Container-grown Nursery Crops Research Articles

A Base Layer of Ferrous Sulfate-Amended Pine Bark Reduces Phosphorus Leaching from Nursery Containers

Phosphorus (P) fertilizers applied to container-grown nursery crops readily leach through pine bark-based substrates and can subsequently runoff and contribute to surface water contamination. The objectives of this research were to determine the effect of adding a layer of FeSO4·7H2O-amended pine bark (FSB) to the bottoms of nursery containers on P leaching characteristics. Phosphorus and iron (Fe) leaching in response to FSB layer height (4 or 7.5 cm), FeSO4·7H2O rate (0.3, 0.6, or 1.2 kg·m−3 Fe), and form (i.e., granular versus liquid) used to formulate the FSB layer, and the inclusion of dolomite in the FSB layer were also investigated. Greenhouse studies lasting 15 and 19 weeks were conducted, in which 2.5 L nursery containers containing the FSB layer treatments below non-amended pine bark substrate were fertilized with 199 or 117 mg P from a soluble or controlled-release fertilizer, respectively. Leachate resulting from daily irrigation was collected and analyzed for P and Fe weekly. All FSB treatments leached less P than the control (non-amended pine bark only), with P reductions ranging from 22% (4 cm FSB with 0.3 kg·m−3 Fe) to 73% (7.5 cm FSB with 1.2 kg·m−3 Fe). Phosphorus leaching decreased linearly with an increase in Fe rate or layer height. The amount of Fe that leached from containers with FSB was <5% of that applied, regardless of the Fe rate. Granular- and liquid-applied FeSO4·7H2O with or without dolomite were equally effective at reducing P leaching. Adding 0.6 kg·m−3 Fe to the bottom 500 cm3 of pine bark increased P adsorption by 0.053 mg·cm−3 P, which equates to 17.9 mg P adsorbed per gram of FeSO4·7H2O added. Results from this research suggest that including an FSB layer in the bottom of nursery containers is an effective strategy for reducing P runoff from container-based nursery production sites.

Container Color and Compost Substrate Affect Root Zone Temperature and Growth of “Green Giant” Arborvitae

Container-grown nursery crops are commonly exposed to root zone stress due to inadequate moisture and supraoptimal root zone temperature (RZT). Compost substrates can improve water and nutrient retention but plant responses can vary due to physical and chemical properties. Dark color containers absorb solar radiation through the container side wall leading to excessive heat buildup in the substrate, yet white containers can reduce RZT. Compost substrates and container color were examined for effects on RZT and growth of “Green Giant” arborvitae (Thuja standishii × plicata “Green Giant”). “Green Giant” arborvitae were transplanted into white or black containers (11.3 L) filled with a pine bark substrate (PB) or PB mixed with compost (C) at two different proportions [PB:C (9:1) and PB:C (7:3)]. White containers reduced maximum RZT by up to 7 °C and RZT remained above 38 °C for only 3% of the time compared to 21% of the time in black containers. Shoot growth increased over 50% in white containers compared to black containers. Compost increased substrate volumetric water content (VWC), increased shoot growth by up to 24%, and reduced total irrigation volume by up to 40%. Utilizing white containers for minimizing RZT and compost-amended substrates to maintain adequate VWC can improve root and shoot growth and overall crop quality while reducing nursery production inputs.

Efficacy of preemergence herbicides over time

AbstractPreemergence herbicides are applied to container-grown nursery crops repeatedly throughout the year, often in 8 to 10 week intervals. Preemergence herbicide efficacy may decline over time, resulting in reduced weed control several weeks after application if weed seed density remains high. The objective of this research is to evaluate efficacy of preemergence herbicides on creeping woodsorrel (Oxalis corniculata L.) and flexuous bittercress (Cardamine flexuosa With.) by applying weed seed from 0 to 10 weeks after herbicide application. Granular formulations of pendimethalin, prodiamine + isoxaben, oxyfluorfen + pendimethalin, and flumioxazin were applied at their maximum labeled rates to separate groups of containers every two weeks for ten weeks. After the herbicide application at 10 weeks, 40 seeds of creeping woodsorrel and flexuous bittercress each were applied to all containers. All herbicides provided effective control when seed were applied within 2 weeks of herbicide application. Herbicides containing oxyfluorfen or flumioxazin provided effective preemergence bittercress and creeping woodsorrel control when seed were applied up to 8 to 10 weeks after herbicide application. Other herbicide products resulted in reduced control as the time between herbicide and seed application increased.Index words: weed control, container crops, substrates.Species used in this study: flexuous bittercress (Cardamine flexuosa With.), creeping woodsorrel (Oxalis corniculata L.).Chemicals used in this study: pendimethalin (Pendulum 2G), prodiamine + isoxaben (Gemini G), pendimethalin + oxyfluorfen (OH2), and flumioxazin (BroadStar).

