Plant Growth Regulators to Enhance Branching of Clematis spp.
The purpose of this experiment was to test the effects of five plant growth regulators (PGRs) on growth of Clematis L. large flowering hybrids, Ernest Markham and Hagley Hybrid, and Clematis viticella ‘Polish Spirit.’ Foliar sprays of dikegulac (Atrimmec), BA+GA4+7 (Fascination), ethephon (Florel), thidiazuron (Dropp 50 WP) and forchlorfenuron (CPPU), were applied to actively growing plants. Data collected on the two large flowering hybrids included a count of branches, a measure of leader lengths,and the number of weeks to bloom. Mean branch number and mean leader lengths were compared within a chemical between cultivars and between rates. Leader lengths were measured on ‘Polish Spirit’ and compared between rates within each chemical. Results indicate clematis growers could use 800 mg·L-1 dikegulac or either 800 or 1200 mg·L-1 BA+GA4+7 to increase branch number, and 1,000 mg·L-1 ethephon or 800 mg·L-1 dikegulac to effectively suppress leader lengths. Plants treated with BA+GA4+7 expressed bud blast, leaf curl and tip dieback until 4 weeks after treatment (WAT). A second experiment was performed on ‘Ernest Markham’ to optimize the ratio of BA:GA4+7 in an attempt to reduce phytotoxicity. Data taken were similar to the first experiment. Plants treated with any of the chemical ratios expressed an equal amount of phytotoxicity. A ratio BA:GA4+7 of 1:1 (Fascination) produced the most branches; with an increase in leader length. In a third experiment thidiazuron at the rates of 500 to 2000 mg·L-1 linearly decreased leader length throughout the 8 week test but increases in branch numbers were significant only at 2 and 4 WAT. Forchlorfenuron at rates of 5 to 25 mg·L1 had no significant effect on branch number or leader length. Chemical names used:dikegulac; 2,3:4,6-bio-O- (1- methylethylidene) – O-(2)-hexulofuranosonic acid; BA; N- (phenylmethyl)-1H-purine 6-amine; ethephon; 2-chloroethylphosphonic acid; thidiazuron; N-phenyl-N’- 1,2,3,-thiadiazol-5-ylurea; and forchlorfenuron; N (2_chloro4-pyridyl)-N’-phenylurea
Clematis vines are a popular garden plant cherished for their showy blooms and twining habit. However, the growth of many clematis hybrids is primarily from the main leader, producing a long, thin plant. This is a disadvantage for the retail market because consumers want well-branched, full plants. Producers prefer a well-branched, compact plant for easy handling and shipping (personal communication, Becky Moss, Riverbend Nursery, Riner VA). To achieve this, the grower needs to increase the lateral branching of the plants, and decrease length of the leaders. Pinching the apical meristem, or“cutting back” the plant stimulates axillary buds. This activity is tedious, labor intensive and delays flowering. Growers who are buying liners in the spring for summer sales typically have to make the choice between pinching to increase lateral branching or selling a plant with fewer branches that is in bloom. Those who choose to start clematis in the winter generally apply two or more pinches before May sales. Some species are pinched as often as once a week until the sale date (personal communication, John Patterson, Lancaster Farms). Clematis that are grown through the summer and fall, then over wintered, have more time to grow into a large, well-branched plants and therefore do not require such frequent pinching. However, keeping a plant in the nursery for a long period of time costs more to produce than one that can be sold in only 8 weeks, reducing profit margins.There are no chemical branch-enhancing plant growth regulators (PGRs) that are currently labeled for use on clematis. Use of chemical PGRs may induce branching by releasing dormant buds from apical dominance without the necessity of a manual pinch.PGRs would be an economical alternative to a manual pinch. The cost of cutting back a flat of Vinca minor L. ‘Bowles’, a vine with a similar growth rate, is $2.31 a flat (average worker pay of $9.25/hour, personal communication, Becky Moss, Riverbend Nursery,Riner VA.). Cost of PGR application would be directly related to the chemical used and method of application, however, costs would be less than manual pinching. An addedn benefit of PGRs may be a suppression of leader length for easier shipping and handling by the producer. Although PGRs have not been tested on Clematis spp. they have been effective in increasing branch numbers on various other perennials. Dikegulac (Atrimmec) has been reported to increase shoot number while decreasing shoot length of Lonicera x heckrotti Rehd. (Bruner et al., 2000), Hedra helix L. (Al-Juboory and Williams, 1990), Hypericum calycinum C. (Thomas et al., 1992), and Vinca minor L.(Foley and Keever, 1993). Bruner et al. (2000) observed shoot lengths linearly or quadratically decreased with an increase in dikegulac concentration of pruned and nonpruned plants. Foley and Keever (1993) experienced a decrease of primary runner length of Vinca minor with an increase in dikegulac rates beginning 4 WAT and persisting through the experiment, 10 WAT. Under the trade name Promalin (Abbott, Abbott Park,Ill.), BA+GA4+7 (Fascination), increased lateral bud break and increased shoot length in Euphorbia lathyris L. (Preece, 1989), H. calycinum (Thomas et al., 1992), and Portulaca grandiflora Hook. ‘Sundial’ (Banko and Stefani, 1997). Ethephon (Florel) treatments of 500 mg·L-1 suppressed the main shoot length of Salvia farinacea Benth. ‘Victoria Blue’and allowed the lateral shoots to grow prolifically, thereby producing fuller plants (Banko and Stefani, 1996). Ethephon, applied to geraniums (Pelargonium x hortorum L.H. Baily ‘Hollywood Star’) produced a decrease in axillary shoot length, and an increase in axillary shoot number (Foley and Keever, 1992).
LIST OF TABLES
LIST OF FIGURES
STATEMENT OF PURPOSE
DESCRIPTION OF PLANT MATERIAL
PLANT GROWTH REGULATORS
DESCRIPTION OF EACH PLANT GROWTH REGULATOR
Dropp 50 and CPPU
PREVIOUS USE OF CHEMICALS AS BRANCH ENHANCERS
PLANT GROWTH REGULATORS TO ENHANCE BRANCHING OF CLEMATIS SPP.
MATERIALS AND METHODS
Data and Statistics:
PGRS REPLACE PINCHING CLEMATIS SPP. TO INCREASE BRANCHING
MATERIALS AND METHOD