Daniel C. Cloutier

Morphology and yield response to weed pressure by corn hybrids differing in canopy architecture

Abstract Recently, corn ( Zea mays L.) hybrids accumulating more leaf area above the ear, maturing earlier, yielding better in narrower row spacings and tolerating higher population densities than conventional hybrids have been developed. However, no research has been conducted to assess their ability to compete with weeds. The objective of this study was to quantify morphological and grain yield responses of hybrids with differing canopy architectures to the presence and absence of weeds. Field experiments were conducted in 1996, 1997, and 1998 at Ste. Anne de Bellevue, Quebec and in 1996 at Ottawa, Ontario. Three hybrids, leafy reduced-stature (LRS), late maturing big leaf (LMBL), and conventional Pioneer 3979 (P3979), were evaluated at two population densities (normal and high), row spacings (38 and 76 cm) and weed pressure levels (weed-free and weedy). Weed pressure reduced the plant height of LRS less (only 4 cm) than the tall hybrids (average reduction of 26 cm). The overall grain yield of the LMBL hybrid was much greater (12.7 mg ha −1 ) than the LRS (9.6 mg ha −1 ) and P3979 (11.0 mg ha −1 ) hybrids in the absence, but not in the presence (LRS, 6.5; LMBL, 6.7; and P3979, 6.8 mg ha −1 ), of weeds. The yield of early-maturing LRS and P3979 (especially LRS) hybrids, were least affected by weed pressure, suggesting better tolerance of, and competition with, weeds. However, further research with more LRS hybrids is needed, as is the development of better yielding LRS hybrids, before they can be recommended over conventional hybrids.

Weed Biomass Production Response to Plant Spacing and Corn (Zea mays) Hybrids Differing in Canopy Architecture1

Field experiments were conducted in 1996, 1997, and 1998 at Ste. Anne de Bellevue, Quebec, Canada, and in 1996 at Ottawa, Ontario, Canada, to quantify the impact of corn hybrids, differing in canopy architecture and plant spacing (plant population density and row spacing), on biomass production by transplanted and naturally occurring weeds. The treatments consisted of a factorial combination of corn type (leafy reduced stature [LRS], late-maturing big leaf [LMBL], a conventional Pioneer 3979 [P3979], and, as a control, a corn-free condition [weed monoculture]), two weed levels (low density [transplanted weeds: common lambsquarters and redroot pigweed] and high density [weedy: plots with naturally occurring weeds]), two corn population densities (normal and high), and row spacings (38 and 76 cm). At all site-years under both weed levels, the decrease in biomass production by both transplanted and naturally occurring weeds was greater due to the narrow row spacing than due to the high plant population density. The combination of narrower rows and higher population densities increased corn canopy light interception by 3 to 5%. Biomass produced by both transplanted and naturally occurring weeds was five to eight times less under the corn canopy than in the weed monoculture treatment. Generally, weed biomass production was reduced more by early-maturing hybrids (LRS and P3979) than by LMBL. Thus, hybrid selection and plant spacing could be used as important components of integrated pest management (weed control) for sustainable agriculture. Nomenclature: Common lambsquarters, Chenopodium album L. #3 CHEAL; corn, Zea mays L.; redroot pigweed, Amaranthus retroflexus L. # AMARE. Additional index words: Competitivness, early maturity, weed management. Abbreviations: LAI, leaf area index; Lfy, leafy; LMBL, late-maturing big leaf; LRS, Leafy reduced stature; P3979, Pioneer 3979; rd1, reduced stature.

The use of thermal time to model common lambsquarters (Chenopodium album) seedling emergence in corn

Abstract A mathematical model was developed to predict common lambsquarters seedling emergence in southwestern Quebec. The model was based on the thermal-time concept, using air temperatures in the double-sine calculation method. The model was built using data from five experiment-years for corn naturally infested with weed populations. Once developed, the model was calibrated using different crop seedbed preparation times. The base temperature was then adjusted for each time of seedbed preparation. A power regression function was used to relate adjusted base temperatures and the accumulated thermal units at seedbed preparation time. A modified Weibull function was then fitted to the field emergence data, expressed as the cumulative proportion of the total seedling emergence over the growing season as a function of cumulative thermal units. The simplicity and accuracy of this model would make it an excellent tool to predict common lambsquarters seedling emergence in field situations, facilitating the determination of the timing of scouting in integrated weed management systems. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; corn, Zea mays L. ‘Pioneer 3921’.

Weed response to flame weeding at different developmental stages.

Abstract Flame weeding is often used for weed control in organic production and other situations where use of herbicides is prohibited or undesirable. Response to cross-flaming was evaluated on five common weed species: common lambsquarters, redroot pigweed, shepherds-purse, barnyardgrass, and yellow foxtail. Dose-response curves were generated according to species and growth stage. Dicot species were more effectively controlled than monocot species. Common lambsquarters was susceptible to flame treatment with doses required for 95% control (LD95) ranging from 0.9 to 3.3 kg/km with increasing maturity stage. Comparable levels of control in redroot pigweed required higher doses than common lambsquarters, but adequate control was still achieved. Flaming effectively controlled shepherds-purse at the cotyledon stage (LD95  =  1.2 kg/km). However, the LD95 for weeds with two to five leaves increased to 2.5 kg/km, likely due to the rosette stage of growth, which allowed treated weeds to avoid thermal injury. Control of barnyardgrass and yellow foxtail was poor, with weed survival > 50% for all maturity stages and flaming doses tested. Flame weeding can be an effective and labor-saving weed control method, the extent of which is partially dependent on the weed flora present. Knowledge of the local weed flora and their susceptibility to flame weeding is vital for the effective use of this method. Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; common lambsquarters, Chenopodium album L. CHEAL; redroot pigweed, Amaranthus retroflexus L. AMARE; shepherds-purse, Capsella bursa-pastoris (L.) Medik. CAPBP; yellow foxtail, Setaria pumila (Poir.) Roemer and J.A. Schultes SETLU.

