Trifluralin Reduces Oat Establishment and Yield But Not Quality

Frank A. Manthey, Richard K. Zollinger,
Michael S. McMullen, and Orval R. Swenson
Department of Cereal Science and Department of Plant Sciences
North Dakota State University


Abstract
Tolerance of 10 oat (Avena sativa L.) genotypes to trifluralin 4 EC (Dow Agrosciences) applied preplant incorporated (PPI) at 0.12, 0.25, and 0.37 lb ai/acre was investigated in a field experiment located at Prosper and Thompson, North Dakota in 1993 and 1994. Trifluralin reduced emergence of all oat genotypes. Oat seedling emergence decreased with increased rate of trifluralin. The reduction in oat emergence by trifluralin at 0.12 and 0.25 lb/acre was partially compensated by increased tillering and seed/panicle. Trifluralin decreased the yield of ‘Paul’, a hull-less oat, more than other genotypes. Average yield reduction from trifluralin at 0.12 lb/acre was 9%, at 0.25 lb/acre was 23%, and at 0.37 lb/acre was 46%. Trifluralin did not affect oat kernel weight, test weight, groat percentage, and lipid or protein content. This article is only available online at http://www.ag.ndsu.nodak.edu/ndagres/ndagres.htm

Impact — This research indicates that oat are injured by trifluralin residues that could occur in soil one year after application. Results of this study would be useful when planning crop rotations.
Audience — Oat producers; herbicide manufacturers and sales representatives; crop consultants.

Keywords
Genotype response; trifluralin carryover; trifluralin injury.

Introduction
Trifluralin is used extensively in the northern Great Plains to control grass and broadleaf weeds in barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), dry bean (Phaseolus vulgaris L.), potato (Solanum tuberosum L.), soybean [Glycine max (L.) Merr.], and sunflower (Helianthus annuus L.). Trifluralin is applied PPI at 0.5 to 1 lb ai/acre for broadleaf crops and is applied PPI and pre-emergence incorporated at 0.35 to 0.5 lb ai/acre for barley and wheat. Small grains differ in their tolerance to trifluralin. Trifluralin tolerance is greatest for barley, intermediate for wheat, and least for oat (Lemerle et al. 1985; O’Sullivan et al. 1985; Morrison et al. 1989).

Trifluralin is volatile and must be incorporated into the soil where it is adsorbed by clay and organic matter. Trifluralin dissipates from soil primarily through volatilization and microbial degradation. Soil water is the most important factor affecting the rate of trifluralin dissipation (Grover et al. 1988; Morrison et al. 1989). In the Canadian Prairie, 26% of trifluralin spring applied remained in the soil the following spring, with over 85% of the remaining residues still present in the top 3 inches of the field soil (Grover et al. 1988).

Growers have observed that seeding oat the year following trifluralin application can reduce stand, growth, and yield of some oat genotypes. Risk of injury was greatest when a dry season followed application, which reduced degradation of trifluralin. Environmental conditions at seeding that promote slow seedling emergence generally are conducive to crop injury from trifluralin. Injury to small grains is greatest with cool, wet conditions, deep seeding, and low seed vigor (O’Sullivan et al. 1985; Morrison et al. 1991).

Studies on the effect of trifluralin residue in the soil on wheat and barley establishment and yield have been conducted; however, we are not aware of any studies conducted on oat. Therefore, our objectives were to determine oat tolerance to trifluralin and the impact of injury from trifluralin on seedling establishment and grain yield and quality.

Materials and Methods
Field experiments were conducted at Prosper and Thompson, N.D. in 1993 and 1994. The soil at Prosper is a Bearden silty clay loam (fine, silty, frigid, Aeric Calciaquoll) with 3.6% organic matter and 7.5 pH. The soil at Thompson is a Bearden silt loam (fine, silty, frigid, Aeric Calciaquoll) with 4.6% organic matter and 8.2 pH.

The experimental design was a randomized complete block with a split plot arrangement and four replicates. Main plots were four trifluralin rates and subplots were 10 oat genotypes. Experimental units consisted of four 8-ft long rows, with 1 ft between rows.

Trifluralin was applied on May 3, 1993, and May 12, 1994 at Thompson, and on May 10, 1993 and 1994 at Prosper. Trifluralin at 0, 0.12, 0.25, and 0.37 lb ai/acre was applied to a dry soil surface and immediately incorporated 2 inches deep using a rototiller. These rates reflect residues that could occur the season following trifluralin application in soybean, sunflower, or dry bean in North Dakota assuming 25% trifluralin residual (Grover et al. 1988). Treatments were applied with a bicycle-wheel-type plot sprayer delivering 17 gal/acre at 40 psi with 8002 flat fan nozzles (Spraying Systems Co.).

