North Dakota State University

ABSTRACT

Treflan or Sonalan can be used effectively for control of yellow foxtail [Setaria glauca (L.)Beauv.] and green foxtail [S. viridis (L.) Beauv.] in conservation-till wheat (Treflan only) and soybeans, despite the volatility and photodecomposition potential that has traditionally required soil incorporation in conventional till. Success with these conservation-till applications in North Dakota requires application in mid to late October in standing small grain stubble and incorporation with an implement designed for Soil and/or residue disturbance in high residue conditions. Such implements include the rotary hoe, undercutter, or Phoenix harrow. Satisfactory performance of October-applied Treflan and Sonalan granules also can be achieved without incorporation if applied in standing stubble, although foxtail control the following season tends to be somewhat lower than when granules are incorporated by conservation-till implements. Treflan and Sonalan granules applied in standing stubble in early spring when soil and air temperatures are low also provide good foxtail control when incorporated by conservation-till implements.

INTRODUCTION

Approximately 20% of North Dakota cropland was managed with conservation-till practices in 1991, including 3.8 million acres of small grains and 62,000 acres of soybeans (1). Current and future compliance with USDA farm programs, which require practices that reduce erosion, have been and likely will continue to increase the percentage of acreage handled by conservation-tillage. It is widely believed that the trend toward shallow and less frequent tillage in North Dakota and the surrounding region has led to increasing infestation levels of yellow foxtail and green foxtail. A 1978 and 1979 survey of weed infestations in North Dakota (2) reported green foxtail in 94% of surveyed fields, with average densities of 48 plants/yd2.

Treflan and Sonalan effectively and economically control foxtail in wheat and barley as well as in several broadleaf crops. Because of losses due to volatilization and photodecomposition (5, 6), however, these herbicides have required soil incorporation, and thus have not been candidates for most conservation-till systems. In the mid-1980s, Dr. Al Black, USDA scientist at Mandan, North Dakota, began successfully applying Treflan granules in standing stubble in the early spring followed by incorporation with an undercutter (sweep plow). Subsequent research by our group at North Dakota State University with fall-applied Treflan and Sonalan granules "incorporated" with an undercutter or rotary hoe, along with the development of additional conservation-till implements, has facilitated the adoption of use of these herbicides in conservation-till systems by a growing number of farmers.

MATERIALS AND METHODS

Carrington and Minot. 1990/91 and 1991/92. Experiments were established in the fall of 1990 and 1991 at Carrington and Minot, North Dakota. Soil at Carrington was a HeimdalEmrick loam with 3.8-4.0% organic matter and at Minot was a Max-Williams loam with 3.2% organic matter. Treflan and Sonalan (soybeans only) granules were applied in standing wheat stubble and were fall-applied between October 15 and the third week in November or spring-applied in mid April using an air-flow applicator. Herbicides were left on the surface or were "incorporated" within 24 hours by an undercutter (Haybuster brand) (one pass) or a rotary hoe (one pass). A standard conventional-till treatment was established by first destroying crop residues with deep tillage, and then applying the herbicides followed by a single incorporation pass with a field cultivator soon after application and a second incorporation pass immediately before seeding. Adapted varieties of wheat or soybeans were seeded in early May or late May, respectively. Wheat was fertilized according to soil test and broadleaf weeds were controlled in both crops as needed. Wheat and soybeans were seeded with planting equipment causing minimal residue disturbance (John Deere MaxEmerge row crop planter, John Deere 750 drill) except for the light to moderate surface disturbance obtained with a Tye no-till drill used for seeding wheat at Carrington. Burndown treatments of glyphosate were applied at planting to control emerged weeds.

Foxtail control was evaluated by visual estimate of control in the treated area compared to control in an adjacent untreated strip. Crop yields were taken at maturity using a small plot combine. Aboveground small grain residue was measured using the line transect (7) and residue sampling (8) methods, both before experiment initiation and after seeding. Plot size was 15 by 35 ft and all experiments were randomized complete block designs with four replications.

Carrington soybeans, 1994. An experiment was established in the spring of 1994 at Carrington. Methods and site information are similar to those given above for Carrington experiments, except for the following: 1) Herbicide granules were applied April 20 and incorporated within 24 h of application, 2) In addition to the undercutter and rotary hoe, the Phoenix harrow and John Deere Mulch Master were used to incorporate granules applied in standing stubble, 3) Plots were seeded May 17, half using a John Deere MaxE merge planter and the other half using a Concord air seeder with 12-inch sweeps (10-inch row spacing). Weed control was evaluated but residue levels were not measured and yields were not taken.

