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J. Raymond Kessler, Jr. and Gary
J. Keever
Achillea × ‘Coronation Gold’ is a widely grown
garden perennial with yellow flowers that bloom in early summer
at a height of about 2.5 feet. ‘Coronation Gold’ has
an obligate requirement for 6 to 8 weeks of vernalization at
41oF followed by long photoperiods (>14 hours or
night-break lighting) for complete flowering. Because control
of flowering is known, ‘Coronation Gold’ has potential
as a greenhouse pot crop, but flower peduncles grow too tall
in small containers for market acceptance. Therefore, product
quality may be improved by using plant growth retardants. This
investigation was conducted to determine the plant growth retardant
type, rate, and application timing required to produce a marketable
greenhouse pot plant of Achillea × ‘Coronation
Gold’ grown in 4-inch pots.
METHODS
Offsets of Achillea × ‘Coronation Gold’
were removed from vegetative stock plants and stuck in 6006-cell
flats containing Fafard Germinating Mix. Offsets were rooted
under intermittent mist in a shaded glass greenhouse under natural
short photoperiod with 85oF bottom heat. Rooted offsets
were removed from mist after 19 days and placed in a plastic
covered greenhouse with a heating set point temperature of 65oF
and ventilation at 78oF. Offsets were transplanted
to 4-inch round plastic pots containing Fafard 4-P 31 days after
sticking and initially spaced pot-to-pot on a greenhouse bench.
Fertilization throughout the experiment was applied as a constant
liquid fertilization 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.
After 5 weeks growth, all plants were placed in a walk-in cooler
at 40oF for 8 weeks of vernalization treatment. Incandescent
light (60 watt) was provided at a minimum of 10 foot-candles
for 24 hours per day and clear water was applied as needed while
in the cooler. After vernalization, plants were placed in a glass
covered greenhouse with a heating set point of 65oF
and ventilation at 78oF. Plants were provided long
photoperiods beginning one week after removal from the cooler
until the end of the experiment by lighting from 10:00 p.m. to
2:00 a.m. using a minimum 10 foot-candles from incandescent lamps
(60 watt). Plant growth retardant treatments were applied as
a spray 1 week after removal from vernalization as follows: B-Nine
at 0, 2,550, 5,100, or 7,650 ppm; B-Nine + Cycocel at 0+0, 1,275+1,534,
2,550+1,534, or 3,825+1,534 ppm, respectively; Bonzi at 0, 32,
64, 96, 128 or 160 ppm; Cutless at 0, 40, 80 or 120 ppm; Cycocel
at 0, 767, 1,534 or 2,301 ppm; or Sumagic at 0, 11, 22, 33, 44
or 55 ppm. Plant growth retardants were applied with a pressurized
CO2 sprayer calibrated to 20 psi at a rate of 0.5
gallon per 100 square feet. After treatment, plants were spaced
on 8-inch centers. Data recorded at the time of first open flower
were flower date, shoot height, market quality rating (1=very
poor, unsalable; 2=poor, unsalable; 3=average, salable; 4=good,
salable; 5=excellent, salable), and length of the five longest
lateral shoots.
RESULTS
The highest rates of B-Nine, B-Nine+Cycocel, Bonzi, Cutless,
Cycocel, and Sumagic reduced peduncle length by 36%, 61%, 75%,
75%, 39%, and 52% compared to untreated plants, respectively
(see table). However, the highest rates of B-Nine, B- Nine+Cycocel,
and Bonzi increased time to flower by 5 days whereas Cutless,
Cycocel, and Sumagic did not have an appreciable effect. The
highest rates of Bonzi, Cutless, and Sumagic decreased flower
size by 17%, 14%, and 18%, respectively, whereas B-Nine, B-Nine+Cycocel,
and Cycocel did not have an appreciable effect. B-Nine and Cycocel
had very little effect on market quality rating while increasing
concentrations of B-Nine+Cycocel increased market quality rating.