Eighty oat genotypes currently used in tame oat breeding programs in the North Central region of the United States were screened using a petri dish bioassay (Beckie et al. 1990) to determine their tolerance to trifluralin. Ten oat genotypes, five tolerant (‘Dane’, MN90217, MN90218, MN90219, ND863146) and five susceptible (‘Fidler’, ‘Hazel’, ‘Paul’, ‘Riel’, ‘Whitestone’) were selected to be used in the field experiments. Paul is a hull-less oat. The oat genotypes were seeded 1.5 inches deep at 72 lb/acre on May 4, 1993 and on May 16, 1994 at Thompson, and on May 11, 1993 and 1994 at Prosper.

Seedling emergence was determined from the center 1 yd of the second row when oat was in the 2.5 leaf stage. Oat height was determined at maturity from four measurements per plot. The number of culms/yd of row was determined from the center 1 yd of the second row after harvest.

Entire plots were harvested at maturity with a plot combine. Oat grain samples were dried using a forced air dryer to approximately 10% moisture, and cleaned. Grain yield, test weight, and 1000-kernel weight were determined.

Oat grain was dehulled with an impact dehuller and the groat percentage (weight of dehulled oat/weight of oat grain) was determined. Lipid contents of whole groats were determined using wide-band nuclear magnetic resonance (Conway and Earle, 1963). The groats were ground in a centrifugal mill through a 0.02 inch (0.5 mm) screen. Groat protein was determined using a crude protein combustion method (American Association of Cereal Chemists, 1995). Chemical analysis of each sample was determined twice and reported on a dry weight basis.

Genotypes differed genetically in their seedling emergence, culm production, height, and yield. Therefore, data are presented as percentage reduction compared to the same genotype in the nontreated control for these agronomic traits. Data were subjected to analysis of variance. The means were separated by Fisher’s Protected LSD test at the 0.05 level of significance.

Results and Discussion
Seedling emergence in untreated plots varied from 47 plants/yd for Dane and Paul to 57 plants/yd for ND873146, when averaged over locations and years (Table 1). Trifluralin reduced seedling emergence of all oat genotypes, but the reduction was greater at Thompson than at Prosper. Individual genotype response to trifluralin was erratic and did not consistently follow the preliminary tolerant and susceptible genotype classification from the original petri dish bioassay. For example, trifluralin reduced the emergence of Paul more than the other genotypes in 1994. Conversely at Prosper in 1993, Paul had one of the lowest reductions in seedling emergence of the 10 genotypes exposed to trifluralin. At Prosper in 1993, seedling emergence of Dane and ND873146 were reduced more than the other genotypes, but were least affected of all genotypes evaluated at Prosper in 1994.

Oat seedling emergence was reduced 12% at 0.12, 43% at 0.25, and 63% at 0.37 lb/acre of trifluralin, averaged over genotype and environment (data not shown). Seedling emergence was less at Prosper than at Thompson in 1993 and 1994 (Table 2). Seedling emergence might have been more difficult in the finer textured silty clay loam soil at Prosper than the silt loam at Thompson. Little or no reduction in seedling emergence occurred when trifluralin at 0.12 lb/acre was applied at Prosper in 1993 and 1994. However, trifluralin at 0.12 lb/acre reduced oat emergence 31% in 1993 and 12% in 1994 at Thompson.

Trifluralin at 0.12 and 0.25 lb/acre did not reduce the number of culms/yd, except at Thompson in 1994 where trifluralin at 0.25 lb ai/acre reduced culm density 30% (Table 2). Trifluralin at 0.37 lb/acre reduced culms/yd 12 to 57% at Prosper and Thompson in 1993 and 1994. Based on culms produced, increased tillering by oat resulted in enough extra culms to compensate for the reduction in emergence whenever emergence was reduced less than 50% and provided partial compensation whenever the stand reduction was 60% or more. However, increased tillering often did not result in comparable yield compensation. Morrison et al. (1989) reported increased tillering in spring wheat that recovered from early-season trifluralin injury.

Oat also compensated for the reduction in oat emergence by trifluralin by producing more seed/panicle (Table 3). The number of seed/panicle increased from 3 to 22% for all genotypes, except Paul. The greatest increase in the number of seed/panicle occurred with MN90217 at 22% and Whitestone at 18%, when averaged over trifluralin rates, locations, and years.

Oat yield varied from 80 bu/acre for Paul, the hull-less oat, to 120 bu/acre for MN90217 (Table 3). The yield for Paul, adjusted for the lack of hulls, would be 107 bu/acre. Trifluralin reduced yield 40% for Paul compared to 20 to 28% for the other genotypes. The average yield reduction from trifluralin at 0.12 lb/acre was 9%, at 0.25 lb/acre was 23%, and at 0.37 lb/acre was 46%, averaged over environments and genotypes (data not shown). Trifluralin at 0.12 lb/acre caused yield reductions of 5 to 15% at Prosper and Thompson in 1993 and 1994 (Table 2). Trifluralin at 0.25 and 0.37 lb/acre caused greater yield reduction at Thompson (32 to 67%) than at Prosper (10 to 33%) in both years.

