Effect Of Herbicide Rates Research Articles

Pethoxamid dissipation and microbial activity and structure in an agricultural soil: Effect of herbicide rate and organic residues

Soil is a non-renewable resource, and its degradation compromises human health, natural ecosystems, and even the climate. The application of organic amendments and herbicides is commonplace in agriculture, and their impact on soil fertility needs to be evaluated. Therefore, the objective was to evaluate the effect on soil microbial activity and structure of amendments, sewage sludge (SS) and green compost (GC), and the rate of herbicide pethoxamid applied (2, 10 and 50 mg kg−1). Herbicide dissipation kinetics, soil dehydrogenase activity (DHA) and the profile of phospholipid-derived fatty acids (PLFAs) extracted from the soil have been determined in unamended (S) and amended (S + SS and S + GC) soils. The dissipation curves of pethoxamid applied at the three rates closely fitted a single first order kinetics model in all the soils. The dissipation rate decreased with the rate applied in the order 2 mg kg−1 > 10 mg kg−1 > 50 mg kg−1 in unamended and amended soils. However, the half-life or time required for 50% dissipation (DT50) of pethoxamid was not significantly different in unamended and amended soils when applied at 2 and 10 mg kg−1, but it was lower in the amended soils than in the unamended one when the herbicide was applied at the highest rate. The highest DHA mean values were obtained in S + GC treated with pethoxamid at 2, 10 and 50 mg kg−1; however, DHA was lower in S + SS than in S. Peak DHA values were observed in S and S + GC soils treated with pethoxamid at 2 mg kg−1 at 15 days of incubation, and in S, S + GC and S + SS treated with the herbicide at 10 and 50 mg kg−1 at 35 days of incubation. These peak DHA values are close to 50% of herbicide dissipation. A statistical analysis of the PLFA results has revealed significant effects for sampling time in all the soils, for the pethoxamid rate, and for the interaction between time and pethoxamid rate only in S + GC and S + SS. The application of organic amendments to soil accelerated the dissipation of higher rates of pethoxamid compared to the unamended soil, which is important to prevent the herbicide's negative impacts on the soil microbial community.

Effects of application date and rate of foliar-applied glyphosate on pine seedlings in Turkey

Glyphosate is the herbicide most extensively used for site preparation and conifer release. It is a broad-spectrum herbicide and therefore crop safety is a critical issue. This study assessed the early effects of 14 different treatments, including no weed control, manual weed control, and 12 foliar-applied herbicide treatments at low, intermediate, high, and highest application rates and application timing on glyphosate phytotoxicity of containerized seedlings of Austrian pine (Pinus nigra J.F. Arnold.), Scots pine (P. sylvestris L.) and maritime pine (P. pinaster Aiton), conifer species widely used for afforestation and supplementary plantings in Turkish forestry. In general, Scots pine seedlings were tolerant to glyphosate compared to the other species. Glyphosate phytotoxicity varied significantly according to the time and rate of application. Seedlings were relatively tolerant to glyphosate in April whereas they were intolerant in May. The highest herbicide rate (1.2% v:v) was consistently phytotoxic to all species. Moreover, the effect of herbicide rate on seedling survival and growth varied significantly according to application date (i.e., application rate × date interaction). Seedlings appeared tolerant to glyphosate at low and intermediate rates (0.2, 0.4% v:v) between mid-spring and mid-summer, whereas they demonstrated significant sensitivity to the highest rate across all time periods. Glyphosate at the high rate (0.8% v:v) was particularly more phytotoxic when applied in May. Application of glyphosate at rates up to 0.8% could be recommended for weed control without significant pine damage in mid-spring when the needles presumably have a dense leaf epicuticular wax layer limiting herbicide penetration. Applications of 0.8 and 1.2% v:v are not recommended during May–June.

Herbicide Rate, Glyphosate/Glufosinate Sequence and Corn/Soybean Rotation Effects on Weed Seed Banks

