Plant Growth Regulator Treatments Research Articles

Benefit of using plant growth regulators in fodder barley

The study was conducted to investigate the effect and benefit of applying plant growth regulators (PGR) to two easily lodging barley cultivars, Arra and Kilta, which were commonly used for fodder production all over Finland. Field trials were conducted at six experimental sites in different parts of the country. Of the PGRs tested, ethephon and mepiquat/ethephon were the most effective in shortening the culm and preventing lodging. However, neither could prevent the lodge adequately in all growing circumstances. When applied at flag-leaf stage (FS 10) they increased yield under conditions favourable for lodging. They also raised the volume weight of barley, which was important for the final price of the yield. The most important factors determining future lodging of barley were an effective temperature sum of over +5°C and precipitation during the period from sowing to the beginning of tillering (FS 2). About 64-68% of the lodging risk of the cultivars studied could be predicted from weather conditions during early development of the crop. Local growing conditions and the presence of lodge had a marked impact on the results obtained with PGRs. In the case of moderate lodging the compound used determined whether a profit or loss was made on the crop. In the case of heavy lodging, compounds containing ethephon contributed to an economic return. Their application at flag-leaf stage gave a profit of FIM 70 - 390 ha-1. Since the profitability of PGR treatments depended on lodging, treatments are recommended for fodder barley only when lodging is expected. The lodging risk can be predicted within certain limits at the tillering stage of barley.

Varietal Differences between Two Cultivars of Viola tricolor `Blue'

Seeds of `Majestic Giant Blue Shade' and `Medallion Blue/Blotch' were initially begun in plug trays and later transplanted into flats of 32s. Observations included percent germination, rate of emergence, plant heights before treatment of plant growth regulators (PGR), plant fresh weight, plant dry weight, plant height after treatments, and visual appearance. PGR treatments included paclobutrazol at 16 and 25 ppm, uniconazole at 2 and 4 ppm, and B-Nine as the control. `Majestic Giant' had a higher percent germination rate and rate of emergence than `Medallion'. Overall growth of Medallion seemed to be behind by ≈5 days when compared to that of `Majestic Giant'. The `Medallion' group showed more of a response to PGR treatments than `Majestic Giant'.

Contribution of the wheat (Triticum aestivum L.) flag leaf to grain yield in response to plant growth regulators

In West-Europe, intensive cereal management uses plant growth regulators (PGRs) especially for wheat. A green-house experiment compared the effects of two PGRs on flag leaf characteristics and yield of winter wheat. Chlormequat chloride + choline chloride (CCC) and chlormequat chloride + choline chloride + imazaquin (CCC+I) were applied to winter wheat at growth stage 5 (Feekes Large scale). CCC and CCC+I significantly increased flag leaf surface area at anthesis. Both treatments also enhanced chlorophyll content of the main stem flag leaf. The grain filling period was extended with PGR application by 2 days. CCC and CCC+I significantly increased net CO2 assimilation rates during the flag leaf life. No effects of PGR spraying were observed on the pattern of 14C labelled assimilate distribution. Increased grain yield was due to the increase in average grain weight. The results indicate that PGR treatments increased flag leaf contribution to grain filling. The addition of imazaquin (I) to chlormequat (CCC) improved the effects of CCC.

Experimental control of floral reversion in isolated shoot apices of the long‐day plant Silene coeli‐rosa

