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Effectiveness of selective herbicides for the control of annual weed species in lathyrus (Lathyrus sativus L.)
496
I
Effectiveness of selective herbicides for the control of annual weed species in lathyrus (Lathyrus sa tivus L. )
|
D. A. Wall* and G. H. Friesen Agriculture Canada, Research Station, PO Box 3001, Morden, Manitoba, ROG 1JO,Canada
Abstract
Field research was conducted over a four-year period, 1987-1990, to evaluate the efficacy and selectivity of trifluralin, metribuzin, cyanazine, bentazone, imazethapyr and several formulations of MCPA in lathyrus (Lathyrus sativus L.). Lathyrus exhibited satisfactory tolerance to trifluralin applied pre-planting soil incorporated and to postemergence applications of bentazone and imazethapyr. Lathyrus tolerated both pre-planting soil-incorporated and postemergence applications ofmetribuzin in dry years, but was injured by this herbicide in years with adequate precipitation. Tank mixtures of metribuzin or cyanazine with sethoxydim plus surfactant markedly increased the phytotoxicity of these herbicides to lathyrus. Lathyrus was sensitive to all formulations of MCPA and phytotoxicity increased with the addition ofsethoxydim plus surfactant to the spray mixture.
Keywords Lathyrus; Lathyrus sativus L.; MCPA; metribuzin; tolerance; environment; adjuvants
Introduction Lathyrus is currently under evaluation by Agriculture Canada as an annual grain legume for the prairie provinces of Western Canada. This crop is of interest to prairie farmers as an alternate to traditional cereal grains owing to its ability to produce high yields under a wide range of environmental conditions, from excess moisture to drought (Jackson and Yumus, 1984; Smartt, 1984). Its development as a commercial crop would enable farmers in drought-prone regions to incorporate a legume into their crop rotations. This practice has not previously been successful owing to the poor performance of currently recommended pulse crops in regions with low annual precipitation. The acceptance of lathyrus as a new commercial crop may be limited by the lack of registered herbicides for the control of annual weed species in this crop. Lathryus is highly susceptible to weed competition and a clean seed-bed is essential for successful production of this crop (Silsbury, 1975). Wall, Friesen and Dryden (1988) reported that lathyrus seed yields were reduced by 54-95% when annual grasses and broad-leaved weeds were not controlled. Attempts to introduce new crops to prairie grain farmers often fail, owing to the noncompetitiveness of new crops and/or the lack of weed control recommendations, including registered products. Trifluralin and metribuzin have been identified as promising herbicides for the control of annual broad-leaved weeds in lathyrus (Wall et aL, 1988). These herbicides are applied regularly to other pulse crops grown in Western Canada (lentils and field peas) and are thus products with which producers already have considerable experience. *To whom correspondence should be addressed 0261-2194/91/06/0496-05 © 1991 Butterworth-Heinemann Ltd
Wall et al. (1988) reported that lathyrus tolerated 2.2 kg a.i. ha- ~of trifluralin, twice the maximum recommended rate for pulse crops in Manitoba (Anonymous, 1990). A satisfactory safety margin has, however, not yet been established for metribuzin. The objective of the research reported here was to evaluate the performance, in iathyrus, of herbicides currently registered for use on larger-acreage crops grown in Western Canada, and to provide data to support the registration and recommendation of suitable herbicides when commercial lathyrus cultivars become available to farmers.
Materials and methods Field experiments were conducted at the Agriculture Canada Research Station, Morden, Manitoba, from 1987 to 1990. The experimental site was located on land which had been summer-fallowed each year before cropping. The soil type was a sandy loam (73% sand, 10% silt, 17%oclay and 4% organic matter). Lathyrus was sown with a double-disc press drill at 80kg h a - i in rows 30cm apart and at a depth of 5 cm. Field plot size was 2 x 8 m. All experiments were conducted as randomized complete block designs with four replicates. Seed yields were determined by harvesting the entire plot area (16m 2) with a self-propelled plot combine, drying the seed to a uniform moisture content (14°,/o) and weighing the seed.
