Table of Contents
Webber, C.L. III. 1993. The effects of metolachlor and trifluralin on kenaf
yield components. p. 413-416. In: J. Janick and J.E. Simon (eds.), New crops.
Wiley, New York.
The Effects of Metolachlor and Trifluralin on Kenaf Yield Components
Charles L. Webber III*
- MATERIALS AND METHODS
- Plant Injury and Weed Control
- Plant Populations
- Plant Heights
- Stalk Yields
- Table 1
- Table 2
While kenaf (Hibiscus cannabinus L.) shows great promise as a new source
of fiber, commercialization depends on successful development of production
systems. Researchers have reported that kenaf is a good competitor with weeds
once the plants are of sufficient size to shade the ground (Burnside and
Williams 1968; Orsenigo 1964), yet weeds can significantly reduce kenaf yields.
Weed control therefore becomes an important consideration in obtaining optimum
Williams (1966) reported that weed competition, with moderate weed pressure,
reduced stalk yields during one season by an average of 1.0 t/ha. Weed
competition in a three year Nebraska study significantly reduced yields by an
average of 9.0 t/ha (69%) and reduced plant height and stalk diameter (Burnside
and Williams 1968).
Presently, no herbicides are registered for kenaf in the United States.
Literature examining the effects of preemergence herbicides on kenaf
development and stalk yields is limited. Many herbicides originally evaluated
for use in kenaf production are either no longer available, phytotoxic to
kenaf, or reduce kenaf populations (Orsenigo 1964; Williams 1966; Burnside and
Williams 1968). Two efficacious herbicides that have registration potential are
trifluralin and metolachlor; trifluralin has been the standard herbicide used
by kenaf researchers (White et al. 1970).
Burnside and Williams (1968) tested seven herbicides and found that kenaf was
most tolerant to trifluralin, which also provided excellent weed control.
However trifluralin, at 2.2 kg/ha, significantly reduced kenaf yields by 3.9
t/ha (25%) during the first year; although stalk heights and diameters were
unaffected by the application of trifluralin. Orsenigo (1964) reported a 50%
phytotoxicity and a 50% stand reduction when trifluralin was applied to kenaf
at 6.7 kg/ha, but 100% tolerance and no stand reductions when applied at 2.2,
3.4, and 4.5 kg/ha. In south Texas, trifluralin, at 0.9 and 1.7 kg/ha, and
metolachlor at 3.4 kg/ha provided excellent (90%) grass control while
acceptable (80%) total weed control was obtained with metolachlor at 3.4 kg/ha
(Hickman and Scott 1989). Trifluralin did reduced stalk yields at the rates
tested. In Mississippi, metolachlor (3.0 kg/ha) gave no visual injury to the
kenaf, although stalk yields may have been reduced (Kurtz and Neill 1990).
As the commercial production of kenaf in the United States grows closer, weed
control strategies must be developed and the best herbicides identified and
registered. The objective of this research was to determine the effects of
metolachlor and trifluralin on kenaf plant development and stalk yields.
A two-year field plot study was conducted at Lane, Oklahoma on a Bernow fine
sandy loam, 0 to 3% slope, (fine-loamy, siliceous, thermic Glossic Paleudalf).
Fertilizer was applied and incorporated prior to herbicide application at a
rate of 168-72-139 kg/ha (N-P-K). Trifluralin
[2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl) benzenamine] and metolachlor
[2-choro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] were
applied at 0.56, 1.12, and 2.24 kg ai/ha using fan nozzles at 187 liters/ha.
The trifluralin treatments were incorporated twice to a depth of 5 to 7.5 cm,
with the second incorporation at 90° to the first. A combination secondary
tillage tool with cultivator shovels, cutting blades, spike tooth harrow, and
rolling baskets was used for the trifluralin incorporation and to prepare the
seedbed for all treatments prior to planting. Metolachlor was applied after
seedbed preparation and prior to planting. The experiments also included a
weed-free (kept as such via handweeding) and weedy check treatments.
Plots were 3 m wide (four 76-cm rows), 6 m long, and were oriented in a
east-west direction. Kenaf cultivar 'Tainung #1' was planted on June 22, 1989
and June 12, 1990. All plots were planting the same day as herbicide
Crop injury ratings were collected at two and four weeks after planting using a
0 to 5 rating system; 0 represents no visual injury, 5 represents crop death.
Grass and broadleaf weed control ratings were collected at four weeks after
planting, using a 0 to 10 rating system; 0 represents no weed control, 10
represents 100% weed control. Kenaf plant populations, plant heights, and
stalk data were collected at harvest. Kenaf plots were hand-harvested 18 weeks
after planting on Oct. 23, 1989 and Oct. 17, 1990. A 2.25 m2 (1.5
by 1.5 m) quadrant was harvested from the center of the second and third row of
each plot. Plant counts from the harvest quadrant were used to determine plant
populations. The harvested plants were cut at ground level and fresh weights
determined. Three plants were randomly selected from the harvested material
for plant height. Leaves, flowers and flower buds were removed from the stalks
and weighed separately before and after samples were oven dried at 66deg.C for
48 h. The fresh and oven dry weights of the three plants were used to determine
the percent moisture of the plants and the percent stalks by weight. The
percent plant moisture and percent stalks were used to convert the fresh weight
of the 2.25 m2 quadrant sample to dry weight of stalks. Stalk
yields are based on oven dry weights.
In both years, the experiments were randomized complete block designs with four
replications. Crop injury and weed control data were converted to percentages
and transformed using an arcsin transformation before analysis (Snedecor and
Rainfall during the growing season, from planting to harvest, was 6.1 cm below
and 9.2 cm above the 20-year average rainfall for 1989 and 1990 respectively.
