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Gary J. Keever, James C. Stephenson,
Jr., and Donna C. Fare
During
the growing season, numerous shoots or sprouts develop on the
lower trunk of budded ‘Bradford’ pear, especially below
the bud union, necessitating repeated hand removal. Tre-Hold,
a commercial formulation of the plant hormone naphthelene acetic
acid (NAA), has been effective in controlling watersprouts and
rootsuckers on several fruit and nut crops, grapevines, and woody
landscape plants but is not labeled for use on ‘Bradford’
pear. The objective of this study was to evaluate the effectiveness
of Tre-Hold in controlling basal sprout development on ‘Bradford’
pear following terminal shoot removal.
METHODS
The terminal shoot of container-grown, budded, 4.5 to 5.5 foot,
unbranched whips of ‘Bradford’ pear was pruned at 49
inches and Tre-Hold was applied to the lower 30 inches of each
trunk on March 11, 1997. Treatments were Tre-Hold at 0, 2,875,
5,750, 8,625, and 11,500 parts per million active ingredient
(ppm ai). Treatments were equivalent to Tre-Hold RTU (ready-to-use
formulation) at 0, 0.25x, 0.5x, 0.75x,and x. Sprout numbers and
lengths from the lower 30 inches of trunk both above and below
the bud union were recorded at 30, 60, 120, 180, and 210 days
after treatment (DAT). Plant height and diameter 6 inches above
the bud union were measured at 240 DAT.
RESULTS
Trunks of trees sprayed with Tre-Hold developed an oil-soaked,
darkened appearance following treatment that increased with concentration
but diminished with time. Appearance was apparently due to the
emulsion wax carrier but did not detract from overall plant quality.
No other abnormal symptoms were observed on treated or non-treated
trees. Sprouts on the trunk and rootstock and total sprout number
decreased with all concentrations of Tre-Hold (see table). The
most dramatic reduction in sprout numbers occurred between control
plants and those receiving the lowest rate of Tre- Hold, with
similar levels of sprout control for all rates.
|
Sprout Numbers On ‘Bradford’
Pear Treated With Tre-Hold |
|
|
Trunk sprout number1 |
Rootstock sprout number2 |
Total sprout number |
|
Tre-Hold |
DAT3 |
DAT |
DAT |
|
(ppm ai) |
30 |
60 |
120 |
180 |
210 |
30 |
60 |
120 |
180 |
210 |
30 |
60 |
120 |
180 |
210 |
|
0 |
5.2 |
5.3 |
5.3 |
5.3 |
5.3 |
1.6 |
1.6 |
1.6 |
1.6 |
1.6 |
6.8 |
6.9 |
6.96 |
6.9 |
6.9 |
|
2,875 |
0.3 |
0.3 |
0.3 |
0.3 |
0.4 |
0.6 |
0.6 |
0.6 |
0.9 |
1.0 |
0.9 |
0.9 |
0.9 |
0.9 |
1.4 |
|
5,750 |
0.0 |
0.0 |
0.0 |
0.5 |
0.5 |
0.0 |
0.0 |
0.0 |
0.0 |
0.0 |
0.0 |
0.0 |
0.0 |
0.5 |
0.5 |
|
8,625 |
0.1 |
0.2 |
0.2 |
1.1 |
1.2 |
0.0 |
0.0 |
0.1 |
0.1 |
0.1 |
0.1 |
0.2 |
0.3 |
1.2 |
1.3 |
|
11,500 |
0.0 |
0.0 |
0.0 |
0.8 |
0.8 |
0.0 |
0.0 |
0.4 |
1.4 |
1.4 |
0.0 |
0.0 |
0.4 |
2.2 |
2.2 |
1Sprouts
that developed on the lower 30 inches of each trunk above the
bud union.
2Sprouts that developed from the rootstock.
3DAT = days after treatment. |
Essentially all sprouts that developed on control
plants were present 30 DAT with no change thereafter; more sprouts
developed on trunks than on rootstocks. Very few trunk or rootstock
sprouts developed on treated plants throughout the study, although
there was a noticeable increase in total sprout numbers between
120 and 180 DAT in plants receiving the two highest Tre-Hold
rates. This response may in part relate to the more viscous nature
of solutions of higher concentrations. Spray solutions of higher
concentrations foamed more and spread less readily when applied
than those of lower concentrations, which may have reduced coverage.
Trunk sprout length was greater at 30, 60, and 120 DAT in control
plants than in treated plants that formed sprouts. However, between
180 and 210 DAT, elongation of sprouts in treated plants accelerated
such that sprout lengths were similar among all treatments at
210 DAT. In plants where sprouting from rootstocks occurred,
sprout lengths were similar among treatments through 180 DAT.
Between 180 and 210 DAT sprout length doubled in plants that
had received the highest Tre-Hold rate; at 210 DAT average sprout
length was three times that of control plants.
Tree height and change in diameter increased up to 5,750 ppm
Tre-Hold before decreasing at higher rates. With 5,750 ppm, trees
were 15% taller and increased 20% more in diameter than control
plants. With the highest Tre-Hold rate, trees were 9% taller
but change in diameter was 9% less compared to control plants.
The stimulatory effects on tree height and change in diameter
were inversely related to total sprout dry weight. Perhaps less
photosynthate was channeled into developing sprouts and, therefore,
more was available for height and diameter increase in treated
trees.
Results of this study indicate that Tre-Hold at concentrations
less than that in the Tre-Hold RTU formulation (11,500 ppm) can
provide excellent control of basal sprout in ‘Bradford’
pear. Concomitant to excellent sprout control, which should reduce
expense incurred in hand pruning, was an increase in tree height
and diameter with an application of Tre-Hold at 5,750 ppm. Based
on results of this study, the manufacturer of Tre-Hold has expanded
the label to include ‘Bradford’ pear.
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