Evaluating On-demand Irrigation Systems for Container-grown Woody Plants Grown in Biochar-amended Pine Bark

Controlling irrigation using timers or manually operated systems is the most common irrigation scheduling method in outdoor container production systems. Improving irrigation efficiency can be achieved by scheduling irrigation based on plant water needs and the appropriate use of sensors rather than relying on periodically adjusting irrigation volume based on perceived water needs. Substrate amendments such as biochar, a carbon (C)-rich by-product of pyrolysis or gasification, can increase the amount of available water and improve irrigation efficiency and plant growth. Previous work examined two on-demand irrigation schedules in controlled indoor (greenhouse) environments. The goal of this study was to evaluate the impact of these on-demand irrigation schedules and hardwood biochar on water use and biomass gain of container-grown Hydrangea paniculata ‘Silver Dollar’ in a typical outdoor nursery production environment. Eighteen independently controlled irrigation zones were designed to test three irrigation schedules on ‘Silver Dollar’ hydrangea grown in pine bark amended with 0% or 25% hardwood biochar. The three irrigation schedules were conventional irrigation and two on-demand schedules, which were based on substrate physical properties or plant physiology. Conventional irrigation delivered 1.8 cm water in one event each day. The scheduling of substrate-based irrigation was based on the soilless substrate moisture characteristic curve, applying water whenever the substrate water content corresponding to a substrate water potential of –10 kPa was reached. The plant-based irrigation schedule was based on a specific substrate moisture content derived from a previously defined relationship between substrate moisture content and photosynthetic rate, maintaining the volumetric water content (VWC) to support photosynthesis at 90% of the maximum predicted photosynthetic rate. Total water use for the substrate-based irrigation was the same as for the conventional system; the plant-based system used significantly less water. However, plant dry weight was 22% and 15% greater, water use efficiency (WUE) was 40% and 40% greater, and total leachate volume was 25% and 30% less for the substrate-based and plant-based irrigation scheduling systems, respectively, than for conventional irrigation. The 25% biochar amendment rate reduced leachate volume per irrigation event, and leaching fraction, but did not affect total water use or plant dry weight. This research demonstrated that on-demand irrigation scheduling that is plant based or substrate based could be an effective approach to increase WUE for container-grown nursery crops without affecting plant growth negatively.

Growth Response, Mineral Nutrition, and Water Utilization of Container-grown Woody Ornamentals Grown in Biochar-amended Pine Bark

Container-grown nursery crops generally require daily irrigation applications and potentially more frequent applications during the hottest part of the growing season. Developing management practices that make more efficient use of irrigation water is important for improving the sustainability of nursery crop production. Biochar, a byproduct of pyrolysis, can potentially increase the water-holding capacity and reduce water and nutrient leaching. In addition, the development of sensor-based irrigation technologies has made monitoring substrate moisture a practical tool for irrigation management in the nursery industry. The objective of this research was to determine the effect of switchgrass biochar on water and nutrient-holding capacity and release in container substrates of Buxus sempervirens L. × Buxus microphylla (‘Green Velvet’ boxwood) and Hydrangea paniculata (Pinky Winky® hardy hydrangea). Containers were filled with pine bark and amended with 0%, 10%, or 25% volume of biochar. Plants were irrigated when the volumetric water content (VWC) reached the water-buffering capacity set point of 0.25 cm3·cm−3. The sensor-based irrigation in combination with the low cost biochar substrate amendment increased substrate water-holding capacity and reduced irrigation requirements for the production of hydrangea, a high water use plant. Biochar application rate influenced irrigation frequency, which likely affected plant biomass for hydrangea, but boxwood dry weight was unaffected by biochar rate. Total irrigation applied was decreased by 32% in 10% biochar treatment without reducing hydrangea dry weight. However, in the 25% biochar treatment, total irrigation applied was reduced by 72%, whereas dry weight decreased by 50%. Biochar application reduced leaching volume and leaching fraction in both plants. Leachate analysis over the course of the 8-week experiment showed that the average mass of phosphate (PO4), potassium (K), and total carbon was greater in the leachate from containers that received 25% biochar compared with those receiving 0% or 10% biochar for both plant species. For hydrangea, mass of total nitrogen (TN) and nitrate (NO3) in leachate was not significantly affected by increasing the biochar rate. However, for boxwood, the mass of NO3 and TN was greater in the 25% biochar treatment leachate, whereas the mass of ammonium (NH4) was unaffected. In hydrangea, total nutrients lost from the containers was lower in biochar-amended containers (both 10% and 25% biochar) because of receiving a lower total volume of water. Amendment with biochar also affected concentration of phosphorus (P) and K, with the highest concentration in both leaf tissue and substrate from the 25% biochar application rate.

