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Girish K. Panicker and Frank B. Matta

Growth regulators ABA and paclobutrazol were used at different concentrations to induce hardiness in blueberry flower buds and floral parts. Critical freezing temperatures and the effectiveness of the treatments were determined by differential thermal analysis (DTA), electrolyte leakage, visual browning, and tetrazolium staining. Treatment effects of growth regulators were nonsignificant on whole flower buds, but treatments induced hardiness in floral parts on the second flush of flowers at stage six produced in April. Induction of cold hardiness by ABA and paclobutrazol was concentration dependent. The higher the concentration, the greater the response. Viability test results on each floral part showed a close relationship with the critical freezing temperatures recorded by DTA. Control treatments showed that floral parts at stage six developed in April were more prone to freezing injury compared to floral parts at stage six developed in early March.

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Laura J. Lehman, C.R. Unrath, and Eric Young

Mature spur-type `Delicious'/seedling apple trees (Malus domestica Borkh.) were examined for 2 years after paclobutrazol (PB) foliar sprays with or without a soil cover to direct spray runoff away from the root zone, soil sprays, or a trunk drench. Foliar sprays with runoff reduced shoot number and fruit pedicel length in the year of treatment, but had no effect on shoot length. Trees that received foliar sprays with no runoff had fewer and shorter shoots and shorter pedicels the year after treatment. Soil sprays or a trunk drench reduced shoot number and pedicel length for 2 years after application, while only soil sprays reduced fruit weight, diameter, and length. Chemical name used: β- [(4-chlorophenyl)methyl]- α -(1,1-dimethylethyl)-1 H -1,2,4,-triazol-1-ethanol (paclobutrazol).

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John E. Kaminski, Peter H. Dernoeden, and Cale A. Bigelow

The tolerance of creeping bentgrass (Agrostis stolonifera L.) seedlings to many herbicides has not been evaluated. Three field studies were conducted between fall and spring from 1998 to 2002 to assess creeping bentgrass seedling tolerance to five herbicides and paclobutrazol. The primary objectives of this investigation were to assess bentgrass tolerance to these chemicals when applied at various timings following seedling emergence, and establishment of new seedlings as influenced by potential soil residues in the spring following a fall application of the chemicals. Treatments were applied 2, 4, or 7 weeks after either `Crenshaw' or `L-93' creeping bentgrass seedlings had emerged. Siduron (6.7 and 9.0 kg·ha-1) and bensulide (8.4 kg·ha-1) were noninjurious when applied two weeks after seedling emergence (2 WASE). Bensulide (14 kg·ha-1), ethofumesate (0.84 kg·ha-1), prodiamine (0.36 kg·ha-1) and paclobutrazol (0.14 kg·ha-1) were too injurious to apply 2 WASE, but they were generally safe to apply at 4 WASE. Chlorsulfuron (0.14 kg·ha-1) was extremely phytotoxic to seedlings when applied 2 WASE. Plots were treated with glyphosate and overseeded the following spring. The overwintering soil residuals of prodiamine and bensulide (14.0 kg·ha-1) unacceptably reduced spring establishment. All other herbicides and paclobutrazol had little or no adverse residual effects on spring establishment. Chemical names used: N-(phosphonomethyl)gycline (glyphosate); (±)-(R*,R*)-beta-[(4-chlorophenyl)methyl]-alpha-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol); 2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate (ethofumesate); S-(0,0-diisopropyl phosphorodithioate) ester of N-(2-mercaptoethyl) benzenesulfonamide (bensulide); [1-(2-methylcyclohexyl)-3-phenylurea] (siduron); N3,N3-di-n-propyl-2,4-dinitro-6-(trifluoromethyl)-m-phenylenediamine (prodiamine); 2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl] benzenesulfonamide (chlorsulfuron).

