Weed management in common buckwheat
(Fagopyrum esculentum)
David A. Wall1,2 and Majorie A. H. Smith3
1Agriculture
Can. J. Plant Sci. Downloaded from cdnsciencepub.com by 181.43.242.46 on 09/10/21
For personal use only.
and Agri-Food Canada, Brandon Research Centre, P.O. Box 1000A, R.R. #3, Brandon, Manitoba,
Canada R7A 5Y3; 3Agriculture and Agri-Food Canada, Cereal Research Centre, 195 Dafoe Rd., Winnipeg,
Manitoba, Canada R3T 2M9. Received 30 September 1998, accepted 3 February 1999.
Wall, D. A. and Smith, M. A. H. 1999. Weed management in common buckwheat (Fagopyrum esculentum). Can. J. Plant Sci.
79: 455–461. There are currently no broadleaf herbicides registered in Canada for use in common buckwheat (Fagopyrum esculentum Moench.). Greenhouse and field studies were conducted from 1994 to 1997 at Morden and Brandon, Manitoba, to investigate potential herbicide treatments for buckwheat when cultural methods fail to control broadleaf weeds. Dose-response studies
conducted in the greenhouse showed that buckwheat tolerance to desmedipham was three to five times greater than that of volunteer canola (Brassica napus L. and B. rapa L.), lamb’s-quarters (Chenopodium album L.), redroot pigweed (Amaranthus
retroflexus L.) and wild mustard (Sinapis arvensis L.). A separate experiment showed that buckwheat cultivars did not differ in
tolerance to desmedipham. Another greenhouse study demonstrated that low dosages of bentazon caused severe injury in buckwheat. In field studies, 500 to 700 g a.i. ha–1 of desmedipham effectively suppressed the annual broadleaf weed biomass in buckwheat without reducing seed yields. At a low dosage of 300 g a.i. ha–1 of desmedipham there were no yield losses even though no
weed biomass reduction was evident. Imazamethabenz at 150 to 250 g a.i. ha–1 and metribuzin at 140 and 210 g a.i. ha–1 severely injured buckwheat and usually reduced yields. 2,4-D at 140 g a.i. ha–1 suppressed weed biomass, but caused severe injury and
often reduced buckwheat yield. At 70 g a.i. ha–1, 2,4-D suppressed weed growth as effectively as the higher dosage with less visual injury, but sometimes reduced buckwheat yields. Thus, desmedipham is the most promising postemergence broadleaf herbicide
for use in common buckwheat.
Key words: Common buckwheat, crop tolerance, dose response, weed management, yield
Wall, D. A. et Smith, M. A. H. 1999. Maîtrise des mauvaises herbes dans les cultures de sarrasin (Fagopyrum esculentum).
Can. J. Plant Sci. 79: 455–461. Il n’existe actuellement aucun herbicide antidicotylédones homologué pour le désherbage du sarrasin (Fagopyrum esculentum Moench.). Des expériences en serre et au champ ont été réalisées à Morden (Manitoba) de 1994 à
1997 pour examiner divers traitements herbicides pour cette culture advenant l’échec des méthodes culturales contre les mauvaises herbes dicotylédones. Des études dose-réponse menées en serre ont montré que la tolérance du sarrasin au desmédiphame était
3 à 5 fois plus forte que celle des repousses de canola (Brassica napus L. et B. rapa L.), du chénopode blanc (Chenopodium album
L.), de l’amarante à racine rouge (Amaranthus retroflexus L.) et de la moutarde des champs (Sinapis arvensis L.). Une expérience
distincte a permis de constater que les cultivars de sarrazin ne différaient pas quant au degré de tolérance au desmédiphame. Dans
une autre expérience en serre, on a constaté que même à faible dose, le bentazone endommageait gravement le sarrasin. Dans les
expériences au champ, le desmédiphame aux doses de 500 à 700 g m.a. ha–1 était efficace contre les dicotylédones annuelles dans
le sarrasin, sans réduire le rendement grainier de la culture. À la faible dose de 300 g m.a. ha–1, l’herbicide ne causait pas de perte
de rendement, même si l’on ne constatait aucune réduction de la biomasse adventice. L’imazaméthabenz à raison de 150 à 250 g
m.a. ha–1 et le métribuzin, de 140 et 210 g m.a. ha–1 provoquaient de graves endommagements au sarrasin et, habituellement, réduisaient son rendement. Le 2,4-D à la dose de 140 g m.a. ha–1 diminuait la biomasse adventice, mais au prix de graves dommages
et souvent de pertes de rendement pour le sarrasin. À la dose de 70 g m.a. ha–1, le 2,4-D inhibait la croissance des mauvaises herbes
aussi efficacement qu’à la dose supérieure sans laisser d’endommagement visible à la culture, bien que parfois le rendement était
touché. Il semble donc que le desmédiphame soit l’herbicide antidicotylédone de post-levée le plus intéressant pour le désherbage
des cultures de sarrasin.
