Weed Control in Kenaf
Mark E. Kurtz
Moderate yield reductions in kenaf have been reported from weed
competition (3, 10) without mention of species. Significant
reductions in kenaf yields (75 to 85%) from common cocklebur
(Xanthium strumarium L.) competition have also been reported (6,
7). Even though several studies have been conducted to evaluate
chemical weed control in kenaf (1, 2, 3, 4, 5) information is
still quite limited.
Research conducted using herbicides applied prior to emergence
of kenaf and weeds demonstrated that trifluralin (Treflan*),
chloramben (Amiben*), monuron (Monuron TCA*), diuron (Karmex*),
and mecoprop (Vipex*) gave acceptable results in kenaf (1, 2, 3)
unlike fluordifen (Preforan*) where kenaf injury was noted (2,
4). The herbicide oxadiazon (Ronstar*) tankmixed with Karmex
was not safe for use in kenaf nor was the high rate of nitrofen
(TOK*) or EPTC (Eptam*) (4). White et al. (9) reported that
propachlor (Ramrod*) was safe for use in kenaf.
There is a need for the evaluation of newer classes of
herbicides for use in kenaf. Kurtz and Neill (6) evaluated 14
herbicides registered for use in either cotton, soybeans, or milo
for kenaf tolerance. Metribuzin (Sencor*, imazaquin (Scepter*),
chlorimuron + metribuzin (Canopy*), atrazine (AAtrex*) and
imazethapyr (Pursuit*) all reduced kenaf height below that of
untreated kenaf and reduced yield significantly. In light of
some of the early research, it is imperative that studies be
conducted to elucidate the selectivity of herbicides (currently
registered for use in the United States) to kenaf.
Results
Preemergence
An experiment with preemergence herbicides was conducted and the
herbicides AAtrex, Canopy, Scepter, Command*, Karmex, Sencor, and
Bladex×reduced kenaf population below that of the untreated. The
same herbicides, in addition to Zorial* and Cotoran* all caused
kenaf phytotoxicity. However, not all of the treatments that
reduced stand or increased phytotoxicity, reduced yield.
Cotoran did not reduce stand, did increase phytotoxicity, and
did reduce yield. Zorial increased phytotoxicity but didn't
decrease stand or yield. Bladex and Scepter increased
phytotoxicity and reduced stand but didn't reduce yield.
Sonalan*, Pursuit, Prowl*, Dual*, and Lasso* did not reduce
stand, increase phytotoxicity, or reduce yield. Sencor, Karmex,
Command, Canopy, and AAtrex all increased phytotoxicity, reduced
stand, and reduced yield.
How can an herbicide reduce stand and not reduce yield?
Kenaf has an ability to adjust its stalk size to accommodate the
area available for its given population. If the population is
high, kenaf produces slender stalks. If the population is low,
kenaf produces stalks with a larger diameter. This effect will
sometimes make up for the weight lost by the death of surrounding
plants; however, one cannot depend on this happening in every
case. At this point in kenaf research, if data suggest that a
given herbicide causes kenaf phytotoxicity and stand reduction,
this herbicide should not be considered for use until all aspects
of herbicide rate, placement, and timing have been fully
investigated. Of the preemergence herbicides tested, those used
for grass control seem to be the safest to use in kenaf.
However, until these herbicides are registered for use in kenaf
in Mississippi it is not legal to use any of these mentioned in
this article.
Postemergence
In 1989 and 1990, experiments were conducted to evaluate
cotylodonary kenaf tolerance to Bueno6*, Basagran*, Scepter,
Pursuit, Cadre*, Blazer*, Cobra*, Reflex*, Fusilade*, Poast*,
Assure*, Select*, Classic*, Ally*, and Oust*. From these studies,
only Bueno6, Fusilade, Poast, Assure, and Select could be used
without kenaf injury in both years. This injury was expressed as
reduced height and dead tissue (necrosis) both years.
Bueno6, Basagran, Scepter, Pursuit, Cadre, Blazer, Cobra, Reflex, and Classic were evaluated both years for their effects on 14inch kenaf. In 1989, at the 7 DAT (days after treatment) rating, all herbicides caused injury. By 16 DAT, kenaf injury persisted for all treatments except Bueno6 and Basagran. In
1990 only the Bueno6 treatment was noninjurious at the early
rating (8 DAT), but at 34 DAT, neither Bueno6 and Basagran
showed any signs of injury. All treatments, with the exception
of Bueno6, caused height reduction both years.
It is apparent that kenaf tolerates the selective herbicides
(Bueno6, Fusilade, Poast, Assure, and Select) in a similar
fashion as other broadleaf crops. Basagran, Scepter, Pursuit,
Cadre, Blazer, Cobra, Reflex, Classic, Ally and Oust applied
broadcast postemergenceoverthetop (POT) are too injurious to
be considered for use in kenaf. However, application as
postdirected sprays should be considered.
From this work Bueno6 and Fusilade have been registered for
use in kenaf in Mississippi under 24C special local needs registration.