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Brian Whipker and P. Allen Hammer

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

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Jason A. Ferrell, Timothy R. Murphy, Ron R. Duncan, and William K. Vencill

The usage of seashore paspalum (Paspalum vaginatum Swartz) as a recreational turf has increased in recent years. On similar species, such as bermudagrass (Cynodon ssp.), plant growth regulators (PGRs) are used to decrease mowing frequency. However, no data currently exists for the use of PGRs on seashore paspalum. Therefore, field experiments were conducted over 2 years to determine the effects of trinexapac-ethyl and paclobutrazol on seashore paspalum. Paclobutrazol was non-injurious to turf when applied sequentially, 4 weeks apart, at rates as high as 0.56 kg·ha-1 of a.i. However, these same treatments failed to reduce vegetative growth. Conversely, trinexapac-ethyl treatments produced unacceptable injury (>15%) when applied sequentially, 4 weeks apart, at rates higher than 0.19 kg·ha-1 of a.i. As trinexapac-ethyl rates were reduced to ≤0.14 kg·ha-1 of a.i., injury was reduced to ≤ 12% while vegetative growth was suppressed to ≥59%, relative to nontreated seashore paspalum. Therefore, trinexapac-ethyl can serve as an effective option for those managing seashore paspalum turf areas. Chemical names used: 4-(Cyclopropyl-α-hydroxymethylene)-3,5-dioxo-cyclohexanecarboxylic acid ethyl ester (trinexapac-ethyl); (+/-)-R *,R *-β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazol-1-ethanol (paclobutrazol).

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Douglas A. Bailey and Bernadette Clark

Summer spray applications of 5000 ppm daminozide (1× or 2×), 62 ppm paclobutrazol (1× or 2×), or 5 ppm uniconazole (1× or 2×) were applied to seven cultivars (Böttstein, Enziandom, Kasteln, Mathilde Gütges, Merritt's Supreme, Red Star, and Schenkenburg) of florists' hydrangea [Hydrangea macrophylla subsp. macrophylla var. macrophylla (Thunb.) Ser.] to evaluate cultivar response to plant growth retardants (PGRs). Both daminozide treatments and the 2× uniconazole treatment effectively reduced plant height for all cultivars during the summer growth period; cultivars varied in response to the paclobutrazol treatments and the 1× uniconazole treatment. Daminozide and uniconazole treatments resulted in less elongation than all other treatments during forcing for most cultivars tested. Paclobutrazol treatments had no residual effect on shoot elongation during forcing of the cultivars tested. The 2× treatments of all PGRs decreased inflorescence diameter of some of the cultivars tested compared with nonsprayed controls. Results from this study indicate that 1) summer application of PGRs can have a residual effect on plant height and inflorescence diameter of hydrangeas during the spring greenhouse forcing phase; and 2) hydrangea cultivars differ significantly in response to the PGRs tested. Therefore, the need for height control during the spring forcing period of hydrangeas will vary with cultivar, and it will depend on how plants were treated the previous summer growing season. We recommend that producers of dormant hydrangeas provide records of their summer height control program to forcers so that height control programs during spring forcing can be adjusted appropriately.

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C.C. Pasian and M.A. Bennett

Bedding plants and many vegetable crop seeds are often sown in plug trays. Some crops, like marigold (Tagetes sp. L.), tend to stretch early after germination, especially if grown in low light environments. By the time growers apply plant growth regulators (PGRs), stretching of the hypocotyl has already occurred and seedling applications are ineffective. Seedling height may be controlled by applying the plant growth regulator directly to the seed. Seeds of `Bonanza Gold' marigold (Tagetes patula L.), `Cherry Orbit' geranium (Pelargonium {XtimesX} hortorum L.H. Bailey), and `Sun 6108' tomato (Lycopersicon esculentum Mill.) were soaked for 6, 16, or 24 hours in paclobutrazol solutions of 0, 500, or 1000 mg·L-1. After the soak treatment, seeds were dried for 24 hours prior to laboratory germination testing or sowing in plug trays. Percentage of emergence and seedling height were measured 16, 26, and 36 days after sowing. Laboratory germination of treated seeds was less than that of the control, which was attributed to the PGR being concentrated around the seed on the blotters. In contrast, seedling survival was unaffected in plugs. The higher concentration of PGR and longer times of soaking increased growth regulation, but also inhibited emergence of geraniums (71% vs. 99%). When seeds were imbibed 6, 16, or 24 hours, growth restriction was 31%, 31%, and 40%, respectively, for tomato, 61%, 37%, and 76%, respectively, for geranium and 30%, 38%, and 41%, respectively, for marigold. These results indicate that PGR application to geranium, marigold, and tomato seeds may be feasible using a 6- or 16-hour soak in 500 mg·L-1 paclobutrazol. Chemical name used: (±)-(R *,R *)-ß-[(4-chlorophenyl)methyl]-{XsalphaX}-(1,1-dimethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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Amy D. McDaniel* and Yin-Tung Wang