Weed control in lathyrus with selective herbicides The efficacy and selectivity of pre-planting soil-incorporated (PPI) applications of trifluralin, metribuzin and
Herbicide efficacy in lathyrus: D. A. Wall and G. H. Friesen
497
Table 1. Monthly and 30-year mean precipitation and mean air temperatures recorded at Morden, Manitoba, 1987-1990
Precipitation(mm)
Daily mean temperature(*C)
Month
30-yearaverage
1987
1988
1989
1990
30-yearaverage
1987
1988
1989
1990
April May June July August Total
41.4 66.3 75.8 73.2 71.1 327.8
0.4 47.2 63.2 148.0 64.2 323.0
0.0 21.4 43.0 42.8 20.8 128.0
2 ! .2 46.8 97.4 18.0 26.2 209.6
46.6 43.6 185.4 42.4 47.0 365.0
4.0 11.9 17.4 20.2 19.0
10.0 15.5 19.7 20.1 18.0
6.9 15.5 22.7 22.1 21.1
4.0 14.3 16.9 23.2 20.2
4.2 11.2 17.9 19.6 20.3
cyanazine and postemergence (Post) applications of metribuzin, cyanazine, bentazone and imazethapyr were examined in lathyrus from 1987 to 1990. PPI and Post herbicides were examined in separate experiments. Seeds of
Amaranthus retroflexus, Avena fatua, Chenopodittm album, Setaria viridis, and Sinapis arvensis were hand broadcast over the experimental site before seeding, to supplement the natural weed population. PPI herbicides were applied one day before planting and incorporated to a depth of I 0 cm by double tandem discing and harrowing. Lathyrus was planted on 6 May 1987, 17 May 1988, 12 May 1989 and 14 May 1990. Post herbicides were applied when the lathyrus was 8-10cm in height and the weeds had 1-2 true leaves. Hand weeded and weedy check plots were included in each experiment as control treatments. All herbicide applications were made with a small-plot sprayer equipped with flat-fan nozzles (SS 8002, supplied by Spraying Systems Co., Wheaton, IL 60187, USA) delivering 1101 h a - t of total solution at 210 kPa. Crop injury was evaluated visually at 2 and 4 weeks after herbicide application and a median injury rating determined for the combined evaluation dates. A 0 - 9 scale was used to rate crop injury (9, no noticeable injury; 0, complete crop kill; 7, minimum rating necessary for commercial acceptance). Weed control was determined by counting the number of surviving weeds, by species, in four randomly selected 0.25m 2 quadrats in each plot. The weed control data were normalized between years by converting the weed density for each plot to weed density as a percentage of the density recorded in the weedy check. Lathyrus was harvested on 8 August 1987, 6 September 1988, 23 August 1989 and 5 September 1990 and the seed yields determined. T o l e r a n c e of l a t h y r u s to M C P A f o r m u l a t i o n s
The tolerance oflathyrus to several formulations of MCPA was examined over a 3-year period as a possible low-cost treatment for the control of annual broad-leaved weeds in this crop. Trifluralin was applied PPI at 1. I kg a.i. h a - t as an overall treatment to control annual broad-leaved and grass weeds. Lathyrus was planted on 17 May 1988, 11 May 1989 and 14 May 1990. Sodium and potassium salt and amine formulations of MCPA and a mixture of MCPB: MCPA (15:1) were applied in combination with sethoxydim plus surfactant [Assist Oil Concentrate, paraffin base mineral oil (83%) and surfactant blend (17%), BASF Canada Inc., 10 Constellation Court, Rexdale, Ontario, Canada, M9W 1K 1] either as a tank mixture
or as a split application 4 days apart. Application rates were 0.28kg a.i. h a - i for MCPA salt and amine tbrmulations and 1.5kg a.i. ha - I for the mixture of MCPB:MCPA. The rates used in this study are those currently recommended for application in field peas in Manitoba (Anonymous, 1990). The lathyrus was 8-I0 cm in height at the time o f the initial herbicide application. Crop injury was evaluated as previously described. Plots were desiccated with diquat 3-4 days before harvest to facilitate mechanical harvest. Lathyrus was harvested on 17 August 1989 and 5 September 1990. Poor herbicide performance in 1988 resulted in heavy weed pressure and consequently no lathyrus seed was harvested in that year. Lathyrus t o l e r a n c e to metribuzin The tolerance oflathyrus to metribuzin was examined in a dose-response experiment. Lathyrus was sown on 17 May 1988, 11 May 1989 and 14 May 1990. Trifluralin was applied at 1.1 kg a.i. h a - t PPI as an overall treatment to control annual weeds. Metribuzin was applied at 0.14, 0.28, 0.42, 0.56, 0.70 and 0.84 kg a.i. h a - t as PPI and Post treatments. Control treatments consisted of one untreated (hand-weeded) plot in each replicate. When applied PPI, metribuzin was tank-mixed with trifluralin and incorporated, one day before planting, with two tandem discings to a depth of 10 cm followed by harrowing. Post applications were made when the lathyrus was 8-10 cm in height.,Crop injury was rated visually as previously described. Lathyrus was harvested on 31 August 1988, 16 August 1989 and 29 August 1990 and the seed yield determined. The effect of metribuzin on lathyrus seed yield was determined by regression analysis of the yield data. Results and discussion Meteorological
The four years over which this study was conducted differed markedly in the amount of precipitation received (Table 1). Total precipqtation from 1 April to 31 August, inclusive, for 1987, 1988, 1989 and 1990 was 99, 39, 64 and 111%, respectively, of the 30-year average of 327.8 mm recorded at Morden. Weed c o n t r o l w i t h s e l e c t i v e h e r b i c i d e s
No single herbicide applied PPI provided complete weed control when used alone. This was reflected in the lower
498
H e r b i c i d e efficacy in lathyrus: D. A. Wall and G. H. Friesen
