Abul Hashem

Resistance of Wild Radish (Raphanus raphanistrum) to Acetolactate Synthase-Inhibiting Herbicides in the Western Australia Wheat Belt1

Abstract: Of 78 biotypes of wild radish (Raphanus raphanistrum) collected from Western Australia (WA), 42% were resistant and 14% intermediate to acetolactate synthase (ALS)-inhibiting herbicides. Based on the LD50 and GR50 ratios, the resistant biotype K96071 was 81-fold more resistant to chlorsulfuron and 114- to 116-fold more resistant to metosulam than the susceptible biotype K96041. More resistant biotypes were found in northern zones than in southern zones of WA. Resistant biotypes evolved after five applications of chlorsulfuron in a predominantly cereal–lupin rotation. Where resistant biotypes were found, ALS-inhibiting herbicides were not rotated with herbicides with different modes of action as frequently as in fields with susceptible biotypes. Cross-resistance to chlorsulfuron and metosulam was found in the resistant biotypes even though only 15% of the 78 biotypes were exposed to two applications of metosulam over a 10-yr period. All 78 biotypes were effectively controlled by simazine and 2,4-D amine. Nomenclature: Chlorsulfuron; metosulam; simazine; 2,4-D; wild radish, Raphanus raphanistrum L. #3 RAPRA. Additional index words: Weed survey, cross-resistance, crop rotations, herbicide rotations. Abbreviations: ALS, acetolactate synthase; GR50, rate of herbicide required to inhibit growth by 50%; I, intermediate; R, resistant; S, susceptible; SU, sulfonylurea; WAP, weeks after planting.

Manipulating Crop Row Orientation to Suppress Weeds and Increase Crop Yield

Abstract Crop rows oriented at a right angle to sunlight direction (i.e., east–west within the winter cropping system in Western Australia) may suppress weed growth through greater shading of weeds in the interrow spaces. This was investigated in the districts of Merredin and Beverley, Western Australian (latitudes of 31° and 32°S) from 2002 to 2005 (four trials). Winter grain crops (wheat, barley, canola, lupines, and field peas) were sown in an east–west or north–south orientation. Within wheat and barley crops oriented east–west, weed biomass (averaged throughout all trials) was reduced by 51 and 37%, and grain yield increased by 24 and 26% (compared with crops oriented north–south). This reduction in weed biomass and increase in crop yield likely resulted from the increased light (photosynthetically active radiation) interception by crops oriented east–west (i.e., light interception by the crop canopy as opposed to the weed canopy was 28 and 18% greater in wheat and barley crops oriented east–west, compared with north–south crops). There was no consistent effect of crop row orientation in the canola, field pea, and lupine crops. It appears that manipulation of crop row orientation in wheat and barley is a useful weed-control technique that has few negative effects on the farming system (i.e., does not cost anything to implement and is more environmentally friendly than chemical weed control). Nomenclature: Barley, Hordeum vulgare L, canola, Brassica napus L, field pea, Pisum sativum L, lupine, Lupinus angustifolius L, wheat, Triticum aestivum L

Triazine Resistance in a Biotype of Wild Radish (Raphanus raphanistrum) in Australia1

This study documents the first case of triazine resistance in wild radish and the resistance mechanism involved. The high survival (57 to 97%) of the resistant (R) biotype progeny plants treated at a rate four times higher than the commonly recommended rate of simazine or atrazine clearly established that the R biotype plants were resistant to triazines. All the plants of the susceptible (S) biotype plants were killed when treated at half the commonly recommended rate of atrazine (0.5 kg/ha) or simazine (0.25 kg/ha). The dry weight of the S biotype was reduced by 89 to 96% at the commonly recommended rate of atrazine or simazine, while the dry weight of the R biotype plants was reduced by only 36 to 54% even when treated at a rate four times higher than the commonly recommended rate of atrazine or simazine. The growth-reduction–ratio values indicated that the R biotype progeny plants were 105 and 159 times more resistant to atrazine and simazine, respectively, than the S biotype plants. Leaf chlorophyll fluorescence yield was reduced by 97% in the S biotype 24 h after application of triazine compared with only 9% reduction in the R biotype, indicating that the resistance mechanism involved is target-site based. The R biotype was effectively controlled by herbicides of different modes of action. Nomenclature: Atrazine; simazine; triazine; wild radish, Raphanus raphanistrum L. #3 RAPRA. Additional index words: Dry weight, leaf chlorophyll fluorescence. Abbreviations: ALS, acetolactate synthase; DAE, days after emergence; GR50 ratio, the ratio of the herbicide rate required to inhibit the growth of resistant biotype progeny plants by 50% to the rate required to inhibit the growth of S biotype plants by 50%; PS II, photosystem II; R, resistant (biotype); S, susceptible (biotype); SE, standard error; TT, triazine tolerant; WA, Western Australia.

