Off-target glyphosate deposits from aerial silvicultural applications under various meteorological conditions

Aerial spray applications of the herbicide glyphosate were made over a forest canopy under various meteorological conditions. A ‘Thru Valve Boom’ dispersal system carried by a Cessna 188 fixed-wing aircraft flying at 49 m s^?1 was used to generate an aqueous spray cloud with a volume median diameter of 150 μm. Glyphosate deposits from multiple overlaid crosswind line sources released at 10 m above ground level were measured on ground sheets and artificial foliage at downwind distances between 50 and 400 m. Trials were conducted in stable, neutral and unstable atmospheric boundary layers with average wind speeds between 2·2 and 5·7 m s^?1 and vertical intensities of turbulence between 0·07 and 0·16. Linear regression lines fitted to logarithmically transformed measurements and downwind distances (x) gave statistically significant correlation coefficients (P = 0·01), and were compared by ANOVA. Glyphosate deposits on ground sheets and artificial foliage were attenuated at rates inversely proportional to x to the power 1·7-4·3. Regression line comparison showed that, in general, deposits on ground sheets decreased with increasing wind speed and intensity of turbulence, and some statistically significant differences were found in slopes and elevations of regression lines from different trials. However, deposits at the 50-m station increased with wind speed due to the large-drop cloud component. Regression line comparison for deposits on artificial foliage showed that, in general, they were highest in the intermediate wind speed-neutral stability case and similar in the high wind speed-unstable and low wind speed-stable boundary layers, although deposits at the 50-m station also increased with wind speed.     

Spray deposit patterns and persistence of diflubenzuron in some terrestrial components of a forest ecosystem after application at three volume rates under field and laboratory conditions

Spray deposit patterns and persistence of diflubenzuron [1-(4-chlorophenyl)- 3-(2,6-difluorobenzoyl)urea] in white pine (Pinus strobus L.) and sugar maple (Acer saccharum Marsh.) canopies, forest litter and soil were studied after aerial application of a 250 g kg^?1 wettable powder formulation, ‘Dimilin® WP-25’, at 70 g active ingredient (a.i.) ha^?1, using three volume rates (10, 5 and 2.5 liters ha^?1) over three blocks in a mixed forest near Kaladar, Ontario, Canada, during 1986. Spray droplets were sampled at ground level using ‘Kromekote®’ cards, and diflubenzuron deposits were collected on glass plates. Droplets were the largest (with a volume median diameter of 250 μm) at the 10 liters ha^?1 rate, resulting in the highest number of droplets per cm² on the Kromekote cards and deposits of diflubenzuron on glass plates. Deposits on foliage, litter and soil were also correspondingly the highest. At the 5.0 and 2.5 liters ha^?1 rates, volume median diameter values were smaller (195 and 150 μm, respectively) and deposits on the substrates were markedly lower. In the spray block that received 10 liters ha^?1, diflubenzuron persisted in foliage as long as 120 days after treatment, but it lasted for only about a week in forest litter and soil samples. At 5 and 2.5 liters ha^?1, diflubenzuron failed to persist in foliage as long, and residues in litter and soil, which were barely above the quantification limit, persisted only for a few days. Laboratory studies, conducted under constant meteorological conditions using different droplet-size spectra, showed that deposit levels were not affected when the volume median diameter of the spray cloud decreased from 253 μm to 145 μm, but were markedly reduced as this progressively decreased from 92 to 37μm. The dissimilarities between the field and laboratory findings were attributed to meteorological and other factors influencing droplet deposition on tree canopy in aerial applications of pesticides over forests.     

