Paclobutrazol drenches were applied at 0, 2, 4, 8, 16, or 32 mg a.i./pot to potted sunflowers (Helianthus annuus L. `Pacino') to determine its effect on growth. Plant height was shorter as paclobutrazol dose increased up to 16 mg; however, additional increases in dose had little effect on height. Severe height retardation of `Pacino' plants was evident at 16 and 32 mg. Plants treated with 2 mg of paclobutrazol were 17% and 25% smaller in diameter than untreated plants in Expts. 1 and 2, respectively. Plant diameter was smaller as paclobutrazol dose increased up to 16 mg, with additional increases in dose having little effect on plant diameter in Expt. 2. Plants treated with 16 or 32 mg of paclobutrazol exhibited phytotoxicity symptoms including crinkled leaves and stunted growth, and smaller and greener leaves. Sunflower plant growth was greater in the summer (Expt. 1) than in winter (Expt. 2). In the summer higher doses of paclobutrazol will be required than in winter for growth control. Marketable sized plants grown in 15- to 16.5-cm-diameter pots were produced with doses of paclobutrazol at 2 and 4 mg in both seasons, and doses up to 8 mg can also be used in summer for growth control.
Shravan Dasoju, Michael R. Evans, and Brian E. Whipker
Michael R. Evans, James N. Smith, and Raymond A. Cloyd
Coir and peat-based substrates were tested for their effectiveness in inhibiting the development of fungus gnat populations. The first experiment was conducted in July under relatively high temperatures (20 to 35 °C) and a second experiment was conducted in April under relatively low temperatures (20 °C). Euphorbia pulcherrima Willd. ex Klotzch `Freedom' plants were planted into 18-cm-diameter containers filled with substrates containing 80% sphagnum peat or coir, with the remainder being perlite. Half of the containers of each substrate were inoculated with fungus gnat larvae and sealed with either cheesecloth or thrips screen for Expts. 1 and 2, respectively. After 6 and 8 weeks for Expts. 1 and 2, respectively, fungus gnat adult and larval populations were sampled. Adults and larvae were recovered from coir and peat-based substrates in both experiments. In Expt. 1, significantly more adults and larvae were recovered from coir-based than peat-based substrates. In Expt. 2, significantly more adults and larvae were recovered from the peat-based than coir-based substrates. In a third experiment, the peat- and coir-based substrates used in Expts. 1 and 2 were used as well as the Iowa State greenhouse substrate, which contained 40% Sphagnum peat, 40% perlite, and 20% loam (v/v). Helianthus annuus L. `Pacino' seeds were sown into 18-cm-diameter containers filled with the test substrates. Natural infestation was allowed to occur for 6 weeks, after which time potato disks were used to sample the fungus gnat larvae population. Larvae were recovered from all substrates, and there was no significant difference in the number of larvae collected from the three substrates. Based on the results of these experiments, we concluded that coir does not inhibit the development of fungus gnat larvae populations and, when presented with options, fungus gnats will infest coir-based substrates as readily as peat-based substrates.
Shravan Dasoju, Michael R. Evans, and Brian E. Whipker
Paclobutrazol drench applications of 0, 2, and 4 mg a.i./pot were applied to `Pacino' potted sunflowers (Helianthus annuus L.) and `Red Pigmy' tuberous rooted dahlias (Dahlia variabilis Willd.) grown in substrates containing 50%, 60%, 70%, or 80% (by volume) sphagnum peat or coir, with the remainder being perlite, to study the efficacy of paclobutrazol (Bonzi). Potted sunflower plant height differed significantly for peat- and coir-based substrates, with greater plant height being observed in coir-based substrates. Plant diameter was significantly greater at higher percentages of peat or coir in the substrate at 2 and 4 mg of paclobutrazol. Inflorescence diameter also was significantly decreased as paclobutrazol concentration increased. When the percent of height control from the untreated plants for potted sunflower was compared between coir and peat-based substrates, the percent height reduction was similar for peat- and coir-based substrates at 2 mg of paclobutrazol and height control was greater at 4 mg of paclobutrazol in coir-based substrates. The differences in plant growth observed in peat- and coir-based substrates can be attributed to differences in physical properties of these substrates. Dahlia plant height, diameter, and number of days until anthesis were not influenced by substrate type or percentage. However, dahlia growth was significantly reduced as paclobutrazol concentration increased. Coir-based substrates did not reduce the activity of paclobutrazol drenches compared to peat-based substrates, although to compensate for the greater amount of plant growth in coir-based substrates, paclobutrazol concentrations may need to be increased slightly to achieve a similar plant height as with peat-based substrates.