Evaluating the double knockdown technique: sequence, application interval, and annual ryegrass growth stage

Applying glyphosate followed by a mixture of paraquat + diquat in the same season for pre-planting weed control may reduce the risk of developing resistance to either herbicide. Glasshouse and field experiments at Merredin and Beverly, Western Australia, were conducted over 2 seasons to determine the best herbicide application sequence, growth stage of annual ryegrass at which to apply the 2 herbicides, and application time and interval to be allowed between applications for optimum control of annual ryegrass (Lolium rigidum Gaud.). Annual ryegrass plants were treated at 3 growth stages with either glyphosate 540 g a.i./ha alone, paraquat + diquat 250 g a.i./ha alone, glyphosate followed by paraquat + diquat 250 g a.i./ha, or paraquat + diquat 250 g a.i./ha followed by glyphosate 540 g a.i./ha (the double knockdown treatment). The herbicides were applied at different times of the day, with varied intervals between herbicides when applied in sequence. The glasshouse experiment showed that herbicides in sequence more effectively killed annual ryegrass plants at the 3–6-leaf stage than a single application of either herbicide. Field experiments showed that applying glyphosate followed by paraquat + diquat provided 98–100% control of annual ryegrass plants when applied at the 3- or 6-leaf stage in 2002 and at all 3 growth stages in 2003. Generally, the sequence of paraquat + diquat followed by glyphosate was less effective than the reverse sequence, although the difference was not large. Averaged over 2 seasons, herbicides in sequence were most effective when the first herbicide was applied at the 3- or 6-leaf stage of annual ryegrass. An interval of 2–10 days between applications of herbicides was more effective than 1 day or less. The application time did not significantly affect the efficacy of double knockdown herbicides on annual ryegrass plants under field conditions.

Competition Effects on Yield, Tissue Nitrogen, and Germination of Winter Wheat (Triticum aestivum) and Italian Ryegrass (Lolium multiflorum)1

Abstract: Field experiments were conducted to study the competition effect of winter wheat planted in a square arrangement and Italian ryegrass planted randomly on biomass yields of both species, ryegrass seed yield, N use efficiency, and progeny seed germination. Increases in wheat density up to 800 plants/m2 reduced ryegrass seed yield by 87% but increased its harvest index up to 42% compared to its monoculture yield. Species densities and their interactions accounted for 66 to 73% of the total variation in per-unit area biomass of species, and their association was more favorable to ryegrass biomass than wheat. Seeds of each species had three times greater nitrogen percentage than did shoots. Intra- and interspecific competition increased nitrogen percentage in wheat seeds. In Italian ryegrass, only interspecific competition increased N percentage in seeds. Although total nitrogen uptake by winter wheat was three times greater than in Italian ryegrass, Italian ryegrass was two times more efficient than wheat at producing biomass per unit of N taken up and specific leaf area at heading stage in mixture. Germination percentages of progeny seeds of both species in mixtures were greater in presence of high densities of the companion species than in their monocultures. Nitrogen was not the main limiting factor for competition between winter wheat and Italian ryegrass in this study. Nomenclature: Italian ryegrass, Lolium multiflorum (Lam) #3 LOLMU; wheat, Triticum aestivum L. Additional index words: Ryegrass harvest index, nitrogen uptake, nitrogen concentration in seeds and shoots, nitrogen use efficiency, biomass production, progeny seed germination, specific leaf area. Abbreviations: DAE, days after emergence; HI, harvest index; NUE, nitrogen use efficiency; R, Italian ryegrass; RE, rectangularity; SLA, specific leaf area; W, winter wheat; WR, interaction between winter wheat and Italian ryegrass.