In 1991 another experiment was conducted to evaluate Poast and
Assure II at two rates and three timings. Timings were
cotylodonary, 2-leaf kenaf, and two weeks later. Bueno-6 (2.0
lb/A) was applied to 3-inch kenaf over-the-top and separate
treatments to 3-inch kenaf followed by another treatment 1-3
weeks later. We also looked at the insecticides Orthene and
Asana XL on 1-2 leaf kenaf at two rates and then reapplied the
treatments every 10 days until five applications were made at
each rate. Initially, Bueno-6 caused some blotching but this
disappeared rapidly. No treatment reduced stand, height, or
yield.
This test led us to feel confident with the application of Poast,
Assure II, orthene, and Asana XL on kenaf. If these chemicals
are registered in kenaf there will be a wide margin of safety.
Because of the need for herbicides to control broadleaf weeds in
kenaf, we continued our efforts looking at Cobra, Goal*, Karmex,
Lorox*, Bladex, Basagran, Scepter, Cadre, and Pursuit. Many of
these herbicides have been proven to injure kenaf when applied
POT.
Post-Directed
Two experiments were conducted in 1992 to evaluate the
previously listed herbicides as postdirected sprays. Each was
tankmixed with Bueno6 for a broader spectrum of weed control.
Results concerning injury were somewhat variable; however, at no
time was injury above 26%. At the Delta Branch Experiment
Station, only Goal + Bueno6 caused injury greater than the
control.
At Vance, MS, Karmex, Lorox, Bladex, and Scepter all had some form of injury symptoms. Karmex and Bladex showed a whitening effect on the leaves. This was due to the herbicide being taken up from the soil by kenaf roots. These symptoms soon went away. Scepter injury was evidenced as pronounced shortening
of kenaf plants and lasted season long. Lorox caused necrosis of
leaf tissue preceded by chlorosis. Only Scepter resulted in yield
reduction in both tests.
Bueno6 is registered for use in Mississippi as a postdirected
spray.
Cobra, Goal, Bladex, or Basagran each look promising for
postdirected use in kenaf.
In 1993, the following herbicides were evaluated as postdirected sprays: Bladex (0.8, 1.06, 1.6 lb ai/A), Blazer (0.375, 0.5, 0.75 lb ai/A), Caparol (0.5, 0.65, 1.0 lb ai/A, Cobra (0.2, 0.26, 0.4 lb ai/A), Cotoran (1.0, 1.33, 2.0 lb
ai/A, Karmex (0.6, 0.8, 1.2 lb ai/A), and Reflex (0.375, 0.5, 0.75 lb ai/A). All treatments were mixed with X77 at 0.25% v/v, and sprays were directed toward the base of 8inch kenaf. Minor plant injury symptoms were expressed as necrotic lesions on leaves. Yield was not affected.
Herbicide Carryover
Trials were conducted in 1991 and 1992 on a silty clay loam and a Sharkey clay soil to evaluate possible herbicide carryover problems to the kenaf crop. Results are shown in Tables 1 and 2. Zorial, Scepter, Pursuit, Command, Karmex, Cotoran, and Bladex were evaluated on each soil at two rates. Herbicides were
applied in a fallowed area in 1991 on the silty clay loam soil
and in soybeans on the Sharkey clay. Kenaf was planted to these
areas in 1992.
The higher rate of Karmex reduced stand on the silty clay loam
and the high rate of Command lowered stands on the Sharkey clay.
The high rate of Zorial, Scepter, Pursuit, and Cotoran reduced
kenaf height on the Sharkey clay. The high rates of Scepter
reduced height on the silty clay loam.
In 1992, Scepter carryover damage was noted in a farmer's field
at Vance, MS. Scepter had been used in soybeans the previous
growing season. Kenaf emerged and grew to about 812 inches tall
and stayed there for several weeks without growing. This type of
injury is critical because of the early growth potential of kenaf
that is lost. When rotating crops, one should be careful not to
rotate kenaf into a field that has been treated with Scepter the
previous growing season until this problem can be further
investigated. No yield reductions occurred on the silty clay
loam.
Control of Kenaf
Another experiment was set up to look at controlling kenaf when it becomes a weed in a soybean crop. This probably will not be a problem except under the following conditions. (1) If kenaf is planted in one field and unusually heavy rainfall occurs, kenaf seeds can be washed into adjacent fields carried by run
off water. (2) If planters are not cleaned out carefully kenaf seed can be planted in fields where they are not supposed to be planted. Kenaf seed will probably not survive in the soil to a point of being a problem the following year. However, if kenaf is left standing in the field over winter, seed can be knocked to the ground during a spring harvest and there is a potential for a
kenaf weed problem. Seed viability studies need to be conducted
to shed more light on this problem.
The following preemergence herbicides were evaluated for kenaf control in soybeans: Canopy, Command, Sencor, Scepter, and Zorial. When kenaf control was averaged across two soil types and two rating dates, only Canopy, Sencor, and Scepter proved to be effective. Canopy and Sencor treatments will do a good job
at the recommended rate according to soil type, but if you feel
like you are going to have kenaf as a problem weed, don't cut
rates.