Table 2. Crop injury, weed control and lathyrus seed yield following the application of pre-planting soil-incorporated herbicides, 1987 and 1988 Weed control (percentage of the weedy check plot) Crop injury (0-9) Treatment Weedy check Hand-weeded check Trifluralin Metribuzin Cyanazine
Rate (kg a.i. h a - 1) --1.1 0.28 3.0
1987 9 9 7.5 5.5 9
A. fatua
1988 9 9 7 9 8
S. viridis
S. arvensis
Seed yield ( g m - 2)
A. retroflexus
1987
1988
1987
1988
1987
1988
1987
1988
1987
1988
0 I00 95 85 49
0 100 75 38 88
0 100 100 38 57
0 100 94 3 5
0 100 28 I00 98
0 100 0 100 100
0 100 100 95 79
0 100 79 56 19
16 149 51 20 39
3 248 171 19 14
37
122
l.s.d. (p = 0.05) "Crop injury rating scale: 9, no noticeable injury; 0, complete crop kill; > 7, commercial acceptance
Table 3. Effect of postemergence herbicides on S. arvensis control in lathyrus, 1987-1990 S. arrensis control (percentage o f the weedy check plot)
Treatment"
Rate (kg a.i. h a - 1)
1987
1988
--0.21 0.50 1.08 0.04
0 100 94 h 83 l,
0 100 h ~ 100 100
Weedy check Hand-weeded check Metribuzin Cyanazine Bentazone Imazethapyr
1989(1)
1989(2)
0 100 94 89 84 100
1990
0 100 85 87 96 100
0 I00 i 00 40 30 62
"Bentazone plus Assist Oil Concentrate at 1.0% (v/v); imazethapyr plus DM 710 at 0.3*/, (v/v); ~'treatment not included
Table4. Effect of postemergence herbicides on crop injury and lathyrus seed yield, 1987-1990 Seed yield ( g m - 2)
Crop injury (0-9) h Treatment a Weedy check Hand-weeded check Metribuzin Cyanazine Bentazone lmazethapyr
Rate (kg a.i. h a - i)
1987
1988
--0.21 0.50 !.08 0.04
9 9 5 c 8 c
9 9 c c 8 8
1989(1)
1989(2)
1990
9 9 6.5 4 9 9
9 9 8.5 9 9 9
9 9 8.5 8.5 9 9
l.s.d. (p = 0.05)
1987
1988
1989(1)
1989(2)
1990
9 81 49 c 44 c
I 47 c c 4 27
123 254 246 232 227 281
78 194 153 63 196 238
208 271 276 273 260 262
19
32
71
40
56
"Bentazone plus Assist Oil Concentrate at 1.0% (v/v); imazethapyr plus DM 710 at 0.3% (v/v); hcrop injury rating scale as in Table 2; qreatment not included
seed yields when compared with the hand-weeded check (Table 2). Trifturalin consistently controlled annual weeds other than S. arvensis, although this species was effectively controlled by metribuzin and cyanazine when applied PPI. Post applications of metribuzin, cyanazine, bentazone and imazethapyr provided satisfactory control of S. arvet~is in all years except 1990 (Table 3). Among the PPI treatments, metribuzin produced an unacceptable amount of crop injury in 1987, but tolerance was satisfactory in 1988 (Table 2). The greater precipitation in 1987 resulted in more favourable soil moisture conditions during early plant growth. This may have subsequently increased the availability of metribuzin to the root system of lathyrus and increased the amount of crop injury observed in that year. In both years, lathyrus exhibited satisfactory tolerance to PPI applications oftrifluralin and cyanazine. Crop tolerance to Post applications of imaze-
thapyr was good to excellent in all years (Table 4). Metribuzin in 1987 and metribuzin and cyanazine in 1989 were applied as tank mixtures with sethoxydim plus surfactant. This mixture produced an unacceptable amount of foliar chlorosis and necrosis. Lathyrus tolerance to Post applications of cyanazine and metribuzin was satisfactory when these products were applied without the" addition of surfactants. Seed yields reflected both the degree of crop injury and weed control obtained with each herbicide. Only imazethapyr produced consistently high yields when applied alone, reflecting both superior weed control and low crop phytotoxicity. Tolerance of lathyrus to MCPA formulations All formulations of MCPA produced symptoms typical of phenoxy herbicide injury, including stem and petiole
Herbicide efficacy in lathyrus: D. A. Wall and G. H. Friesen
499
Table 5. Crop injury ratings and seed yields of lathyrus following postemergence applications of several formulations of MCPA Seed yield (g m - 2)
Crop injury (0-9) ¢ Rate (kg a.i. h a - ~)
Treatment" Untreated MCPA-K + sethoxydim MCPA-Na + sethoxydim MCPA-Amine + sethoxydim MCPB:MCPA + sethoxydim MCPA-K/sethoxydim MCPA-Na/sethoxydim MCPA-Amine/sethoxydim MCPB:MCPA/sethoxydim
Method of application '~
-0.28 + 0.25 0.28 + 0.25 0.28 + 0.25 1.50+0.25 0.28 + 0.25 0.28 + 0.25 0.28 + 0.25 1.50+0.25
-Post t/m Post t/m Post t/m Post t/m Split Split Split Split
1988
1989
i 990
9 3.5 4.5 -4.5 6 7.5 -6
9 3.5 4.5 4 3.5 6.3 6 6 6
9 4 4 4.5 5 6.8 7.5 7.5 6.3
l.s.d. (p = 0.05)
1990
230 120 128 118 85 184 169 204 146
303 220 201 252 211 240 278 294 252
71
51
"Sethoxydim plus Merge at 0.5% (v/v); '~Post, postemergence; Split, 4-day split application; t/m, tank mixture; ~crop injury rating scale as in
Table6. Lathyrus injury following the application of metribuzin by two methods, 1988-1990 Crop injury (0-9)" 1988 Rate of metribuzin (kg a.i. h a - 1)
1989
1989
PPI h
Post"
PPI
Post
9 9 9 9 9 9 --
9 9 9 9 9 9 --
9 8.5 8 6.8 6.5 6 5
9 8 7 7 7 6.5 6.3
0.00 0.14 0.28 0.42 0.56 0.70 0.84
"Crop injury rating scale as in Table postemergence to the crop
2;
1990 PPI 9 8 7 4 4 5 2
Post 9 7.5 6.5 4,5 4 3 3.5
Table2
mulation, was applied in tank mixtures with sethoxydim plus surfactant. Lathyrus tolerance did not differ markedly between sodium, potassium or amine MCPA formulations. Given the unacceptable crop phytotoxicity and the tendency towards reduced seed yields it is unlikely that MCPA would be recommended as a herbicide for broadleaved weed control in lathyrus. The use of MCPA, and the associated yield reduction, may be justified only where annual weeds have escaped control and less phytotoxic herbicides are not available.