Michael R. Evans, Harold F. Wilkins, and Wesley P. Hackett
The poinsettia [Euphorbia pulcherrima (Willd. ex. Klotzsch)] is a short-day plant (SDP) for floral initiation that will also initiate floral structures (cyathia) under long days (LD) after the apical meristem produces a cultivar-dependent number of nodes (long-day node number). Leaf removal, root restriction, and air layering failed to affect the long-day node number (LDNN) of the apical meristem. Repeated rooting of shoots, which resulted in the removal of nodes, did not affect the total number of nodes initiated by the apical meristem before floral initiation, although the number of nodes intact on the plant at the time of floral initiation was reduced. Reciprocal grafting of axillary buds of `Eckespoint Lilo' and `Gutbier V-14 Glory' plants did not affect the LDNN of the grafted meristem since the LDNN was the same as for nongrafted buds of the same cultivar. Further, grafting axillary buds from different positions along the main axis that differed in LDNN did not affect the LDNN of the grafted meristems. On the basis of these results, it was concluded that LD floral initiation in poinsettia is a function of the ontogenetic age of the meristem and that the LDNN represents a critical ontogenetic age for floral initiation to occur under LD.
Michael R. Evans, Harold F. Wilkins, and Wesley P. Hackett
Exogenous foliar spray applications of gibberellic acid (GA3) applied at 7- or 14-day intervals providing 50 or 125 μg per plant inhibited long-day (LD) floral initiation in poinsettia [Euphorbia pulcherrima (Willd. ex. Klotzsch)]. Periodic application of GA3 resulted in an additional number of nodes being produced by the plant before floral initiation equivalent to the number of nodes over which GA3 was applied. Further, GA, application eliminated the nodal position dependence of the long-day node number (LDNN) of axillary meristems observed in control plants. It was concluded that GA3 application inhibited the inclusion of nodes into the LDNN count and thus inhibited ontogenetic aging of the meristem. Exogenous application of GA, also inhibited LD floral initiation, while application of GA4 had no effect. Application of GA7 delayed LD floral initiation, but plants did initiate cyathia by the termination of the experiment. All gibberellins increased the average internode lengths similarly. The gibberllin-biosynthesis inhibitors chlormequat and paclobutrazol had no effect on LD floral initiation when applied as single or multiple foliar sprays or as soil drenches, although heights and internode lengths were reduced by application of the inhibitors. The LDNN of plants grown at 31C was significantly higher than of plants grown at 16, 21, or 26C. All plants eventually initiated cyathia regardless of temperature. When plants were grown under a range of day/night temperatures, an increase in the LDNN occurred only when plants were grown at 31C during the day. Chemical names used: 2-chloroethyl-trimethyl-ammonium chloride (chlormequat); (+/-)-(R*,R*)-β -(4-chlorophenyl)methyl-α -(1,1-dimethylethyl)-1-H-1,2,4-triazole-1-ethanol (paclobutrazol).
Michael R. Evans, Todd J. Cavins, Jeff S. Kuehny, Richard L. Harkess, and Greer R. Lane
Economics and logistics have greatly reduced or eliminated the ability of horticulture instructors to use field trips or on-site visits as educational tools. This is especially problematic in the field of greenhouse management and controlled environment agriculture, since the facilities and technologies used are essential to the discipline. To address this problem, we developed 15 DVD-based virtual field trips (VFT's) that instructors may use to demonstrate to students the most up-to-date facilities, technologies, and management strategies used in greenhouse management (ornamental and food crops) and controlled environment agriculture (GCEA). Each VFT included a preface with background information about the company, a tour organized by subject chapters, self-examination, and a teacher's guide with additional information and case studies. Each land-grant institution with an instructional program in greenhouse management of controlled-environment agriculture will be provided a free copy of each VFT, which will benefit all instructors of GCEA in the United States.
Michael R. Evans, Bernard W. Krumpelman, Ramsey Sealy, and Craig S. Rothrock
Vinca (Catharanthus roseus) is a common annual bedding plant species that is susceptible to root and stem rot caused by Phytophthora nicotianae. The experimental design was a 6×2×1 factorial with a total of 12 treatment combinations that had five replications and was repeated twice. Vinca seeds were planted in the middle nine plugs of a 5×5 five-milliliter round plug tray filled with sphagnum peat (control) or peat amended with 2.1 kg/m3 calcitic lime, 5.9 and 7.3 kg/m3 potassium silicate alone and combined with 3.0 kg/m3 calcium sulfate. A peat control drenched with metalaxyl after inoculation was also included. After germination, when the seedlings had one true leaf, half of the treatments were inoculated with 500 cfu of Phytophthora nicotianae per plug cell while the other half remained uninoculated. The percentage of germination for the potassium silicate combined with calcium sulfate (KSCS) (79% and 78%) was similar to the control (86%) and the metalaxyl treatment (83%), whereas the potassium silicate alone had poorer germination (69% and 71%) and plant growth. The percentage of mortality for the KSCS treatment (6% and 14%) was similar to the metalaxyl treatment (9%) but was significantly less than the control (100%). The average dry shoot and root weights for the KSCS treatments (4.4 and 4.9 mg; 2.7 and 2.2 mg) were similar to the metalaxyl treatment (5.0 and 3.6 mg) and the uninoculated control (5.0 and 3.2 mg), but were higher than the potassium silicate treatment alone (2.1 and 1.6 mg; 0.7 and 0.6 mg).