Mots clés: Sarrasin, tolérance de la culture, dose-réponse, maîtrise des mauvaises herbes, rendement
In Canada, common buckwheat is grown primarily for
export to Japan to be used in noodle (soba) production. In
1995, 15 500 ha of buckwheat were grown in Canada, mostly in the province of Manitoba. Weed control has always
been a major problem in buckwheat production, and there
are currently no herbicides registered to control broadleaf
weeds in this crop. Only diclofop methyl, used to control
some annual grasses, is currently registered in Canada for
use in this crop (Manitoba Agriculture 1997). In Manitoba,
buckwheat producers frequently report that lamb’s-quarters,
redroot pigweed, wild mustard and volunteer canola are the
most troublesome weeds.
2Present
Abbreviations: GR50, herbicide dosage required to reduce
plant fresh and dry weight by 50%; WAT, wk after treatment
address: Agriculture and Agri-Food Canada,
Research Centre, 107 Science Place, Saskatoon,
Saskatchewan, Canada S7N 0X2.
455
Can. J. Plant Sci. Downloaded from cdnsciencepub.com by 181.43.242.46 on 09/10/21
For personal use only.
456
CANADIAN JOURNAL OF PLANT SCIENCE
Buckwheat is grown in solid stands, which precludes
inter-row cultivation as a cultural method of weed control.
Therefore, most producers rely on cultivation prior to seeding to destroy emerged weeds. Good seedbed preparation to
ensure rapid emergence and stand establishment assists in
controlling weeds since good stands of buckwheat compete
strongly and smother weeds (Campbell and Gubbels 1986).
When cultural weed control fails, producers often resort to
the use of a non-registered product to control broadleaf
weeds and rescue the crop.
Several herbicides registered for use in other crops that
may control broadleaf weeds in buckwheat have been identified. Desmedipham, a herbicide used in sugarbeet, has
shown the greatest potential to selectively control some
annual broadleaf weeds in buckwheat when applied at 500
to 1000 g a.i. ha–1 (Friesen and Campbell 1986; Friesen
1988). However, at the 1998 suggested retail price of $358
10 L–1 (150 g a.i. L–1), desmedipham is a relatively expensive herbicide when applied at these rates. In sugarbeets,
desmedipham is frequently applied only over the row in
combination with inter-row cultivation to reduce treatment
costs. When used as an overall treatment in buckwheat,
desmedipham may not be cost effective at dosages currently recommended for sugarbeets. Both 2,4-D and metribuzin
are broad-spectrum broadleaf herbicides registered for use
in a variety of crops. There are many anecdotal reports of
farmers using low dosages of 2,4-D (70 to 140 g a.i. ha–1) as
a low-cost option to control or suppress annual broadleaf
weeds in buckwheat. Wall (1996) showed that 2,4-D at
dosages of 76 to 151 g a.i. ha–1 always resulted in severe
foliar injury, but seed yields were not always reduced.
Similar results were obtained by Friesen and Campbell
(1986) when buckwheat was treated postemergence with
130 g a.i. ha–1 of metribuzin (approximately 62% of the recommended rate for lentil crops in Manitoba). Imazamethabenz is registered for wild mustard control in sunflowers
and some cereals. In drift simulation studies, Wall (1995a)
reported that buckwheat tolerated imazamethabenz dosages
up to 120 g a.i. ha–1 without yields being affected.
The objective of this research was to investigate the
potential of low dosages of desmedipham to selectively control annual broadleaf weeds in buckwheat. A further objective was to investigate the use of low dosages of 2,4-D,
bentazon, imazamethabenz, and metribuzin as potential
selective herbicides in buckwheat.
MATERIALS AND METHODS
Greenhouse Studies
DESMEDIPHAM DOSE-RESPONSE. A dose-response experiment
was conducted in the greenhouse to investigate the relative
tolerance of common buckwheat and four annual broadleaf
weed species to postemergence applications of
desmedipham. Mancan buckwheat, canola (B. napus ‘AC
Excel’), wild mustard, lamb’s-quarters and redroot pigweed
were seeded separately in 10-cm-diameter pots filled with a
mixture of soil:peat:sand:vermiculite (3:2:1:1). One week
after emergence, plants were thinned to three per pot.
Desmedipham was applied at 0, 125, 250, 375, 500, 625,
750, 1000, and 1250 g a.i. ha–1 when buckwheat and weeds
were in the two- to three-leaf stage. Herbicide treatments
were applied in a spray chamber (Model RC-5000-500EP
Agrochemical Research Sprayer, Mandel Scientific Co.