Micronutrient Availability from Steel Slag Amendment in Pine Bark Substrates

Steel slag is a byproduct of the steel industry that can be used as a liming agent, but also has a high mineral nutrient content. While micronutrients are present in steel slag, it is not known if the mineral form of the micronutrients would render them available for plant uptake. The objective of this research was to determine if steel slag could be used as the sole micronutrient source for container-grown nursery crops. Butterfly bush (Buddleja davidii ‘Pink Delight’) and rose (Rosa ‘Radrazz’) were grown in #3 (3 gal) containers in a base substrate composed of pine bark and peatmoss (80:20, by vol). The base substrate was amended with the following treatments: with a complete controlled release fertilizer (CRF) including micronutrients (C-control), a substrate amended with a different CRF containing only N, P, and K along with a granular micronutrient package (M-control), and three additional treatments amended with the CRF (N, P, and K only) and either 1.2, 2.4, or 4.8 kg·m−3 (2, 4, and 8 lb·yd−3) of steel slag. Plants were harvested at 2 and 4 months after potting (MAP). None of the plants displayed any sign of nutrient deficiency or toxicity throughout the experiment. However, plants grown in the substrate amended with the highest slag rate [4.8 kg·m−3 (8 lb·yd−3)] had lower shoot dry weight (SDW) than both control groups. Substrate pH increased with increasing slag rate, which may have affected micronutrient availability in those substrates. Among the micronutrients analyzed, only Copper (Cu) was consistently deficient in both the substrate and foliar tissue of slag-amended treatments. Steel slag either does not provide a sufficient quantity of Cu or the concomitant increase in pH with increasing rates of steel slag renders Cu unavailable for plant uptake. Steel slag should not be used as the sole source of micronutrients for shrubs grown in pine bark-based substrates.

Impact of Application Rate, Timing, and Indaziflam Formulation on Early Postemergence Control ofOxalis stricta

Although primarily used as an effective PRE herbicide, indaziflam has been shown to provide early POST control of some weeds commonly found in nursery production. Previous investigation on the early POST efficacy of indaziflam focused on the liquid formulation, and the ability of the granular formulation to provide early POST weed control is unknown. Nursery trials were conducted to evaluate early POST control of oxalis using two formulations of indaziflam. Oxalis seeds were surface sown to nursery containers at two separate dates and grown until they reached the two- to four-leaf stage (2-4L) and six- to eight-leaf stage. Both growth stages were treated with indaziflam at 12.6, 25.1, 50.2, and 100.4 g ai ha−1using either a granular (G) or liquid (SC) formulation. A chemical control treatment (glyphosate) and a nontreated control were also included for comparison. The SC formulation provided > 90% control of both oxalis growth stages at all four rates and was similar to glyphosate. The G formulation at 12.6 and 25.1 g ha−1only provided marginal control, but overall performed similarly to the SC formulation at the 50.2 and 100.4 g ha−1rate in most experiments. In contrast to the SC formulation, the G formulation is labeled for use over the top of container-grown nursery crops. Results of this research indicate that in areas where oxalis is the primary weed of concern, the G formulation of indaziflam could be applied to control small oxalis up to the 2-4L stage at the currently labeled rate (50.2 g ha−1).

