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Michelle L. Bell, Roy A. Larson, and Douglas A. Bailey

Experiments were designed to determine if the combination of 6-benzyl adenine + gibberellic acid 4+7 can promote increased lateral shoots of desirable number and length on azaleas (Rhododendron simsii Planch.). The use of dikegulac-sodium with the addition of GA4+7 was also investigated to determine if GA4+7 could overcome decreased plant height and diameter caused by dikegulac application. Treatments were applied by spraying 204 ml·m-2 to pinched plants of mean diameter and mean height of 16 and 13 cm, respectively, potted in 1.3 liter plastic containers. Shoot number, plant height and plant diameter were measured 9 weeks after application for the commercially prominent cvs. `Gloria' and `Prize'. Preliminary results indicate that 2100 mg·l-1 ai BA + 2100 mg·l-1 ai GA4+7 increases number of lateral shoots. Initial results suggest the addition of 2100 mg·l-1 ai GA4+7 to 3900 mg·l-1 ai dikegulac overcomes inhibition of internodal elongation induced by dikegulac alone. Further studies will determine the effectiveness of Promalin (N-(phenylmethyl)-1H-purine-6-amine + GA4+7, 1:1) as a pinching agent on azaleas.

Free access

Michelle L. Bell, Roy A. Larson, and Douglas A. Bailey

Dikegulac, dikegulac + GA4+7, BA, and Promalin (GA4+7 + BA) were evaluated as lateral shoot-inducing agents on greenhouse forcing azalea, Rhododendron cultivars Gloria and Prize. The addition of GA4+7 (1000 or 2000 mg.L-1) to a commercial rate of dikegulac (3900 mg.L-1) did not effectively increase plant diameter or leaf width compared to plants sprayed with dikegulac alone. The combination of dikegulac and GA4+7 (3900 + 2000 mg.L-1, respectively) was more phytotoxic than dikegulac alone. Foliar sprays of BA and Promalin at 1000 and 2000 mg.L-1 and 1000 and 1816 mg.L-1, respectively, did not increase lateral shoot count. Neither the addition of GA4+7 to dikegulac nor the use of Promalin is a viable alternative to dikegulac application for inducing lateral branch development of dikegulac-sensitive cultivars. Chemical names used: Na 2,3:4,6-Bis-0-(l-methylethylidene)-α-L-xylo-2-hexulofuranosonic acid (dikegulac), (lα,2β,4aα,4bβ,10β)-2,4a,7-trihydroxy-l-methyl-8-methylenegibb-3-ene-l,10-dicarboxylic acid l,4a-lactone (GA4+7),N-(phenylmethyl)-lH-purin-6-amine (BA), and Promalin [1:1 (wt/wt) GA4+7 and BA].

Free access

Michelle L. Bell, Roy A. Larson, and Douglas A. Bailey

Experiments were designed to determine if the combination of 6-benzyl adenine + gibberellic acid 4+7 can promote increased lateral shoots of desirable number and length on azaleas (Rhododendron simsii Planch.). The use of dikegulac-sodium with the addition of GA4+7 was also investigated to determine if GA4+7 could overcome decreased plant height and diameter caused by dikegulac application. Treatments were applied by spraying 204 ml·m-2 to pinched plants of mean diameter and mean height of 16 and 13 cm, respectively, potted in 1.3 liter plastic containers. Shoot number, plant height and plant diameter were measured 9 weeks after application for the commercially prominent cvs. `Gloria' and `Prize'. Preliminary results indicate that 2100 mg·l-1 ai BA + 2100 mg·l-1 ai GA4+7 increases number of lateral shoots. Initial results suggest the addition of 2100 mg·l-1 ai GA4+7 to 3900 mg·l-1 ai dikegulac overcomes inhibition of internodal elongation induced by dikegulac alone. Further studies will determine the effectiveness of Promalin (N-(phenylmethyl)-1H-purine-6-amine + GA4+7, 1:1) as a pinching agent on azaleas.