Ltd., Hanlon Business Park, 2 Admiral Place, R.R. #6,
Guelph, Ontario, Canada M9W 6N9) equipped with a flatfan (Teejet 8001EVS Tip, Spraying Sytems Co., Wheaton,
IL 60187, USA) nozzle delivering 200 L ha–1 of total solution at 207 kPa. The experimental design was a split-plot
with six replicates. Main and subplot effects were species
and herbicide dosage, respectively. Plants were harvested 3
WAT and total aboveground fresh and dry weights per pot
were determined. Plants were dried for 24–48 h at 60°C.
Data were subjected to analysis of variance (ANOVA) and
nonlinear regression. Where a significant dose response was
indicated by ANOVA (at P < 0.05), nonlinear regression
was used to describe the relationship between herbicide
dosage and plant response. Data were fitted to the following
nonlinear model:
Y = a + e(b + cX)
where a, b, and c are estimated nonlinear regression parameters and X is desmedipham dosage (g a.i. ha–1). Nonlinear
regression parameters were fitted to the data by a modified
Marquardt algorithm for least-square estimation of nonlinear parameters, using PRISMTM Scientific Graphics
Package V 1.0 (GraphPad Software, San Diego, CA). The
herbicide dosage required to reduce plant fresh and dry
weight by 50% (GR50) was calculated for each species. The
experiment was repeated once.
In a separate dose-response experiment, four cultivars of
common buckwheat were compared for their tolerance to
desmedipham. Cultivars Mancan, Manor, Manitoba and
BS87368 were seeded in 10-cm pots and treated with
desmedipham using the procedures and dosages described
previously. The experimental design was a split-plot with
six replicates. Main and subplot effects were cultivars and
herbicide dosages, respectively. Plants were harvested 3
WAT and total plant fresh and dry weight per pot were
determined. Data were analyzed by ANOVA and nonlinear
regression as previously described. The experiment was
repeated twice.
BENTAZON DOSE-RESPONSE. A dose-response experiment was
conducted in the greenhouse to investigate the tolerance of
common buckwheat to bentazon. Mancan buckwheat was
seeded in 10-cm-diameter pots as previously described and
thinned to three plants 1 wk after emergence. Bentazon was
applied at 0, 60, 120, 240, 360, 480, 600, 840, 1080 and
1320 g a.i. ha–1 when buckwheat was in the two- to threeleaf stage. The recommended dosage for use against lamb’squarters and redroot pigweed is 1080 g a.i. ha–1 (Manitoba
Agriculture 1997). Herbicide treatments were applied as
previously described. The experimental design was a randomized complete block with six replicates. Plants were
harvested 3 WAT and the total plant fresh and dry weights
per pot were determined. Data were analyzed by ANOVA
WALL AND SMITH — WEED MANAGEMENT IN COMMON BUCKWHEAT
457
Table 1. Significant dates relating to buckwheat crop growth and weed control
Morden
Event
Previous crop
Buckwheat seeding
Crop emergence
Herbicide application
Crop leaf stage
Weed leaf stagez
Weed sampling (WAT)
Buckwheat harvest
Can. J. Plant Sci. Downloaded from cdnsciencepub.com by 181.43.242.46 on 09/10/21
For personal use only.
zWild
yCrop
Brandon
1994
1995
1996
1997
1995
1996
1997
Flax
23 June
29 June
8 July
2
2–3
5
30 Sept.
Wheat
31 May
7 June
26 June
4
6
6
22 Sept.
Wheat
4 June
11 June
21 June
2
2–4
7
19 Sept.
Fallow
30 May
4 June
19 June
2
4–6
6
17 Sept.
Fallow
2 June
9 June
30 June
6
Cotyledon
7
–y
Fallow
10 June
17 June
28 June
3
2–4
6
26 Sept.
Wheat
24 June
2 July
14 July
3–4
2–4
4
24 Sept.
mustard, redroot pigweed and lamb’s-quarters were all at similar stages at herbicide application.
not harvested due to severe wind damage.
and nonlinear regression as previously described. The
experiment was repeated twice.
Field Studies
Field studies were conducted at the Agriculture and AgriFood Canada Research Centres at Morden (1994 to 1997)
and Brandon (1995 to 1997) in Manitoba, Canada. The soil
at the Morden site was a Neuhorst clay loam while at
Brandon it was an Assinaboine complex clay loam. The
crop grown in the previous year varied each year (Table 1).
The experiment site was fertilized as required and cultivated using a power harrow, then a diamond harrow. Wild
mustard, lamb’s-quarters and redroot pigweed were broadcast prior to cultivation to supplement the natural weed population and ensure adequate weed pressure. Mancan
buckwheat was seeded 3 cm deep at 55 kg ha–1 in late May
or June (Table 1) using a double disc press drill. At Morden,
row spacing was 18 cm in 2 by 8 m plots, and at Brandon,
row spacing was 25 cm in 2 by 5 m plots.
