J. Raymond Kessler, Jr. and Gary J. Keever

Coreopsis verticillata ‘Moonbeam’ is a herbaceous perennial, which blooms in late spring to early summer. It has no vernalization requirement, but an obligate requirement for long photoperiods (>14 hours or night-break lighting) to flower. Because vegetative growth and flowering can be controlled using photoperiod, it may be possible to develop the plant as a greenhouse pot crop. However, Coreopsis grows too tall in small containers under greenhouse conditions for market acceptance, and therefore may benefit from plant growth retardants (PGR).

In previous work, several PGRs were reported to be effective in reducing shoot height and improving market quality rating of Coreopsis grown in 4-inch pots when applied 10 days after shearing. In a second study (data not presented), a different series of PGRs were tested, some in common with the first study, with very poor results. In the case of the second study, PGR application were made 1 day after shearing rather than 10 days after shearing. We hypothesized that the timing of PGR application after shearing may have an impact on the effectiveness of treatments. Therefore, the purpose of this study was to determine the effects of application timing after shearing and concentration of B-Nine or Cutless applied as a foliar spray on plant size and flowering of Coreopsis verticilata ‘Moonbeam’.

METHODS
Terminal cuttings (2.5 inches long) of Coreopsis verticillata ‘Moonbeam’ were removed from vegetative plants and stuck in 72-celled flats containing Fafard 3B. Cuttings were rooted using intermittent mist in a shaded glass greenhouse under natural photoperiod. Rooted cuttings were removed from mist, given a soft terminal pinch after 26 days, and placed in an unshaded glass greenhouse with a 65^oF heat set point and ventilation at 78^oF. Short photoperiods were maintained from the time of removal from propagation to when PGR treatments were applied by pulling black cloth from 7:00 p.m. to 10:00 a.m. daily. Cuttings were transplanted 21 days after removal from propagation to 4-inch square pots containing Fafard 3B and initially placed pot-to-pot on a greenhouse bench. All cuttings were sheared to 2.5 inches above the pot rim 20 days after transplanting. Long photoperiods were provided beginning the day of shearing by lighting from 10:00 p.m. to 2:00 a.m. using a minimum of 10 foot-candles from incandescent lamps (60 watt). Fertilization throughout the experiment was applied as a constant liquid feed consisting of 150 ppm nitrogen using a 20-10-20 with one clear water application per week to prevent soluble salts buildup. Plants were watered/fertilized when the medium appeared dry, but before plants wilted.

PGR treatments were B-Nine at 0, 2,550, 5,100, or 7,650 ppm and Cutless at 0, 50, 100, or 150 ppm. The PGR treatments were applied at 0, 3, 6, 9, 12, or 15 days after shearing. Foliar spray solutions of the PGRs were applied at a rate of 0.5 gallon per 100 square feet using a pressurized CO₂ sprayer set at 20 psi. Data recorded at the time of first open flower was flower date, shoot height, and market quality rating (1=very poor, unsalable; 2=poor, unsalable; 3=average, salable; 4=good, salable; 5=excellent, salable).

RESULTS
Time to flower of Coreopsis verticillata ‘Moonbeam’ increased by 7 days when B-Nine was applied at all concentrations compared to untreated plants over all application times (see table). All B-Nine concentrations reduced shoot height and increased market quality rating compared to untreated plants. The highest market quality rating, 3.2, was assigned to plants that received 5,100 ppm B-Nine and these plants were 36% shorter than untreated plants. Shoot height declined from 0 days after shearing to 6 or 9 days and then increased up to 15 days after shearing over all B-Nine concentrations (Figure 1). A mathematical model of the relationship between shoot height and application timing predicted that a minimum shoot height could be achieved by applying B-Nine between 6 and 8 days after shearing.

Response of Coreopsis Verticillata ‘Moonbeam’ to Spray Applications of B-Nine and Cutless Across All Application Times
Growth retardant	Rate (ppm)	Days to flower	Shoot height (cm)1	Market quality rating2
B-Nine	0	42	32.9	2.1
	2550	51	22.8	3.0
	5100	51	21.2	3.2
	7650	49	24.5	3.1
Cutless	0	43	30.5	2.1
	50	44	15.8	3.0
	100	44	17.8	2.9
	150	45	17.2	2.8
1 English conversion 2.54 cm = 1 inch. 2 Quality rating: 1=very poor, unsalable; 2=poor, unsalable; 3=average, salable; 4=good, salable; 5=excellent, salable.

Figure 1. Effect of all spray concentrations of B-Nine applied 0, 3, 6, 9, 12, or 15 days after shearing on shoot height of Coreopsis verticillata‘Moonbeam’

Figure 2. Effect of all spray concentrations of B-Nine applied 0, 3, 6, 9, 12, or 15 days after shearing on market quality rating of Coreopsis verticillata ‘Moonbeam’