08 mg a.i. uniconazole per 1.6 1 pot or grown as untreated controls. Light levels (PAR) and potting medium and plant canopy temperatures were continuously monitored.
Over the course of the study, the day-night temperature differential (DIF), in the plant canopy, averaged 4.2C in the warm day regime and -1.4C in the cool day regime. The average daily temperature was lower (16.9C) in the warm day regime than in the cool day regime (18.7C).
DIF treatment significantly affected final leaf area, leaf and total plant dry weight, leaf area ratio and specific leaf weight, The DIF treatment by cultivar interaction was significant for final poinsettia leaf area, stem, leaf and total plant dry weight, break number and average break length. Uniconazole significantly affected final plant height, stem and total plant dry weight, break number, average break length and specific leaf weight. Uniconazole by DIF treatment effects were not significant,
Richard J. McAvoy
Root-zone and plant canopy temperatures were continuously monitored as a poinsettia (Euphorbia pulcherrima Willd. ex JSI.) crop was grown in the greenhouse under warm day/cool night [(+) DT-NT] or cool day/warm night [(-) DT-NT] temperature regimes. Day temperatures were imposed from 0900 to 1700 hr. Light levels photosynthetic photon flux (PPF) and outside ambient air temperatures were also monitored. Temperature differences between the root-zone and plant canopy microenvironments were most extreme during the night-to-day and day-to-night temperature transition periods. The temperature difference between the plant canopy and the root zone following temperature transition periods had been previously identified as a critical factor affecting stem elongation. Overall poinsettia height was consistently shorter under the (-) DT-NT than under the (+) DT-NT environment.
Richard J. McAvoy
`Rose Grenadine' and `Buckaroo' garden chrysanthemums [Dendranthema ×grandiflorum (Ramat.) Kitamura] were produced in 15-cm pots in the greenhouse and fertilized with either 550 or 1000 ml of a 15 mol·m-3 N solution at each irrigation. The nutrient solution applied to half the pots contained a wetting agent (WA), and the remaining pots received no WA. Core samples were removed at 15-cm increments to a depth of 90 cm from the soil beneath the pots. The average leaching fraction (LF) from pots receiving a WA was 0.29 but was 0.26 from pots receiving no WA. However, WA did not affect the leachate NO3-N concentration or the total NO3-N deposited on the soil beneath; these were most influenced by LF. After week 2, NO3-N concentration in the upper 15 cm soil layer was 3.4 times higher with a high LF than with a low LF (30 and 8.8 g·m-3 respectively). At week 10, the NO3-N concentration in the 30 to 45 cm soil layer averaged 71.9 g·m-3 under the high LF and 35.5 g·m-3 under the low LF. Total N and NO3-N in the potting medium was higher in the low LF pots than the high LF pots, while NO3-N was higher in the medium of pots irrigated without WA than with WA. Final plant shoot mass was higher in pots irrigated to a high LF or without WA than in pots irrigated to a low LF or with WA.
Kranti Macherla and Richard J. McAvoy
As water resources become limited, agricultural producers must resort to alternative sources for irrigation, including municipal reclaimed water which may contain impurities such as salts that can adversely impact irrigation management practices and crop yield. To test the effects of salinity on plant growth and nutrient composition under greenhouse conditions, zinnia (Zinnia elegans) was produced under two different subirrigation management regimes and exposed to various concentrations of NaCl to simulate the crop production challenges associated with poor water quality. Plants received either short- or long-cycle subirrigation to achieve differing levels of potting medium saturation at each irrigation event. Plants under these two irrigation management regimes were challenged with NaCl at concentrations up to 1.5 g·L−1 or 3 dS·m−1 . Zinnia plants accumulated more Na in shoot tissues as salinity in the irrigation water increased from 0 to 1.5 g·L−1. The electrical conductivity (EC) in the potting medium also increased over time, and the rate of leaf area expansion decreased with increasing levels of salinity in the irrigation water. Short-cycle irrigation management has been shown to increase fertilizer and water use efficiency (WUE), thereby reducing the costs associated with these resources and also reducing the environmental impacts of agricultural crop production. In our study, the medium under short-cycle subirrigation management had lower gravimetric water content (GWC), both before and after irrigation, than the medium under long-cycle subirrigation, but the drier medium conditions did not increase susceptibility to salt injury. Furthermore, plants grown under short-cycle irrigation management for 4 to 6 weeks accumulated less Na in shoot tissue than plants grown under long-cycle irrigation management. Sodium accumulation in the shoot tissues was a product of both the amount of sodium in the irrigation solution and the amount of water used by the plant over time. Therefore, short-cycle subirrigation can be used as an effective water management technique even when raw water quality is poor as represented by elevated salinity. Our research indicates that zinnia can be irrigated with saline water up to 0.5 g·L−1 NaCl (an EC of 1 dS·m−1) in a 5-week production cycle without adverse effects on growth.
