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M.W. Duck, B.M. Cregg, R.T. Fernandez, R.D. Heins, and F.F. Cardoso

Tabletop Christmas tree growers whose greenhouse-grown conifers have undesirable shoot growth may alleviate this problem by applying plant growth retardants (PGRs). Some of the most common PGRs in the horticulture industry were evaluated to determine their effectiveness in controlling plant height: ancymidol at 100 μL·L-1 (ppm), daminozide at 5000 μL·L-1, paclobutrazol at 60 μL·L-1, chlormequat at 1500 μL·L-1, uniconazole at 15 μL·L-1, and ethephon at 500 μL·L-1 compared to a nontreated control. The following conifer species were used: colorado blue spruce (Picea pungens), black hills spruce (P. glauca var. densata), serbian spruce (P. omorika), noble fir (Abies procera), grand fir (A. grandis), fraser fir (A. fraseri), concolor fir (A. concolor), arborvitae (Thuja occidentalis), port orford cedar (Chamaecyparis lawsoniana), and douglas-fir (Pseudotsuga menziesii). Chlormequat was the only PGR that caused phytotoxicity and damage to the foliage was minimal. Noble fir, douglas-fir, colorado blue spruce, and arborvitae were unaffected by any PGR treatment. Daminozide reduced growth of port orford cedar and concolor fir; uniconazole reduced growth of black hills spruce and serbian spruce; paclobutrazol reduced growth of fraser fir; and ethephon reduced growth of grand fir.

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Manjula S. Bandara, Karen K. Tanino, and Doug R. Waterer

Seed potato growers seek to maximize yields of desirable sized tubers. This study examined how foliar applications of plant growth regulators influence yields of drop or single-cut seed tubers under field conditions. In 1993, paclobutrazol (PTZ; 300, 450, and 600 mg·liter–1), kinetin (KIN; 10 and 20 mg·liter–1), and methyl jasmonate (MJ; 10–7, 10–6, 10–5, and 10–4 M) were applied to `Norland' (NOR) and `Russet Burbank' (RB) potatoes. In 1994, PTZ (300 mg·liter–1), KIN (both rates), and MJ (10–7 and 10–6 M) treatments were eliminated, and GA3 at 250 mg·liter–1 or KIN at 20 mg·liter–1 was applied to some of PTZ treatments. In 1994, the cultivar Shepody (SH) also was included. Plants were treated at two growth stages; NOR (1993), RB (1993 and 1994), and SH (1994) were treated when tubers were <10 mm or <20 mm in diameter. NOR (1994) was treated at stolon initiation (no tubers) or early tuber initiation (<8 mm in diameter). PTZ had no effect on seed tuber (25–50 mm in diameter) yield in NOR in either season. PTZ increased seed tuber number (STN) in RB by 29% to 40% and in SH by 57% to 70% over the controls. KIN had no effect on STN in any cultivar. MJ had no effect on STN in NOR (1993) or in RB in either season or in SH in 1994. In 1994, the highest rate of MJ (10–4 M) increased STN in NOR by 40% over the controls. GA3 had no beneficial effect on STN when applied after PTZ. This study suggests that, under field conditions, PTZ can increase seed tuber production in RB and SH while MJ was effective in NOR potatoes.

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Edward W. Bush, Wayne C. Porter, Dennis P. Shepard, and James N. McCrimmon