Increased Carrier Volume Improves Preemergence Control of Rigid Ryegrass (Lolium rigidum) in Zero-Tillage Seeding Systems

Abstract PRE herbicides are less effective in the zero-tillage system because of increased residual crop stubble and reduced soil incorporation. However, since weeds are not physically controlled in the zero-tillage system, reliance on efficacy of PRE herbicides is increased. This research investigated the impact of carrier volume and droplet size on the performance of PRE herbicides (in wheat crops at four sites in 2010) to improve herbicide efficacy in conditions of high stubble biomass in zero-tillage systems. Increasing carrier volume from 30 to 150 L ha−1 increased spray coverage on water-sensitive paper from an average of 5 to 32%. Average control of rigid ryegrass by trifluralin (at Cunderdin and Merredin sites) and trifluralin or pyroxasulfone (at Wickepin and Esperance sites) improved from 53 to 78% with increasing carrier volume. Use of ASABE Medium droplet size improved spray coverage compared with ASABE Extremely Coarse droplet size, but did not affect herbicide performance. It is clear that increased carrier volume improves rigid ryegrass weed control for nonwater-soluble (trifluralin) and water-soluble (pyroxasulfone) PRE herbicides. Western Australian growers often use low carrier volumes to reduce time of spray application or because sufficient high-quality water is not available, but the advantages of improved weed control justifies the use of a high carrier volume in areas of high weed density. Nomenclature: Pyroxasulfone; trifluralin; rigid ryegrass; Lolium rigidum Gaudin; wheat; Triticum aestivum L. Resumen Los herbicidas PRE son menos efectivos en sistemas de labranza cero debido a su menor incorporación en el suelo y la mayor cantidad de residuos de cultivo. Sin embargo, como las malezas no son controladas físicamente en los sistemas de labranza cero, la dependencia en la eficacia de herbicidas PRE es mayor. Se investigó el impacto del volumen de aplicación y el tamaño de gota en el desempeño de los herbicidas PRE (en cultivos de trigo en cuatro localidades en 2010) para mejorar la eficacia de herbicidas en condiciones de alta biomasa de residuos de cultivo en sistemas de labranza cero. El incrementar el volumen de aplicación de 30 a 150 L ha−1 aumentó la cobertura de la aplicación, medida con papel sensible al agua, de 5 a 32%. El control promedio de Lolium rigidum con trifluralin (en las localidades Cunderdin y Merredin) y trifluralin o pyroxasulfone (en Wickepin y Esperance) mejoró de 53 a 78% al incrementar el volumen de aplicación. El uso de gotas ASABE de tamaño mediano mejoró la cobertura de la aspersión al compararse con gotas ASABE extremadamente grandes, pero no afectó el desempeño del herbicida. Está claro que el incrementar el volumen de aplicación mejoró el control de L. rigidum con herbicidas PRE insolubles en agua (trifluralin) y solubles en agua (pyroxasulfone). Los productores del Oeste de Australia usan frecuentemente volúmenes bajos de aplicación para reducir el tiempo de aplicación o porque no hay suficiente agua de alta calidad disponible, pero las ventajas del mayor control de malezas justifica el uso de altos volúmenes de aplicación en áreas con alta densidad de malezas.