Experiments consisted of 10 herbicide treatments plus
weed-free (hand-weeded) and weedy checks, arranged in a
randomized complete block design with four replicates.
Herbicides were applied about 10–15 d after emergence of
buckwheat and weeds (Table 1), with a plot sprayer
equipped with flat-fan nozzles [Teejet 8002SS (Morden) or
XR8001 (Brandon) Tip, Spraying Systems Co., Wheaton,
IL 60187, USA], delivering 139 L ha–1 of total solution at
262 kPa at Morden and 100 L ha–1 at 207 kPa at Brandon.
Treatments consisted of 2,4-D amine at 70 and 140 g a.i.
ha–1, desmedipham at 300, 500 and 700 g a.i. ha–1, imazamethabenz at 150, 200 and 250 g a.i. ha–1 and metribuzin at
140 and 210 g a.i. ha–1. In 1994, desmedipham was applied
only at 500 and 700 g a.i. ha–1. At application, buckwheat
growth stage varied from two-leaf (10 cm) to six-leaf (35
cm), while wild mustard, redroot pigweed and lamb’s-quarters were usually at the two-leaf (2 cm) to four-leaf (3–5 cm)
stage (Table 1). Sethoxydim, when required, was applied at
250 g a.i. ha–1 to control annual grasses.
Crop injury was visually estimated at 2 and 4 WAT on a
0 to 100% scale, where 0 and 100% injury corresponded to
no visible effect and complete mortality. Injury levels higher than 15% were considered to be severe, since injury
above 15% almost always results in yield losses
(Anonymous 1992). Crop injury ratings were not recorded
at Brandon in 1995. Weed control was determined between
4 and 7 WAT (Table 1), depending on year and location, by
counting the number of surviving wild mustard, lamb’squarters and redroot pigweed plants in four randomly selected 0.25 m–2 quadrats in each plot. Total broadleaf weed dry
weight (g m–2) was also determined. Buckwheat was
swathed when 75% of the seeds had turned brown. After
drying, the buckwheat was mechanically harvested, seed
was dried to a uniform moisture content, cleaned and the
seed yield (g m–2) determined. Swathing and harvesting
were not possible at Brandon in 1995 because the buckwheat was severely wind damaged and crop yields could not
be determined.
Data from each trial were analyzed using ANOVA. Weed
counts and dry weights were transformed prior to analysis
using {square root (X + 0.5)}, and means were back transformed for presentation. Where treatment effects were significant according to ANOVA, means were separated at P =
0.05 by Duncan’s multiple range test.
RESULTS AND DISCUSSION
Greenhouse Studies
DESMEDIPHAM DOSE-RESPONSE. The experiments did not differ significantly according to ANOVA and the data were
therefore combined. Responses were similar for fresh and
dry weights, so only dry weight data are presented. Plant
species differed significantly in their responses, but the
interaction between species and herbicide dosage was also
significant; therefore, the response of each species was analyzed separately. Buckwheat dry weights were reduced as
desmedipham dosage increased, but the effect was less than
that observed in the other test species, as indicated by the
GR50s (Fig. 1). Wild mustard, lamb’s-quarters, and redroot
pigweed dry weights decreased rapidly with dosages up to
375 g a.i. ha–1. There was little change in plant weight with
further increases in desmedipham dosage. Canola response
to increasing dosage was intermediate to buckwheat and the
three weed species. The GR50 for buckwheat dry weight
response was 1005 g a.i. ha–1, approximately 3.1 times higher than the GR50 for canola, and 6.0 times higher than the
average for the three weed species (Fig. 1). The results of
this experiment suggests that there are sufficient differences
in tolerance to desmedipham between buckwheat and some
Can. J. Plant Sci. Downloaded from cdnsciencepub.com by 181.43.242.46 on 09/10/21
For personal use only.
458
CANADIAN JOURNAL OF PLANT SCIENCE
Fig. 1. Effect of desmedipham dosage on dry weight of common
buckwheat, GR50 = 1005 g a.i. ha–1; canola, GR50 = 329 g a.i. ha–1;
wild mustard, GR50 = 171 g a.i. ha–1; lamb’s-quarters, GR50 = 175
g a.i. ha–1; and redroot pigweed, GR50 = 155 g a.i. ha–1. Combined
data from two greenhouse experiments, 1995.
common weed species for this herbicide to be used for
selective weed control in this crop.
When tolerance to desmedipham was compared among
the four buckwheat cultivars, fresh weight differed significantly among cultivars in two of the three trials (P < 0.006).
Herbicide dosage was significant in all trials (P < 0.0001).
However, there were no significant interactions between
cultivars and herbicide dosage (P > 0.1). Similar results
were obtained when dry weights were analyzed (data not
presented). Therefore, there is no evidence that cultivars are
responding differently to desmedipham dosage.