Lathyrus tolerance to rnetribuzin
'~PPI, pre-planting soil-incorporated; "Post,
bending and leaf curling and cupping. Tank mixtures of MCPA with sethoxydim plus surfactant were more phytotoxic to lathyrus when compared with a 4-day split application. Crop injury was unacceptable at 2-4 weeks after herbicide application, regardless of formulation or method of application (Table 5). By harvest lathyrus had recovered visibly from the injury caused by the split applications of MCPA and sethoxydim; however, lathyrus that had received the tank mixture of MCPA and sethoxydim were visibly stunted at harvest. Seed yields were reduced in plots treated with MCPA when compared with the untreated check plot. However, seed yield reductions were significant only when MCPA, regardless of for-
In 1988 and 1989, lathyrus tolerated Post applications of metribuzin at rates up to 0.84 kg a.i. h a - i (Figure 1). However, lathyrus was less tolerant of PPI applications and in 1988 and 1989 seed yields were reduced noticeably when application rates exceeded 0.42 kg a.i. ha- i. Severe crop injury occurred in 1990 when application rates exceeded 0.14kg a.i. ha -I, regardless of application method. Lathyrus tolerance to metribuzin appeared to be related to the amount of precipitation received at or near the time of herbicide application. In wet years more herbicide may be available in the soil solution for uptake through roots. The data indicate that in dry years there is a threefold safety margin in the current recommended Post rate (0.21-0.28 kg a.i. ha- i) for pulse crops grown in Manitoba. In years with above-normal precipitation before or after herbicide application, lathyrus may be injured when
Table 7. Regression coefficients and coefficients of determination for the regression of lathyrus seed yield (g m - 2) on rate of metribuzin Regression coefficientsh Treatment Trifluralin + metribuzin Trifluralin + metribuzin Trifluralin + metribuzin Trifluralin/metribuzin Trifluralin/metribuzin Trifluralin/metribuzin
Method of application"
Year
a
b
PPI t/m PPI t/m PPI t/m PPI/Post PPl/Post PPI/Post
1988 1989 1990 1988 1989 1990
52.90 200.21 241.97 48,10 174.39 251.43
71.26 96.92 - 226.71 9.96 - 14.54 - 454.53
c
R2
- 139.00 - 214.69
0.18 0.69 0.77 0.02 0.04 0.86
241.97
oPPI, pre-planting soil-incorporated; Post, postemergence; t/m. tank mixture; ~regression coefficients were fitted to the general models for a first- and second-order polynomial y = a + b x and y = a + b x + cx2, respectively, ~ here )' is the estimated seed yield in g m - 2 and x is the dosage of metribuzin in kg a.i. ha- t
500
H e r b i c i d e efficacy in lathyrus: D. A. Wall a n d G. H. F r i e s e n
200
a
150
I00
........ .A._ •
50'
l
A_
• ..... ~" ........ .4,....
•
I
I
o0lb ...... , .........., ......... ,
a °°°°,°•
I
I
- "°°°''°'l~A,°o° o°.
15o
•
I
•
• ' " " ...
°.~
rates exceed 0.14 kg a.i. h a - i . Metribuzin phytotoxicity, however, is unlikely to be a principal concern to pulse growers as lathyrus would be grown largely in regions with low annual precipitation. It is suggested that, should metribuzin be recommended to lathyrus producers, postemergence rates should not exceed 0.21 kg a.i. h a - ' for this crbp. Although metribuzin is not currently recommended as a pre-planting soil-incorporated treatment for pulse crops in Manitoba (Anonymous, 1990) the data indicated that this herbicide could safely be soil applied in lathyrus production at rates up to 0.28 kg a.i. h a - t. This rate would allow for a twofold safety margin in dry years which is desirable to prevent crop injury resulting through misapplication or sprayer overlap.
I00
Acknowledgements 50 0
I
I
I
I
I
I
C 250 •
200
•
•
"'" ""-....... ,~"°°oe
References
"'X...
eso
~'"'-
I00
Anonymous (1990) 1990 Guide to Chemical IVeed Control. Manitoba Agriculture, Winnipeg, Manitoba, 220 pp
•
Jackson, 1%1.T. and Yumus, A. G. (1984) Variation in the grass pea (Lathyrus sativus L.) and wild species. Euphytica 33, 549-559
50 0.00
The technical assistance of Mr R. Klassen is gratefully acknowledged. Appreciation is also expressed to BASF Canada Inc., Chemagro Ltd, Ciba-Geigy Canada Ltd, Cyanamid Canada Inc., DowElanco Canada Inc., Du Pont Canada Inc. and Rhone-Poulenc Canada Inc. for supplying the herbicides used in these studies.