Effects of Repeated Applications of Roundup Pro® Over the Top of Container-Grown Nursery Crops

Three experiments studying the effects of repeated over-the-top applications of Roundup Pro® to container-grown nursery crops were conducted. Plants in 3.8 liter (1 gal) containers were treated with either single or multiple applications of Roundup Pro® at 1.12 kg ai·ha−1 (1.0 lb ai·A−1) in July, August, September, or October, 2008 or 2009. Plants treated with multiple applications were treated in July and August (J+A); July, August, and September (J+A+S); July, August, September, and October (J+A+S+O); or July and September (J+S). Injury ratings were taken at multiple times after treatments. Growth indices (GI) [(height + width1 + width2) / 3] were taken in January and June 2009 and February and May 2010. Plants were rated for vigor and marketability in May 2009 or June 2010. Liriope muscari ‘Big Blue,’ Camellia sasanqua ‘Shishigashira,’ and Gardenia jasminoides ‘Radicans’ were evaluated in Experiment 1 (2008, Auburn). Liriope showed minor injury from two or more applications with reduced growth from 3 or 4 applications, but all plants were rated as marketable in June of the following season. ‘Shishigashira’ camellia exhibited no injury from any glyphosate application and all parameters were similar to non-treated controls (NTC). Gardenia showed fall chlorosis and stunting through early spring from multiple applications, but all plants were marketable. Even those treated 3 or 4 times were small but marketable. In Experiment 2 (2009, Auburn. AL), ‘Big Blue’ liriope, ‘Radicans’ gardenia, Camellia sasanqua ‘Martha Sims,’ and Juniperus conferta ‘Blue Pacific’ showed no injury from any treatment and GI in January and June were similar to NTC. Ilex cornuta ‘Dwarf Burfordi’ GI were similar to NTC with occasional chlorosis observed after July treatments. Ternstroemia gymnathera (cleyera) exhibited chlorosis, necrosis, and stunting of shoot tips for all treatments. Cleyera GI in January and June indicated that J+A+S, J+A+S+O, and J+S-treated plants were smaller than NTC, but regrowth was similar to NTC for all treatments the following spring. All plants were vigorous and marketable. In Experiment 3 (2009, Mobile, AL), ‘Big Blue’ liriope, ‘Radicans’ gardenia, ‘Blue Pacific’ juniper, ‘Martha Sims’ camellia, Ilex cornuta ‘Carissa,’ and cleyera GI were similar to NTC in February and late May. Slight injury occurred only on the new growth of cleyera and ‘Carissa’ holly with primary symptoms being chlorosis and/or slight stunting seen in mid-September and October from some single and double applications.

Duration of Flumioxazin-Based Weed Control in Container-Grown Nursery Crops

Flumioxazin is used in nursery production and landscape maintenance industries. In these situations, weed control provided by flumioxazin often lasts longer than that reported in soil. Our objective was to quantify flumioxazin longevity under conditions found in nursery production. Pots were filled with 6 : 1 (v/v) pine bark : sand mixture. This nonsoil media is typical of what is used for nursery crop production. Pots were treated with flumioxazin at either 0.28 or 0.42 kg ai ha−1, and subsequently sown with either hairy bittercress (two winter experiments) or spotted spurge (two summer experiments) at weekly intervals. Weed seed germination, emergence, and seedling establishment in the treated pots was compared with nontreated control and used as a proxy for herbicide activity. Flumioxazin provided approximately 7 wk of complete (100%) hairy bittercress control regardless of rate. However, a rate effect was evident in only one of the two experiments conducted with hairy bittercress. In both experiments with hairy bittercress, marginal and highly variable activity was still evident at 18 wk after treatment. Flumioxazin at 0.28 and 0.42 kg ha−1provided 2- and 4-wk complete spotted spurge control, respectively. No spotted spurge control was evident after about 8 wk. Subjecting this less-variable data to nonlinear regression revealed that the time required for 50% reduction in flumioxazin activity was approximately 5.5 and 6.6 wk for the two rates, respectively. A column leaching study revealed that flumioxazin activity remained localized near the surface (0 to 4 cm). Therefore the dissipation observed was likely the result of in situ degradation and not displacement. The high organic matter content of the nonsoil media contributes to the observed persistence of flumioxazin activity.