No visual crop injury was observed during 1989 or 1990 as a result of the
herbicides applied at the given rates (data not shown). The only year by
treatment interaction detected was reflected in the degree of grass weed
control, which was less in 1990 by metolachlor (Table 1). Metolachlor at 0.56
kg/ha, in 1990, was the only herbicide treatment in either year that had less
grass weed control than any other herbicide treatment (Table 1). Broadleaf
weed control data showed no differences in weed control (Table 1).
The primary weeds present during both years were large crabgrass [Digitaria
sanguinalis (L.) Scop.] and tumble pigweed (Amaranthus albus L.).
Both these weed species were present at moderate populations.
Except for metolachlor at 0.56 kg/ha and trifluralin at 1.12 kg/ha all
herbicide treatments reduced plant populations compared to the weed-free plots
(Table 2). No kenaf population differences were detected between the herbicide
treatments or between the herbicide treatments and the weedy check plots (Table 2). No weed control by year interactions were detected for plant populations,
plant heights, or stalk yields as a result of the combined analysis of the
eight weed control treatments and the two years. Populations, when combined
over weed control treatments, were greater in 1990 than those in 1989 (Table 2). The differences in populations were attributed to less than ideal planting
conditions and less rainfall in 1989 compared to 1990.
Plant heights were greater in 1990 (311 cm) than in 1989 (176 cm) when combined
over all weed control treatments (Table 2). Increased height in 1990 may in
part be from an earlier planting date (10 days) and 15.3 cm greater seasonal
rainfall. No differences in plant height were detected between herbicide rates
within either trifluralin or metolachlor (Table 2).
Stalk yields were greater in 1990 (21.3 t/ha) than 1989 (5.2 t/ha) (Table 2).
An earlier planting date in 1990 (10 days) and greater seasonal rainfall
contributed to greater stalk yields. No differences in stalk yields were
detected between any of the weed control treatments indicating that rates of
trifluralin and metolachlor which decrease plant populations and plant height
did not significantly reduce stalk yields (Table 2).
Trifluralin and metolachlor provided excellent (>90%) weed control of
moderate weed populations. The herbicides did not induce visual injury or
reductions in stalk yields, though plant populations were adversely affected.
The moderate weed populations did not reduce stalk yields, but weed
interference did reduce kenaf heights and populations. Trifluralin and
metolachlor are promising for use in kenaf production. The probability of
expanding the registration label of these herbicides to include use in kenaf
remains a serious problem to overcome.
- Burnside, O.C. and J.H. Williams. 1968. Weed control methods for kinkaoil,
kenaf, and sunn crotalaria. Agron. J. 60:162-164.
- Hickman, M.V. and A.W. Scott. 1989. Preemergence herbicides for kenaf
production. Proc. Assoc. Adv. Indust. Crops. (Abstr.)
- Kurtz, M.E. and S.W. Neill. 1990. Possible herbicides for use in kenaf.
Proc. Second Annu. Int. Kenaf Assoc. Conf. (Abstr.)
- Orsenigo, J.R. 1964. Weed Control in kenaf. Proc. Int. Kenaf Conf.
- Snedecor, G.W. and W.G. Cochran. 1967. Statistical methods. 6th ed. Iowa
State University Press, Ames.
- White, G.A., D.G. Cummins, E.L. Whiteley, W.T. Fike, J.K. Greig, J.A. Martin,
G.B. Killinger, J.J. Higgins, and T.F. Clark. 1970. Cultural and harvesting
methods for kenaf. USDA Prod. Res. Rpt. 113.
- Williams, J.H. 1966. Influence of row spacing and nitrogen levels on dry
matter yields of kenaf (Hibiscus cannabinus L.). Agron. J. 58:166-168.
*I am indebted to David A. Iverson, Research Technician, Agricultural Research
Service, South Central Agricultural Research Laboratory, Lane, Oklahoma for
field plot work, data entry and data analysis.
Table 1. Influence of herbicide application on the percentage of grass
and broadleaf weed control in 1989 and 1990.
zMeans within each column followed by the same letters are not
significantly different at the 0.05 level using LSD.
| ||Weed control (%)|
| ||Grass ||Broadleaf|
|Herbicide treatment ||Rate (kg/ha) ||1989 ||1990 ||1989 ||1990|
|Trifluralin ||0.56 ||98az ||93b ||99a ||99a|
| ||1.12 ||99a ||95b ||98a ||99a|
| ||2.24 ||100a ||96b ||100a ||100a|
|Metolachlor ||0.56 ||99a ||70c ||99a ||98a|
| ||1.12 ||99a ||91b ||100a ||97a|
| ||2.24 ||100a ||96b ||100a ||100a|
|Weedy Check ||--- ||0b ||0d ||0b ||0b|
|Weed-Free ||--- ||100a ||100a ||100a ||100a|
Table 2. Influence of trifluralin and metolachlor on kenaf stand
establishment, heights, and stalk yields for 1989 and 1990.
|Plant pop. |
|Plant heights |
|Trifluralin ||0.56 ||116 ||245 ||13.6|
| ||1.12 ||137 ||240 ||13.7|
| ||2.24 ||115 ||235 ||13.2|
|Metolachlor ||0.56 ||134 ||251 ||13.6|
| ||1.12 ||117 ||248 ||13.1|
| ||2.24 ||117 ||253 ||13.5|
|Weedy Check ||--- ||124 ||232 ||12.2|
|Weed-Free ||--- ||154 ||247 ||13.3 |
|LSD (0.05) || ||26 ||12 ||NS|
|Across all herbicide treatments|
|1989 || ||107 ||176 ||5.2|
|1990 || ||147 ||311 ||21.3|
|LSD (0.05) || ||13 ||6 ||1.0|
Last update April 23, 1997