= 0.14
I 0.28
r 0.42 Metribuzin(kg
0.'56
I 0.70
, 0.84
a.i. ho "e)
Figure 1. Effect of pre-planting incorporated, PPI ( ...... ), and postemergence, Post ( ), applications of metribuzin (kg a.i. h a - ') on the seed yield ( g m -=) of lathyrus in (a) 1988, (b) 1989 and (c) 1990. Mean seed yields for PPI ( • ) and Post ( • ) methods of application are illustrated, a: Post, no correlation; PPI, 52.90+71.26x-139.00x =, R==0.18. b: Post, no correlation; PPI, 200.21+96.92x-214.69x =, R z=0.69, c: Post, 251.43-454.53x+241.97x =, R 2=0.88; PPI, 241.97- 226.61x, R2 = 0.77
Silsbury, J. 11. (1975) Grain yield and flowering of some introduced grain legumes in South Australia. Aust. J. ExplAgric. Anita. ttusb. 15, 556-560 Smartt, J. (1984) Evolution of grain legumes. I. Mediterranean pulses. Expl Agric. (Camb.) 20, 275-296 Wall, D. A., Friesen, G. H. and Dryden, D. (1988) Effect o f herbicides and annual weeds on the yield and seed quality oflathyrus (Lathyru.isativus L.). Crop Prot. 7, 372-377 Received 30 November 1990 Revised 8 April 1991 Accepted 8 April 1991
I
Effectiveness of selective herbicides for the control of annual weed species in lathyrus (Lathyrus sa tivus L. )
|
D. A. Wall* and G. H. Friesen Agriculture Canada, Research Station, PO Box 3001, Morden, Manitoba, ROG 1JO,Canada
Abstract
Field research was conducted over a four-year period, 1987-1990, to evaluate the efficacy and selectivity of trifluralin, metribuzin, cyanazine, bentazone, imazethapyr and several formulations of MCPA in lathyrus (Lathyrus sativus L.). Lathyrus exhibited satisfactory tolerance to trifluralin applied pre-planting soil incorporated and to postemergence applications of bentazone and imazethapyr. Lathyrus tolerated both pre-planting soil-incorporated and postemergence applications ofmetribuzin in dry years, but was injured by this herbicide in years with adequate precipitation. Tank mixtures of metribuzin or cyanazine with sethoxydim plus surfactant markedly increased the phytotoxicity of these herbicides to lathyrus. Lathyrus was sensitive to all formulations of MCPA and phytotoxicity increased with the addition ofsethoxydim plus surfactant to the spray mixture.
Keywords Lathyrus; Lathyrus sativus L.; MCPA; metribuzin; tolerance; environment; adjuvants
Introduction Lathyrus is currently under evaluation by Agriculture Canada as an annual grain legume for the prairie provinces of Western Canada. This crop is of interest to prairie farmers as an alternate to traditional cereal grains owing to its ability to produce high yields under a wide range of environmental conditions, from excess moisture to drought (Jackson and Yumus, 1984; Smartt, 1984). Its development as a commercial crop would enable farmers in drought-prone regions to incorporate a legume into their crop rotations. This practice has not previously been successful owing to the poor performance of currently recommended pulse crops in regions with low annual precipitation. The acceptance of lathyrus as a new commercial crop may be limited by the lack of registered herbicides for the control of annual weed species in this crop. Lathryus is highly susceptible to weed competition and a clean seed-bed is essential for successful production of this crop (Silsbury, 1975). Wall, Friesen and Dryden (1988) reported that lathyrus seed yields were reduced by 54-95% when annual grasses and broad-leaved weeds were not controlled. Attempts to introduce new crops to prairie grain farmers often fail, owing to the noncompetitiveness of new crops and/or the lack of weed control recommendations, including registered products. Trifluralin and metribuzin have been identified as promising herbicides for the control of annual broad-leaved weeds in lathyrus (Wall et aL, 1988). These herbicides are applied regularly to other pulse crops grown in Western Canada (lentils and field peas) and are thus products with which producers already have considerable experience. *To whom correspondence should be addressed 0261-2194/91/06/0496-05 © 1991 Butterworth-Heinemann Ltd
Wall et al. (1988) reported that lathyrus tolerated 2.2 kg a.i. ha- ~of trifluralin, twice the maximum recommended rate for pulse crops in Manitoba (Anonymous, 1990). A satisfactory safety margin has, however, not yet been established for metribuzin. The objective of the research reported here was to evaluate the performance, in iathyrus, of herbicides currently registered for use on larger-acreage crops grown in Western Canada, and to provide data to support the registration and recommendation of suitable herbicides when commercial lathyrus cultivars become available to farmers.
Materials and methods Field experiments were conducted at the Agriculture Canada Research Station, Morden, Manitoba, from 1987 to 1990. The experimental site was located on land which had been summer-fallowed each year before cropping. The soil type was a sandy loam (73% sand, 10% silt, 17%oclay and 4% organic matter). Lathyrus was sown with a double-disc press drill at 80kg h a - i in rows 30cm apart and at a depth of 5 cm. Field plot size was 2 x 8 m. All experiments were conducted as randomized complete block designs with four replicates. Seed yields were determined by harvesting the entire plot area (16m 2) with a self-propelled plot combine, drying the seed to a uniform moisture content (14°,/o) and weighing the seed.