Distribution and activity of spray deposits in an oak canopy following aerial application of diluted and undiluted formulations of Bacillus thuringiensis Berliner against the gypsy moth,Lymantria dispar L. (Lepidoptera: Lymantriidae)

The distribution and biological activity of spray deposits resulting from aerial applications of diluted and undiluted Bacillus thuringiensis, ‘Dipel 64AF’ against the gypsy moth, Lymantria dispar L., were examined in oak stands in south-eastern Ontario, Canada. The sprays were applied by fixed-wing aircraft equipped with four ‘Micronair AU4000’ atomizers. Application of diluted formulation at 30 BIU ha^?1 in 6.0–6.4 litre generally resulted in a higher droplet density (10–28 cm ^?2 leaf) than application of undiluted product at the same dosage rate in 1.8 litre ha^?1 (4–10 cm ^?2). However, spray deposits of undiluted product with a volume median diameter (D_v.5) of 90–130 μm caused as much mortality of gypsy moth larvae in bioassays of sprayed foliage as deposits of diluted product with a D_v.5 of 150–350 μm despite a two- to three-fold reduction in droplet density. Our data suggest that by using fine spray atomization, undiluted application of these formulations can offer the same efficacy against gypsy moth as coarsely atomized sprays of diluted product.     

Deposition of aerially applied tebufenozide (RH5992) on balsam fir (Abies balsamea) and its control of spruce budworm (Choristoneura fumiferana [Clem.])

A field trial was conducted in 1994 to determine the foliar deposit of tebufenozide (RH5992), applied aerially, and its efficacy against spruce budworm, Choristoneura fumiferana (Clem.). A commercial 240 g litre^-1 formulation of the insecticide (Mimic 240LV) was mixed with water, dyed with a tracer dye (Rhodamine WT) and sprayed with a light fixed-wing aircraft. Six application strategies were tested. Five used 70 g AI ha^-1 in a spray volume of 1 or 2 litre^-1 ha^-1 with single or double applications; the sixth was an unsprayed control. Results show that the spectra of the spray applications were, with one exception, fairly uniform. Volume and number median diameters ranged from 100 to 130 μm and 27 to 72 μm, respectively. Mean number of drops cm^-2 on Kromekote cards were <2·0 for strategies where either 1 or 2 litre ha^-1 were sprayed. Nevertheless no one strategy produced droplet densities that were significantly different (P<0·05) from the other strategies. Tebufenozide recovered from foliage averaged 2·5 to 5·9 μg g foliage^-1 when 1 litre ha^-1 was sprayed and 5·8 to 6·8 μg g foliage^-1 after 2 litre ha^-1 were sprayed. When a single application was the strategy used, the mean number of droplets cm^-2 and μg tebufenozide g foliage^-1 ranged from 1·2 to 1·4 and 2·5 to 5·9, respectively. With double applications, the same response parameters ranged from 0·3 to 1·9 and 2·5 to 6·8, respectively. Budworm population reductions (%) and the number of larvae that survived tebufenozide treatments were significantly different (P<0·05) from the controls. After strategies that used 1 litre spray ha^-1, mean percentage population reductions ranged from 61·4 to 93·6 whereas populations were reduced by 85·6 to 98·3% when 2 litre ha^-1 were sprayed. After double applications the mean percentage population reductions ranged from 93·6 to 98·3, but single application strategies resulted in mean reductions of 61 to 86%. Mean population reductions in the controls were 61%. The mean number of larvae per branch that survived spray strategies of 1 litre ha^-1 ranged from 1·3 to 7·4, and from 0·4 to 1·3 when 2 litre ha^-1 was the spray volume. In the controls an average of 10·2 larvae survived. With one exception, mean percentage defoliation in the treated areas was also significantly less (P<0·05) than that in the control. Mean defoliation in trees sprayed at 1 litre spray ha^-1 ranged from 40 to 62·8% whereas those treated at 2 litre ha^-1 had mean defoliation levels from 31·5 to 62·8%. In contrast, average defoliation in the controls was 92·1%. When a single application was the spray strategy, mean defoliation ranged from 31·5 to 62·8%. These data imply that a double application of tebufenozide at 70 g in 2 litre ha^-1 was the most efficacious strategy. However, analyses of the data also show that the primary influence on deposits and defoliation was interactions between number of applications and spray. Nevertheless the two independent variables acted without significant interactions when influencing percentage reductions of spruce budworm populations. © 1998 SCI     