Developing a physiological-based, on-demand irrigation system for container production

A demand-based irrigation system was developed for Hibiscus rosa-sinensis ‘Cashmere Wind’ based on the relationship between photosynthesis and substrate moisture level (moisture response curve). An experiment was conducted to evaluate the premise that biomass would decrease only when substrate moisture levels caused a significant reduction in photosynthetic rate. Irrigation set points were based on the moisture response curve and corresponded to 49, 41, 30, and 22m3m−3 volumetric water content (89–61% container capacity). Gas exchange and leaf water potential were greater for plants in the three wettest irrigation treatments. Plants under these treatments used 1.4, 1.2, and 1.05 times more water during the experiment than plants in the driest treatment. Biomass metrics were generally unaffected by treatments or were greater for one or both intermediate treatments. This research demonstrates that a demand-based irrigation system with a physiological basis (predicated on the relationship between photosynthesis and substrate moisture potential) could be an effective biorational approach for scheduling irrigation and reducing water consumption in container-grown nursery crops.

Ornamental Plant Response to Percentage of Reclaimed Water Irrigation

Vinca [Catharanthus roseus (L.) G. Don], salvia (Salvia splendens F. Sellow ex Roem. and Schult.), Dwarf Yaupon holly (Ilex vomitoria Ait. ‘Nana’), and ‘Helleri’ holly (Ilex crenata Thunb. ‘Helleri’) were grown in 2.3-L containers with soilless substrates in a greenhouse. Irrigation was applied as needed to the substrate surface or applied to the substrate surface and applied over plant foliage. Irrigation for both application methods was composed of 0%, 25%, 50%, 75%, or 100% reclaimed water (processed sewage) with deionized water composing the remainder. Shoot dry weights of marketable-sized plants were either larger or similar when 100% reclaimed water was used compared with 0% reclaimed water (deionized). Root dry weights exhibited a similar response except for salvia roots that were smaller with 100% reclaimed water irrigation regardless of application method. Leachate NO3-N, phosphorus (P), and potassium (K) generally decreased throughout the experiments for vinca and Dwarf Yaupon holly and were highest at experiment midpoint for ‘Helleri’ holly and lowest for salvia. Leachate electrical conductivities (ECs) were generally highest at experiment termination for vinca and salvia, whereas ECs of Dwarf Yaupon and ‘Helleri’ holly tended to peak at experimental midpoint and then decrease slightly at termination. ECs were usually less than 2 dS·m−1 except at experimental midpoint (4.5 months) for ‘Helleri’ holly. Based on the response of plants in this research, high-quality reclaimed water is a viable water source for annual and woody container-grown nursery crops.

Comparison of Water Management in Container-Grown Nursery Crops using Leaching Fraction or Weight-Based On Demand Irrigation Control

Abstract Water management should be the foundation of container nursery production as it is linked directly to both water use and nutrient uptake efficiency and ultimately, environmental impact. In this study a gravimetric water management technique was used by means of a load cell/computer interface to determine irrigation volume and time of application. Cotoneaster dammeri ‘Skogholm’ was grown in 14 liter (#5) containers with an 8: 1 pine bark: sand mixture. The treatments were: an industry control that was irrigated cyclically at 1200, 1500, and 1800 HR to maintain a 0.2 LF (PM 0.2 LF); and a gravimetric treatment that irrigated when container capacity (CC) dropped below 94% and returned the CC to 98% with percentages lowered over the course of the season, always in a 4% spread, to maintain < 0.15 LF (On Demand). The number of irrigation cycles were similar until the end of the study when On Demand cycled up to seven times a day. PM 0.2 LF had a greater WUEp (gram of dry weight produced per mL of water retained in the substrate). Time averaged application rate for On Demand was always lower than PM 0.2 LF resulting in a LF of 0.06 compared to 0.14 LF for PM 0.2 LF.