Weed control in lathyrus with selective herbicides The efficacy and selectivity of pre-planting soil-incorporated (PPI) applications of trifluralin, metribuzin and
Herbicide efficacy in lathyrus: D. A. Wall and G. H. Friesen
497
Table 1. Monthly and 30-year mean precipitation and mean air temperatures recorded at Morden, Manitoba, 1987-1990
Precipitation(mm)
Daily mean temperature(*C)
Month
30-yearaverage
1987
1988
1989
1990
30-yearaverage
1987
1988
1989
1990
April May June July August Total
41.4 66.3 75.8 73.2 71.1 327.8
0.4 47.2 63.2 148.0 64.2 323.0
0.0 21.4 43.0 42.8 20.8 128.0
2 ! .2 46.8 97.4 18.0 26.2 209.6
46.6 43.6 185.4 42.4 47.0 365.0
4.0 11.9 17.4 20.2 19.0
10.0 15.5 19.7 20.1 18.0
6.9 15.5 22.7 22.1 21.1
4.0 14.3 16.9 23.2 20.2
4.2 11.2 17.9 19.6 20.3
cyanazine and postemergence (Post) applications of metribuzin, cyanazine, bentazone and imazethapyr were examined in lathyrus from 1987 to 1990. PPI and Post herbicides were examined in separate experiments. Seeds of
Amaranthus retroflexus, Avena fatua, Chenopodittm album, Setaria viridis, and Sinapis arvensis were hand broadcast over the experimental site before seeding, to supplement the natural weed population. PPI herbicides were applied one day before planting and incorporated to a depth of I 0 cm by double tandem discing and harrowing. Lathyrus was planted on 6 May 1987, 17 May 1988, 12 May 1989 and 14 May 1990. Post herbicides were applied when the lathyrus was 8-10cm in height and the weeds had 1-2 true leaves. Hand weeded and weedy check plots were included in each experiment as control treatments. All herbicide applications were made with a small-plot sprayer equipped with flat-fan nozzles (SS 8002, supplied by Spraying Systems Co., Wheaton, IL 60187, USA) delivering 1101 h a - t of total solution at 210 kPa. Crop injury was evaluated visually at 2 and 4 weeks after herbicide application and a median injury rating determined for the combined evaluation dates. A 0 - 9 scale was used to rate crop injury (9, no noticeable injury; 0, complete crop kill; 7, minimum rating necessary for commercial acceptance). Weed control was determined by counting the number of surviving weeds, by species, in four randomly selected 0.25m 2 quadrats in each plot. The weed control data were normalized between years by converting the weed density for each plot to weed density as a percentage of the density recorded in the weedy check. Lathyrus was harvested on 8 August 1987, 6 September 1988, 23 August 1989 and 5 September 1990 and the seed yields determined. T o l e r a n c e of l a t h y r u s to M C P A f o r m u l a t i o n s
The tolerance oflathyrus to several formulations of MCPA was examined over a 3-year period as a possible low-cost treatment for the control of annual broad-leaved weeds in this crop. Trifluralin was applied PPI at 1. I kg a.i. h a - t as an overall treatment to control annual broad-leaved and grass weeds. Lathyrus was planted on 17 May 1988, 11 May 1989 and 14 May 1990. Sodium and potassium salt and amine formulations of MCPA and a mixture of MCPB: MCPA (15:1) were applied in combination with sethoxydim plus surfactant [Assist Oil Concentrate, paraffin base mineral oil (83%) and surfactant blend (17%), BASF Canada Inc., 10 Constellation Court, Rexdale, Ontario, Canada, M9W 1K 1] either as a tank mixture
or as a split application 4 days apart. Application rates were 0.28kg a.i. h a - i for MCPA salt and amine tbrmulations and 1.5kg a.i. ha - I for the mixture of MCPB:MCPA. The rates used in this study are those currently recommended for application in field peas in Manitoba (Anonymous, 1990). The lathyrus was 8-I0 cm in height at the time o f the initial herbicide application. Crop injury was evaluated as previously described. Plots were desiccated with diquat 3-4 days before harvest to facilitate mechanical harvest. Lathyrus was harvested on 17 August 1989 and 5 September 1990. Poor herbicide performance in 1988 resulted in heavy weed pressure and consequently no lathyrus seed was harvested in that year. Lathyrus t o l e r a n c e to metribuzin The tolerance oflathyrus to metribuzin was examined in a dose-response experiment. Lathyrus was sown on 17 May 1988, 11 May 1989 and 14 May 1990. Trifluralin was applied at 1.1 kg a.i. h a - t PPI as an overall treatment to control annual weeds. Metribuzin was applied at 0.14, 0.28, 0.42, 0.56, 0.70 and 0.84 kg a.i. h a - t as PPI and Post treatments. Control treatments consisted of one untreated (hand-weeded) plot in each replicate. When applied PPI, metribuzin was tank-mixed with trifluralin and incorporated, one day before planting, with two tandem discings to a depth of 10 cm followed by harrowing. Post applications were made when the lathyrus was 8-10 cm in height.,Crop injury was rated visually as previously described. Lathyrus was harvested on 31 August 1988, 16 August 1989 and 29 August 1990 and the seed yield determined. The effect of metribuzin on lathyrus seed yield was determined by regression analysis of the yield data. Results and discussion Meteorological
The four years over which this study was conducted differed markedly in the amount of precipitation received (Table 1). Total precipqtation from 1 April to 31 August, inclusive, for 1987, 1988, 1989 and 1990 was 99, 39, 64 and 111%, respectively, of the 30-year average of 327.8 mm recorded at Morden. Weed c o n t r o l w i t h s e l e c t i v e h e r b i c i d e s
No single herbicide applied PPI provided complete weed control when used alone. This was reflected in the lower
498
H e r b i c i d e efficacy in lathyrus: D. A. Wall and G. H. Friesen
