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Herbicides and Treefern
R. H. Stamps Central Science
University of Florida, IFAS Library
Central Florida Research and Education Center Apopka
CFREC-Apopka Research Report RH-87-4 OCr 14 1987
Treefern, Asparagus virgatus Bak., has become a p pularI cut foliage,
crop for the florist industry due to its symmetrical ;hapeU WtfilyOf Fiorida
appearance. One significant problem facing producers of this op is d
control. Weeds compete with treefern for water, light and nutrients;
harbor insect pests; and interfere with harvesting of the crop. Since
treefern does not form a dense canopy that excludes much weed competition
(like crops such as leatherleaf fern), mechanical and/or chemical methods
are often employed to reduce weed competition. Hand-weeding is expensive
and the crop is physically damaged during the weeding process, so growers
are interested in chemical weed control. However, no herbicides are
specifically labeled for treefern at this time. The following experiment
was conducted to determine if any of several herbicides could be used
safely on treefern.
Materials and Methods
This. test was conducted at the. Central Florida Research and Education
Center-Apopka on established treefern beds growing under shadecloth
designed to exclude 70% of incoming midday light. Plots were 3' x 5.3' in
this randomized block design experiment with three replications. The soil
in the plots was Blanton fine sand containing about 2.2% organic matter.
The plots were watered two times per week with about 1" of water using a
fixed overhead irrigation system. Beds were fertilized at a rate of 500 lb
N/acre/yr with Osmocote 19-6-12 (first year) and Sierra 17-6-12 (after year
1) applied every two months. The fernery was lined with polyethylene
plastic from about Nov. 15th to April 15th each year and temperatures were
maintained above 36*F using forced air heaters.
Treatments consisted of 1) control, no herbicide; 2) alachlor 15G
(Lasso II, Monsanto Agricultural Products) at 4 lb a.i./acre/application;
3) oxadiazon 2G (Ronstar G, Rhone-Poulenc) at 4 lb a.i./acre/application;
4) oxyfluorfen 2G + pendimethalin 1G (Ornamental Herbicide 2, Scotts
Progrow) at 3 lb a.i./acre/application; and 5) prodiamine 50WP (first
year), 4F (after year 1) (Blockade, Sandoz Crop Protection; formerly Rydex,
U.S. Borax) at 4 lb a.i./acre/application. Granular herbicides were hand-
broadcast and prodiamine was applied as a dilute solution (equivalent to
about 2700 gal/acre) over the plots. One-half inch of irrigation water was
applied immediately after herbicide application. Treefern beds were mowed
prior to the initiation of herbicide treatments in June, 1984. Treatments
were reapplied at 3 month intervals, immediately after all plots were hand
weeded. Herbicide applications continued through June, 1986.
Assistant Professor of Ornamental Horticulture, Central Florida Agricul-
tural Research and Education Center-Apopka, 2807 Binion Road, Apopka, FL
Weeds were oven dried and then weighed to determine the relative
effects of the treatments on weed biomass production. Treefern stems were
harvested Nov. and Dec. 1984, Mar. and Jul. 1985, and Jan., Feb., May,
Jul., and Sep. 1986. The number of stems harvested and their fresh weights
(except when the foliage was wet) were recorded. However, the yield data
are not representative of commercial production potential because the
treefern had to be clear-cut in early 1986 due to severe bleaching of the
treefern foliage that occurred after oxyfluorfen + oryzalin (Rout, Sierra
Chemical) was experimentally applied to nearby leatherleaf fern beds.
Visual ratings of treefern vigor and weed coverage in plots were made in
April 1987 to monitor the long-term effects of the treatments. The vigor
rating scale was: O=treefern dead; 1=poor treefern growth, sparse and or
stunted growth; 2=fair growth, growth sparse but with little stunting;
3=good amount of new growth, no stunting; and 5=very vigorous and dense
growth. Weed coverage percentages were transformed to the arcsine of the
square root of the percentage before statistical analysis.
Treefern Yield. None of the herbicide treatments increased or reduced
yields compared to the control, but oxyfluorfen + pendimethalin reduced
stem yield compared to o'xadiazon (Table 1). Additionally, vigor ratings
'taken 10 months after the last herbicide application showed reduced growth
for the oxyfluorfen + pendimethalin treated treefern when compared to the
control. Average stem weights were not influenced by treatments.