The fate of shoot meristems of the long day (LD) plant Silene coeli‐rosa in culture was examined (complete, reverted or arrested flowers) to establish whether these different patterns were related to a particular stage of morphogenesis and the extent to which the fate of the pattern was regulated by either added plant growth regulators (PGRs) or changing the carbohydrate source in the medium. In particular, the frequency of reversion was measured to test the stability of the determined state for each whorl. The plants were given various inductive treatments (4–7 LD, 7 LD + 1 to 3 SD) and the apices were explained onto Murashige‐Skoog medium supplemented with 3% sucrose (controls) ± IAA, ± kinetin, ± GA3 or onto the basal medium containing 1 or 3% sucrose, glucose or fructose or 7% sucrose. The apices were examined 12 weeks later. When the data were pooled from all inductive treatments, IAA resulted in more reversions, GA3 caused more arrested flowers while kinetin hardly affected the pattern of meristem fate compared with the controls. However, each PGR treatment did not perturb the pattern of organ formation for those apices that formed either arrested or complete flowers. The time for determination (days) of the earlier formed whorls (determination times for the controls in brackets): sepals (2), stamens 1–5 (3) and petals (3), was shortened by about a day in all PGR treatments whereas the corresponding times for the later formed whorls: stamens 6–10 (4) and carpels (4), were either lengthened to 5 days or unaffected. The response of the apices to the various sugars was simply a reflection of concentration. Hence, more complete flowers formed at 7 or 3% and more flowers were arrested at 1 % regardless of the sugar moiety. However, the frequency of reversion was similar on each of the media. Pooling all data from all treatments enabled a statistical analysis of the pattern of reversion and the pattern of arrest. Reversion was more common from apices which exhibited the later‐formed whorls (stamens 6–10 and carpels) than from the earlier whorls. Moreover, the stronger the inductive treatment the less frequent was reversion. The most common stage of arrest was at the stamen 6–10 whorl and this was particularly so for the GA3 treatment. The data indicated that reversion could occur from any whorl, which suggests that determination of each whorl is independent of the next. This conclusion is underlined by the more frequent occurrence of reversion from the carpel whorl. However, the longer the inductive treatment the less likelihood of reversion; this suggests that in Silene, the floral stimulus is required continuously to stabilise the determined state of each whorl and to ensure smooth completion of floral morphogenesis.

EFFECTIVENESS OF PACLOBUTRAZOL ON HEIGHT CONTROL OF MINI-POINSETTIAS

Mini-poinsettias are a popular form of potted plant, but there is a need to control plant height because tall growing cultivars are used. A study was conducted to determine the suitability of paclobutrazol to control height of mini-poinsettias. Cuttings of poinsettia cultivars Freedom and Red Sails were taken on 10 Sept. 1993 and rooted under mist. On 11 Oct. when short days began, plant height was measured and 4 plant growth regulator (PGR) treatments were applied as foliar sprays using a volume of 204 ml·m-2: paclobutrazol at 15, 30, 45 and 60 mg·liter-1, plus an untreated control. At anthesis, plant height (pot rim to top of plant) and bract diameter (measured in 2 directions and averaged) were measured. Data for plant height gain (PHG), the difference between plant height at anthesis and when PGRs were applied, and bract diameter were analyzed statistically. PHG was significantly different at the cultivar × treatment interaction. For `Red Sails' all paclobutrazol treatments significantly retarded PHG, but there were no significant differences in PHG with increased rates of application. For `Freedom' only paclobuuazol rates at 30 and 45 mg·liter-1 significantly retarded PHG. Bract diameter was significantly different at paclobunazol rates 30 mg·liter-1 or greater, with diameter decreasing as the rate of PGR applied increased

Manipulation of flowering and vegetative growth of Brown Boronia ( Boronia megastigma Nees.) and White Myrtle ( Hypocalymma angustifolium Endl.) using plant growth regulators

Plant growth regulators had a variety of effects on growth and flowering of Brown Boronia and White Myrtle. Morphactin, TIBA and benzyladenine stimulated lateral vegetative growth in warm conditions. Benzyladenine treatment of plants decreased the number of weeks of cool conditions (17°C day/9°C night) required to reach anthesis in both species, in Brown Boronia reducing the number of weeks required from 22 to 14. Paclobutrazol also decreased the number of weeks to anthesis in Brown Boronia and increased the percentage of axils with flowers. Paclobutrazol enabled White Myrtle plants to flower in an environment considered non-inductive for flowering. Many treatments that encouraged vigorous vegetative growth inhibited flowering in both species. The timing of growth regulator treatment in relation to flower evocation, and the environment in which the plants are growing can greatly influence the response of these species to plant growth regulator treatment.

THE ENVIRONMENT UNDER WHICH THE STOCK PLANT IS GROWN INFLUENCES EXPLANT PERFORMANCE IN VITRO

Environmental factors under which the stock (mother, donor) plant has been grown, including temperature; light duration, quality, and intensity; mineral nutrition; and ambient gases can have significant impact on explant responses in vitro. Bulblet production in hyacinth has been influenced by mother bulb storage temperature. Shoot proliferation and rootability of microshoots of rhododendron have been modified by light intensity and light quality. Photoperiod has been demonstrated to affect tuber and callus formation on potato and dahlia. Furthermore, plant growth regulator treatments of the stock plant can strongly influence in vitro responses of explants taken from such plants. Implications of these latter responses will be discussed with regard to possible endogenous hormonal activity.