Table 2. Crop injury, weed control and lathyrus seed yield following the application of pre-planting soil-incorporated herbicides, 1987 and 1988 Weed control (percentage of the weedy check plot) Crop injury (0-9) Treatment Weedy check Hand-weeded check Trifluralin Metribuzin Cyanazine
Rate (kg a.i. h a - 1) --1.1 0.28 3.0
1987 9 9 7.5 5.5 9
A. fatua
1988 9 9 7 9 8
S. viridis
S. arvensis
Seed yield ( g m - 2)
A. retroflexus
1987
1988
1987
1988
1987
1988
1987
1988
1987
1988
0 I00 95 85 49
0 100 75 38 88
0 100 100 38 57
0 100 94 3 5
0 100 28 I00 98
0 100 0 100 100
0 100 100 95 79
0 100 79 56 19
16 149 51 20 39
3 248 171 19 14
37
122
l.s.d. (p = 0.05) "Crop injury rating scale: 9, no noticeable injury; 0, complete crop kill; > 7, commercial acceptance
Table 3. Effect of postemergence herbicides on S. arvensis control in lathyrus, 1987-1990 S. arrensis control (percentage o f the weedy check plot)
Treatment"
Rate (kg a.i. h a - 1)
1987
1988
--0.21 0.50 1.08 0.04
0 100 94 h 83 l,
0 100 h ~ 100 100
Weedy check Hand-weeded check Metribuzin Cyanazine Bentazone Imazethapyr
1989(1)
1989(2)
0 100 94 89 84 100
1990
0 100 85 87 96 100
0 I00 i 00 40 30 62
"Bentazone plus Assist Oil Concentrate at 1.0% (v/v); imazethapyr plus DM 710 at 0.3*/, (v/v); ~'treatment not included
Table4. Effect of postemergence herbicides on crop injury and lathyrus seed yield, 1987-1990 Seed yield ( g m - 2)
Crop injury (0-9) h Treatment a Weedy check Hand-weeded check Metribuzin Cyanazine Bentazone lmazethapyr
Rate (kg a.i. h a - i)
1987
1988
--0.21 0.50 !.08 0.04
9 9 5 c 8 c
9 9 c c 8 8
1989(1)
1989(2)
1990
9 9 6.5 4 9 9
9 9 8.5 9 9 9
9 9 8.5 8.5 9 9
l.s.d. (p = 0.05)
1987
1988
1989(1)
1989(2)
1990
9 81 49 c 44 c
I 47 c c 4 27
123 254 246 232 227 281
78 194 153 63 196 238
208 271 276 273 260 262
19
32
71
40
56
"Bentazone plus Assist Oil Concentrate at 1.0% (v/v); imazethapyr plus DM 710 at 0.3% (v/v); hcrop injury rating scale as in Table 2; qreatment not included
seed yields when compared with the hand-weeded check (Table 2). Trifturalin consistently controlled annual weeds other than S. arvensis, although this species was effectively controlled by metribuzin and cyanazine when applied PPI. Post applications of metribuzin, cyanazine, bentazone and imazethapyr provided satisfactory control of S. arvet~is in all years except 1990 (Table 3). Among the PPI treatments, metribuzin produced an unacceptable amount of crop injury in 1987, but tolerance was satisfactory in 1988 (Table 2). The greater precipitation in 1987 resulted in more favourable soil moisture conditions during early plant growth. This may have subsequently increased the availability of metribuzin to the root system of lathyrus and increased the amount of crop injury observed in that year. In both years, lathyrus exhibited satisfactory tolerance to PPI applications oftrifluralin and cyanazine. Crop tolerance to Post applications of imaze-
thapyr was good to excellent in all years (Table 4). Metribuzin in 1987 and metribuzin and cyanazine in 1989 were applied as tank mixtures with sethoxydim plus surfactant. This mixture produced an unacceptable amount of foliar chlorosis and necrosis. Lathyrus tolerance to Post applications of cyanazine and metribuzin was satisfactory when these products were applied without the" addition of surfactants. Seed yields reflected both the degree of crop injury and weed control obtained with each herbicide. Only imazethapyr produced consistently high yields when applied alone, reflecting both superior weed control and low crop phytotoxicity. Tolerance of lathyrus to MCPA formulations All formulations of MCPA produced symptoms typical of phenoxy herbicide injury, including stem and petiole
Herbicide efficacy in lathyrus: D. A. Wall and G. H. Friesen
499
Table 5. Crop injury ratings and seed yields of lathyrus following postemergence applications of several formulations of MCPA Seed yield (g m - 2)
Crop injury (0-9) ¢ Rate (kg a.i. h a - ~)
Treatment" Untreated MCPA-K + sethoxydim MCPA-Na + sethoxydim MCPA-Amine + sethoxydim MCPB:MCPA + sethoxydim MCPA-K/sethoxydim MCPA-Na/sethoxydim MCPA-Amine/sethoxydim MCPB:MCPA/sethoxydim
Method of application '~
-0.28 + 0.25 0.28 + 0.25 0.28 + 0.25 1.50+0.25 0.28 + 0.25 0.28 + 0.25 0.28 + 0.25 1.50+0.25
-Post t/m Post t/m Post t/m Post t/m Split Split Split Split
1988
1989
i 990
9 3.5 4.5 -4.5 6 7.5 -6
9 3.5 4.5 4 3.5 6.3 6 6 6
9 4 4 4.5 5 6.8 7.5 7.5 6.3
l.s.d. (p = 0.05)
1990
230 120 128 118 85 184 169 204 146
303 220 201 252 211 240 278 294 252
71
51
"Sethoxydim plus Merge at 0.5% (v/v); '~Post, postemergence; Split, 4-day split application; t/m, tank mixture; ~crop injury rating scale as in
Table6. Lathyrus injury following the application of metribuzin by two methods, 1988-1990 Crop injury (0-9)" 1988 Rate of metribuzin (kg a.i. h a - 1)
1989
1989
PPI h
Post"
PPI
Post
9 9 9 9 9 9 --
9 9 9 9 9 9 --
9 8.5 8 6.8 6.5 6 5
9 8 7 7 7 6.5 6.3
0.00 0.14 0.28 0.42 0.56 0.70 0.84
"Crop injury rating scale as in Table postemergence to the crop
2;
1990 PPI 9 8 7 4 4 5 2
Post 9 7.5 6.5 4,5 4 3 3.5
Table2
mulation, was applied in tank mixtures with sethoxydim plus surfactant. Lathyrus tolerance did not differ markedly between sodium, potassium or amine MCPA formulations. Given the unacceptable crop phytotoxicity and the tendency towards reduced seed yields it is unlikely that MCPA would be recommended as a herbicide for broadleaved weed control in lathyrus. The use of MCPA, and the associated yield reduction, may be justified only where annual weeds have escaped control and less phytotoxic herbicides are not available.