Herbicide Efficacy in Alternative Substrates for Container-grown Nursery Crops

Abstract Three experiments were conducted to evaluate the influence of alternative substrates on herbicide efficacy in container grown nursery crops. In Experiment 1, alternative substrates evaluated were either pine wood chips hammer-milled, to pass between 0.48 cm (0.19 in) screen (PWCH1) or 0.64 cm (0.25 in) screen (PWCH2), whole pine trees chipped or hammer-milled (WTCH), to pass between a 0.48 cm (0.19 in) screen, or the previously mentioned combined with pinebark. A commercial pine bark substrate (PB) with a 6: 1 (by vol) ratio of pine bark to sand was maintained as a control treatment. Rout® at 3 lbs aia (oxyfluorfen + oryzalin at 2.24 + 1.12 kg·ha−1) and Ronstar at 4.0 lb aia (oxadiazon at 4.48 kg·ha−1) were applied at recommended label rates. Herbicides were applied and irrigated, and each container was overseeded with 25 spotted spurge (Euphorbia maculata) seed per container. In general, the greatest spurge numbers occurred in PB substrates. Rout provided superior spurge control compared to Ronstar. In Experiment 2, substrates evaluated were PWCH2, WTCH and PBS with 7.0 kgm−3 (12 lbsyd−3) of Polyon 17-6-12 or with an additional 8 lbs·yd−3 of Polyon 17-6-12, or PWCH2 and WTCH combined with composted poultry litter (CPL). PWCH2 tended to have the fewest spurge numbers throughout the experiment, while WTCH and PBS tended to have similar spurge numbers and spurge fresh weight. Addition of CPL and additional fertilizer tended to increase spurge numbers and spurge fresh weight in all substrates. Rout and Ronstar provided similar spurge control in this study. In Experiment 3, substrates evaluated were PB (100%), WTCH (100%), CCR (100%), and PB: S (6: 1 vol), WTCH: S (6: 1 vol), and CCR: S (6: 1 vol). Rout and Ronstar were each applied at 0.25×, 0.50×, 075×, and 1.0× label rate. There was a significant substrate affect on all dates except 14 DAT. Spurge numbers and spurge fresh weight were greatest in PB or PB: S substrates. Spurge numbers and spurge fresh weight in general decreased with increasing herbicide rates. At 45 DAT and 60 DAT, Rout had superior spurge control compared to Ronstar. With WT and CCR substrates, Rout provided excellent control (less than 1.0 gram fresh weight) at the 0.50× and 1.0× rates. In general, weed control in alternative substrates was superior to that obtained in commercially used pinebark.

Preemergence Control of Doveweed (Murdannia nudiflora) in Container-Grown Nursery Crops

Abstract Preemergence herbicides were evaluated for control of doveweed (Murdannia nudiflora), a summer annual weed of increasing importance in nurseries of the southeastern United States. In the first experiments, broad-spectrum nursery herbicides OH2 (oxyfluorfen + pendimethalin), Snapshot TG (isoxaben + trifluralin), and BroadStar (flumioxazin) were compared. OH2 and Snapshot provided poor and variable control whereas BroadStar controlled doveweed 82 to 100%. In the second set of experiments, recommended rates of all major active ingredients labeled for use in container nursery crops and landscape plantings were compared for control of doveweed. Doveweed was controlled ≥ 95% by BroadStar, Pennant Magnum (s-metolachlor), and Tower (dimethenamid-p). Barricade (prodiamine), Dimension (dithiopyr), Gallery (isoxaben), OH2, Pendulum (pendimethalin), Regal O-O (oxyfluorfen + oxadiazon), Ronstar (oxadiazon), Rout (oxyfluorfen + oryzalin), Showcase (trifluralin + isoxaben + oxyfluorfen), Snapshot TG, and Surflan (oryzalin) did not control doveweed.

Weed Growth and Efficacy of PRE-Applied Herbicides in Alternative Rooting Substrates Used in Container-Grown Nursery Crops