Market quality rating increased with increasing concentration
of Bonzi, Cutless, and Sumagic up to the middle of the treatment
range and then declined at higher concentrations. Market quality
ratings of 2.6 or higher were received by plants treated with
B-Nine+Cycocel at 3,825+1,534 ppm; Bonzi at 32, 64, and 96 ppm;
Cutless at 40 ppm; and Sumagic at 11 and 22 ppm.
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Response of Achillea × `Coronation
Gold' to Spray Application of B-Nine, B-Nine + Cycocel, Bonzi,
Cutless, Cycocel, or Sumagic |
Growth
retardant |
Rate (ppm) |
Shoot
height (cm)1 |
Flower diameter (cm)1 |
Market quality rating2 |
Days to flower |
|
B-Nine |
0 |
48.2 |
5.2 |
2.0 |
39 |
|
|
2550 |
41.8 |
5.1 |
2.0 |
40 |
|
|
5100 |
39.8 |
5.1 |
2.0 |
41 |
|
|
7650 |
31.0 |
5.0 |
2.1 |
44 |
|
B-Nine+Cycocel |
0 |
47.9 |
5.3 |
2.0 |
39 |
|
|
1275+1534 |
32.3 |
5.2 |
2.1 |
40 |
|
|
2550+1534 |
27.0 |
5.1 |
2.4 |
43 |
|
|
3825+1534 |
18.8 |
4.9 |
2.8 |
44 |
|
Bonzi |
0 |
47.6 |
5.4 |
2.0 |
39 |
|
|
32 |
30.1 |
5.3 |
2.6 |
39 |
|
|
64 |
20.5 |
4.7 |
3.0 |
42 |
|
|
96 |
17.7 |
4.7 |
2.9 |
42 |
|
|
128 |
12.3 |
4.6 |
2.3 |
42 |
|
|
160 |
11.9 |
4.5 |
2.3 |
43 |
|
Cutless |
0 |
45.2 |
5.0 |
2.0 |
40 |
|
|
40 |
16.1 |
4.5 |
2.6 |
41 |
|
|
80 |
13.4 |
4.5 |
2.4 |
42 |
|
|
120 |
11.3 |
4.3 |
2.0 |
43 |
|
Cycocel |
0 |
49.1 |
5.2 |
2.0 |
38 |
|
|
767 |
40.8 |
5.1 |
2.0 |
40 |
|
|
1534 |
37.6 |
5.0 |
2.2 |
41 |
|
|
2301 |
30.0 |
4.9 |
2.3 |
41 |
|
Sumagic |
0 |
48.4 |
5.6 |
2.0 |
40 |
|
|
11 |
29.5 |
4.9 |
2.6 |
41 |
|
|
22 |
26.0 |
4.7 |
2.9 |
41 |
|
|
33 |
26.3 |
4.7 |
2.4 |
40 |
|
|
44 |
25.6 |
4.6 |
2.3 |
41 |
|
|
55 |
23.1 |
4.6 |
2.2 |
42 |
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. |
Bonzi and Sumagic at moderately high concentrations
yielded adequate peduncle length control for acceptable quality
4-inch pots of Achillea × ‘Coronation Gold’.
However, the highest rates resulted in excessive stunting as
indicated by the decrease in market quality ratings. B-Nine and
Cycocel alone had only moderate effects on peduncle length and
market quality rating but were considerably more effective in
combination, indicating a synergistic effect. None of the treatments
received market quality ratings greater than 3.0 because plants
only had one to two flowering shoots and therefore were not full
enough to warrant higher ratings. Further work needs to be done
to increase the number of flowering shoots for a higher quality,
4-inch pot plant. A flowering delay of 3 to 5 days by several
of the plant growth retardants would probably not be a significant
problem in commercial application. These results provide growers
with several choices of plant growth retardants for growing ‘Coronation
Gold’ as a 4- inch pot crop in the greenhouse.
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