Lathyrus tolerance to rnetribuzin
'~PPI, pre-planting soil-incorporated; "Post,
bending and leaf curling and cupping. Tank mixtures of MCPA with sethoxydim plus surfactant were more phytotoxic to lathyrus when compared with a 4-day split application. Crop injury was unacceptable at 2-4 weeks after herbicide application, regardless of formulation or method of application (Table 5). By harvest lathyrus had recovered visibly from the injury caused by the split applications of MCPA and sethoxydim; however, lathyrus that had received the tank mixture of MCPA and sethoxydim were visibly stunted at harvest. Seed yields were reduced in plots treated with MCPA when compared with the untreated check plot. However, seed yield reductions were significant only when MCPA, regardless of for-
In 1988 and 1989, lathyrus tolerated Post applications of metribuzin at rates up to 0.84 kg a.i. h a - i (Figure 1). However, lathyrus was less tolerant of PPI applications and in 1988 and 1989 seed yields were reduced noticeably when application rates exceeded 0.42 kg a.i. ha- i. Severe crop injury occurred in 1990 when application rates exceeded 0.14kg a.i. ha -I, regardless of application method. Lathyrus tolerance to metribuzin appeared to be related to the amount of precipitation received at or near the time of herbicide application. In wet years more herbicide may be available in the soil solution for uptake through roots. The data indicate that in dry years there is a threefold safety margin in the current recommended Post rate (0.21-0.28 kg a.i. ha- i) for pulse crops grown in Manitoba. In years with above-normal precipitation before or after herbicide application, lathyrus may be injured when
Table 7. Regression coefficients and coefficients of determination for the regression of lathyrus seed yield (g m - 2) on rate of metribuzin Regression coefficientsh Treatment Trifluralin + metribuzin Trifluralin + metribuzin Trifluralin + metribuzin Trifluralin/metribuzin Trifluralin/metribuzin Trifluralin/metribuzin
Method of application"
Year
a
b
PPI t/m PPI t/m PPI t/m PPI/Post PPl/Post PPI/Post
1988 1989 1990 1988 1989 1990
52.90 200.21 241.97 48,10 174.39 251.43
71.26 96.92 - 226.71 9.96 - 14.54 - 454.53
c
R2
- 139.00 - 214.69
0.18 0.69 0.77 0.02 0.04 0.86
241.97
oPPI, pre-planting soil-incorporated; Post, postemergence; t/m. tank mixture; ~regression coefficients were fitted to the general models for a first- and second-order polynomial y = a + b x and y = a + b x + cx2, respectively, ~ here )' is the estimated seed yield in g m - 2 and x is the dosage of metribuzin in kg a.i. ha- t
500
H e r b i c i d e efficacy in lathyrus: D. A. Wall a n d G. H. F r i e s e n
200
a
150
I00
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l
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• ..... ~" ........ .4,....
•
I
I
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rates exceed 0.14 kg a.i. h a - i . Metribuzin phytotoxicity, however, is unlikely to be a principal concern to pulse growers as lathyrus would be grown largely in regions with low annual precipitation. It is suggested that, should metribuzin be recommended to lathyrus producers, postemergence rates should not exceed 0.21 kg a.i. h a - ' for this crbp. Although metribuzin is not currently recommended as a pre-planting soil-incorporated treatment for pulse crops in Manitoba (Anonymous, 1990) the data indicated that this herbicide could safely be soil applied in lathyrus production at rates up to 0.28 kg a.i. h a - t. This rate would allow for a twofold safety margin in dry years which is desirable to prevent crop injury resulting through misapplication or sprayer overlap.
I00
Acknowledgements 50 0
I
I
I
I
I
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200
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References
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~'"'-
I00
Anonymous (1990) 1990 Guide to Chemical IVeed Control. Manitoba Agriculture, Winnipeg, Manitoba, 220 pp
•
Jackson, 1%1.T. and Yumus, A. G. (1984) Variation in the grass pea (Lathyrus sativus L.) and wild species. Euphytica 33, 549-559
50 0.00
The technical assistance of Mr R. Klassen is gratefully acknowledged. Appreciation is also expressed to BASF Canada Inc., Chemagro Ltd, Ciba-Geigy Canada Ltd, Cyanamid Canada Inc., DowElanco Canada Inc., Du Pont Canada Inc. and Rhone-Poulenc Canada Inc. for supplying the herbicides used in these studies.
= 0.14
I 0.28
r 0.42 Metribuzin(kg
0.'56
I 0.70
, 0.84
a.i. ho "e)
Figure 1. Effect of pre-planting incorporated, PPI ( ...... ), and postemergence, Post ( ), applications of metribuzin (kg a.i. h a - ') on the seed yield ( g m -=) of lathyrus in (a) 1988, (b) 1989 and (c) 1990. Mean seed yields for PPI ( • ) and Post ( • ) methods of application are illustrated, a: Post, no correlation; PPI, 52.90+71.26x-139.00x =, R==0.18. b: Post, no correlation; PPI, 200.21+96.92x-214.69x =, R z=0.69, c: Post, 251.43-454.53x+241.97x =, R 2=0.88; PPI, 241.97- 226.61x, R2 = 0.77
Silsbury, J. 11. (1975) Grain yield and flowering of some introduced grain legumes in South Australia. Aust. J. ExplAgric. Anita. ttusb. 15, 556-560 Smartt, J. (1984) Evolution of grain legumes. I. Mediterranean pulses. Expl Agric. (Camb.) 20, 275-296 Wall, D. A., Friesen, G. H. and Dryden, D. (1988) Effect o f herbicides and annual weeds on the yield and seed quality oflathyrus (Lathyru.isativus L.). Crop Prot. 7, 372-377 Received 30 November 1990 Revised 8 April 1991 Accepted 8 April 1991