Modification of Tiller Productivity in Spring Barley by Application of Chlormequat or Ethephon

Application of plant growth regulators (PGR) to control lodging in cereal crops often increases the number of tillers and/or spikes. It is not clear whether the increment in spike numbers is due to enhanced tiller production or to an increased percentage of tiller spikes. The objective of this study was to evaluate the timing of chlormequat (2‐ chloroethyl‐N,N,N‐trimethylammonium chloride) (CCC) or ethephon (2‐chloroethyl phosphonic acid) application on tiller production and subsequent tiller growth and development in spring barley (Hordeum vulgare L.). A 3‐yr field study with two widely grown cultivars, Leger and Cadette, was conducted on Bearbrook clay soil (fine, mixed, nonacid Mesic Humaquept) at the Emile A. Lods Agronomy Research Center, McGill University, Canada, from 1988 to 1990. Treatments consisted of CCC (1.2 kg a.i. ha−1) or ethephon (0.48 kg a.i. ha−1) applied at Zadoks growth stages (ZGS) 13,30, or 39. Tiller production was monitored at ZGS 12,32,51, and 90. Plants treated with an early application of CCC (ZGS 13 or ZGS 30) or ethephon (ZGS 30) produced greater numbers of shoots, appearing later in time, than control plants. Early PGR treatment increased the number of spike‐bearing shoots, primarily by enhancement of tiller number (tiller‐derived spikes) rather than the spike production rate (tiller survival). Late application of CCC or ethephon at ZGS 39, when most of the tillers had emerged, resulted in a higher number of spike‐bearing shoots, mostly through the increased percentage of tiller spikes.

Manipulating Primocane Architecture in Thornless Blackberry with Uniconazole, GA3, and BA

The potential for plant growth regulator (PGR) manipulation of `Chester Thornless' blackberry (fibus spp.) primocane growth was evaluated. PGR treatments included combinations of soil-applied uniconazole at 1, 5, 25, and 125 mg/plant and GA, foliar-applied one or two times at 100 ppm 3 and 4 weeks after a 25-mg/plant uniconazole application. Also, GA and BA were applied at 100 ppm alone or in combination one, two, or three times. Increasing rates of uniconazole reduced primocane length, leaflet count, and leaf, cane, and root dry weights. GA, applications reduced primocane length and increased branch elongation but failed to reverse the effects of uniconazole at 25 mg/plant, except those on branch length, leaflet count, and primocane dry weight. Only applications of BA + GA, increased both branch production and elongation and dry weights of some component tissues, while BA alone generally had no effects. Chemical names used: (E)-1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (uniconazole); N-(phenylmethyl)-1H-purin-6-amine (benzyladenine, BA); gibberellic acid (GA).

Improving fruit set on young red ‘Delicious’ apple trees using autumn sprays of paclobutrazol and ethephon

SummaryYoung, vigorous red ‘Delicious’ apple trees were treated in the autumn of their second year with sprays of paclobutrazol and ethephon. Sprays of paclobutrazol were applied in mid-February, mid-March and mid-April 1989 at 0, 50, 100 or 200 mg l-1. Other trees were sprayed with ethephon in mid-March at 200 mg l-1 with paclobutrazol at 0, 50, 100 or 200 mg I“1. Blossoming in the spring of 1989 showed no consistent effects of autumn plant growth regulator (PGR) treatments. However, PGRs did affect fruit set in these trees. Although no significant differences occurred between any of the paclobutrazol concentrations, or timing treatments, treated trees all yielded more than the control ones. Where ethephon was used with paclobutrazol, fruit set was similar to that after paclobutrazol alone, except when paclobutrazol was used at 100 mg l-1, where the highest fruit set was achieved. Ethephon alone, while promoting better set than the control was not as effective as when combined with paclobutrazol.

Root development of bermudagrass and tall fescue as affected by cutting interval and growth regulators