Field studies were performed on established carpetgrass (Axonopus affinis Chase) in 1994 and 1995 to evaluate plant growth regulators (PGRs) and application rates. Trinexapac-ethyl (0.48 kg·ha-1) improved turf quality and reduced cumulative vegetative growth (CVG) of unmowed and mowed plots by 38% and 46%, respectively, in 1995, and suppressed seedhead height in unmowed turf by >31% 6 weeks after treatment (WAT) both years. Mefluidide (0.14 and 0.28 kg·ha-1) had little effect on carpetgrass. Sulfometuron resulted in unacceptable phytotoxicity (>20%) 2 WAT in 1994 and 18% phytotoxicity in 1995. In 1995, sulfometuron reduced mowed carpetgrass CVG 21%, seedhead number 47%, seedhead height 36%, clipping yield 24%, and reduced the number of mowings required. It also improved unmowed carpetgrass quality at 6 WAT. Sethoxydim (0.11 kg·ha-1) suppressed seedhead formation by 60% and seedhead height by 20%, and caused moderate phytotoxicity (13%) in 1995. Sethoxydim (0.22 kg·ha-1) was unacceptably phytotoxic (38%) in 1994, but only slightly phytotoxic (7%) in 1995, reduced clipping yields (>24%), and increased quality of mowed carpetgrass both years. Fluazasulfuron (0.027 and 0.054 kg·ha-1) phytotoxicity ratings were unacceptable at 2 WAT in 1994, but not in 1995. Fluazasulfuron (0.054 kg·ha-1) reduced seedhead height by 23% to 26% in both years. Early seedhead formation was suppressed >70% when applied 2 WAT in 1994, and 43% when applied 6 WAT in 1995. The effects of the chemicals varied with mowing treatment and evaluation year. Chemical names used: 4-(cyclopropyl-x-hydroxy-methylene)-3,5 dioxo-cyclohexane-carboxylic acid ethyl ester (trinexapac-ethyl); N-2,4-dimethyl-5-[[(trifluoro-methyl)sulfonyl]amino]phenyl]acetamide] (mefluidide); [methyl 2-[[[[(4,6-dimethyl-2-pyrimidinyl) amino]carbonyl] amino] sulfonyl]benzoate)] (sulfometuron); (2-[1-(ethoxyimino)butyl-5-[(2-ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one) (sethoxydim); 1-(4,6-dimethoxypyrimidin-2yl)-3-[(3-trifluoromethyl-pyridin 2-yl) sulphonyl] urea (fluazasulfuron).

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Duane W. Greene

Plant growth regulators (PGRs) play an important commercial role in horticulture. Although often expensive, they are generally used on high value crops where the costs can be retrieved through the increased value their usage creates in a given crop. The impetus for development of new PGRs is generally initiated by the agrochemical industry where they perceive a need that has a profit potential, whereas the motivation for the development of a PGR by researchers is largely to aid the industry they serve. University and government researchers initially follow a prescribed protocol early in the development process, but once they have gained personal experience with a PGR, further research is often guided by personal observations and keen technical insight. During the development and evaluation process, university and government researchers are optimistic, and negative effects are generally viewed as challenges, that can and will be overcome. Discussion and effective communication are critical components in the overall development of a new PGR. Researchers generally exchange information very freely, unless restricted from doing so by a nondisclosure or other contract agreement. The underlying goal for university and government researchers is to get approval of a new PGR product and/or use that will allow growers to produce a high quality product for consumers with an improved profit margin for growers. Development of new PGRs is undergoing major change that unfortunately will lead to the development and registration of fewer compounds. There are not as many agrochemical companies, there are a decreasing number of university and government researchers, and diminishing funds available to support the development of new PGRs.

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Brian E. Jackson, Robert D. Wright, and Michael C. Barnes

CC (16.8% and 65%, respectively; Saunders et al., 2006 ). These results demonstrate that a 100% PTS can be produced with physical properties similar to commercial substrates if ground finely enough and that plant growth in 100% PTS is comparable to

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Janni Bjerregaard Lund, Theo J. Blom, and Jesper Mazanti Aaslyng

One of the environmental concerns in the production of potted plants is the use of plant growth retardants (PGRs) for the control of plant height. In the search for alternatives to PGRs, changes in light quality [e.g., increased red to far

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Kevin R. Cope and Bruce Bugbee

The application of LEDs for plant growth lighting has been studied for over two decades ( Barta et al., 1992 ; Bula et al., 1991 ). Initial studies included only red LEDs because they were the most efficient and emit light that coincides with the

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Bernadine C. Strik, Amanda J. Davis, David R. Bryla, and Scott T. Orr

analyzed by clipping the thermal layer with the reclassified NDVI layer. Plant growth and development. The volume of the canopy was estimated before leaf senescence in October each year using the following equation for a circular cone: V = ( 1 / 3 ) π r 2 h

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Kevin M. Heinz, Polly A. Harding, Maria Julissa Ek-Ramos, Heather Hernandez, Peter C. Krauter, and Gregory A. Sword

) can also be inoculated as endophytes within various monocot and dicot crops, including bean, wheat, corn, pumpkin, tomato, and cotton. Endophytic fungi enhance plant growth in some field crops ( Jaber and Enkerli, 2017 ; Vega et al., 2009 ); however

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Fang Geng, Renae Moran, Michael Day, William Halteman, and Donglin Zhang

of explant collection date, chilling nodal explants, and media concentration of the plant growth regulators GA 3 , EBR, BA, ZT, and TDZ on shoot growth of ‘G.30’ and ‘G.41’ apple during the initial proliferation stage of micropropagation. The focus of