Postemergence studies were also conducted evaluating Basagran, Blazer, Classic, Cobra, Pursuit, Reflex, and Scepter at labeled rates for soybeans. Blazer, Reflex, and Cobra were the best treatments on the Sharkey clay followed by Classic, Scepter, and Pursuit. Basagran was the weakest but was the safest of
these herbicides in the kenaf tolerance studies. Of the seven
chemicals tested, Blazer, Cobra, and Reflex would be the best
postemergence chemicals to control kenaf in soybeans.
Several herbicides tested have shown much promise for use in
kenaf in a variety of use applications.
However, as we go to print with this article, only Treflan or
Trilin are registered for use PPI, and Bueno6 or Fusilade 2,000
are registered for use postemergence for weed control in kenaf in
Mississippi.
References
1. Burnside, O.C., and J. H. Wilburn. 1968. Weed control methods kenka oil, kenaf, and sun crotalaria. Agron. J. 60:162164.
2. Dean, M.L., and C. Parker. 1971. The preemergence selectivity of some recently developed herbicides in jute, kenaf, and sesame, and their activity against Oxalis latifolia. Tech. Rep., A.R.C. Weed Res. Organ. No. 19, 24 p.
3. Fageiry, K.A. 1985. Chemical weed control in kenaf, Hibiscus cannabinus L. in Central Sudan. Trop. Pest Manage. 31:2729.
4. Fageiry, K.A. 1978. Effect of some herbicides on weed control and yield of kenaf. Ann. Rep. of Kenana Res. Stn., Sudan.
5. Kurtz, M.E., and S.W. Neill. 1990. Kenaf tolerance to herbicides. Proc. South. Weed Sci. Soc. 43:32.
6. Kurtz, M.E., and S.W. Neill. 1990. Tolerance of kenaf to selected herbicides applied preemergence and postemergence. MAFES Info. Sheet 1325.
7. Kurtz, M.E., and S.W. Neill. 1991. Effects of common cocklebur (Xanthium strumarium) competition of kenaf (Hibiscus cannabinus) yield. Proc. South. Weed Sci. Soc. 44:149.
8. Kurtz, M.E. and S.W. Neill. 1992. Tolerance of kenaf to selected postemergence herbicides. Weed Tech. 6:125128.
9. White, G.A., D.G. Cummires, E.L. Whiteley, W.T. Fike, J. K. Grieg, J.A. Martin, G.B. Killinger, J.J. Higgins, and T. F. Clark. 1970. Cultural and harvesting methods for kenaf: an annual crop source of pulp in the Southeast. ARS, USDA Production Res. Rep. 113.
10. Williams, J.H. 1966. Influence of row spacing and nitrogen
levels on dry matter yields of kenaf. Agron. J. 58:166168.
Table 1. Herbicide carryover in kenaf on a silty clay loam.
Treatment Rate Stand Phyto Height Yield
lb/A plant/10ft % ft Ton/A
Zorial 1.000 55 0 3.08 4.5
Zorial 2.000 53 0 3.35 4.9
Scepter 0.125 57 15 2.90 4.4
Scepter 0.250 45 45 2.20 4.0
Pursuit 0.094 50 21 3.10 4.8
Pursuit 0.188 46 3 2.80 4.9
Command 1.250 59 0 3.28 4.4
Command 2.500 58 0 3.55 5.2
Karmex 1.600 56 0 3.25 4.6
Karmex 3.200 41 0 3.67 5.4
Cotoran 1.500 55 0 3.63 5.3
Cotoran 3.000 55 0 3.65 4.4
Bladex 1.200 62 0 3.32 5.0
Bladex 2.400 54 0 3.08 4.6
Untreated 58 0 3.40 4.4
LSD (.05)1 17 22 0.77 1.0
1For comparison of any two means within a column.
Table 2. Herbicide carryover in kenaf on a Sharkey clay.
Kenaf (19911992)
Treatment Rate Stand Height Yield1
lb/A Plant/10ft ft ton/A
Zorial 1.000 55 3.0 1.9
Zorial 2.000 53 2.7 1.5
Scepter 0.125 57 3.2 2.1
Scepter 0.250 45 2.6 1.6
Pursuit 0.094 50 2.8 1.9
Pursuit 0.188 46 2.7 1.6
Command 1.250 59 3.5 3.1
Command 2.500 58 3.0 2.9
Karmex 1.600 56 3.0 1.6
Karmex 3.200 41 2.9 2.1
Cotoran 1.500 55 3.2 2.3
Cotoran 3.000 55 2.7 1.3
Bladex 1.200 62 2.9 2.0
Bladex 2.400 54 3.2 2.0
Untreated 58 3.4 2.1
LSD (0.05)1 17 0.7 1.1
1For comparison of any two means within a column.
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Mark Kurtz is a Plant Physiologist, Delta Branch Experiment Station, Stoneville, MS.