Control of Achillea millefolium L. (yarrow) by rotary cultivation and glyphosate

Various control strategies for Achillea millefolium L. (yarrow) were investigated in a dense stand of the weed at Lincoln College in 1977–1978. In early spring plots were either rotary cultivated or left undisturbed. In late spring, plots of both previous treatments were either left undisturbed, rotary cultivated or sprayed with glyphosate at 1·5 kg ha^?1. The whole experiment was rotary cultivated twice 1 week later and sown with Hordeum vulgure L. cv. Zephyr (barley) at 144 kg seed ha^?1. MCPA + dicamba at 0·9+0·15 kg ha^?1 was applied to half of each plot when the second node was detectable (Zadok 32). Rotary cultivation and glyphosate both substantially reduced the regrowth of A. millefolium but glyphosate reduced regrowth by a greater proportion when applied to undisturbed plants than when applied to plants regenerating after cultivation. Both gave a more than 95% reduction compared to the control (rotary cultivation only at sowing time) in the amount of A. millefolium present in the barley stubble in the autumn. MCPA + dicamba caused seedling mortality but did not affect the numbers of primary shoots from rhizome fragments. The grain yield of the barley increased from 2·91 t ha^?1 when A. millefolium was not controlled to 4·23 t ha^?1 with good control. The barley yield appeared to be restricted by competition from regenerating A. millefolium and by a nitrogen deficiency induced in some regimes by nitrogen immobilization in decaying rhizomes.     

Biological responses to glyphosate drift from aerial application in non‐glyphosate‐resistant corn

BACKGROUND: Glyphosate drift from aerial application onto susceptible crops is inevitable, yet the biological responses to glyphosate drift in crops are not well characterized. The objectives of this research were to determine the effects of glyphosate drift from a single aerial application (18.3 m swath, 866 g AE ha^?1) on corn injury, chlorophyll content, shikimate level, plant height and shoot dry weight in non‐glyphosate‐resistant (non‐GR) corn. RESULTS: One week after application (WAA), corn was killed at 3 m from the edge of the spray swath, with injury decreasing to 18% at 35.4 m downwind. Chlorophyll content decreased from 78% at 6 m to 22% at 15.8 m, and it was unaffected beyond 25.6 m at 1 WAA. Shikimate accumulation in corn decreased from 349% at 0 m to 93% at 15.8 m, and shikimate levels were unaffected beyond 25.6 m downwind. Plant height and shoot dry weight decreased gradually with increasing distance. At a distance of 35.4 m, corn height was reduced by 14% and shoot dry weight by 10% at 3 WAA. CONCLUSIONS: Corn injury and other biological responses point to the same conclusion, that is, injury from glyphosate aerial drift is highest at the edge of the spray swath and decreases gradually with distance. The LD₅₀ (the lethal distance that drift must travel to cause a 50% reduction in biological response) ranged from 12 to 26 m among the biological parameters when wind speed was 11.2 km h^?1 and using a complement of CP‐09 spray nozzles on spray aircraft. Published 2010 by John Wiley & Sons, Ltd.     

Agronomic effects from the control of Agropyron repens in barley by pre-harvest application of glyphosate

Pre-harvest application of glyphosate in barley at 1·44 and 0·72 kg ha^?1 was compared with post-harvest application at 1·44 kg ha^?1 at six sites in south-east Scotland, three sprayed in 1980 and three in 1981. Both levels of pre-harvest application gave consistent 95–99% control of A. repens compared with 0–76% control from post-harvest application. Yields of crops grown in 1981 were significantly increased after all the 1980 pre-harvest treatments and after one post-harvest treatment. No significant depressions in grain germination were recorded from the lower rate of pre-harvest application but one significant depression was recorded from the higher rate. Combine harvesting throughput at a given grain loss level was significantly improved by pre-harvest application and moisture content of grain at harvest was significantly reduced by up to 2·5%. Wheeling losses from pre-harvest spraying ranged from 1 to 5%. Crop yield increases in the year after spraying compensated for herbicide and application costs plus any yield losses through tractor wheelings.     