Efficacy of Interrow Weed Control Techniques in Wide Row Narrow-Leaf Lupin

Abstract The sharp decline in the area of lupin grown in Australia is partly attributed to the failure to control herbicide-resistant weeds in narrow-leaf lupin crops grown with the conventional 25-cm-wide row spacing. Growing lupin with wider row spacing allows for interrow weed control by nonselective herbicides using a sprayshield or physical methods. During 2003 to 2006, two experiments conducted at five sites evaluated the efficacy of interrow weed control techniques in narrow-leaf lupin crops grown in 55- to 65-cm-wide rows within the Western Australia wheatbelt. Interrow herbicides were applied POST using sprayshields, intrarow herbicides were banded on lupin rows at seeding, and interrow weeds were mowed using a garden mower. The main weed species at each site was rigid ryegrass, blue lupin, or wild radish. Paraquat plus diquat applied on the interrow of the lupin crop with sprayshields controlled up to 100% of weeds between rows, leading to increases in lupin grain yield in most of the sites. Glyphosate alone, a mixture of glyphosate plus metribuzin, and glyphosate followed by paraquat plus diquat also controlled interrow weeds, but did not increase lupin grain yield at any site. Thus, paraquat plus diquat is a better choice for interrow weed control in wide row lupin than glyphosate. Mowing did not improve weed control, but mowing followed by paraquat plus diquat increased lupin grain yield at one site. Regression models predicted that there was a strong relationship between weed biomass and lupin grain yield. Nomenclature: Diquat; glyphosate; paraquat; propyzamide(3,5-dichloro-N-(1,1-dimethyl-2-propynyl)benzamide); blue lupin, Lupinus cosentinii Guss; rigid ryegrass, Lolium rigidum Gaud. LOLRI; wild radish, Raphanus raphanistrum L. RAPRA; narrow-leaf lupin, Lupinus angustifolius L

Emergence, survival, biomass production, and seed production of Chloris truncata (windmill grass) in the Western Australian wheatbelt

Chloris truncata is a C4 grass species, native to Australia. Within the wheatbelt of Western Australia (WA), it is a weed of grain cropping systems and a beneficial forage species within pasture systems. Plant emergence, density, survival, biomass production, seed production, and seed germinability were investigated, in pasture or cropping systems, at two trial sites (in Merredin, WA) over two years (from 2007 to 2009). Chloris truncata predominantly emerged and set seed during spring and early summer. This species is usually referred to as a short-lived perennial, and could survive for >14 months, but predominantly grew as a spring/summer annual in the WA wheatbelt. Maximum plant density, biomass, and seed production were, respectively, 4.2–28.2 plants/m2, 8.3–146.1 g dry biomass/m2, and 3325–61 383 seeds/m2, depending on location. Cohorts emerging in spring produced more seeds than those that emerged during other seasons. Average seed germinability reached a maximum of 62%, following an initial 3–4-month period of dormancy. There are few herbicides to control plants growing within the winter/spring annual grain crops, and so further research into increased crop competitive ability is required to reduce growth of spring cohorts and potentially reduce seed set. However, the biomass produced by C. truncata (range 0–1460 kg/ha) can be used as forage in a pasture system, or over the summer/autumn feed gap in a cropping system.

