Trifluralin Reduces Oat Establishment and Yield But Not Quality (continued)

Keywords

Introduction

Materials and
Methods

Results and
Discussion

References

Project
Background

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.

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Table of Contents – Summer 1998