BENTAZON DOSE-RESPONSE. Buckwheat was very sensitive to
bentazon under greenhouse conditions and plant fresh
weight decreased rapidly with increasing dosage (data not
presented). For buckwheat fresh weight, GR50 values for the
three experiments were 624, 316 and 383 g a.i. ha–1. Under
field conditions, Wall (1995b) reported that 600 g a.i. ha–1
of bentazon provided poor control of weeds in dry beans.
This dosage likely represents the minimum dosage that
would be required to control weeds in buckwheat under
field conditions. At this dosage, buckwheat fresh weight
was reduced by 48, 68, and 64% in the three experiments.
Based on the severe injury to buckwheat that occurred under
greenhouse conditions at the minimum dosage required for
weed control in the field, bentazon was not considered to be
a suitable candidate herbicide for field evaluation.
Field Studies
In all years of the study, the average temperature for the
May to September period (growing season) was within
0.7°C of the 30-yr (1961–1990) average of 16.5°C at
Morden and 15.4°C at Brandon. At Morden in 1994, May
and September mean temperatures were above normal, but
July and August were cooler than normal. In 1995, 1996 and
1997, temperature patterns over the growing season were
similar at Morden and Brandon. In all 3 yr, May was cooler
and June was warmer than normal, whereas temperatures
during the remainder of the growing season were near normal. Total rainfall at Morden over the growing season was
within 10% of the 30-yr average of 335 mm in all years
except in 1995 (39% higher). In 1995, June and July were
drier than normal but August received more than three times
the monthly average. At Brandon, total rainfall over the
growing season was 65, 84 and 62% of the 30-yr average of
312 mm in 1995, 1996 and 1997, respectively. In 1995 and
1996, July and August were both drier than average. At both
locations, the 1997 growing season was relatively dry
except for July, which received about twice the average
monthly rainfall.
Injury levels at 2 WAT were similar to those at 4 WAT in
all trials, except at Brandon in 1996, when all ratings at 2
WAT were twice those at 4 WAT. Therefore, only the ratings at 4 WAT are presented. For most treatments, injury
tended to be higher in 1994 and 1995 than 1996 and 1997 at
Morden (Table 2). Injury by desmedipham at 4 WAT was
generally acceptable except in 1994 and 1995 (highest
dosage only) at Morden, whereas injury by the other herbicides was generally severe in all trials (Table 2).
Desmedipham caused some leaf burn and necrosis around
the leaf margins and stunting, similar to that reported by
Friesen (1988). Although there were no significant differences in injury levels among dosages, there was a trend for
the severity of injury to increase with increasing dosage.
Metribuzin injury was more severe than injury from any
other treatment at Morden except in 1997 (Table 2).
Symptoms consisted of foliar chlorosis and necrosis and
severe stand reduction. Stand reductions were more severe
in 1994 than in other years. Injury by 2,4-D at 140 g a.i. ha–1
was severe, and greater than at 70 g a.i. ha–1 in all trials. 2,4D produced typical phenoxy injury symptoms including
severe stem epinasty, leaf cupping and adventitious root formation. Imazamethabenz injury was similar at the three
dosages (Table 2), and caused slight leaf chlorosis and stunting. Injury was severe in all trials except at Morden in 1996.
Weather conditions around the time of spraying may have
contributed to the lower levels of injury seen in 1996.
Imazamethabenz performs well under warm, dry conditions
(Manitoba Agriculture 1997). At Morden in 1996 cool, wet
conditions prevailed for several days after spraying. In
1997, 22 mm of rain was received several hours after spraying, and may have resulted in lower injury levels by both
imazamethabenz and metribuzin that year.
In most trials, populations of wild mustard and lamb’squarters were very low, with mean densities ranging from 0
to 11 and from 0 to 5 plants m–2, respectively, and control by
herbicide treatments could not be effectively evaluated (data
WALL AND SMITH — WEED MANAGEMENT IN COMMON BUCKWHEAT
459
Table 2. Visual injury (%) to common buckwheat by postemergence herbicides at 4 WAT
Can. J. Plant Sci. Downloaded from cdnsciencepub.com by 181.43.242.46 on 09/10/21
For personal use only.