A study was conducted to characterize changes in bermudagrass (Cynodon dactylon [L.] Pers.) and tall fescue (Festuca arundinacea Schreb.) root development over time and with depth, and to determine the effects of defoliation interval and chemical seedhead suppression on root and shoot growth. Field plots were established on a fine-silty, mixed mesic Typic Fragiudult soil in Fayetteville, AR, USA, and each plot contained three minirhizotrons (plexiglass observation tubes) to a depth of 40 cm. Images of roots in 10-cm depth increments were periodically videorecorded, and total root length (RL) and root length density (RLD) were measured with a computer-interfaced tracing probe. Treatments consisted of two cutting intervals, 3 and 6 weeks, and two plant growth regulator (PGR) treatments, an untreated control and either 300 g ha-1 mefluidide on tall fescue in early spring of both years or 10 g ha-1 each of metsulfuron methyl (MSM) and sulfometuron methyl (SMM) applied in late May of both post-establishment years. Data were analyzed separately for the establishment period (planting to the first date of PGR application) and the subsequent post-establishment period. Bermulagrass exhibited a two-stage root establishment pattern characterized first by minimal root development in conjunction with stolon proliferation and soil surface colonization, followed by accumulation of total RL over two subsequent forage production seasons. There was a net accumulation of root mass during the winter dormancy period of 1986–87. Total RL of tall fescue peaked one and a half years after planting. Cutting interval had no influence on RL and RLD. Application of a PGR did not affect RL but did alter RLD of both species. Application of mefluidide to tall fescue stimulated RLD 64 days after application, whereas bermudagrass RLD was retarded by MSM and SMM up to 50 days after application. Trends in root growth did not closely follow patterns of shoot growth.

Effects of Flurprimidol, Mefluidide, and Soil Moisture on St. Augustinegrass Evapotranspiration Rate

The objective of this study was to determine the effects of two plant growth regulators (PGR) and two soil moisture levels (SML) on the evapotranspiration (ET) rate, leaf extension rate (LER), and visual turfgrass quality of `Texas Common' St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] grown under glasshouse conditions in black plastic minilysimeters. Treatments included mefluidide at 0.42 kg·ha-1, flurprimidol at 0.84 kg·ha-1, and no PGR, each grown under optimal (– 0.01 MPa) or suboptimal (– 0.8 MPa) SML. Both flurprimidol and mefluidide significantly affected ET rate, LER, and turfgrass quality, whereas the durations of the responses to both PGR treatments were affected by SML. For both SML, the durations of significant reduction in ET rate, LER, and turfgrass quality were longer for flurprimidol than for mefluidide. Application of either PGR at either SML caused a significant reduction in ET rate averaging 18% and a significant reduction in LER averaging 83%. Flurprimidol was more effective than metluidide in terms of ET rate and LER reduction. However, the considerably longer duration of reduced turfgrass quality of flurprimidol-treated turf was a negative effect. Chemical names used: α-(1 -methylethyl)- α -[4-trifluoromethoxy)phenyl]-5-pyrimidinemethanol (flurprimidol) and N- [2,4-dimethyl-5-[[(trifluoromethyl) sulfonyl]amino]phenyI] acetamide (mefluidide).

EFFECT OF PLANT GROWTH REGULATORS AND HARVEST DATE ON YIELD, BOTANICAL COMPOSITION, CHEMICAL CONSTITUTION, INTAKE AND DIGESTIBILITY OF CRESTED WHEATGRASS-ALFALFA HERBAGE BY SHEEP

The effects of the plant growth regulators mefluidide (M) and maleic hydrazide (MH) were compared to untreated controls (C) at each of two harvest dates in 1987 (14 Aug. and 14 Sept.) and 1988 (27 June and 25 July). Plant growth regulators (PGR) were applied at rates of 0.28 kg active ingredient (a.i.) Mha−1 and 1.12 kg a.i. MH ha−1on 14 and 15 July 1987 and on 11 May 1988 to a mixed crested wheatgrass-alfalfa pasture. Application of PGR to the pasture reduced yield (P < 0.01) and increased (P < 0.05) the proportion of alfalfa in the mixture in 1987 only. Chemical composition of crested wheatgrass subsamples was largely unaltered by PGR treatment in 1987 but in 1988 crude protein (P < 0.01), in vitro organic matter disgestibility (P < 0.05) and ash (P < 0.001) were increased and neutral detergent fiber was decreased (P < 0.01). In 1987 the crude protein (P < 0.01) and ash (P < 0.05) contents of alfalfa were increased but were unaffected by PGR treatment in 1988. There were large differences in nutritional value between early- and late-harvest dates in 1987 when moisture was available but only small differences during the drought of 1988. In vivo digestibility of hay from treated plots in 1987 had lower organic matter digestibility (P < 0.001), hemicellulose digestibility (P < 0.001), cellulose digestibility (P < 0.05), acid detergent fiber digestibility (P < 0.05) and neutral detergent fiber digestibility (P < 0.01). In 1987, late-harvested material had lower digestible organic matter intake kg−0.75 and digestibilities of dry matter, organic matter, crude protein, hemicellulose, cellulose, acid detergent fiber, neutral detergent fiber and ash were significantly (P < 0.01) lower than for material harvested earlier. The improvements in forage quality were not sufficient to offset the large yield reductions which are likely to occur in a semi-arid environment. Key words: Plant growth regulators, mefluidide, maleic hydrazide, forage quality, sheep, intake