Open access

Joseph W. Love, Roy A. Larson, and Bobby G. Hilliard

Abstract

Two poinsettia cultivars, ‘Annette Hegg’ and ‘Eckespoint C-l’ were grown at 60° and 65°F night temperatures, and subjected to growth retardant treatments. 2-ChloroethyI trimethyl ammonium chloride (CCC) soil drenches resulted in the shortest plants, but effective height control was achieved with combination spray applications of CCC and succinic acid 2,2-dimethylhydrazide (SADH), or CCC and N-pyrrolidinosuccinamic acid (F 529) applied once, or 2 foliar applications of CCC applied 3 weeks apart. Date of flowering was not appreciably affected by the growth retardants, but was affected by temperature. Flowering was accelerated at the warmer temperature, but plant heights and bract diam were similar at both temperatures.

Open access

T. Davis Sydnor, R. Kent Kimmins, and Roy A. Larson

Abstract

Low light intensity caused an increase in size and a delay in flowering of gloxinias (Sinningia speciosa Benth and Hooke cv. Dwarf Delight and Royal Frosted Red). The growth regulators succinic acid-2,2-dimethyl hydrazine (SADH) and (αcyclopropyl-α-(4 methoxyphenyl)-5-prymidinemethanol (ancymidol) decreased plant size and delayed flowering. ‘Dwarf Delight’ showed damage in response to ancymidol at 250 mg/liter and higher but ‘Royal Frosted Red’ showed no damage. SADH caused a noticeable increase in anthocyanin content of the inflorescence and chlorophyll content of the leaves.

Open access

Mikal E. Saltveit Jr. and Roy A. Larson

Abstract

Periodic shaking increased the resistance of potted poinsettia (Euphorbia pulcherrima Klotzsch ex. Willd., cv. Annette Hegg Diva) plants to mechanically induced leaf epinasty, but this resistance was lost within 24 hours of discontinuing the shaking. Bending petioles, not their reorientation in the gravitational field, caused increased ethylene production by excised petioles. Foliar sprays containing 40 μm cycloheximide, which were applied 24 hours before the plants were sleeved for 24 hours, completely prevented mechanically induced leaf epinasty, but were phytotoxic to the bracts.

Open access

Roy A. Larson and Richard L. Biamonte

Abstract

Vegetative growth, flower bud initiation, and early flower development of ‘Red American Beauty’ azaleas were enhanced at temp of 30-26°, 26-22°, 30-22°, 26-18°, and 22-18°C. Earliest flowering occurred following temp of 22-18°, 22-14°, and 18-14°C. The 4°C difference between day and night temp resulted in plants superior in quality to those exposed to an 8° difference.

Open access

Mikal E. Saltveit Jr. and Roy A. Larson

Abstract

Foliar sprays of either 10 mM aminoethoxyvinylglycine or 3 mM silver ions applied 24 hours before potted poinsettia plants (Euphorbia pulcherrima Klotzsch ex. Willd., cv. Annette Hegg Diva) were sleeved for 24 hours, significantly reduced the development of leaf epinasty after removal of the sleeves.

Open access

Roy A. Larson and T. Davis Sydnor

Abstract

Flower bud development was ascertained by biweekly dissections of shoot apices, until bud color was apparent. Satisfactory results were obtained when plants were given 3 weeks at 2 or 9°C, followed by 3 applications of GA3 at 250 ppm. The results were less satisfactory when attempts were made to completely substitute GA3 for the cool temp requirement to break dormancy.

Open access

Mikal E. Saltveit, D. M. Pharr Jr., and Roy A. Larson

Abstract

Mechanically bent petioles of potted poinsettia plants (Euphorbia pulcherrima Klotzsch ex. Willd., cvs. V-14, Eckespoint C-1 Red, Annette Hegg Diva, Annette Hegg White, and Annette Hegg Hot Pink) produced 3 to 70 times as much ethylene as petioles from unstressed plants. The Annette Hegg cultivars which were most susceptible to leaf epinasty after being sleeved for 24 hours showed the greatest enhancement of ethylene evolution after being mechanically stressed for 24 hours. Exposure to 10 ppm ethylene in air produced the same cultivar dependent pattern of epinasty in 4 hours as was produced by 24 hours of mechanical stress. Spraying with 250 ppm AgNO3, an antagonist of ethylene synthesis and action, reduced the severity of epinasty in ‘Annette Hegg Diva’ plants sleeved for 24 hours. The less susceptible ‘Eckespoint C-1 Red’ and ‘V-14’, produced less stress ethylene and were less susceptible to ethylene-induced epinasty.