Treatment
Weedy
Weed-free
2,4-D
2,4-D
Desmedipham
Desmedipham
Desmedipham
Imazamethabenz
Imazamethabenz
Imazamethabenz
Metribuzin
Metribuzin
CV (%)
Morden
Brandon
Dosage
(g a.i. ha–1)
1994
1995
70
140
300
500
700
150
200
250
140
210
0d
0d
16c
36b
–
16c
25bc
30b
26bc
29bc
74a
85a
0e
0e
28c
44b
8de
10de
19cd
25c
25c
28c
46b
69a
0d
0d
12bc
19b
5cd
6cd
7cd
10bcd
4cd
12bc
56a
56a
0f
0f
7de
15bc
4ef
6def
9cde
12bcd
18ab
23ab
15bc
23ab
0d
0d
15c
31a
1d
4d
4d
25b
35a
35a
15c
16c
0c
1c
1c
31a
0c
0c
0c
25b
26ab
31a
21b
23b
27
38
37
38
26
29
1996
1997
1996
1997
a–fMeans within columns followed by a common letter are not significantly different according to Duncan’s multiple range test at P = 0.05.
not presented). Wild mustard was controlled by herbicides
only at Morden in 1994, when all treatments reduced density of this weed (0–2 plants m–2 compared to 24 plants m–2 for
the weedy check). Wild mustard densities were moderate to
high in 1997 at Morden (26–55 plants m–2), and no treatment
was effective. Densities of lamb’s-quarters were high only at
Brandon in 1995, and were controlled by metribuzin and 140
g a.i. ha–1 of 2,4-D. Redroot pigweed populations were moderate to heavy in all trials (Table 3), except at Morden in
1995 (0–7 plants m–2; data not presented), but no herbicide
consistently controlled its density. Redroot pigweed was
controlled by desmedipham and metribuzin in 1994 at
Morden and in 1997 at Brandon, and by 2,4-D in 1996 (140
g a.i. ha–1 only) and 1997 at Brandon (Table 3).
In this study, the higher densities of redroot pigweed
compared to wild mustard and lamb’s-quarters may have
been a result of the relative ability of these three weeds to
compete for light as the buckwheat stand developed. Wild
mustard grows mainly in habitats with a high light intensity
(Mulligan and Bailey 1975), and shading inhibits the germination of lamb’s-quarters (Basset and Crompton 1978).
Redroot pigweed, on the other hand, germinates at high temperatures throughout the season regardless of light level
(Weaver and McWilliams 1980) and would not have been
inhibited by the buckwheat canopy to the same extent.
Total broadleaf weed biomass was significantly reduced
by 2,4-D at 140 g a.i. ha–1 in three of the seven trials and by
desmedipham at 500 and 700 g a.i. ha–1 in four trials.
Metribuzin at 210 g a.i. ha–1 reduced weed dry weight in
1994 and 1997 at Morden (Table 3), but was otherwise not
effective in suppressing weed biomass. Imazamethabenz did
not reduce weed dry weight except at the highest dosage in
one trial. In fact, dry weights were significantly higher than
in the weedy checks at Brandon in 1996 and 1997 (Table 3).
Severe buckwheat injury and stand reductions likely
allowed these weed populations to increase, indicating the
extent to which good stands of untreated buckwheat can
smother weed growth (Campbell and Gubbels 1986).
This study indicates that, even though weed densities are
not controlled, 140 g a.i. ha–1 of 2,4-D and 500 and 700 g
a.i. ha–1 of desmedipham can effectively suppress total
broadleaf weed biomass. Weed densities of the three weed
species fluctuated widely among years and between locations, while total weed dry weights were more consistent.
However, specific comparisons of weed densities and biomass cannot be made because dry weights included the total
of all broadleaf weeds, but densities were recorded only for
the three most commonly reported weed species in buckwheat.
Treatment differences in buckwheat seed yields were significant in all trials. However, due to the amount of variation
among plots, yields in many herbicide treatments did not
differ from either the weed-free or the weedy check
(Table 4). There was a general consistency among trials in
the effects of desmedipham and imazamethabenz on buckwheat seed yield, while the effect of 2,4-D and metribuzin
on yield varied considerably among trials.
Crop yield in plots treated with desmedipham at all three
dosages were equal to or better than that of any other herbicide treatment (Table 4). Desmedipham treated plots outyielded imazamethabenz treated plots in four of six trials,
and plots treated with metribuzin and the higher dosage of
2,4-D in three of six trials. Buckwheat yield losses due to
desmedipham were significant only in 1994 at Morden.
While desmedipham provided good weed control in 1994,
lower yields may reflect sustained effects of early season
injury. The 1994 test was seeded late in the season and this
may have reduced yield potentials due to the limited time
available for crop recovery, particularly with the cool temperatures in July and August that year.
Buckwheat treated with imazamethabenz generally sustained high yield losses at all dosages (Table 4). At Morden
in 1996 and 1997, when imazamethabenz injury was relatively low, buckwheat yields did not differ from the weedfree check for two of the three dosages. Buckwheat yields
were significantly lower than the weedy check in the four
trials where injury was severe. These high yield losses are
likely due to reduced competitive ability, which resulted in
the higher weed biomass observed in these trials.
31
51
38
30
33
52
39
26
25
41
23
19
38
transformed prior to analysis using a square root transformation {sqrt(X + 0.5)}.
a–fMeans within columns followed by a common letter are not significantly different according to Duncan’s multiple range test at P = 0.05.