Chemical control of nodding thistle (Carduus nutans L.) in New Zealand pastures

Broadcast sprays of several herbicides were applied at different times of the year at several sites in Hawkes Bay, Canterbury and Otago. For good thistle control, date of application was more important than types of herbicide. In Hawkes Bay, applications made in April, May and June tended to be the most effective. Under slightly cooler Canterbury conditions, April, September and October were the best application dates. In the Otago trials, spring emergence of thistle seedlings meant that the most consistent results came from September or October applications. At all sites, applications made in July or August were relatively ineffective, probably because of low winter temperatures and slow thistle growth rates. MCPA (potassium salt) at 1·0 kg ha^?1 was the standard herbicide used in all experiments. MCPA at 0·5 kg ha^?1, MCPB (sodium salt) at 0·5 and 1·0 kg ha^?1 and 2,4-D at 0·5 kg ha^?1 did not kill as many thistles as MCPA at 1·0 kg ha^?1. MCPA at 1·5 kg ha^?1 and MCPB (butyl) ester + clopyralid at 0·5 + 0·015 or 1·0+0·03 kg ha^?1 gave consistently better control than MCPA at 1·0 kg ha^?1 2,4-D at 1·0 or 1·5 kg ha^?1, MCPB at 1·5 or 2·0 kg ha^?1, and MCPA + MCPB at 0·33 + 1·0 or 0·67 + 0·5 kg ha^?1 gave results very similar to MCPA at 1 kg ha^?1. Thistle control varied between sites and years. Some of the variation may have been due to different proportions of first and second year thistles present at spraying, and to variation in genetically determined herbicide susceptibility. Chemical control of thistles was short term only, because of dormant seeds in the soil.     

Glyphosate effects on Canada thistle (Cirsium arvense) roots, root buds, and shoots

Glyphosate ? ? Mention of irademark or proprietary product does not constitute a gtiarantee or warranty oC the product by the U.S. Department of Agriculture and does nut imply its approval to the exclusion of other products thai may also be suitable.
was sprayed at 0009–1·12 kg a.i. ha^?1 on the foliage of large potted glasshouse-grown Canada thistle [Cirsium arvense (L.) Scop.], which had extensive, well-developed roots. Increasing the glyphosate rate progressively reduced the total number of visible adventitious root buds plus emerged secondary shoots per plant proportionately more than root biomass, 10 days after treatment. Cortical tissue of thickened propagative roots became soft, water-soaked, darkened, and some regions decomposed, exposing strands of vascular tissue. Lateral roots completely decomposed. When thickened roots were segmented to stimulate secondary shoot emergence from root buds 10 days after foliar treatment, Fewer secondary shoots emerged than expected from the number of visible adventitious root buds present on both control and herbicide-treated plants. Increasing the rate of glyphosate also reduced the regrowth potential of root buds proportionately more than root biomass. Regrowth potential was measured as the number of emerged secondary shoots 35 days after segmenting unearthed roots from plants that had been sprayed 10 days earlier. When foliar-applied at 0·28 kg ha^?1, glyphosate decreased the regrowth potential of root buds to zero in 2 and 3 days, as measured by secondary shoot dry weight and number, respectively, even though root fresh weight was unchanged 3 days after foliar treatment. These dose-response and time-course experiments demonstrate that glyphosate did not reduce root biomass as much as it decreased root bud numbers and secondary shoot regrowth potential from root buds.     

Some physicochemical factors influencing foliar uptake enhancement of glyphosatemono(isopropylammonium) by polyoxyethylene surfactants