In vitro propagation of Vicia faba L. by micro-cutting and multiple shoot induction

The influences of nitrogen sources, culture temperature and activated charcoal supplements were studied in relation to the rooting ability of V. faba cuttings. The interaction of these factors led to quantitative and qualitative modifications of the culture responses. Low temperatures (14–18°C) were suitable for in vitro culture, limiting the formation of phenolics in plant material and making activated charcoal supplement unnecessary. Nitrogen supplements contributed in modifying the different plant responses, in accordance with temperature. Multiple shoot formation was obtained from the cotyledonary node and from the stem nodes cultivated in the presence of 6-benzylaminopurine (BAP). BAP at 4 mg l-1 was the most effective concentration in promoting high rates of shoot development. The original position of stem nodes was found to determine the explant response to plant growth regulator treatments, possibly due to the effect of residual apical dominance.

Response of Centipedegrass (Eremochloa ophiuroides) to Plant Growth Regulators and Frequency of Mowing

When centipedegrass was unmowed, seedhead suppression generally was better with imazethapyr than with mefluidide either alone or with flurprimidol, but these treatments were not effective for 8 weeks. In several instances, imazethapyr at 0.30 kg ai/ha and MH at 2.2 and 4.5 kg ai/ha severely injured (>30%) centipedegrass. Mowing weekly did not control seedhead development effectively, and none of the plant growth regulator plus mowing treatments effectively suppressed seedheads for 12 weeks. To effectively suppress seedhead production for 8 weeks, centipedegrass treated with mefluidide required mowing 3 weeks after treatment, while centipedegrass treated with imazethapyr or flurprimidol plus mefluidide required mowing at 3 and 6 weeks.

Effects of combining priming and plant growth regulator treatments on the synchronisation of carrot seed germination

SUMMARYOsmotic priming of carrot seeds for 2 wk in polyethylene glycol (PEG, — 10 MPa) at 15 °C led to more rapid and synchronous germination at 20 °C compared to untreated seeds. These responses were enhanced by a 24 h pre‐priming soak in water or a change of solution after the first 24 h of priming to remove leachate. The inclusion of 200 mg litre‐1N‐substituted phthalimide in the pre‐priming soak and/or in the PEG further enhanced the results of priming. Leachate removal combined with phthalimide inclusion gave 79% and 86% germination from seeds of two carrot cultivars during the first day in 20°C water following priming. In contrast, cumulative germination of untreated seeds of the same cultivars was 18% and 61% respectively after 3 days in 20°C water. Seeds primed in PEG containing 200 mg phthalimide litre‐1with the solution replaced after the first 24 h germinated earlier and more synchronously than untreated seeds over a range of germination temperatures (5, 10, 15, or 20°C), but the effects of priming were most marked at 5°C.

Influence of Plant Growth Regulators on Transition of Bermudagrass Putting Green Overseeded with Perennial Ryegrass

Abstract Field studies were conducted for 3 years on putting green turf to determine the influence of the plant growth regulators (PGR) pronamide (PRON), ethephon (ETHR), mefluidide (MEFL), and maleic hydrazide (MH) on the transition from overseeded perennial ryegrass (Lolium perenne L. ‘Yorktown II’) turf to hybrid bermudagrass [Cynodon dactylon (L.) pers. × C. transvaalensis Burtt-Davy ‘Tifgreen’] in the spring. All PGR treatments were effective in increasing bermudagrass coverage over untreated grass; however, all reduced turf quality to some degree, with the exception of ETHR. The high PGR rates generally had lower turfgrass quality than the low rates. The March and early April application had the greatest bermudagrass coverage in 1982 and 1985, whereas the early March treatment generally had lower turfgrass quality than later applications. PRON at 0.28 kg·ha−1 applied as a single application in 1985 had higher initial bermudagrass coverage than when applied as split application, but split application maintained higher turfgrass quality than the single application. The split application of MEFL at 0.56 kg·ha−1 provided greater bermudagrass coverage than the single application when applied 6 Mar. or 3 Apr.; however, the split application resulted in lower quality than obtained from a single application applied on 6 Mar. in 1985. PRON at 0.28 kg·ha−1 and higher rates reduced growth and corresponding mowing requirements. Chemical names used: 1,2-dihydro-3,6-pyridazinedione (maleic hydrazide); N-(2,4-dimethyl-5-[([trifluoromethyl]-suIfonyl)amino]phenyl) acetamide (mefluidide); 2-chloroethyIphosphonic acid (ethephon); and 3,5-dichloro-(N-1,1-dimethyl-2-propynyI) benzamide (pronamide).

