Weed control in glyphosate-tolerant sugarbeet (Beta vulgaris L.)

The effect of glyphosate on weeds was evaluated in greenhouse bioassays with five weed species and compared with a commercial mixture of phenmedipham and ethofumesate. Glyphosate was more active than a mixture of phenmedipham and ethofumesate on the weeds. Solanum nigrum was the most sensitive species to both herbicide treatments. The relative potency of glyphosate between the weeds showed consistency at 50% and 90% control levels for four out of five weed species, which could be ranked independently of control level because of similar response curves. In a field trial on sugarbeet genetically engineered to acquire glyphosate tolerance, a total of 720 g a.i. ha^?1 of glyphosate applied in one, two or three applications gave similar or superior control of weeds to a total of 3.17 kg a.i. ha^?1 mixture of metamitron, phenmedipham and ethofumesate applied in three repeated applications.     

Impact of Irrigation Timing and Weed Management Practices on Chlorophyll Content and Morphological Traits of Tomato (Solanum lycopersicum Mill.)

Weeds are a major biotic constraint; compete with crop for the same resources and ultimately reduce productivity. This study evaluated the impact of irrigation intervals and weed management treatments on chlorophyll content and morphological growth of tomato to find an appropriate integrated weed management strategy. Two-year field experiments (2018/2019) were conducted at district Mardan (34°15′38″ N and 72°6′36″ E). Tomato F1 hybrid (Taj?3592) was transplanted during March. The experiments were laid out in a randomized complete-block design in split-plot arrangement with three replications. The main block comprised three irrigation intervals (3, 6, and 9 days) and the sub-block included weed management treatments: transparent polythene, black polythene, weeding except Orobanche, sole weeding of Orobanche, weeding of all weeds, copper oxychloride 1.5?kg a.i ha^?1 (single dose), copper oxychloride 1.5?kg a.i ha^?1 (split doses), copper oxychloride?+?humic acid 25?kg ha^?1 (single dose), copper oxychloride?+?humic acid 25?kg ha^?1 (split doses), copper sulphate 2?kg ha^?1 (single dose), copper sulphate 2?kg ha^?1 (split doses), ammonium sulphate 200?kg ha^?1 (single dose), ammonium sulphate 200?kg ha^?1 (split doses), pendimethalin 33 EC 1.44?kg a.i ha^?1, glyphosate 48 SL 1.5?kg a.i ha^?1, and weedy check. Lowest relative weed density (RWD) of O. cernua (2.23%) and highest RWD of O. cernua (38.01%) were recorded in the 3? and 9?day irrigation intervals, respectively. However, 3?day irrigation interval resulted in highest fresh weed biomass (5794?kg ha^?1). Moreover, the 6?day irrigation interval significantly increased chlorophyll content by 11 and 5%, leaf area by 23 and 6%, and number of branches plant^?1 by 30 and 22% compared to 9? and 3?day irrigation intervals, respectively. Among the weed management treatments, black polythene resulted in the highest weed control efficiency (96%), increasing chlorophyll content by 16%, leaf area by 33%, and number of branches plant^?1 by 64% vs. weedy check. Consequently, 6?day irrigation intervals?×?black polythene could be the best weed management strategy, followed by transparent polythene, weeding of all weeds, pendimethalin, glyphosate, and ammonium sulphate.

     

Grain sorghum response and Palmer amaranth control with postemergence application of fluthiacet-methyl