Calibration and validation of a common lambsquarters (Chenopodium album) seedling emergence model

Abstract Studies were conducted to calibrate and validate a mathematical model previously developed to predict common lambsquarters seedling emergence at different corn seedbed preparation times. The model was calibrated for different types of soil by adjusting the base temperature of common lambsquarters seedling emergence to the soil texture. A relationship was established with the sand mineral fraction of the soil and was integrated into the model. The calibrated model provided a good fit of the field data and was accurate in predicting cumulative weed emergence in different soil types. The validation was done using data collected independently at a site located 80 km from the original experimental area. There were no differences between observed and predicted values. The accuracy of the model is very satisfactory because the emergence of common lambsquarters populations was accurately predicted at the 95% probability level. This model is one of the first to take into consideration seedbed preparation time and soil texture. This common lambsquarters emergence model could be adapted to model other weed species whose emergence is limited by low spring temperature. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL.; corn, Zea mays L. ‘Pioneer 3921’.

Effect of the Presence or Absence of Corn on Common Lambsquarters (Chenopodium album L.) and Barnyardgrass [Echinochloa crus-galli (L.) Beauv.] Emergence1

A 3-yr study was conducted to establish if the presence of corn had an effect on the emergence patterns and total weed seedling density under growing conditions in southwestern Québec. Weed seedling emergence was monitored in permanent quadrats throughout the growing season in the presence and absence of growing corn. Common lambsquarters and barnyardgrass were prevalent in most site-years. The presence of corn did not affect the patterns of common lambsquarters and barnyardgrass emergence nor their total weed seedling density except in 1994. Corn canopy was probably not sufficiently developed to affect light levels or soil temperature needed for weed germination and, consequently, seedling emergence. In 1994, in the absence of corn, some soil crusting was observed on a fine-textured soil, and the total number of seedlings was reduced. The results of these weed emergence studies in corn can be extended to other crops growing with wide row spacing and relatively slow canopy closure similar to those of grain corn. Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; common lambsquarters, Chenopodium album L. # CHEAL; corn, Zea mays L. ‘Pioneer 3921’. Additional index words: Amaranthus retroflexus L., AMARE, crop competition, redroot pigweed, weed density, weed seedling emergence. Abbreviations: CHU, corn heat units; PAR, photosynthetically active radiation.

Mechanical Weed Control in Agriculture

Weeds are plants that are considered undesirable in a crop at a given time.Weeds are harmful for a number of reasons. They reduce crop yields, interfere with the harvest, support pathogens and insect pests and contaminate seeds.

Carbon and nitrogen supplementation to soybean through stem injection and its effect on soybean plant senescence

Abstract Plant senescence studies have indicated that internal competition for nutrients such as carbon (C) and nitrogen (N) can be an important factor in the initiation of senescence. A greenhouse experiment was conducted to determine the effect of increased supplies of C and N on senescence of soybean (Glycine max [L.] Merr) plants. Soybean plants were injected with solutions of sucrose (150gL‐1), N (15 mM N), and distilled water from the onset of flowering until senescence using a modified stem injection technique. The average uptake rate of all solutions was 1.3 mL d‐1 per plant. The plants injected with sucrose accumulated the most biomass, followed by those injected with N and distilled water. Soybean plants injected with sucrose senesced 17 days later than the distilled water control while senescence was not delayed for plants injected with N. Injection of either N or sucrose increased the concentration and content of N in soybean plants. The results indicated that intra‐plant‐competition for reduced C plays an important role in plant senescence. Because the total amount of N injected was only 2% of the total plant N, as compared to 31 % for C, the role of intra‐plant competition for N was less clear.

Mechanical Weed Control in Corn (Zea mays L.)

Mechanical weed control in corn was practised as early as the 19th century. Over the past 30 years, however, effective selective herbicides have more or less replaced mechanical cultivation (Lampkin 1990). Although cultivation, or tillage, is still done because of the benefits to the soil, weed control is performed through an early-season application of herbicide. Tillage not only controls weeds but loosens the soil and breaks the surface crust, a common problem in corn growing. Crusts tend to form in silty clay soils after a period of rain followed by hot, windy weather. The crust slows oxygen diffusion and reduces heat transfer, makes emergence difficult for corn seedlings, and has a negative impact on crop uniformity. Removing the surface crust by cultivation also promotes mineralization of the nutrients required by corn (Souty and Rode 1994). In addition, cultivation helps to preserve soil moisture needed for plant growth, since the layer of loosened soil limits the capillary rise of moisture. This function of cultivation is most effective in regions with a dry climate and when the corn root system is not very well developed. When the roots are well distributed throughout the soil or the foliage provides shade, little moisture is lost even if the field has not been cultivated.