Growth and Partitioning in Peanut as Influenced by Gibberellic Acid and Daminozide

AbstractPeanut (Arachis hypogaea L.) cultivars differ in growth habit and potential for vegetative and reproductive growth modification with plant growth regulators (PGRs). Cultivars differing in growth habit were studied in light, dark, and field environments in 1982 and 1983 to assess the effects of two PGRs on apparent assimilate partitioning, and on vegetative and reproductive growth. The cultivars used were Dixie Runner (indeterminate spreading type), Florunner (somewhat determinate spreading type), and Pronto (bunch type). The PGR foliar spray treatments were gibberellic acid (GA), a growth stimulant, and daminozide (DA) (Kylar), a growth retardant. The field‐study treatments included Dixie Runner and Florunner, and GA and DA in one and two applications, beginning at pod initiation. Gibberellic acid (0.01 or 0.1 g L−1) increased stem petiole elongation in the light, dark, and field environments. Dixie Runner in most comparisons was slightly less responsive to GA than was Florunner. Daminozide (0.5 g L−1) retarded main‐stem, cotyledonary‐branch, and petiole elongation in both cultivars in light and dark environments. Response to a mixture (1:1,v/v) of GA and DA was similar to the water control in most comparisons. Darkness stimulated greater stem elongation than did GA; the two effects were additive. Daminozide decreased leaf area and shoot/root ratio, and increased chlorophyll concentration on a leaf‐area basis. Effects of PGR treatments were similar for Dixie Runner and Florunner. It is concluded that cultivars diverse in growth habit respond similarly to GA and DA, and modification of vegetative growth by PGRs to alter assimilate partitioning and fruiting appears problematic.

Modification of Root‐Shoot‐Ratio of Sunflower (Helianthus annuus, L.) by Nitrogen Supply and a Triazole‐Type Plant Growth Regulator

AbstractA factorial nutrient solution experiment with 3 N levels and 4 plant growth regulator (PGR) rates with sunflower (Helianthus annuus, L., cv. Sorex) was conducted to investigate the effect of both variables on shoot and root development. Nitrogen shortage resulted in reduced shoot and root growth throughout the experiment, but root growth was less affected than the shoot PGR treatments drastically reduced shoot biomass production. Root growth was promoted. Both reduced nitrogen supply and application of a triazole plant growth regulator (BAS 111. W) increased the proportion of roots relative to the shoot.

Influence of Growth Retardants (Anti‐Gibberellins) on Corn Vegetative Growth, Water Use, and Grain Yield under Different Levels of Water Stress1

AbstractCorn (Zea mays L.) grown under the semiarid conditions of the Central Great Plains requires supplemental irrigation to obtain maximum yields. This practice has become increasingly less profitable as the cost of application of irrigation water has risen. It may prove to be more cost effective to reduce the water requirement of corn by limiting the vegetative development of the plant. Two anti‐gibberellin, seed‐applied, experimental plant growth regulators (PGRs), BAS 106. .W and BAS 110. .W, were used on corn grown under low and high levels of irrigation in a 2‐yr (1984 and 1985) field study on a Rago silt loam soil (fine, montmorillonitic, mesic Pachic Argiustolls) to determine the effect of these PGRs on vegetative growth, water use, water stress, grain yield, and yield components. The PGRs were applied at three rates in both years (0, 100, and 200 mg a.i. kg−1 of BAS 106. .W in 1984 and 0, 125, and 250 mg a.i. kg−1 of BAS 110. .W in 1985). Increasing application rates of the PGRs caused a significant reduction in early season plant height, leaf area index (monitored in 1985 only), and dry matter accumulation (monitored in 1985 only), resulting in reduced early season evapotranspiration in both years. The PGR treatments reduced plant water stress during silking and early grain fill, particularly under the low irrigation treatment. The changes in plant growth and development associated with the PGRs resulted in a 9 and 16% increase in grain yield in 1984 and 1985, respectively, under the low irrigation treatment and a 7 and 9% reduction in grain yield in 1984 and 1985, respectively, under the high irrigation treatment. Therefore, reducing early season vegetative growth with the PGRs proved to be advantageous to productivity under water stress and counterproductive under nonlimiting water conditions.