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Technical grade prohexadione-calcium (93.2% a.i. P-Ca) applied to `Fuji'/M.9 trees in three applications in deionized water reduced shoot growth by 25%, but the addition of (NH4)2SO4 to P-Ca suppressed shoot growth by 47%. If P-Ca was mixed in well water (high in calcium salts), P-Ca did not suppress shoot growth at all. The commercially formulated prohexadione-calcium [Apogee: 27.5% P-Ca + 56.1% (NH4)2SO4 + 16.4% other proprietary additives] + Regulaid in well water (high calcium) was not as effective (reduced growth by 30%) as when additional (NH4)2SO4 was added (reduced growth by 53%), and if CaCl2 (used to control corking) was tank mixed with Apogee + Regulaid, the Ca++ interfered with the growth suppression of P-Ca. If (NH4)2SO4 was added at the same rate as CaCl2 (w/w), the Apogee growth suppression was completely restored (reduced growth by 50%). Choice (a commercial water conditioner that has (NH4)2SO4 in the formulation, among other ingredients) + Li-700, or (NH4)2SO4 + Silwet L-77, or (NH4)2SO4 + Silwet L-77 + Oil were among the most effective adjuvant combinations with Apogee. The addition of ethephon at 270 mg·L-1 improved the growth suppression of Apogee + (NH4)2SO4 + Regulaid. Solubor compromised the effectiveness of Apogee + Regulaid. Adjusting the pH of the Apogee + (NH4)2SO4+ Regulaid spray to either pH = 4 or pH = 9 did not affect efficacy. The combination of Apogee + (NH4)2SO4 + Regulaid caused increased fruit cracking of `Empire' fruit as compared to the control (7%), presumably due to increased absorption of P-Ca. Chemical names used: Prohexadione-calcium (P-Ca, 3-oxido-4-propionyl-5-oxo-3cyclohexenecarboxylate) formulated as BAS-125 (10% P-Ca); Apogee (27.5% P-Ca), or Technical 93.5% P-Ca); Regulaid (polyoxyethylenepolypropoxy-propanol, alkyl 2-ethoxethanol, and dihydroxy propane); Silwet L-77 (polyalkyleneoxide modified heptametyltrisiloxane, silicon surfactant), LI-700 (80%, phosphatidylcholine, methylacetic acid and alkyl polyoxyethylene ether); Superior Oil (Drexel Damoil 70-second delayed dormant spray oil); ethephon (2-chloroethyl phosphonic acid); Solubor (20.5%, Boron equivalent); captan (N-Trichloromethylthio-4-cyclohenene-1,2-dicarboximide).

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( Evans et al., 1997 ). Plant growth regulators that limit shoot length extension are used most often to improve the light environment in the canopy for better fruit color development and quality. P-Ca (Apogee ® ) is a primary plant bioregulator in pome

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Artichoke is a cool-season perennial crop that is grown as an annual from seed in southern California. Growing artichokes as annuals from seed allows growers to harvest during the winter from November to March. Artichoke seed is planted in May, transplants are moved to the field in July, and harvesting begins as early as November in years with relatively cool fall weather. Hot fall weather during September and October suppresses plant growth and causes premature flowering, which lowers yield and average bud size. Plant growth regulator (PGR) treatments were evaluated in annual artichokes to determine if they could reduce the adverse effects of hot weather during September and October. Treatments included multiple applications of apogee (gibberellin inhibitor), retain (ethylene inhibitor), apogee + retain, cytokinin, and control plots. Harvestable buds were counted as a measure of earlier flowering induced by hot weather. Apogee and cytokinin show promise in reducing heat stress during hot fall artichoke production. Other PGR treatments increased the number of harvestable buds compared to control plots.

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Prohexadione-Ca (BAS 12511W or Apogee™ Plant Growth Regulator) acts within a plant by blocking the biosynthesis of growth-active gibberellin. The result is decreased cell and shoot elongation; thus, vegetative growth in apple trees can be reduced. Air blast applications of prohexadione calcium were made in the Spring 1998 in commercial orchards. Application rate was 125 ppm a.i. applied twice beginning at 5 to 12 cm of new shoot growth. Reduction of shoot growth averaged 45% across locations. As a result of reduced vegetative growth, dormant pruning was reduced. In total, significant benefits to the grower included reduced pruning costs in addition to other positive effects such as improved light penetration and enhanced resistance to some pathogens. Research will continue with the effect of prohexadione-Ca on pruning in multiple year studies.