A study was initiated to determine the effect of GA3 as a counter measure to restore the growth of over-retarded poinsettia. Euphorbia pulcherrima `Sonora Red' plants were treated once foliarly with paclobutrazol at 40 or 80 mg·L-1 one week following pinching. Four weeks later, plants receiving the 80 mg·L-1 rate were treated once foliarly with GA3 at 0, 10, 20, 30 or 40 mg·L-1. The effect of GA3 was visible within 3 days of application. GA3 between 10 and 40 mg·L-1 caused long internodes, excessive stem elongation, as well as small leaves and bracts, resulting in unmarketable plants. Plants receiving 10 mg·L-1 GA3 were nearly twice the height of the over-retarded plants (31 vs. 17 cm), with increasingly taller plants at higher concentrations, up to 30 mg·L-1. In a second experiment, single-stemed plants were treated with one foliar spray of 50 or 150 mg·L-1 paclobutrazol two weeks following the beginning of short days. After another 3 weeks, the overdosed plants were then foliarly treated once with 0, 3, 5, 10, or 15 mg·L-1 GA3. GA3 at all rates promoted stem elongation and resulted in large bracts and much increased inflorescence diameter. The 15 mg·L-1 GA3 rate resulted in undesirable long internodes on the upper stem. Plants that received 3, 5, or 10 mg·L-1 GA3 were of excellent quality, with their heights and inflorescence sizes similar to those of plants receiving 50 mg·L-1 paclobutrazol (26 cm). Parallel experiments using `Burgundy Cortez' had similar results.

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Douglas A. Cox

Paclobutrazol (PBZ) was applied to `Mustang' geranium (Pelargonium × hortorum L.H. Bailey) as a single growth-medium drench at 0.06 mg a.i./pot or as a single foliar spray at 100 mg·liter-l when the plants had three to four expanded true leaves (34 days after sowing). At these rates, PBZ caused excessive growth suppression but plants flowered earlier than untreated controls. A single foliar spray of gibberellic acid (GA) at 100 mg·liter-l applied 0 (same day), 7, 14, or 21 days after PBZ reversed the growth suppression caused by PBZ. Plants treated with GA30 or 7 days after PBZ were as tall or taller and flowered at the same time as or later than the untreated (no PBZ, no GA3) controls. Plants treated with GA, 14 or 21 days after PBZ were shorter and flowered earlier than untreated controls but were taller than plants treated with PBZ alone. Response to GA3 was similar whether PBZ was applied as a drench or as a spray. Chemical name used: (+)-(R*,R*)-β([4-chlorophenyl]methyl)-α-(1,1-dimethylethyl)-1 H -1,2,4-triazole-1-ethanol (paclobutrazol).

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Tony K. Wolf and M. Kay Warren

Examination of `Riesling' grape (Vitis vinifera L.) in Virginia suggested that a high incidence of bud necrosis (BN) in some vineyards was associated with canopy shade and rapid shoot growth. BN appeared to originate as an abortion and dehydration of the primary, and occasionally secondary, buds of the developing dormant bud. BN frequency was lowest among the basal four nodes of a given shoot or cane, and increased in frequency through node 20. Experiments were conducted in 1991 and 1992 to evaluate the specific involvement of shoot growth rate and canopy shade on `Riesling' BN. Shoot growth rate (SGR), measured in a 17-day period around bloom, had a significant, positive relationship with BN in one of two vineyards. BN was positively associated with cane diameter and average internode length. Applying the growth retardant paclobutrazol significantly reduced SGR and BN incidence up to 80% among nodes 6 to 15 in two separate vineyards. Artificial shade (64% or 92% reduction in photosynthetic photon flux), suspended over vine canopies in the 3-week period before véraison, did not affect BN. Shoots of canopies that had been thinned before bloom to 10 shoots/m of canopy expressed slightly lower BN levels than shoots sampled from canopies that had been thinned to 20 shoots per meter. `Riesling' BN appeared more influenced by shoot vigor than shade under Virginia growing conditions. Chemical name β-[(4-chlorophenyl)methyl]-α-(1,1-dimethyl-ethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).