Palmer amaranth is a problematic weed in grain sorghum production in central United States. Due to limited herbicide options available and ever increasing herbicide-resistant weed species, there is a demand for new mode-of-action herbicides for use in grain sorghum. Fluthiacet-methyl is a relatively new active ingredient that inhibits the enzyme protoporphyrinogen oxidase in target plants. Field studies were conducted at three sites in central United States in 2010 and 2011 to evaluate crop response and Palmer amaranth control with postemergence application of fluthiacet-methyl in grain sorghum. Treatments included fluthiacet-methyl at 4.8 and 7.2 g active ingredient (a.i.) ha^?1 alone and tank-mixed with 2,4-D amine at 260 g acid equivalent (a.e.) ha^?1 or atrazine at 840 g a.i. ha^?1. Carfentrazone at 8.8 g a.i. ha^?1, atrazine at 840 g ha^?1, and a non-treated control were also included. Fluthiacet-methyl treatments caused 9–38% crop injury at 4 ± 1 days after treatment. Tank-mixing atrazine with fluthiacet-methyl seldom affected crop injury, while mixing 2,4-D with fluthiacet-methyl often reduced crop injury. Generally, injury caused by fluthiacet-methyl alone or in combination with atrazine or 2,4-D disappeared within 3 weeks after treatment. Grain yields were reduced in one trial, when 2,4-D mixed with 4.8 or 7.2 g ha^?1 of fluthiacet-methyl caused 18% and 13% plant lodging and 24% and 14% grain yield loss, respectively. Across site-years, fluthiacet-methyl alone at 4.8 or 7.2 g ha^?1 provided 55–95% control of Palmer amaranth. Greater Palmer amaranth control (≥75%) with fluthiacet-methyl alone was achieved when weeds were small or density was low at the time of spraying. Tank-mixing atrazine with fluthiacet-methyl increased Palmer amaranth control and sorghum yields considerably. Tank-mixing 2,4-D with fluthiacet-methyl also increased Palmer amaranth control, but to lesser extent and less consistently than with atrazine. Results indicated that fluthiacet-methyl has potential for use in grain sorghum to combat weeds resistant to acetolactase synthase-inhibitors, triazines, and synthetic auxin herbicides. Tank-mixing atrazine or 2,4-D with fluthiacet-methyl is desirable for effective Palmer amaranth control.     

Application timing of asulam for torpedograss (Panicum repens L.) control in sugarcane in Okinawa island

Field and glasshouse experiments were conducted from 1995 through 1996 to evaluate application timing of asulam (methyl sulfanilylcarbamate) for torpedograss (Panicum repens L.) control in relation to plant age in sugarcane. Above‐ground shoots of torpedograss were completely controlled with asulam at 2–4 kg active ingredient (a.i.) ha^?1 applied 60 or 80 days after planting (DAP) in artificially infested pots. But some newly developed rhizome buds survived after asulam application resulting in 1–25 and 76–100% or more regrowth in 60 and 80 DAP‐applied pots, respectively. Whereas the herbicide at 2–4 kg a.i. ha^?1 applied within 60 DAP completely controlled above‐ground shoots, applied 80 DAP at 2 kg a.i. ha^?1 it did not completely control the weed in the artificially infested field. Regrowth levels were 1–25 and 76–100% or more in 60 and 80 DAP‐applied plots, respectively. Asulam at 2–3 kg a.i. ha^?1 applied 20, 40, 60 or 80 DAP in a naturally infested field completely controlled above‐ground shoots and regrowth levels were 76–100 or more, 51–75, 1–25 and 26–50% in these same DAP applied plots, respectively. The herbicide applied at 4 kg a.i. ha^?1 caused chlorosis on younger sugarcane leaves (one‐leaf stage), but when applied at 2–3 kg a.i. ha^?1, no injury symptoms were shown. The herbicide at 2–4 kg a.i. ha^?1 applied within 60 DAP resulted in remarkably higher yield and shoot biomass of sugarcane than that applied 80 DAP. This study suggested that asulam at 2–3 kg a.i. ha^?1 should be applied 60 days after planting for the maximum control of torpedograss regrowth and better yield of sugarcane. This study also indicated that torpedograss cannot be completely controlled with a single application of asulam in a naturally infested field because of rhizome fragmentation by cross plowing and distribution of rhizomes into different soil layers that require different times to emerge. The shoots emerging after asulam application could not be controlled. Another study is required to determine the interval between sequential applications of asulam for better control of torpedograss in a naturally infested field.     

Modelling interactions between herbicide dose and multiple weed species interference in crop–weed competition

The effects of a range of herbicide doses on crop–multiple weed competition were investigated. Competitivity of Galium aparine was approximately six times greater than that of Matricaria perforata with no herbicide treatment. Competitivities of both weeds decreased with increasing herbicide dose, being well described by the standard dose–response curve with the competitivity of M. perforata being more sensitive than that of G. aparine to a herbicide mixture, metsulfuron‐methyl and fluroxypyr. A combined model was then developed by incorporating the standard dose–response curve into the multivariate rectangular hyperbola competition model to describe the effects of multiple infestation of G. aparine and M. perforata and the herbicide mixture on crop yield. The model developed in this study was used to predict crop yield and to estimate the herbicide dose required to restrict crop yield loss caused by weeds to an acceptable level. At the acceptable yield loss of 5% and the weed combination of 120 M. perforata plants m^?2 and 20 G. aparine plants m^?2, the model recommends a mixture of 1.2 g a.i. ha^?1 of metsulfuron‐methyl and 120 g a.i. ha^?1 of fluroxypyr.     