Carrier volume is more likely to impact trifluralin efficiency than crop residue

Abstract PRE herbicides are generally less effective in conservation farming systems because of high levels of crop residue. However, performance can be improved if the herbicides are applied with a high carrier volume. This research investigated the interaction of carrier volume and row spacing or height of crop residue on the control of rigid ryegrass with trifluralin, at Cunderdin and Wongan Hills Western Australia. To create plots with varying residue row spacing in 2011, wheat was seeded in 2010 using a narrow row spacing (25 or 22 cm at Cunderdin and Wongan Hills), wide spacing (50 or 44 cm), or not planted to wheat. Narrow or wide row spacing or no crop plots had an average residue biomass of 4480, 3560, and 2430 kg ha−1 at Cunderdin and 1690, 1910, and 1030 kg ha−1 at Wongan Hills. To vary residue height, the wheat was harvested to produce tall, medium, or short crop residue (22, 13, and 5 cm at Cunderdin and 27, 22, and 17 cm at Wongan Hills). Rigid ryegrass seeds were broadcast onto each site in 2011 and trifluralin was sprayed using 50, 75, or 100 L ha−1 carrier volume (directly prior to seeding). Increased carrier volume increased spray coverage at both sites (average cover of 9, 15, and 26% at 50, 75, and 100 L ha−1), leading to improved control of rigid ryegrass (68, 75, and 82% control at Cunderdin and 23, 41, and 68% control at Wongan Hills). Reduced crop residue height or increased row spacing led to reduced rigid ryegrass density at Cunderdin but had no impact at Wongan Hills. Therefore, carrier volume has a more consistent impact on the performance of trifluralin than crop residue row spacing or height. Nomenclature: Trifluralin; rigid ryegrass, Lolium rigidum Gaudin; wheat, Triticum aestivum L. Resumen Los herbicidas PRE son generalmente menos efectivos en sistemas de producción con conservación de suelos debido al alto nivel de residuos de cultivo. Sin embargo, se puede mejorar el desempeño de los herbicidas si estos son aplicados usando altos volúmenes. Esta investigación estudió la interacción entre el volumen de aplicación y la distancia entre hileras y la altura del residuo del cultivo sobre el control de Lolium rigidum con trifluralin, en Cunderdin y Wongan Hills en el oeste de Australia. Para crear las parcelas con diferentes distancias entre hileras de residuos en 2011, se sembró trigo en 2010 usando una distancia entre hileras corta (25 ó 22 cm a Cunderdin y Wongan Hills), una distancia larga (50 ó 44 cm), o no se sembró trigo del todo. Las distancias entre hileras corta, larga, y sin cultivo tuvieron un promedio de residuos de biomasa de 4480, 3560, y 2430 kg ha−1 en Cunderdin y 1690, 1910, y 1030 kg ha−1 en Wongan Hills. Para variar la altura del residuo, el trigo se cosechó de tal forma que se generaron residuos de cultivo altos, medianos, o cortos (22, 13, y 5 cm en Cunderdin y 27, 22, y 17 cm en Wongan Hills). La semilla de L. rigidum se esparció sobre el área experimental en cada localidad en 2011 y se aplicó trifluralin usando 50, 75, ó 100 L ha−1 de volumen de aplicación (directamente antes de la siembra). El aumentar el volumen de aplicación incrementó la cobertura de la aplicación en ambas localidades (cobertura promedio de 9, 15, y 26% a 50, 75, y 100 L ha−1 ), lo que mejoró el control de L. rigidum (68, 75, y 82% de control en Cunderdin, y 23, 41, y 68% de control en Wongan Hills). Una menor altura en los residuos de cultivo o una mayor distancia entre hileras resultó en una menor densidad de L. rigidum, en Cunderdin, pero no afectó en Wongan Hills. De esta forma, el volumen de aplicación tiene una impacto más consistente en el desempeño de trifluralin que la distancia entre hileras o la altura del residuo del cultivo

Emergence, survival and seed production of Enteropogon ramosus in a pasture–wheat rotation or continuous pasture rotation in the wheatbelt of Western Australia

Enteropogon ramosus is a native, perennial, C4 grass species found within the wheatbelt of Western Australia. Emergence, survival, seed production and seed dormancy of E. ramosus was investigated in a continuous pasture rotation, a pasture–minimum tillage wheat rotation, and a pasture–minimum tillage wheat rotation where a cultivation event at the beginning of the pasture year was used to kill all E. ramosus plants. The results indicated that E. ramosus could germinate throughout the year, although plant density (ranging annually from 0 to 17 plants m−2) was lowest in conditions of low rainfall (summer–autumn drought). Seed production (estimated from seed head production, r = 91.7, P < 0.001) ranged from 0 to 2274 m–2 and was greatest in spring, in the continuous pasture rotation. Seed germinability reached 80–89%, following an initial 3 months of dormancy directly after seed production. Cultivation at the beginning of the pasture-crop rotation killed all plants, reduced emergence and prevented seed production for the 2-year period of the experiment. Soil disturbance from minimum tillage crop sowing reduced but did not eliminate E. ramosus plants. As a result, E. ramosus grew throughout the year in the minimum tillage cropping system. Further research is required to determine the competitive effect of E. ramosus on crop growth.