Fargo soybeans. 1991/92 and 1992. Two experiments were established at Fargo on a Fargo-Ryan silty clay with 4.5% organic matter, one in the fall of 1991 and one in the spring of 1992~ Methods for the fall-initiated experiment were similar to those given above for the fall-initiated Carrington experiments, except that soybeans were seeded with a Hiniker no-till row crop planter (double-disc openers, similar to John Deere MaxEmerge) causing minimal residue and surface disturbance. Weed control was evaluated but residue levels were not measured and yields were not taken. Methods for the spring-initiated experiment were similar to those given above for the 1994 Carrington experiment except for the following: 1) Only the undercutter was used to incorporate granules in conservation till; one pass was done immediately following application on April 16 and a second pass was done for some treatments immediately before seeding on May 15, 2) Conventional-till plots received Treflan or Sonalan emulsifiable concentrate (not granules) as a preplantincorporated treatment, 3) Soybeans were seeded with a Hiniker no-till row crop planter.

RESULTS AND DISCUSSION

Postplant residue levels. All conservation-till methods of incorporating herbicide granules in the fall in standing stubble resulted in more than adequate (1) residue cover after spring planting (Table 1). These measurements were taken in the 1990/91 and 1991/92 experiments at Carrington and Minot. As expected, no-incorporation produced the greatest amounts of postplant residues, with incorporation by a rotary hoe not significantly less. The undercutter, with 26-inch sweeps travelling 1.5 to 2 inches below the surface, preserves most of the stubble in a standing position and causes little breakdown in the amount of surface residues. Plots incorporated with a field cultivator had been rototilled before herbicide application to simulate the degree of residue destruction that might be expected in a field conventionally prepared in the fall for Treflan granule treatment (i.e. one chisel plowing followed by a second shallower tillage pass).

Table 1. Crop residue present on the soil surface after spring planting as affected by tillage practice used for Treflan and Sonalan incorporation the previous fall.
		Residue sampling method (b)
Herbicide incorporation tillage	Tillage before herbicide application	Line transect	Aboveground dry matter
		(% cover)	(kg/ha)
Field cultivator	roto-till	16	955
Undercutter	none	54	3955
Rotary hoe	none	66	4100
Undercutter/rotary hoe	none	49	3365
None	none	70	5075
C.V.%		17	53
LSD (0.05)		12	2400
aData are averaged across Carrington and Minot, ND, in 1991 and 1992. bCrop residue sampling done in May immediately after planting wheat and soybeans. Aboveground dry matter was sampled from 0.25 m2 areas. cUndercutter followed by a rotary hoe (one pass of each).

Wheat at Carrington and Minot 1990/91 and 1991/92. Treflan granules and emulsifiable concentrate formulations are labelled for fall application at rates of 0.5 to 0.75 lb ai/A in wheat to be seeded the following spring (3, 4). Data averaged across Minot and Carrington for 1991 and 1992 indicated that 0.5 lb/A of Treflan granules fall-applied in conventional till and incorporated twice with a field cultivator controlled foxtail (green and yellow foxtail) 83 to 86% in wheat the following year. Treflan granules applied at 0.5 lb/A in standing wheat stubble in the third week of October (Oct. 16 to 25) and incorporated with conservation-till implements (undercutter, rotary hoe, or undercutter followed by rotary hoe) controlled foxtail 79 to 88%.

Foxtail control with Treflan granules applied at 0.5 lb/A in standing stubble in the third week of October and left on the surface averaged 76% (across four environments) in wheat the following season. Surprisingly, Treflan granules applied at the same rate in mid to late November just before expected onset of snow cover) in standing stubble and left on the surface provided only 57% foxtail control. Lower control by the late application suggests that fall rains on non-frozen soil (which occurred only for the October application) may be needed to begin activating Treflan. Grain yields were not appreciably affected by foxtail but were higher for conservation-till treatments than for the conventional-till treatments, probably due to higher available soil moisture in the conservation-till plots.

Carrington soybeans 1994. Foxtail control with Treflan or Sonalan at 1 lb ai/A was best when granules were applied to soil with little surface residue and incorporated twice (once at application, once immediately before planting) with a field cultivator (Table 2).

Table 2. Foxtail control in soybeans with Treflan and Sonalan granules applied April 20, 1994 in standing stubble or conventionally tilled soil and incorporated with various tillage implements at Carrington, North Dakota. Soybeans were seeded May 17 with a Concord air seeder featuring 12-inch sweeps (10-inch spacing between rows) or a John Deere MaxEmerge row crop planter.
				Foxtail control
Herbicide	Rate	Residue at application	Incorporation tool	Concord	MaxEmerge
	lb/A			%
Treflan	1	tilled	field cultivator	95	93
Treflan	1	stubble	no incorporation	90	88
Treflan	1.25	stubble	no incorporation	90	91
Treflan	1	stubble	Haybuster undercutter	92	89
Treflan	1.25	stubble	Haybuster undercutter	95	93
Treflan	1	stubble	rotary hoe	91	86
Treflan	1.25	stubble	rotary hoe	94	92
Treflan	1	stubble	John Deere mulch master	94	88
Treflan	1.25	stubble	John Deere mulch master	93	93
Treflan	1	stubble	Phoenix harrow	91	88
Treflan	1.25	stubble	Phoenix harrow	94	90
Sonalan	1	tilled	field cultivator	96	95
Sonalan	1	stubble	no incorporation	81	74
Sonalan	1	stubble	Haybuster undercutter	92	88
Sonalan	1	stubble	rotary hoe	85	79
Sonalan	1	stubble	John Deere mulch master	91	86
Sonalan	1	stubble	Phoenix harrow	82	76
C.V.%				4.1
LSD (0.05)				5
Planter effect: Not significant