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.     

Modelling the effects of sub-lethal doses of herbicide and nitrogen fertilizer on crop–weed competition

The effects of sub‐lethal dose of herbicide and nitrogen fertilizer on crop–weed competition were investigated. Biomass increases of winter wheat and a model weed, Brassica napus, at no‐herbicide treatment with increasing nitrogen were successfully described by the inverse quadratic model and the linear model respectively. Increases in weed competitivity (β₀) of the rectangular hyperbola and parameter B in the dose–response curve for weed biomass, with increasing nitrogen were also successfully described by the exponential model. New models were developed by incorporating inverse quadratic and exponential models into the combined rectangular hyperbola with the standard dose–response curve for winter wheat biomass yield and the combined standard dose—response model with the rectangular hyperbola for weed biomass, to describe the complex effects of herbicide and nitrogen on crop–weed competition. The models developed were used to predict crop yield and weed biomass and to estimate the herbicide doses required to restrict crop yield loss caused by weeds and weed biomass production to an acceptable level at a range of nitrogen levels. The model for crop yield was further modified to estimate the herbicide dose and nitrogen level to achieve a target crop biomass yield. For the target crop biomass yield of 1200 g m^?2 with an infestation of 100 B. napus plants m^?2, the model recommended various options for nitrogen and herbicide combinations: 140 and 2.9, 180 and 0.9 and 360 kg ha^?1 and 1.7 g a.i. ha^?1 of nitrogen and metsulfuron‐methyl respectively.     

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.     

Monitoring the efficacy and metabolism of phenylcarbamates in sugar beet and black nightshade by chlorophyll fluorescence parameters

Desmedipham, phenmedipham and a 50% mixture of the two decreased the maximum quantum efficiency of photosystem II (F(v)/F(m)) and the relative changes at the J step (F(vj)) immediately after spraying in both sugar beet and black nightshade grown in the greenhouse. Sugar beet recovered more rapidly from phenmedipham and the mixture than from desmedipham. Desmedipham and the mixture irreversibly affected F(v)/F(m) and F(vj) in black nightshade at much lower doses than in sugar beet. Black nightshade recovered from phenmedipham injury at the highest dose in the first experiment (120 g AI ha(-1)) but not in the second experiment (500 g AI ha(-1)). The dry matter dose-response relationships and the energy pipeline presentation confirmed the same trend. There was a relatively good correlation between F(vj) taken 1 day after spraying and dry matter taken 2 or 3 weeks after spraying. The differential speed of herbicide metabolism between weed and crop plays an important role in herbicide selectivity and can be studied by using appropriate chlorophyll a fluorescence parameters.     

Effects of herbicide and timing of removal on interference between barley and weeds

Field experiments were done during the rainy season of 1984–85 and 1985–86 at Harma, Qatar. A weed survey of barley fields was conducted with the primary purpose of identifying the weed vegetation present. The effects of time of hand-weeding and of application of the herbicide metoxuron on the yield and yield components of barley were studied. Removing weeds at 15,30,45 and 60 days after sowing gave yields similar to that of the clean-weeded check. Neither a critical period nor a threshold density below which no yield loss occurred were observed. Metoxuron (1,2 and 3 kg ha^?1) gave good to excellent broad-leaved and grass-weed control. The use of this herbicide at the rate of 1 kg ha^?1 showed considerable promise.     

Effects of repeated applications of fluazifop-butyl, haloxyfop and sethoxydim on Elymus repens in strawberries

Fluazifop-butyl, haloxyfop and sethoxydim with adjuvant oil were applied for three successive growing seasons to established strawberries infested with Elymus repens. The weed was virtually eradicated by three applications of haloxyfop (0.8 kg a.e. ha^?1) in successive years. A similar effect was given by five applications of haloxyfop (0.4 kg a.e. ha^?1) and fluazifop-butyl (1.6 kg AI ha^?1) in three growing seasons. Lower rates of haloxyfop and fluazifop-butyl, and a high rate of sethoxydim (1.6 kg AI ha^?1) applied five times were less effective, the ground cover of E. repens shoots not being reduced by the end of the experiment although weight of living rhizome was only 10-30% of that on untreated plots. Fruit yields on treated plots generally reflected the level of E. repens control, but there was some evidence of crop phytotoxicity from herbicide treatments. During the experiment E. repens untreated plots increased from about 30-100% ground cover and reduced yield 13, 28 and 68% in successive years compared with weed-free plots.     