Trifluralin at 0.12 and 0.25 lb/acre caused little or no reduction in oat height, when averaged over locations and years (Table 4). However, trifluralin at 0.37 lb/acre always reduced oat height; the smallest reduction was 9% for ND873146 and 10% for Riel, whereas the greatest reduction was 22% for Paul. Trifluralin injury to oat did not affect oat kernel weight, test weight, groat percentage, lipid or protein content, regardless of genotype, trifluralin rate, or environment (data not shown).

Oat response to trifluralin could not be explained by air temperature or rainfall (Table 5). Oat was seeded in May when air and soil temperatures and soil moisture were favorable for oat germination and emergence at all environments. Conditions were favorable for growth during the growing season, which should have aided recovery from injury. The greater injury at Thompson than at Prosper may be related to soil type. Trifluralin may have been adsorbed less by the silty loam soil at Thompson than the silty clay loam soil at Prosper.

In the northern Great Plains, oat is usually the first crop seeded in the spring. Cold soil temperatures slow oat germination and emergence, which increases oat exposure time to trifluralin residues. Production practices that enhance the rate of seedling emergence, i.e. delayed seeding into warmer soil and the use of foundation seed with high seed vigor, would reduce the effect of trifluralin residue on oat emergence. However, delayed seeding increases the risk of crop damage by high temperature during grain filling (Coffman and Frey, 1961).

Oat genotypes evaluated, even though classified as tolerant or susceptible in a petri dish bioassay, were not tolerant to trifluralin in the field. Although oat quality was not reduced, grain yields were reduced by trifluralin residues as low as 0.12 lb/acre. Oat partially compensated for reduced emergence by increased tillering and increased number of seed/panicle. These data support the restriction on the trifluralin label that oat should not be seeded on trifluralin-treated fields for 18 months after application.

References
American Association of Cereal Chemists. 1995. Approved Methods of the AACC. Method 46-30. Crude protein combustion. Am. Assoc. Cereal Chem., St. Paul, MN.

Beckie, H.J., L.F. Friesen, K.M. Nawolsky, and I.N. Morrison. 1990. A rapid bioassay to detect trifluralin-resistant green foxtail (Setaria viridis). Weed Technol. 4:505-508.

Coffman, F.A. and K.J. Frey. 1961. Influence of climate and physiological factors on growth of oats. P. 420-464 in F.A. Coffman, ed. Oats and Oat Improvement. Am. Soc. Agron., Madison, WI.

Conway, T.F. and F.R. Earle. 1963. Nuclearmagnetic resonance for determining oil content of seeds. J.Am. Oil Chem. Soc. 40:265-268.

Grover, R., A.E. Smith, S.R. Shewchuk, A.J. Cessna, and J.H. Hunter. 1988. Fate of trifluralin and triallate applied as a mixture to a wheat field. J. Environ. Qual. 17:543-550.

Lemerle, D., A.R. Leys, R.B. Hinkley, and J.A. Fisher. 1985. Tolerances of wheat cultivars to pre-emergence herbicides. Aust. J. Exp. Agric. 25:922-926.

Morrison, I.N., K.M. Nawolsky, M.H. Entz, and A.E. Smith. 1991. Differences among certified wheat seedlots in response to trifluralin. Agron. J. 83:119-123.

Morrison, I.N., K.M. Nawolsky, G.M. Marshall, and A.E. Smith. 1989. Recovery of spring wheat (Triticum aestivum) injured by trifluralin. Weed Sci. 37:784-789.

O’Sullivan, P.A., G.M. Weiss, and D. Friesen. 1985. Tolerance of spring barley to trifluralin deep-incorporated in the fall or spring. Can. J. Plant Sci. 65:169-177.

Project Background

Authors
Frank A. Manthey, Assistant Professor
Department of Cereal Science
North Dakota State University
Fargo, North Dakota 58105
manthey@prairie.nodak.edu
www.ndsu.nodak.edu/cereal-science

Richard K. Zollinger, Associate Professor
Department of Plant Sciences
North Dakota State University
Fargo, North Dakota 58105
rzolling@ndsuext.nodak.edu
www.ndsu.nodak.edu/instruct/hammond/dept/index.html

Michael S. McMullen, Associate Professor
Department of Plant Sciences
North Dakota State University
Fargo, North Dakota 58105
mmcmulle@plains.nodak.edu
www.ndsu.nodak.edu/instruct/hammond/dept/index.html

Orval R. Swenson, Research Director
AGSCO, Inc.
Grand Forks, ND

Corresponding author
Richard K. Zollinger

Primary location of research
Agricultural Experiment Station, North Dakota State University, Fargo, ND

Funding source
Agricultural Experiment Station, North Dakota State University, Fargo, ND

Table of Contents – Summer 1998