Foxtail control was not significantly lower, however, when Treflan granules were applied in standing stubble and incorporated by most conservation-till incorporation implements. Treflan left unincorporated on the surface in standing stubble controlled foxtail 90%. Sonalan incorporated by conservation-till implements in standing stubble did not provide foxtail as good as that achieved in the conventional-till system. The Concord air seeder might have been expected to cause streaking of foxtail control because of soil movement by the 12-inch sweeps. However, control in plots treated with the Concord appeared slightly higher than where the MaxEmerge was used, although there was no significant effect of planter type when data were averaged over all treatments.

Fargo soybeans. October-applied Treflan granules provided good to excellent foxtail control in a conventional-till system as well as in a no-till system with no incorporation or with conservation-till incorporation implements (Table 3). Treflan granules applied in November in standing stubble and left on the surface did not perform as well, however. Similar results were obtained with Sonalan granules except that the undercutter-incorporated granules controlled foxtail only 70%.

Table 3. Foxtail control in soybeans with Treflan and Sonalan granules applied October or November, 1991 in standing stubble or conventionally tilled soil and incorporated with various tillage implements at Fargo, North Dakota.
Herbicide application			Residue of application	Herbicide incorporation method	Foxtail control		Grain yield
Herbicide	Rate	Date			6/24	7/29
	(lb/A)				%		(bu/A)
Treflan	1	Oct. 23	tilled	field cultivator	86	86	23.1
Treflan	1	Oct. 23	stubble	none	95	88	24.9
Treflan	1	Oct. 23	stubble	rotary hoe	97	93	23.8
Treflan	1	Oct. 23	stubble	undercutter	91	83	22.8
Treflan	1	Nov. 13	stubble	none	70	67	19.0
Sonalan	1	Oct. 23	tilled	field cultivator	96	90	24.9
Sonalan	1	Oct. 23	stubble	none	98	90	25.5
Sonalan	1	Oct. 23	stubble	rotary hoe	96	88	26.0
Sonalan	1	Oct. 23	stubble	undercutter	70	61	24.0
Sonalan	1	Nov. 13	stubble	none	73	59	21.2
Handweeded	0		tilled	field cultivator	-	-	29.0
Handweeded	0		stubble	undercutter	-	-	26.6
C.V. %					10	10	10.6
LSD 5%					13	12	3.7

Preplant-incorporated Treflan and Sonalan in conventional till outperformed mid-April applications in standing stubble incorporated with an undercutter (Table 4). A second undercutter pass (at planting) did not improve foxtail control with Treflan granules but did appear to improve control with Sonalan.

Table 4. Efficacy of Treflan or Sonalan granules applied in mid April, 1992 in standing stubble and incorporated with one or two passes with an undercutter at Fargo. All granule applications received one undercutter pass immediately after application. A second undercutter pass was received by some treatments immediately before seeding on May 15.
Application Residue No. of Foxtail			Residue at application	No. of undercuttings	Foxtail control
Herbicide	Rate	Date
	(lb/A)			(No.)	(%)
Treflan-EC	1	5/15	Tilled	-	91
Treflan-G	1	4/16	stubble	1	84
Treflan-G	1	4/16	stubble	2	82
Sonalan-EC	1	5/15	tilled	-	96
Sonalan-G	1	4/16	stubble	1	73
Sonalan-G	1	4/16	stubble	2	84
C.V., %					11
LSD (0.05)					15

REFERENCES

Conservation Tillage Information Center. 1991. National survey of conservation tillage practices. Natl. Assoc. Conserv. Dist., Ft. Wayne, IN.

Dexter, A. 0., J. D. Nalewaja, D. fl. Rasmussen, and J. Buchli. 1981. Survey of wild oats and other weeds in North Dakota in 1978 and 1979. North Dakota Res. Rep. 79.

DowElanco. 1994. Treflan E.C. product label. Indianapolis, IN 46285.

DowElanco. 1994. Treflan TR-l0 product label. Indianapolis, IN 46285.

Parochetti, J. V. and E. R. Ilein. 1973. Volatility and photodecomposition of trifluralin, benefin, and nitralin. Weed Sc. 21:469-473.

Parochetti, J. V. and 0. W. Dec. 1978. Photodecomposition of eleven dinitroaniline herbicides. Weed Sci. 26:153-156.

Sloneker, L. L. and W. C. Moldenhauer. 1977. Measuring the amount of crop residue remaining after tillage. J. Soil Water Conserv. 32:231-236.

Whitfield, C. J., J. J. Bond, B. W. Greb, T. M. McCalla, and F. H. Siddoway. 1962. A standardized procedure for residue sampling. Agric. Res. Serv. 41-68. U. S. Dept. of Agric., Washington, D.C.