Nathan J. Eylands, Michael R. Evans, and Angela M. Shaw
Various saponins have demonstrated allelochemical effects such as bactericidal impacts as well as antimycotic activity against some plant pathogenic fungi, thereby acting to benefit plant growth and development. A commercial saponin solution was evaluated for bactericidal effects against Escherichia coli and growth of lettuce (Lactuca sativa) in a hydroponic system. E. coli (P4, P13, and P68) inoculum at final concentration of 108 colony-forming units (cfu)/mL was added to 130 L of a fertilized solution recirculating in a nutrient film technique (NFT) system used to grow ‘Rex’ lettuce. After 5 weeks in the NFT system, E. coli populations were lowest in the inoculated treatment that did not contain any saponin addition (0.89 log cfu/mL) when compared with all other inoculated treatments (P < 0.001). The treatment containing 100 µg·mL−1 saponin extract had an E. coli population of 4.61 log cfu/mL after 5 weeks that was higher than treatments containing 25 µg·mL−1 or less (P < 0.0001). Thus, higher E. coli populations were observed at higher saponin concentrations. Plant growth was also inhibited by increasing saponin concentrations. Fresh and dry shoot weight were both higher in the inoculated and uninoculated treatments without the saponin addition after 5 weeks in the NFT system (P < 0.0001). Lettuce head diameter was smaller when exposed to saponin treatments with concentrations of 50 and 100 µg·mL−1 (P < 0.0001). Lettuce leaves were also tested for the potential of E. coli to travel systemically to the edible portions of the plant. No E. coli was found to travel in this manner. It was concluded that steroidal saponins extracted from mojave yucca (Yucca schidigera) are not an acceptable compound for use in mitigation of E. coli in hydroponic fertilizer solution due to its ineffectiveness as a bactericide and its negative impact on lettuce growth.
Michael R. Evans, Andrew K. Koeser, Guihong Bi, Susmitha Nambuthiri, Robert Geneve, Sarah Taylor Lovell, and J. Ryan Stewart
Nine commercially available biocontainers and a plastic control were evaluated at Fayetteville, AR, and Crystal Springs, MS, to determine the irrigation interval and total water required to grow a crop of ‘Cooler Grape’ vinca (Catharanthus roseus) with or without the use of plastic shuttle trays. Additionally, the rate at which water passed through the container wall of each container was assessed with or without the use of a shuttle tray. Slotted rice hull, coconut fiber, peat, wood fiber, dairy manure, and straw containers were constructed with water-permeable materials or had openings in the container sidewall. Such properties increased the rate of water loss compared with more impermeable bioplastic, solid rice hull, and plastic containers. This higher rate of water loss resulted in most of the biocontainers having a shorter irrigation interval and a higher water requirement than traditional plastic containers. Placing permeable biocontainers in plastic shuttle trays reduced water loss through the container walls. However, irrigation demand for these containers was still generally higher than that of the plastic control containers.
Andrew M. Birmingham, Eric A. Buzby, Donte L. Davis, Eric R. Benson, James L. Glancey, Wallace G. Pill, Thomas A. Evans, Robert P. Mulrooney, and Michael W. Olszewski
A mechanical planter was developed to sow seed of baby lima beans (Phaseolus lunatus) in small plots. The mechanical seeder allowed small plots to be quickly and consistently seeded at a fixed spacing. Seeds were manually spread along a 10-ft (3.0 m) base plate containing 50 holes of slightly larger diameter than the seed length and at the desired seed spacing [2.4 inches (6 cm)]. Once all the holes were filled, a slider plate below the base plate containing holes of the same diameter and spacing, but which were slightly offset, was slid horizontally so that the holes of the base and slider plates aligned and the seeds dropped to the bottom of the furrow. Compared to manual planting, the mechanical planter increased the precision of seed placement and reduced the time needed to plant 50 seeds. The planter was easy to use and transport, and was inexpensive.