Influence of herbicide application rate and timings for post-emergence control of Sorghum halepense (L.) Pers. maize

Field experiments were carried out in Greece from 1990 to 1992 to study the effect of application timing and rate of nicosulfuron and rimsulfuron on Sorghum halepense (L.) Pers. control and maize yield. All herbicide rates are given in terms of active ingredient (a.i.). Nicosulfuron applied at 22.5, 30.0 and 37.5 g ha^?1 to S. halepense at height 20–35 cm provided greater than 93% control 90 days after treatment, while rimsulfuron applied at 7.5,10.0 and 12.5 g ha^?1 resulted in 81–91% control. Split applications of nicosulfuron and rimsulfuron, as well as tank-mixtures of nicosulfuron+rimsulfuron, gave 91–94% control. Maize yield in all herbicide treatments was greater than that of the weed-infested control and similar to that of the hand-weeded control. S. halepense control with nicosulfuron and rimsulfuron applied to plants 20–35 cm tall was greater than that obtained with their application to plants 5–15, 10–20 or 35–60 cm tall. Rates of 10 and 20 g ha^?1 of rimsulfuron provided control of S. halepense similar to or significantly lower than that achieved with 30 and 60 g ha^?1 of nicosulfuron, respectively. Maize yield produced by all herbicide treatments applied at any time was significantly greater than that of the weed-infested control.     

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.

     

Weeds and weed management in irrigated lentil in northern Sudan

Weeds are a major constraint to increasing production of lentil (Lens culinaris Medik.) in Sudan, Field studies were conducted to determine the yield loss due to weeds, to identify the critical period of weed interference, to evaluate the activity of different herbicide mixtures in controlting weeds and their selectivity for lentil, and to evaluate different methods of weed control for developing an integrated weed management practice. At Rubatab. unrestricted weed growth accounted for up to 84% loss in yield. The critical period of weed control was between 2 and 4 weeks after sowing. However, a weeding regime experiment at Dongola, a cooler location with a longer growing season, indicated that the critical period was between 4 and 6 weeks after sowing. suggesting that the critical period might vary with the environmental conditions. The herbicides imazethapyr (0.05 kg a.i. ha^-1), terbutryn (1.0 kg a.i. ha^-1) and prometryn (1.0 kg a.i. ha^-1), each in a tank mixture with pendimethalin (1.2 kg a.i. ha^-1), were tolerated by lentil, controlled weeds effectively and significantly increased yields at Wad Hamid. Their efficacy in controlling weeds at Rubatab was low, however, because of the presence of Tephrosia apollinea (Del.) DC. and Melilotus indica (L.) All., which tolerated these herbicides. Efficacy was also reduced in heavier soils. One supplementary hand-weeding at 4 weeks after sowing enhanced the performance of these herbicides under such conditions. A tank mixture of oxyfluorfen (0.24 kg a.i. ha^-1) with either terbutryn (1.0 kg a.i. ha^-1) or prometryn (1.0 kg a.i. ha^-1) also provided good weed control and increased yield of lentil at Wad Hamid. Application of a higher dose (1.5 kg a.i. ha^-1) of terbutryn and prometryn caused phytotoxicity. Irrigation before seed-bed preparation reduced grass and broad-leaved weeds by 58% and 40% respectively, and gave a 30% increase in grain yield over no irrigation. Pre-emergence application of oxyfluorfen (0.24 kg a.i. ha^-1) and a supplementary hand-weeding at 4 weeks after sowing gave excellent control of weeds and increased lentil yield by 57% over the weedy control. Thus, use of presowing irrigation, pre-emergence herbicide and one hand-weeding form an effective integrated package for controiling weeds in northern Sudan.     