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Field experiments were conducted in 2002 and 2003 to evaluate the effects of selected plant growth regulators on propagule production in Hemerocallis `Happy Returns' and Hosta `Gold Standard'. Benzyladenine (BA), chlormequat chloride (Cycocel), ethephon (Ethrel), prohexadione calcium (Apogee), and an experimental preparation of commercial seaweed extract (Acadian Seaplants Limited Liquid Seaweed Concentrate) amended with BA and IBA were tested at two times of application and three rates of application. Results with Hemerocallis showed that the application of the seaweed/PGR mixture at 3000 mg·L–1, Cycocel at 3000 mg·L–1 or BA at 2500 mg·L–1 applied at flowering, increased the number of plants producing two divisions compared to control plants. In Hosta, no increase in divisions under any treatments was observed.

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Plant growth regulators that are made available to University researchers usually come with an indication of biological activity, based upon in-house work by chemical companies. Often a practical use of the PGR is suggested. The PRG is applied at a range of concentrations at a timing that is appropriate to get the desired response. Undesirable side effects are noted. Follow up experiments are designed, usually altering concentration, time of application, or formulation, to maximize a response or to overcome and alleviate undesirable side effects. If the PGR is labeled, refinements for its use and grower recommendations are prepared. Critical in the development process is communication and interaction among researchers and industry personnel. This is exemplified by the exchange of ideas, sharing of data, and brain-storming that has occurred over the past 25 years at the Northeast Plant Growth Regulator Working Group meetings. Budget reductions and down sizing of programs at the University have forced researchers to depend more upon grant-in-aid support from companies. Several case studies will be presented to show the commercial development of some PGRs, including: Accel, cultar, Apogee, and ReTain. The evolving role of researches in the development of PGRs will be discussed.

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Balancing vegetative growth with fruiting is a primary concern in strawberry (Fragaria ×ananassa Duch.) production. Where nursery plant selection and preconditioning are inadequate for runner control, additional approaches are needed. The gibberellin biosynthesis inhibitor prohexadione-Ca (commercial formulation Apogee) was tested over two seasons for suppressing fall runners of `Chandler' plug plants in a cold-climate annual hill production system. Prohexadione-Ca was applied as a foliar spray at active ingredient concentrations ranging from 60 to 480 mg·L-1, either as a single application 1 week after planting, or repeated at 3-week intervals. The lowest rate resulted in inadequate runner control, with some runners producing malformed daughter plants. Higher rates resulted in 57% to 93% reductions in fall runner numbers, with a concomitant increase in fall branch crown formation. There were no effects of the prohexadione-Ca treatments on plant morphology the following spring, and no adverse effects on fruit characteristics or yield. Chemical names used: prohexadione-calcium, calcium 3-oxido-4-propionyl-5-oxo-3-cyclohexene-carboxylate.

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APOGEE and REGALIS have recently been introduced in a number of countries for use in pome and other fruit trees. These products contain 27.5% and 10% of prohexadione-Ca (ProCa), respectively. As a result of inhibiting excessive vegetative growth, less summer and dormant pruning is required, the ratio between vegetative growth and fruit formation is improved, and crop protection is facilitated due to the reduction of tree row volume and a more open canopy. Additionally, a lowered incidence of diseases such as fire blight and scab is observed, which is not due to a direct bactericidal or fungicidal effect of the compound. Further, the compound may reduce fruit drop early in the season. Prohexadione is a structural mimic of 2-oxoglutaric and ascorbic acid. Therefore, distinct dioxygenases are blocked, which require these compounds as a co-substrate. Such enzymes catalyze late steps in gibberellin biosynthesis. After treatment with ProCa, less growth-active gibberellins are formed and treated plants remain more compact. ProCa also affects ACC oxidase, another dioxygenase. The resulting reduction of ethylene formation, in addition to the availability of more assimilates for fruit growth, is most likely the cause of reduced fruit drop. 2-Oxoglutaric acid-dependent dioxygenases are also involved in the metabolism of flavonoids and their phenolic precursors: In shoots of apples and pears, ProCa causes considerable changes by inhibiting flavanone 3-hydroxylase. Convincing evidence is now available that ProCa triggers pathogen resistance by inducing the formation of 3-deoxyflavonoids, in particular luteoforol, with phytoalexin-like properties. Morphoregulatory effects caused by ProCa are only of secondary relevance for the reduction of disease incidence.

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content meter (Hansatech Instruments, Hitchin, UK), the Dualex leafclip sensor (Force-A, Paris, France), and the MC-100 chlorophyll meter (Apogee Instruments, Logan, UT) have been developed following a similar protocol ( Kalaji et al., 2017 ). Optical

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. The first test was performed using a pyranometer (total solar radiation) (MP-100; Apogee Instruments, Logan UT) and a quantum meter (measures only the photosynthetically active radiation) (MQ-100; Apogee Instruments). It was found that the light

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