Container-grown nursery crops in the southeastern United States are typically grown in a rooting substrate comprised primarily of the ground bark of pine trees. However, pine bark is becoming less available and more costly because of changes in production and marketing practices within southeastern pine forestry. This shortage has resulted in the economic incentive to seek pine bark alternatives. Two possible alternatives are clean chip residual and whole tree. These alternatives are like pine bark, because both are products of southern pine forestry. Unlike pine bark, which is a single part of the tree, these alternatives contain all parts of the tree, including wood and foliage in various portions. Registration of preemergence-active herbicides has been based solely upon data obtained from pine bark–based nursery production. Research was conducted to determine if the control of (1) large crabgrass with prodiamine, (2) eclipta with flumioxazin, and (3) spotted spurge with isoxaben would be comparable in these alternatives to what has been established in pine bark. Seed germination of all three weed species in no-herbicide controls was approximately 10% and equivalent between pine bark and the alternatives. Foliage fresh weight production of large crabgrass and spotted spurge was less in the alternatives compared to pine bark; eclipta was not affected. For all three weed species–herbicide combinations, weed control was nearly identical between pine bark and the alternative substrates, provided the herbicide had been applied at its registered rate. For all three herbicides, rates that are effective in pine bark substrates will be equally effective in the pine bark alternatives.

Preemergence Herbicide Applications to Six Containerized Woody Ornamental Rootstocks do not Affect Winter Grafting Success

Abstract Five common preemergence herbicides [Scotts OH2 (oxy fluorfen and pendimethalin), Snapshot TG (trifluralin and isoxaben), Ronstar (oxadiazon), SureGuard (flumioxazin), or BroadStar (flumioxazin)] were each applied at the highest labeled rates at 6 to 8 week intervals over the growing season to six species of container-grown seedling rootstocks. Dormant scions were bench-grafted to their respective rootstocks the following winter. Research was conducted in 2006–2007 and repeated in 2007–2008. Treatment effects were compared to non-treated control plants. Preemergence herbicide treatments had no effect on grafting success for any of the cultivars. Data indicate that these preemergence herbicides, labeled for use in container-grown nursery crops, can be used in accordance with label recommendations to control weeds in containerized rootstocks without affecting subsequent grafting success.

Efficacy of Metarhizium anisopliae as a Curative Application for Black Vine Weevil (Otiorhynchus sulcatus) Infesting Container-Grown Nursery Crops

Abstract The black vine weevil (BVW), Otiorhynchus sulcatus (F.) is a serious pest of nursery crops. The fungus, Metarhizium anisopliae (F52), is registered by the U.S. Environmental Protection Agency for BVW control. The objectives of this study were to determine the efficacy of a curative drench application of M. anisopliae for controlling BVW larval infestations in container-grown nursery plants and the effect of temperature on the rate of fungal growth and speed of kill. Trials evaluating the efficacy of M. anisopliae as a curative application were performed in the spring of 2004 and 2005 as well as the fall of 2006. Laboratory studies were performed to quantify the impact of temperature (10, 15, 20, 24 and 28C) on fungal growth and speed of kill. Metarhizium anisopliae applied in the greenhouse and outdoors in 2004 were 92 and 30% effective, respectively. Fungal applications to container-grown plant material maintained outdoors in the spring of 2005 were nearly 100% effective 28 days after application. Fall applications in 2006 provided statistically significant reductions in the number of live BVW larve per pot, but were not as effective as spring applications in 2005. The mean media temperature of containers maintained outdoors in the fall of 2006 dropped considerably (10–12C) over the course of the experiment and were likely the cause for the reduced efficacy. Laboratory experiments demonstrated that temperatures below 20C (68F) significantly slowed fungal growth and the speed at which M. anisopliae infected BVW larvae. In the field, drench applications of M. anisopliae were very effective at eliminating BVW larvae in container-grown nursery plants when media temperatures were adequate (> 15C (59F)). The use of M. anisopliae as a curative drench application has similar temperature-dependent limitations as the use of entomopathogenic nematodes for BVW control. Therefore, applications should occur as early in the fall as possible once egg laying has ended or in late spring just prior to pupation when media temperatures would be most conducive to fungal infection.