Phenmedipham–Ozone Pollution Interactions in Sugarbeet (Beta vulgaris L. cv. Saxon): A Physiological Study

Actively growing sugarbeet is treated with the post-emergent herbicide phenmedipham at times when ozone pollution episodes are likely to occur. There is a possibility of an interaction occurring between ozone and phenmedipham as both treatments produce similar effects in susceptible plants, such as a reduction in growth and photosynthesis and an increase in the activities of endogenous antioxidant enzymes. To investigate this likelihood, laboratory experiments were conducted in which two- to three-leaf sugarbeet plants (Beta vulgaris L. cv. Saxon) were exposed to a simulated two-day ozone episode (100 nl litre⁻¹, 7 h day⁻¹) followed three days later by treatment with field rate phenmedipham (1·14 kg AI ha⁻¹). Growth analysis indicated that an interaction was occurring in which plants treated with ozone and phenmedipham had less reduction in shoot fresh weight than expected. Exposure to phenmedipham alone or ozone followed by phenmedipham reduced net photosynthesis by over 50% and transpiration rate by 30%. The activities of antioxidant enzymes such as catalase, guaiacol peroxidase and superoxide dismutase were stimulated by both treatments individually, but to a greater extent when ozone and phenmedipham were combined. For example, three days after herbicide treatment, the activity of superoxide dismutase increased by 20% in plants treated with ozone alone, 20% in plants treated with phenmedipham alone and 85% in plants that were treated with ozone followed by phenmedipham. We conclude that ozone pollution may predispose sugarbeet to tolerate the herbicide phenmedipham by enhancing the activity of the endogenous antioxidant detoxification enzyme system.     

Evaluation of herbicides against Phalaris minor in wheat in north-western Indian plains

Phalaris minor, the most serious weed in wheat in north‐western India, has developed extensive isoproturon resistance due to continuous isoproturon use. For its control, alternative herbicides (flufenacet, metribuzin and sulfosulfuron) at different application rates and timing were evaluated in wheat. In addition, herbicide carryover risk onto rotational crops (sorghum; maize and green gram, Vigina radiata) was also assessed. Isoproturon at 1 and 2 kg a.i. ha^?1 provided only 10.5% and 51.8%P. minor control respectively. Of the other herbicides, early post‐emergent [15–21 days after sowing (DAS)] flufenacet at 180–480 g a.i. ha^?1 provided acceptable control of P. minor, but failed to control broad‐leaved weeds and was phytotoxic to the wheat crop. Metribuzin at 210 g a.i. ha^?1 was effective in controlling both Phalaris and dicotyledonous weeds. Mixtures of both flufenacet and metribuzin at reduced rates were better than flufenacet for weed control and grain yield. The efficacy of flufenacet and metribuzin was drastically reduced with later growth stages of P. minor (four to five leaf). Whereas sulfosulfuron at 25–30 g a.i. ha^?1, applied either early post‐emergence (19 DAS) or post‐emergence (30–42 DAS), was quite effective. Overall, sulfosulfuron was the most effective treatment with regard to weed control and crop yield. However, maize and sorghum grown in rotation after harvest of sulfosulfuron‐treated wheat plots showed 65–73% crop biomass inhibition. The residual effect of sulfosulfuron was also noticed on Trianthema portulacastrum (Horse purslane), causing 73.5% dry matter reduction. By contrast, no carryover damage with flufenacet was observed on maize, sorghum and green gram. Glasshouse pot experiments and field trials investigating crop sensitivity to pre‐plant applications of sulfosulfuron found the decreasing order: sorghum > maize > green gram. The risk of carryover onto rotational crops should be considered when choosing alternative herbicides for P. minor control in wheat.     

Using chemical seed dormancy breakers with herbicides for weed management in soyabean and wheat

Variable dormancies result in periodicity in the germination of weeds and make weed control a repetitive practice. Under some conditions, repeated applications of selective herbicides can lead to the dominance of perennial weeds like Cyperus rotundus . Our hypothesis was that applying a chemical dormancy breaker (DB ) plus herbicide mixture would better control a mixture of weed species. Three experiments were designed to develop a cost‐effective DB treatment and to evaluate its dose with herbicides tank‐mixtures for effective weed management. KNO ₃ and gibberellic acid GA ₃ as dormancy breakers offered comparable effects, but KNO ₃ was more economical than GA ₃. KNO ₃ at a 6% concentration was more effective in promoting weed germination than a 3% concentration in soyabean. A combination of KNO ₃ (6%) and pre‐emergence pendimethalin 0.75 kg a.i. ha^?1 + imazethapyr 0.10 kg a.i. ha^?1 controlled annual weeds by 99% and reduced C. rotundus growth by 83%. This treatment gave significantly higher soyabean yield and net returns. Similarly, a tank‐mixture comprising of clodinafop 0.06 kg a.i. ha^?1 + metsulfuron 0.006 kga.i. ha^?1 was more effective against weeds than pre‐emergence tank‐mix application of pendimethalin 0.75 kg a.i. ha^?1 + carfentrazone‐ethyl 0.02 kg a.i. ha^?1 and isoproturon 0.75 kg a.i. ha^?1. The use of pre‐emergence tank‐mixture of pendimethalin 0.75 kg a.i. ha^?1 + imazethapyr 0.10 kg a.i. ha^?1 should exhaust seed/tuber bank if repeated and reduce the application cost of herbicides by 50% and the dose, residue and cost of pendimethalin by 25%.     