Structure-concentration–foliar uptake enhancement relationships between commercial polyoxyethylene primary aliphatic alcohol (A), nonylphenol (NP), primary aliphatic amine (AM) surfactants and the herbicide glyphosatemono(isopropylammonium) were studied in experiments with wheat (Triticum aestivum L.) and field bean (Vicia faba L.) plants growing under controlled-environment conditions. Candidate surfactants had mean molar ethylene oxide (EO) contents ranging from 5 to 20 and were added at concentrations varying from 0·2 to 10 g litre^?-1 to [¹⁴C]glyphosate formulations in acetone–water. Rates and total amounts of herbicide uptake from c. 0·2–μl droplet applications of formulations to leaves were influenced by surfactant EO content, surfactant hydrophobe composition, surfactant concentration, glyphosate concentration and plant species, in a complex manner. Surfactant effects were most pronounced at 0·5 g acid equivalent (a.e.) glyphosate litre^?-1 where, for both target species, surfactants of high EO content (15–20) were most effective at enhancing herbicide uptake: surfactants of lower EO content (5–10) frequently reduced, or failed to improve, glyphosate absorption. Whereas, at optimal EO content, AM surfactants caused greatest uptake enhancement on wheat, A surfactants gave the best overall performance on field bean; NP surfactants were generally the least efficient class of adjuvants on both species. Threshold concentrations of surfactants needed to increase glyphosate uptake were much higher in field bean than wheat (c. 2 g litre^?-1 and < 1 g litre^?-1, respectively); less herbicide was taken up by both species at high AM surfactant concentrations. At 5 and 10 g a.e. glyphosate litre^?-1, there were substantial increases in herbicide absorption and surfactant addition could cause effects on uptake that were different from those observed at lower herbicide doses. In particular, the influence of EO content on glyphosate uptake was now much less marked in both species, especially with AM surfactants. The fundamental importance of glyphosate concentration for its uptake was further emphasised by experiments using formulations with constant a.i./surfactant weight ratios. Any increased foliar penetration resulting from inclusion of surfactants in 0·5 g litre^?-1 [¹⁴C]glyphosate formulations gave concomitant increases in the amounts of radiolabel that were translocated away from the site of application. At these low herbicide doses, translocation of absorbed [¹⁴C]glyphosate in wheat was c. twice that in field bean; surfactant addition to the formulation did not increase the proportion transported in wheat but substantially enhanced it in field bean.     

Reduced rates of residual and post-emergence herbicides for weed control in vineyards

In 1997 and 1998, five field studies were conducted at four Portuguese wine‐growing regions in order to evaluate the effectiveness of the chemical control of vineyard weeds under Mediterranean conditions using either reduced doses of residual herbicides or only foliar herbicides. Amitrole (3440 g a.i. ha^?1), amitrole + glyphosate mono‐ammonium salt (1720 + 900 g a.i. ha^?1), amitrole (3400 g a.i. ha^?1), amitrole + diuron (2580 + 1500 g a.i. ha^?1), amitrole + simazine (2580 + 1500 g a.i. ha^?1), amitrole + terbuthylazine (2580 + 1500 g a.i. ha^?1) and amitrole + diuron + simazine (2580 + 1300 + 1400 g a.i. ha^?1) were assayed and compared with the following reference herbicides: glyphosate isopropylamine salt (1800 g a.i. ha^?1), amitrole + diuron (2520 + 1680 g a.i. ha^?1), diuron + glyphosate + terbuthylazine (1275 + 900 + 1425 g a.i. ha^?1), amitrole + simazine (1900 + 3900 g a.i. ha^?1) and glyphosate + simazine (800 + 2200 g a.i. ha^?1). The herbicides were applied during late winter. The results indicated that good control was achieved by the application of foliar herbicides alone or of reduced rates of a mixture of residual herbicides with foliar herbicides for at least 2 months. Three months after application, the efficacy of post‐emergence herbicides and lower rates of residual herbicides decreased significantly in clay soils and under heavy rainfall conditions. Convolvulus arvensis– a weed that is becoming increasingly significant in Portuguese vineyards – was poorly controlled, even when glyphosate was used. Despite this, it can be assumed that in those regions in which the trials were conducted, it is possible to employ weed control strategies that entail the elimination or a reduction in the rate of residual herbicides.     