(47) Herbicide Efficacy in Alternative Substrates for Container-grown Nursery Crops

This study evaluated the effects of nine alternative substrates on herbicide efficacy in container-grown nursery crops: 1) VT (pine wood chips hammer-milled to pass a 0.4-cm screen); 2) USDA (pine wood chips hammer-milled to pass a 0.64-cm screen; 3) AUC (Pinus taeda chipped including needles); 4) AUHM (AUC hammer-milled to pass a 0.48-cm screen; 5) 1 VT: 1 commercial grade pinebark (v/v); 6) 1 USDA: 1 pinebark (v/v); 7) 1 AUC: 1 pinebark (v/v); 8) 1 AUHM: 1 pinebark (v/v); and 9) 6 pinebark: 1 sand (v/v). Each substrate was amended with 6.35 kg of 17–6–12 (17N–2.6P–10K) control-release fertilizer, 2.27 kg of lime, and 0.89 kg micromax per cubic meter. Containers (8.3 cm) were filled on 15 June and three herbicides applied the next day: Rout (oxyfluorfen + oryzalin at 2.24 + 1.12 kg·ha-1), Ronstar (oxadiazon at 4.48 kg·ha-1) and a nontreated control. The next day, containers were overseeded with 25 prostrate spurge seed. Data collected included weed counts 30 and 60 days after treatment (DAT) and weed fresh weights at 60 DAT. Spurge occurred less in the two treatments of 100% pine wood chips followed by the AUC treatment. With spurge, the least weed fresh weight occurred with the USDA and AUC treatments. For example, at 30 DAT, spurge count was reduced by 33%, 40%, and 70%, respectively, when comparing VT, USDA, and AUC to pinebark: sand. Spurge fresh weight at 60 DAT followed a similar trend. With all of the substrates except AUHM, the addition of commercially used pine bark resulted in less weed control. Rout provided superior control followed by Ronstar and the nontreated control. These data show that control of prostrate spurge with commonly used preemergent applied herbicides may actually be improved with some of the alternative substrates currently being tested.

Growth and Flowering Response of Container Grown Passion Flower Cultivars to Fertilizer and Paclobutrazo

Abstract The effects of fertilizer and paclobutrazol applications on growth and flowering in four container grown passion flower cultivars (Passiflora ‘Amethyst’, Passiflora ‘Blue Bouquet’, Passflora ‘Fledermouse’, and Passflora ‘Lady Margaret’) were evaluated. A four month production system was used that included propagating cuttings in late winter, followed by greenhouse liner production in early spring, and finally by two months of outdoor container production. Shoot growth was increased by increasing fertilizer rates and the response was highly cultivar dependent. Fertilizer rates resulting in the highest levels of growth for each cultivar were generally higher than those required for most container grown nursery crops, ranging between 3.2 and 5.3 g/liter (0.44 and 0.73 oz/gal) of Osmocote 14N–6.0P–11.6K (14–14–14). Paclobutrazol reduced overall plant size without increasing the number of nodes or flowers. Cultivars were chosen based on cold tolerance and vigor and cultivar appeared to be the most significant independent variable. Of the cultivars evaluated ‘Lady Margaret’ was most suitable for the four month production system.

Isotopic and Nonisotopic Estimation of Nitrogen Fertilizer Uptake in Container-grown Woody Ornamentals

Accurate methods for determining the fate and recovery of nitrogen (N) fertilizer applied to container-grown nursery crops are essential to comply with regulations and develop innovative fertilizer programs. The objectives of this study were (i) to use 15N techniques to determine the fate of fertilizer N, (ii) to compare nonisotopic and isotopic methods of determining N recovery, and (iii) to determine the relative importance of fertilizer and non-fertilizer N at rates of 25, 50, 100, 200, and 300 mg·L-1 in container-grown Euonymus alatus (Thunb.) Sieb., Cornus sericea L., and Weigela florida (Bunge) A. DC. In all species, root and shoot N increased with N rate, and at each rate more N was stored in the roots than in the shoots. Estimation of N recovery determined by the total N method (Kjeldahl N/applied N) was significantly higher for all species and at each N rate than estimation of N recovery determined by the labeled fertilizer N method (labeled N/total applied N). Increasing fertilizer rates up to 100 mg·L-1 resulted in increased uptake of N derived from other sources (NDFO). NDFO at low N concentrations was a significant portion of the total N in the plant. As a result, the difference in estimation of percent N recovery between each method was larger at lower N concentrations for all species. The nonisotopic total N method produces higher fertilizer N uptake estimates, as much as three to four times the isotopic based estimates, in container-grown plants at N concentrations of 25 mg·L-1. Actual fertilizer N loss increases dramatically from 25 to 300 mg·L-1 (due to dramatic increases in N applied), despite small gains in fertilizer N recovery efficiency.