Richard J. McAvoy and Paige Kishbaugh-Schmidt
Easter lilies, Lilium longiflorum Thumb. cv Nellie White, were grown in a commercial pine bark-based medium (25% by vol.), amended with 0.5 g Acrylamide Acrylate Gel (AAG) per 1.6 liter pot. Lilies were grown in media drenched with ancymidol, at 0, 0.25, 0.375 or 0.5mg a.i.pot-1 following shoot emergence, or grown in media containing ancymidol impregnated AAG at 0, 0.25, 0.375 or 0.5mg a.i.pot-1. AAG applied ancymidol treatments resulted in a significant linear decrease in both lily stem and internode length as the rate of ancymidol increased. Drench applied ancymidol had no affect on stem or internode length. Stem and internode lengths of drench treated lilies were not significantly shorter than lilies not exposed to ancymidol. Bud length, leaf and bud number, and days to anthesis were not affected (P≤0.05) by any treatment. Ancymidol activity in the top, middle and bottom strata of medium filled containers, and in the leachate from these containers, was measured using a lettuce hypocotyl length bioassay. Ancymidol activity was uniformly distributed throughout the bark medium when applied in AAG. With this treatment, 10-15% of the ancymidol activity was detected in the leachate. When ancymidol was applied as a drench, over 95% of the activity was detected in the top two strata, with 70% in the upper most stratum and the rest in the leachate.
Usha R. Palaniswamy and Richard J. McAvoy
Martin P.N. Gent and Richard J. McAvoy
Subirrigation for production of potted ornamental plants reduces the waste of water and fertilizer inherent to conventional overhead watering systems used in greenhouses. Ebb and flow watering systems for flooded floors typically operate slowly so that the substrate takes up water to near effective water-holding capacity during each irrigation event. We used a system that rapidly delivered water to and removed water from the production surface to restrict the water provided to the plants. We examined several parameters that vary between this fast-cycle ebb and flow watering on a flooded floor compared with slow-cycle watering. Water and fertilizer use was reduced by 20% to 30% with fast- compared with slow-cycle watering. Biomass and stem height at bloom were also reduced by 10% to 20% under fast-cycle saturation. This watering method did not affect the rate of flower development or plant nutrient composition. Volumetric water content of the substrate was the only measure that was affected by location on the flooded floor. Despite the fast ebb and flow on pitched floors, none of the aspects of plant growth was affected by location on the floor. This method of watering shows promise as a means to produce uniform crops of container-grown plants while conserving water and fertilizer.
Richard J. McAvoy and Bernard B. Bible
Silica sprays (Na2SiO3 or SiO2·nH2O) markedly reduced the incidence and severity of bract necrosis (BN) of Euphorbia pulcherrima Willd. cv. Supjibi Red compared to plants not sprayed with silica. BN has been associated with low Ca concentrations or high K: Ca ratios in tissues of bract margins. Silica had no effect on Ca or K concentrations in bract margin tissues, and BN was not associated with the macro- or micronutrient composition of bract margin tissues. Sixteen days after initial anthesis, nontreated and deionized-water-sprayed poinsettias developed a higher incidence of BN than did plants sprayed with Na2SiO3 or CaCl2. However, sprays of 3.56, 5.34, and 7.12 mm Na2SiO3 were as effective as 9.98 mm CaCl2 sprays in protecting against BN of `Supjibi Red' and `Angelika White' bracts for up to 30 days after initial anthesis. `Supjibi Red' developed a higher incidence of bract necrosis than did `Angelika White', but both cultivars showed a similar response to the treatments and similar symptoms of necrosis. In both cultivars, initial symptoms appeared as small necrotic lesions on bracts at the looped ends of lateral veins that displayed a closed-vein pattern after the plants reached initial anthesis.
Bernard B. Bible and Richard J. McAvoy
`Angelika White' poinsettias (Euphoria pulcherrima Willd.ex. Klotzch) were grown hydroponically with modified Hoagland's solution concentrations of 2 or 8 mS·cm-1. The 8-mS·cm–1 rate was imposed by proportionate increases in Ca(NO3)2, KNO3, and MgSO4. Water use, whole plant fresh mass, and pan evaporation were measured gravimetrically twice weekly over a 2-week period beginning 12 Oct. 1995. Poinsettia leaf water loss (g H2O/dm2 of estimated leaf area per day) was 0.30 and 0.22 times pan evaporation (g H2O/dm2 of pan area per day) for the plants in the 2 and 8 mS·cm–1 solutions, respectively (a 25% reduction in water loss for plants in the 8 mS·cm–1 solution), as compared to plants in the 2 mS·cm–1 solution. At initial anthesis, a reciprocal transfer of plants between the 2 and 8 mS·cm–1 solutions was used to investigate the time when plants were sensitive to high soluble salts for bract necrosis. Other plants were maintained throughout the experiment in the 2 and 8 mS·cm–1 solutions. On 15 Jan. 1996, plants were harvested and total lamina surface of leaves and bracts, number of necrotic bracts, and dry mass of leaves, bracts, stems, and roots were recorded. The results indicated that exposure to high soluble salts (8 mS·cm–1) prior to anthesis significantly increased the percent incidence of bract necrosis and decreased root growth. The smaller the root dry mass as a percent of total plant dry mass the greater the incidence of bract necrosis (Y = 0.0972X2 – 3.78X + 38.7, r 2 = 0.69).