Effects of fluazifop-butyl on shoot growth and rhizome buds of Elymus repens (L.) Gould

A series of glasshouse experiments was conducted to evaluate the activity of fluazifop-butyl, butyl 2-[4-(5-trifluoromethyl-2-pyridyloxy)phenoxy] propionate, against Elymus repens. Foliar applications of doses 0·25–1·0 kg ha^?1 consistently gave better control than did soil applications. The most obvious phytotoxic symptoms were chlorosis and necrosis, beginning with the youngest leaves 5–6 days after spraying, which spread to all leaves within 2 weeks. Translocation was measured by defoliating plants at different times after spraying and assessing regrowth and by evaluating rhizome-bud viability. At low doses (0·125 and 0·25 kg ha^?1) translocation to rhizomes occurred mainly between 6 and 48 h. When fluazifop-butyl was sprayed at a dose range of 0·125–1·0 kg ha^?1, at least 90% of the rhizome buds had accumulated a lethal dose within 72 h of spraying. In another experiment, with a dose of 0·25 kg ha^?1, 31, 72 and 92% of rhizome buds were found to be non-viable when sampled 2, 24 and 48 h respectively after spraying. At 1·0 kg ha^?1 all the buds had accumulated sufficient herbicide to prevent sprouting 48 h after spraying.     

Spray retention and distribution on apple trees

Total deposits and their distribution on bush and dwarf hedgerow apple trees, sprayed at the late dormant and full foliage stages with a copper fungicide by five different methods, were estimated by colorimetric determination of the acid-extracted copper from all the tree parts, and for comparison purposes were converted to equivalent volumes retained. The bush trees were sprayed by hand lance (4500 litresha-¹), by automatic nozzle mast sprayer (2250 litres ha^?1), by conventional air-blast sprayer at medium volume (1125 litres ha^?1) and low volume (560 litres ha^?1), and by hand-directed ultra-low-volume (ULVH) fan-assisted spinning-disc sprayer (6 litres ha^?1). The hedgerow trees were sprayed by conventional air-blast sprayer at low volume (560 litres ha^?1) and by an experimental tractor-mounted ultra-low-volume air-blast sprayer (45 litres ha^?1). At the late dormant stage, the bush trees retained only 9–22 % of the total spray applied by all methods, except that those sprayed by the hand-directed ULVH sprayer retained 57%. At the full foliage stage, when most of the spray was deposited on the leaves, retention for all methods of application was 22–37%. The hedgerow trees at late dormancy retained 6% of the spray applied in low volume and 10% of that by tractor-mounted ultra-low-volume methods, but at full foliage, retention was 25 and 63 %, respectively. On both types of tree the proportions of the spray deposited on the tree components were related to the surface areas of those components.     

Low doses of glyphosate change the responses of soyabean to subsequent glyphosate treatments

Many herbicides promote plant growth at doses well below the recommended application rate (hormesis). The objectives of this study were to evaluate glyphosate‐induced hormesis in soyabean (Glycine max) and determine whether pre‐treating soyabean seedlings with low doses of glyphosate would affect their response to subsequent glyphosate treatments. Seven doses (1.8–720 g a.e. ha^?1) of glyphosate were applied to 3‐week‐old seedlings, and the effects on the electron transport rate (ETR), metabolite (shikimate, benzoate, salicylate, AMPA, phenylalanine, tyrosine and tryptophan) levels and dry weight were determined. The lowest dose stimulated ETR and increased biomass the most. Benzoate levels increased 203% with 3.6 g a.e. ha^?1 glyphosate. Salicylate content and tyrosine content were unaffected, whereas phenylalanine and tryptophan levels were increased by 60 and 80%, respectively, at 7.2 g a.e. ha^?1. Dose–response curves for these three amino acids were typical for hormesis. In another experiment that was replicated twice, soyabean plants were pre‐treated with low doses of glyphosate (1.8, 3.6 or 7.2 g a.e. ha^?1) and treated with a second application of glyphosate (1.8, 3.6, 7.2, 36, 180 or 720 g a.e. ha^?1) 14 days later. For total seedling dry weight, a 3.6 and 7.2 g a.e. ha^?1 glyphosate dose preconditioned the soyabean seedlings to have greater growth stimulation by a later glyphosate treatment than plants with no preconditioning glyphosate exposure. Optimal hormetic doses were generally higher with pre‐treated plants than plants that had not been exposed to glyphosate. Thus, pre‐exposure to low doses of glyphosate can change the hormetic response to later low‐dose exposures.     