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.     

Physiological interactions between the herbicide EPTC and selected analogues of the antidote naphthalic anhydride on two hybrids of maize

The efficacies of nine structural analogues of the herbicide antidote naphthalene-1,8-dicarboxylic acid anhydride (naphthalic anhydride, NA) for the protection of maize (Zea mays L. cv. DeKalb XL72AA and DeKalb XL67) against injury by the herbicide S-ethyl dipropyl(thiocarbamate) (EPTC) were elevated under greenhouse conditions. The chemical analogues of NA tested were: acenaphthenequinone (ACQ); 4-aminonaphthalene-1,8-dicarboxylic acid anhydride (NH₂NA); 1,8:4,5-naphthalenetetracarboxylic acid dianhydride (NDiA); naphthalene- 1,8-carboximide (NHNA); 4-chloronaphthalene-1,8-dicarboxylic acid anhydride (C1NA); biphenyl-2,2′-dicarboxylic acid anhydride (diphenic anhydride; DA); 2-phenylglutaric anhydride (PGA); phthalic anhydride (PHA); phenalen-1-one (PA). Pre-plant incorporated applications of EPTC at 2.2, 4.5, 6.7, and 9.0 kg ha^?1 were highly toxic to XL67 maize. Appreciable injury to XL72AA maize by EPTC was observed only with the high rates of EPTC (6.7 and 9.0 kg ha^?1). Of the analogues tested PGA and PA were very toxic and inhibited germination of both maize hybrids. NA, ACQ, NH₂NA, NDiA, NHNA, C1NA, DA, and PHA applied as seed dressings at 5.0 and 10 g per kg of seed offered satisfactory protection to XL72AA maize against EPTC rates higher than 6.7 kg ha^?1. The same antidotes significantly antagonised the EPTC activity against XL67 maize but the overall protection obtained was partial and not agronomically important. The presence of the dicarboxylic anhydride group and of at least one aromatic ring attached directly to the anhydride appeared to be essential for the exhibition of protective activity by the structural analogues of NA. NA was slightly toxic to both hybrids of maize and chlorination of NA increased the phytotoxicity of this molecule. A genetic component that is present in the thiocarbamate-tolerant XL72AA hybrid but absent from the thiocarbamate-susceptible XL67 hybrid of maize appeared to be important for the phytotoxic activity of EPTC and may be involved in the protective activity of NA and its structural analogues.     

Uptake of phorate by lettuce

Following experimental and commercial applications to soil of a granular formulalation of phorate (O,O-diethyl S-ethylthiomethyl phosphorodithioate), residues in the soil and in lettuce were determined by gas-liquid chromatography. When applied by the bow-wave method as a continuous logarithmically-changing dose ranging from approximately 0.9 to 16.0 kg a.i. ha^?1, the proportional rate of oxidation in soil of phorate sulphoxide to phorate sulphone was inversely related to dose. Ten weeks after application, total phorate residues in the soil had declined by about 35% at all dose levels. Residues in mature lettuce, from the 1-5 kg ha^?1 dose-range, comprised the parent and oxygen analogue sulphoxides and sulphones; the relative proportions of the individual metabolites were independent of dose. Over this dose-range, total residue concentrations in the crop became proportionally slightly greater with increasing dose. When single doses of 1.1, 2.0 or 2.2 kg a.i. ha^?1 were applied at drilling, the total residue concentrations in the lettuce declined from 5 mg kg^?1 in seedlings from some treatments to <0.05 mg kg^?1 at harvest. In plants raised in peat blocks containing 10 or 20 mg a.i. per block, however, residues in seedlings totalled 45-47 mg kg^?1 and declined to only 0.7 mg kg^?1 at harvest. It was concluded that bowwave applications of phorate when field-sowing lettuce were unlikely to lead to unacceptable residues in the harvested crop, but that residues in lettuce raised in phorate-treated peat blocks may be unacceptably high.