The effect of herbicide rates on weed control and crop yield is the subject of countless and ongoing research projects. Weed seed banks receive very little attention in comparison. The seed bank resulting from 3 yr (2006 to 2008) of single herbicide rates in a cropping system where glyphosate/glufosinate and corn/soybean were rotated or not was evaluated in a field located in St-Augustin-de-Desmaures, Québec, Canada. Field plots under conventional tillage were seeded in corn every year, or corn and soybean (1 yr). These plots received the same herbicide every year or various glyphosate/glufosinate 3-yr sequences. Subplots were sprayed with a single POST application of the recommended rate of glyphosate (900 g ae ha−1) or glufosinate (500 g ai ha−1) or lower rates. Subplots received the same full (1.0×, recommended) or reduced (0.5×, 0.75×) rate every year. After crop harvest in 2008, soil cores were extracted and the weed seed bank was evaluated. Including soybean in the cropping system resulted in lower seed banks compared to those under continuous corn cropping. Including glufosinate in a glyphosate herbicide sequence increased weed seed banks due to the lower efficacy of the glufosinate rates tested at reducing the seed bank of annual grasses. Higher herbicide rates translated into lower seed banks, up to a certain rate. After 3 yr, the lowest seed bank (full glyphosate rates every year) still had 4,339 ± 836 seeds m−2and was higher than the initial seed bank (2,826 ± 724 seeds m−2).

Mesotrione Controls Creeping Bentgrass (Agrostis Stolonifera) in Kentucky Bluegrass

Creeping bentgrass creates a dense, high-quality playing surface on golf courses, but it often encroaches adjacent areas of Kentucky bluegrass. Mesotrione can control creeping bentgrass in Kentucky bluegrass, but more information is needed regarding the effect of herbicide rate and number of applications on creeping bentgrass control and the impact to Kentucky bluegrass. Field experiments were conducted to determine the effect of application rate and number of applications on creeping bentgrass control. One application of mesotrione controlled 7 to 43% of creeping bentgrass in Kentucky bluegrass, and two applications of mesotrione controlled 39 to 88% as rates increased from 70 to 1,120 g ai/ha. Gaps present in the canopy after the creeping bentgrass died reduced overall turfgrass quality 2 to 6 wk after treatment (WAT) before recovering. These data indicate the capability of mesotrione to selectively control creeping bentgrass while providing excellent safety to Kentucky bluegrass.Nomenclature: Mesotrione; creeping bentgrass, Agrostis stolonifera L. AGSST; Kentucky bluegrass, Poa pratensis L. POAPR.

Application Timing of Metribuzin, Chlorimuron, and Imazaquin for Common Cocklebur (Xanthium strumarium) Control

Field experiments were conducted in 1986 and 1987 to evaluate the effect of herbicide rate (two-thirds and maximum labeled rate) and timing of application before soybean planting on common cocklebur control. In 1986, chlorimuron plus metribuzin at 50 plus 320 and 80 plus 480 g ai/ha and imazaquin at 90 g ai/ha applied at planting controlled common cocklebur better than when applied 4 weeks before planting (WBP). Imazaquin at 140 g/ha applied at planting controlled common cocklebur better than when applied 6 WBP. All treatments at two-thirds of the labeled rate applied at planting controlled common cocklebur comparable to the full labeled rate applied 2, 4, or 6 WBP. In 1987, all treatments applied 2 WBP controlled common cocklebur better than when applied 4, 6, or 8 WPB.

Establishment and development of surface sown pasture species in a nitrophilous weed association: effect of herbicide rate

In an experiment carried out between 1976 and 1979 near Orange, New South Wales, the effects of four rates of glyphosate (0.1 25, 0.25, 0.5 and 1.0 kg/ha active ingredient (a.i.)) and three rates of amitrole (0.5, 0.75, 1.0 kg/ha a.i. in association with 2.5 kg/ha a.i. 2,2-DPA) on the suppression of a nitrophilous weed association (broadleafed plants, annual grasses, native perennial grasses, annual legumes) and the resultant establishment and development of surface sown pastures species (Medicago sativa, Phalaris aquatica, Dactylis glomerata, Festuca arundinacea) were measured. The length of weed suppression in the year of spraying (1976) was the most important factor in the eventual development of the sown species. Glyphosate at 1.0 kg/ha a.i. gave better weed suppression for longer (up to and beyond 23 weeks after spraying) than any other herbicide treatment and allowed sown species to establish and survive the first summer better and thus produce a better pasture three years later. Weed suppression between 8 and 19 weeks after spraying affected the initial establishment of sown species; in general, establishment was better on herbicide treatments that reduced ground cover of the weed association to less than 30% in this period. Rate of weed suppression had no effect because no sown species germinated in the eight weeks after spraying. Three years after treatment the ground cover of the nitrophilous weed association was 31% on the best herbicide treatment (glyphosate, 1.0 kg/ha a.i.) and 83% on the unsprayed control; the respective ground cover of sown species was 60% and 7%. The increase in ground cover of sown species during the three years was on most treatments almost entirely due to the increase in basal area of P. aquatica.