Tolerance of spring wheat (Triticum aestivum L.) to trifluralin deep-incorporated in the autumn or spring

Field experiments at Lacombe on a Ponoka loam soil (9·6% organic matter) during 1982 and 1983 investigated the tolerance of spring wheat (Triticum aestivum L.) cv. Neepawa in a weed free situation to trifluralin applied at 0·0–3·0 kg ai ha^?1 in the autumn or spring and incorporated to a depth of 10 cm. Rates of trifluralin above 1·0 kg ai ha^?1 applied in the autumn or spring reduced the percent stand of wheat compared to an untreated control. Two weeks after emergence the crop showed 37 or 47% injury indicated by delayed growth, following application at 1·0 kg ai ha^?1 in the autumn or spring, respectively. The wheat recovered throughout the course of the growing season. At harvest, trifluralin applied in the autumn or spring at rates below 1·0 kg ai ha^?1 caused a yield increase while higher rates caused a yield decrease compared to the untreated control. Spring application caused a greater yield loss than autumn application. The tolerance of spring wheat to trifluralin at rates required for weed control (1·1 kg ai ha^?1 or higher) on this soil type is marginal.     

The role of pendimethalin in the integrated management of propanil-resistant Echinochloa colona in Central America

Pre-emergence activity of pendimethalin on propanil-resistant jungle rice (Echinochloa colona) was demonstrated in glasshouse trials. Both susceptible and resistant populations, collected from Costa Rica, were controlled by 1·25 kg ha^-1, the usual application rate used in the field where Rottboellia cochinchinensis is also a problem. When applied post-emergence, propanil performance was improved by the addition of low doses of pendimethalin to the herbicide mixture. A propanil-resistant selection was controlled by 0·23 kg ha^-1 pendi-methalin+0·54 kg ha^-1 propanil at the one-to-two leaf stage, and 0·23 kg ha^-1 pendimethalin+1·08 kg propanil at the three-to-four leaf stage compared to 1·08 kg and 2·16 kg ha^-1 respectively when propanil was applied alone. This suggests that pendimethalin improves post-emergence control in the field compared to the standard propanil treatment and can provide residual pre-emergence control of late-germinating individuals, so reducing the propanil selection pressure. For effective jungle rice control, growers apply propanil (3·84 kg ha^-1) at 10 and 20 days after planting (DAP) followed by one application of fenoxaprop-P-ethyl (0·045 kg ha^-1) at 35 DAP. Field experiments, conducted in dry-seeded upland rice in southern Costa Rica, demonstrated that under high jungle-rice population pressure, one application of pendimethalin at 1·5 kg ha^-1 provided an effective replacement for propanil, resulting in reduced weed-control costs. ©1997 SCI     

Effects of Low Doses of Glyphosate on Agronomic Traits of Upland Rice

Research has shown the occurrence of the hormesis effect in some upland rice cultures resulting from low-dose application of glyphosate. Glyphosate herbicide is widely used in Brazilian agriculture for controlling the large quantity of weeds. The aim of this work was to verify the effects of low-dose application of glyphosate herbicide on agronomic characteristics in upland rice. The experimental design used was randomized blocks comprising five low-dose applications of glyphosate herbicide (10, 20, 40, 70, and 100?g acid equivalent [a.e.] ha^?1) and the control, in two stages of development of the rice culture (tillering [V4] and floral differentiation [R1]) with four repetitions. The agronomic traits of upland rice were evaluated. Data were subjected to variance analysis, polynomial regression analysis for the quantitative factor, and Tukey’s test for the qualitative factor at p?<?0.05. The grain yield and the number of spikelets per panicle increased with the application of 10?g a.e. ha^?1 of glyphosate at the floral differentiation stage. Until the low dose of 75?g a.e. ha^?1, there was an increase in the number of panicles. Low doses between 70 and 100?g a.e. ha^?1 applied in R1 provided less spikelets per panicle, lower 100-grain weight, and lower grain yield. The leaf flavonoid content increased due to the increase in the low doses of glyphosate herbicide.