Table 1. Effects of herbicide treatments on treefern yield and vigor.
Yieldz Mean stem
Rate (1b Stems Fresh wt Vigor ratingY wt, year 2
Treatment a.i./A) (no) (Ib) Apr. 1987 (lb)
Control 0 432 abw 8.9 a 4.0 a 0.047 a
Oxadiazon 4 586 a 7.9 a 3.0 ab 0.046 a
Alachlor 4 444 ab 7.1 a 3.0 ab 0.047 a
Prodiamine 4 409 ab 8.1 a 2.8 ab 0.065 a
+ pendimethalin 2 + 1 363 b 8.5 a 1.7 b 0.068 a
ZYield per 16 square feet of bed. All yields reduced due to phytotoxicity
from treatment applied to adjacent leatherleaf fern plots (see text).
The vigor rating scale was: O=treefern dead; 1=poor treefern growth,
sparse and or stunted growth; 2=fair growth, growth sparse but with little
stunting; 3=good amount of new growth, no stunting; and 5=very vigorous
and dense growth.
xTen months after last herbicide application.
WWithin each column, values followed by the same letter do not differ at
the 5% level of probability using Duncan's multiple range test.
Weed Control. The predominant weeds during this study were Commelina
communis L. (dayflower), Erechtites hieracifolia (L.) Raf. (fireweed),
Gnaphalium falcatum Lam. cudweedd), Oxalis stricta L. (common yellow
woodsorrel), Phyllanthus tenellus Roxb. (phyllanthus), Richardia scabra L.
RH-87-4, page 2
(Florida pusley), Stellaria media (L.) Cyrillo (chickweed), and Youngia
japonica (L.) DC. (Asiatic hawksbeard). All of the herbicide treatments
reduced the amount of weeds in the plots compared to the controls (Table
2). Reductions ranged from 61 to 78% on a dry weight basis. Oxadiazon,
prodiamine, and oxyfluorfen + pendimethalin treated plots had significantly
fewer weeds in them 10 months after their last application than did the
control and alachlor plots.
Table 2. Effects of herbicide treatments on weed control.
Rate (Ib Weed dry wt Weed coverage
Treatment a.i./A) (Ib) Apr. 1987 (%Y)
Control 0 1.00 bx 48.3 b
Oxadiazon 4 0.39 a 6.3 a
Alachlor 4 0.31 a 50.0 b
Prodiamine 4 0.44 a 0.3 a
+ pendimethalin 2 + 1 0.22 a 1.3 a
Tn mtk 4:+ C 1 k+ lt 1hbid ,A 1;4-t
en1 MVn a a r as C1 .c = app ca o.Vn.
YWeed,coverage percentages were transformed to the arcsine of the square
root of the percentage before statistical analysis.
Within each column, values followed by the same letter do not differ at
the 5% level of probability using Duncan's multiple range test.
The alachlor, oxadiazon, and prodiamine treatments tested did not
reduce yield or vigor of treefern significantly under the conditions and
time span of this test. In addition, all three herbicides significantly
reduced weed growth, and two of them (oxadiazon and prodiamine) appear to
have good residual activity. The oxyfluorfen + pendimethalin combination
treatment produced excellent weed control but reduced treefern vigor with
repeated applications. (As was mentioned earlier, oxyfluorfen + oryzalin
applied to another crop in the same fernery caused severe damage to the
treefern and therefore should not be used on treefern.)
Results from larger scale use of these herbicides may differ from those
in this test. Once registered for use on treefern, tests should be made on
selected areas under grower conditions prior to widespread use at a
particular site. special care should be taken when using herbicides on
soils low in organic matter.
* ****** **************** ****************************************
*Note: Mention of a commercial or proprietary product or pesticide does*
*not constitute a recommendation by the authors or the University of*
*Florida, IFAS, nor does it imply registration under FIFRA as amended or*
*its approval to the exclusion of other products that may be suitable.*
!Pesticides should be applied according to label instructions and safety*
*equipment required on the label or by federal law should be employed.*
*Users should avoid the use of chemicals under conditions that could lead*
*to ground water contamination. *
RH-87-4, page 3