PGR Plug Soaks
Floriculture seniors Charles Leggett and Austin Cowden completed the
first research projects of the W. D. Holley Research Program at Colorado
State University in the summer of 2002. With the financial backing
of Uniroyal Chemical, preplant soaks of plug trays with solutions of Bonziâ
to control the vigor of flowering annuals were investigated. Pre-plant
plug soak is a relatively new method for applying plant growth regulators.
The first project compared Bonzi plug soaks with more traditional
plant growth regulator (PGR) applications on 11 species of vegetatively
propagated annuals; Argyranthemum, Bracteantha, Calibrachoa, Coleus,
Diascia, Double Impatiens, Lamium, Nemesia, Petunia, Scaevola and
Verbena.
Treatments were as follows:
1.
B-Nine (2500 ppm) + Cycocel (1500 ppm) tank mix foliar spray
2.
B-Nine (2500 ppm) foliar spray
3.
Cycocel (1500 ppm) foliar spray
4.
Bonzi (15 ppm) foliar spray
5.
Bonzi (30 ppm) foliar spray
6.
Bonzi (2 ppm) soil drench
7.
Bonzi (4 ppm) soil drench
8.
Bonzi (4 ppm) pre-plant plug soak
9.
Bonzi (8 ppm) pre-plant plug soak
10.
Untreated control
Soak treatments were applied pre-plant by setting 105 cell trays of rooted
cuttings for 2 minutes in pans with either 4 or 8 ppm Bonzi solution,
allowing the trays to drain and then planting in 5" round pots.
All other treatments were first planted in 5" round pots, pinched 2 weeks
later and PGR treatments applied 4 weeks after planting.
Pre-plant plug soaks with Bonzi were more effective in controlling plant
vigor than any of the other PGR treatments in this trial. Argyranthemum,
Calibrachoa, Coleus, Petunia and Lamium all were effectively controlled
with plug soaks without adversely affecting flowering and this usage shows
good potential. On the other hand, Diascia, Double Impatiens and
Scaevola were extremely sensitive to Bonzi plug soaks and severely stunted
at the rates used. Nemesia and Verbena that are basically only slightly
responsive to PGRs had their growth rates only slightly slowed with plug
soaks.
The second project examined the practice of using pre-plant plug
soaks on vigorous annuals when planted in mixed containers with low vigor
species.
Petunia and Coleus were selected for the "vigorous" species and treated
with either 4 or 8 ppm Bonzi as a pre-plant plug soak. Diascia and
Bacopa were selected for the "low vigor" species and were not treated
with plant growth regulators. One rooted plug of each of the four
plants was planted into 10" hanging baskets, the objective being, to determine
if the plug soaks would prevent the normally vigorous plants from "over-growing"
and crowding out the less vigorous plants.
Treatments were as follows:
Bonzi Plug Soak Rates (ppm)
Coleus-0
Petunia-0 Diascia-0
Bacopa-0
Coleus-4
Petunia-0 Diascia-0
Bacopa-0
Coleus-8 Petunia-0
Diascia-0 Bacopa-0
Coleus-0
Petunia-4 Diascia-0
Bacopa-0
Coleus-4 Petunia-4
Diascia-0 Bacopa-0
Coleus-8 Petunia-4
Diascia-0 Bacopa-0
Coleus-0 Petunia-8
Diascia-0 Bacopa-0
Coleus-4
Petunia-8 Diascia-0
Bacopa-0
Coleus-8
Petunia-8 Diascia-0
Bacopa-0
Results of this project were particularly encouraging. Two months
after planting, all four plants were comparable in size and produced a
nicely balanced hanging basket, when petunia and coleus plugs were first
soaked in Bonzi solution pre-plant. In those treatments without a pre-plant
soak treatment, coleus and/or petunia grew more vigorously and soon dominated
the diascia and bacopa. Petunia was more sensitive to the PGR plug
soak than coleus. In this trial, the 8-ppm rate was nearer optimum
for coleus, while the 4-ppm rate may have been sufficient for petunia.
* Report from the W.D. Holley Research Program in Floriculture
Colorado State University
Department of Horticulture and Landscape Architecture
Fort Collins, CO 80523-1173
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