70
140
300
500
700
150
200
250
140
210
CV (%)
zData
16ab
7b
1c
0b
21ab
7b
9bc
2b
12abc
7b
9bc
3b
11bc
3b
33ab
68a
30ab 102a
43a
51a
22ab
8b
25ab
13b
52ab 129a
0e
0e
21bcd 50bcd
19cd
30cd
13cd
72abc
9de
50bcd
12cd
20d
37abc 73abc
35abc 84ab
37abc 54bcd
72a
70abc
65a
59bcd
6ab
0c
2abc
3abc
2abc
1bc
1bc
6ab
10a
7ab
10a
6ab
55ab
0e
3de
7de
–
1de
1de
65a
52ab
32abc
28bc
11cd
91bc
0f
41d
26de
57cd
11e
11e
108ab
168a
121ab
44d
38d
17bcd
0f
19bcd
6e
22bcd
10de
11cde
24abc
30ab
40a
15bcde
21bcd
90ab
0c
91ab
56b
52b
43b
43b
115ab
173a
151ab
65ab
60ab
23a
0b
34a
31a
27a
36a
22a
27a
28a
33a
33a
18a
25bcd
0e
24bcd
24bcd
14d
18cd
26bcd
25bcd
30bc
31bc
54a
34b
19ab
0d
16bc
15bc
–
2d
1d
37a
20ab
21ab
6cd
2d
Weedy
Weed-free
2,4-D
2,4-D
Desmedipham
Desmedipham
Desmedipham
Imazamethabenz
Imazamethabenz
Imazamethabenz
Metribuzin
Metribuzin
Brandon
1996
1996
1995
1996
1996
Treatment
Dosage
(g a.i. ha–1)
1994
Morden
1997
1995
Brandon
1997
1994
Morden
1997
1995
Total weed dry weight (g m–2)z
Redroot pigweed density (plants m–2)z
Table 3. Effect of herbicide treatment on redroot pigweed density and total broadleaf weed dry weight
Can. J. Plant Sci. Downloaded from cdnsciencepub.com by 181.43.242.46 on 09/10/21
For personal use only.
22cd
0f
14de
10de
12de
3ef
3ef
35bc
84a
52b
16cd
19cd
CANADIAN JOURNAL OF PLANT SCIENCE
1997
460
Plots treated with 2,4-D at 70 g a.i. ha–1 yielded as well as
the weed-free check in four of six trials (Table 4). In comparison, plots treated with 2,4-D at 140 g a.i. ha–1 tended not
to yield as well, and yielded significantly less in two trials.
In some trials, yields of buckwheat treated with 2,4-D at 70
or 140 g a.i. ha–1 were less than the weedy check. Reduced
seed yields were commonly associated with severe injury
from 2,4-D applications, but severe injury was not always a
predictor of yield reductions. In 1994, 2,4-D caused severe
injury, but the lower dosage did not reduce seed yields. Wall
(1996) noted that environmental conditions at the time of
and following spraying is an important factor in the ability
of buckwheat to recover from severe injury.
Metribuzin yielded equal to desmedipham in three trials,
but severely reduced yields in 1994 and in 1996 (210 g a.i.
ha–1 only) at Morden (Table 4). The yield losses can be
attributed to the severe injury and stand reduction in 1994
and to both severe injury and lack of weed control in 1996.
However, metribuzin-treated buckwheat sustained severe
injury in 1995 without significant yield loss, while the lower
dosage reduced yields in 1996 at Brandon even though
injury was relatively low. Weather factors at and just after
application are known to influence the effectiveness of
metribuzin (Manitoba Agriculture 1997) and may help to
explain some of these differences. Freeman (1982) found
that metribuzin injury in potatoes was related to temperature
and the amount of sunshine just before, during, and just after
the time of spraying, and that weather during the rest of the
season affected recovery from injury.