     

A scanning electron microscope study of glyphosate deposits in relation to foliar uptake

The effects of several formulations on foliar uptake of glyphosate, and on the morphology of glyphosate deposits on leaves, were examined in Tartary buckwheat (Fagopyrum tataricum (L.) Gaertn.). [¹⁴C]glyphosate, in the form of the free acid or the isopropylamine salt (IPAS), was applied to foliage alone or with various adjuvants. Uptake of all glyphosate IPAS formulations was greater than that of the corresponding acid formulation. Addition of ‘Tween 20’ enhanced the uptake of glyphosate IPAS compared to glyphosate alone, but had no effect on the uptake of glyphosate acid. Ammonium sulfate and the ‘Roundup’ formulation blank increased the uptake of glyphosate acid and IPAS to 2-3 times that of herbicide alone. Surface deposits, as observed by scanning electron microscopy, varied with the formulation of the herbicide, although there were no differences between the acid and IPAS formulations. Glyphosate alone initially formed a deposit with both crystalline and smooth, amorphous areas. Later in the treatment period (48 and 72 h after application), the deposit was almost entirely crystalline. The addition of ‘Tween 20’ or of formulation blank resulted in the formation of a more amorphous, non-crystalline deposit. Herbicide solutions containing ammonium sulfate dried to form a highly crystalline deposit. However, crystals similar to those of glyphosate alone were not visible in these deposits. The ability of these adjuvants to prevent or delay crystal formation may play a role in their enhancement of herbicide uptake.     

Evaluation of the efficacy of glyphosate plus urea phosphate in the greenhouse and the field

BACKGROUND: Glyphosate is a non‐selective, foliar‐applied, systemic herbicide that kills weeds by inhibiting the synthesis of 5‐enolpyruvylshikimate‐3‐phosphate synthase. Urea phosphate (UPP), made by the reaction of urea with phosphoric acid, was applied as an adjuvant for glyphosate in this study. Experiments in the greenhouse and the field were conducted to determine the effects of UPP by comparing the efficacies of glyphosate plus UPP, glyphosate plus 1‐aminomethanamide dihydrogen tetraoxosulfate (AMADS) and Roundup. RESULTS: The optimum concentration of UPP in glyphosate solution was 2.0% when UPP was used as an adjuvant. The ED₅₀ values for glyphosate‐UPP were 291.7 and 462.4 g AI ha^?1 in the greenhouse and the field respectively, while the values for Roundup were 448.2 and 519.6 g AI ha^?1. The ED₅₀ values at 2 weeks after treatment (WAT) and 3 WAT were lowered when UPP was used as an adjuvant in the greenhouse and field study, and the glyphosate + UPP was absorbed over a 2 week period. UPP may increase the efficacy by causing severe cuticle disruption or accelerating the initial herbicide absorption. The result also showed that UPP could reduce the binding behaviour of Ca²⁺ to glyphosate. CONCLUSION: The application of UPP as an adjuvant could increase the efficacy of glyphosate and make it possible to achieve effective control of weeds with glyphosate at lower dose. Moreover, UPP showed less causticity to spraying tools and presented less of a health hazard. Therefore, UPP is accepted as being a new, effective and environmentally benign adjuvant for glyphosate. Copyright © 2011 Society of Chemical Industry     

Residues of Mecoprop in Post-emergence-Treated Wheat and Oat

The dissipation of mecoprop in wheat (Triticum aestivum L.) and oat (Avena sativa L.) was monitored over a growing season following post-emergence application of the dimethylamine salt of mecoprop to each crop at 1·1 kg ha^?1. Residues of mecoprop, as its methyl ester, were determined gas chromatographically using electrolytic conductivity detection. Initial residues in wheat (119 (±20) mg kg^?1) and oat (95·3 (± 10·0) mg kg^?1) on the day of application (four-leaf stage of wheat and four- to five-leaf stage of oat) decreased to 0·1 to 0·2 mg kg^?1, respectively, within six weeks. Residues were non-detectable in the mature seed of both crops. Recoveries of mecoprop were in the order of 90% from the green tissue and seed of both crops fortified at 0·05 mg kg^?1.