When left untreated, moderate to heavy broadleaf weed
populations can affect buckwheat yields, justifying the need
for control measures. Comparison of the untreated check
plots among trials showed that yield loss was associated
with broadleaf weed biomass (Tables 3 and 4). Yield losses
in the weedy checks, relative to the weed-free checks,
ranged from 20 to 40% at Morden in 1994, 1996 and 1997,
when weed dry weights were more than 50 g m–2. When
weed dry weights were less than 22 g m–2, weeds had no
competitive effect on crop yields. Neither metribuzin nor
imazamethabenz can be recommended as candidates for
selective broadleaf weed control in buckwheat because they
cause severe injury to the crop and can seriously affect
yields. At 140 g a.i. ha–1, 2,4-D usually provided good suppression of weed growth, but severely injured buckwheat
and often reduced yields. Although 2,4-D at 70 g a.i. ha–1
suppressed weed growth almost as effectively as the higher
dosage with less buckwheat injury, yield losses were still
significant in two of the six trials. At 300 and 500 g a.i. ha–1,
desmedipham caused an acceptable level of injury to buckwheat, and yields were similar at the two dosages, even
though the lowest dosage did not suppress weed biomass as
well. Friesen (1988) found that 500 g a.i. ha–1 of
desmedipham, when applied at the four-leaf stage of buckwheat, selectively controlled wild mustard without crop
yield losses. This study showed that desmedipham at 500 g
a.i. ha–1 effectively suppressed moderate to heavy broadleaf
weed infestations, and suggests that this herbicide may
reduce redroot pigweed densities. Desmedipham remains
WALL AND SMITH — WEED MANAGEMENT IN COMMON BUCKWHEAT
461
Table 4. Effect of herbicide treatment on buckwheat seed yield (g m–2)
Can. J. Plant Sci. Downloaded from cdnsciencepub.com by 181.43.242.46 on 09/10/21
For personal use only.
Treatment
Weedy
Weed-free
2,4-D
2,4-D
Desmedipham
Desmedipham
Desmedipham
Imazamethabenz
Imazamethabenz
Imazamethabenz
Metribuzin
Metribuzin
CV (%)
Brandonz
Morden
Dosage
(g a.i. ha–1)
1994
1995
1996
1997
1996
1997
70
140
300
500
700
150
200
250
140
210
184b
230a
203ab
171b
–
185b
186b
104c
118c
105c
99c
58d
164ab
209a
162ab
112c
203a
189ab
189ab
155b
111c
108c
183ab
168ab
108cde
180a
126bcd
131abcd
133abcd
136abcd
161ab
128bcd
157abc
146abcd
100de
63e
83c
141ab
143a
129abc
107abc
106abc
149a
94bc
96bc
85c
130abc
127abc
116a
116a
77cd
54e
113ab
97ab
110ab
73d
61de
53e
93bc
94abc
156bcd
162bc
152cd
135d
188a
195a
180ab
110e
104e
101e
147cd
137cd
15
8
23
25
7
12
zCrop
not harvested in 1995 due to severe wind damaged.
a–dMeans within columns followed by a common letter are not significantly different according to Duncan’s multiple range test at P = 0.05.
the most promising postemergence treatment evaluated both
in terms of effectiveness and crop safety.
ACKNOWLEDGMENT
D.A. Wall wishes to acknowledge the technical support of
Abe Fehr and Desiree Czerkawski.
Anonymous. 1992. Herbicide and plant regulator field trials.
Pages 51–82 in Manual for field trials in plant protection. 3rd ed.
Plant Protection Division, Ciba-Geigy Ltd., Basle, Switzerland.
Bassett, I. J. and Crompton, C. W. 1978. The biology of
Canadian weeds. 32. Chenopodium album. L. Can. J. Plant Sci. 58:
1061–1072.
Campbell, C. G. and Gubbels, G. H. 1986. Growing buckwheat.
Agric. Can. Techn. Bull. 1986-7E, Ottawa, ON. 8 pp.
Freeman, J. A. 1982. The influence of weather on the response of
potato cultivars to metribuzin. J. Am. Soc. Hortic. Sci. 107:
189–194.
Friesen, G. H. 1988. Wild mustard, Sinapis arvensis, control in
common buckwheat, Fagopyrum esculentum, with desmedipham
and fluorochloridone. Weed Technol. 2: 175–178.
Friesen, G. H. and Campbell, C. G. 1986. Common buckwheat
(Fagopyrum esculentum) tolerance to herbicides. Weed Sci. 34:
435–439.
Manitoba Agriculture. 1997. Guide to crop protection 1997.
Manitoba Agriculture, Carman, MB. 254 pp.
Mulligan, G. A. and Bailey, L. G. 1975. The biology of Canadian
weeds. 8. Sinapis arvensis L. Can. J. Plant Sci. 55: 171–183.
Wall, D. A. 1995a. Response of four annual broadleaf crops to
simulated imazamethabenz spray drift. Can. J. Plant Sci. 75:
751–757.
Wall, D.A. 1995b. Bentazon tank-mixtures for improved redroot
pigweed (Amaranthus retroflexus) and common lambsquarters
(Chenopodium album) control in navy beans (Phaseolus vulgaris).
Weed Technol. 9: 610–616.
Wall, D. A. 1996. Effect of sublethal dosages of 2,4-D on annual
broadleaf crops. Can. J. Plant Sci. 76: 179–185.
Weaver, S. E. and McWilliams, E. L. 1980. The biology of
Canadian weeds. 44. Amaranthus retroflexus L., A. powellii S.
Wats. and A. hybridus L. Can. J. Plant Sci. 60: 1215–1234.
