Retention and degradation of metribuzin in sandy loam and clay soils of Lebanon

The retention and degradation of metribuzin herbicide were studied under two environmental conditions. Field studies were carried out on two soils, a sandy loam soil (soil A) and a clay soil (soil B). Metribuzin was applied with a jet sprayer at 1060 g a.i. ha^?1 and 1960 g a.i. ha^?1 on soils A and B respectively. Reconstituted soil columns were used to study the herbicide movement and metabolism in the two soils. Analyses of metribuzin and its metabolites were carried out using standardized methods. The results indicated a very weak capacity of adsorption of metribuzin in the two soils, and the weak adsorbed fraction is easily desorbed. Degradation and mobility of metribuzin in the field and laboratory soil columns were very intense and rapid. Soil A favoured reductive deamination whereas soil B favoured oxidative desulphuration and the respective metabolites deaminometribuzin and diketometribuzin yield the same product deaminodiketometribuzin. Both leaching by rainfall and degradation were important in the disappearance of metribuzin from the soils.     

Promising herbicides for weed control in chickpea

Abstract

Chickpea suffers severe competition due to Chenopodium album L. infestation. Two to three hoeings are generally given to check C. album but increasing labour costs and scarcity of farm labour make the manual weeding difficult. Usage of herbicides appears to be a logical solution. Pre‐emergence applications of pendimethalin or ametryn alone at 1.5 kg ai ha^?1 or one handweeding at 35–40 days after seeding following either 1 kg ai ha^?1 of pendimethalin, ametryn or fluchloralin or metribuzin at 0.3 kg ai ha^?1 applied pre‐emergence gave effective control of C. album and seed yields similar to clean‐weeded chickpeas. There was an 84% reduction in seed yield of chickpea without weeding.     

Weed competition and control in sugarcane

Losses of about 40% in cane yields due to natural stands of weeds were found in experiments conducted in sugarcane var. Co 527 in the year of planting at Guneid Sugarcane Research Station, Sudan. Weed competition lowered millable stalks per metre row by 32%, stalk height by 24%, stalk thickness by 15% and number of nodes per stalk by 14%. Tillering was the growth phase most affected by weed competition. Cane yields were increased as number of hand weedings increased, but four weedings were not markedly better than three. The average yield (67·04 t ha^?1) obtained from four weedings was not significantly (P= 0·05) better than that of three weedings carried out at 3, 6 and 9 weeks after cane planting. Juice analysis components were also affected by weeds and a 15% reduction in sucrose recovery was recorded. Reductions in the other components were only 4–7%. Atrazine and diuron (3·3 kg ha^?1), metribuzin (2·4 kg ha^?1) and metribuzin (1·3 kg ha^?1) in tank mixture with diuron (1·5 kg ha^?1) gave excellent residual weed control of the dominant weed species, Ipomoea cordofana Choisy., Brachiaria eruciformis (Sm.) Griseb., Corchorus fascicularis Lam., Ocimum basilicum L. and Dinebra retroflexa (Vahl) Panz., for most of the first growing season. Excellent control of weeds achieved by the herbicide treatments resulted in comparable yields to frequently-weeded cane. These herbicides were not phytotoxic to sugarcane var. Co 527.     

Effects of arbuscular mycorrhizal fungal symbiosis for control of Egyptian broomrape (Orobanche aegyptiaca Pers.) in tomato (Lycopersicon esculentum L.) cultivation

The present study assessed the effect of arbuscular mycorrhizal fungi (AMF) on broomrape (Orobanche aegyptiaca Pers.) control to determine its effects on tomato (Lycopersicon esculentum L.) growth indices. This experiment was carried out using a randomized complete block design with four replications. The treatments included three strains of AMF (Glomus mosseae, Glomus intraradices and Glomuse hoe ) at three levels (100, 200 and 300 kg ha^?1). The control treatments (without mycorrhiza) were with and without broomrape (weed infest and weed free). The results showed that the use of G. intraradices and G. mosseae decreased broomrape seed germination, the number of nodules and the dry weight of the broomrape and increased root area and dry weight of the tomato plant when compared to G. hoe and the control treatments without broomrape. The tomato yield in G. intraradices 300 kg ha^?1 treatment increased by 10 and 205% than weed free and weed infest treatments, respectively. Finally, G. intraradices and G. mosseae at, respectively, 200 and 300 kg ha^?1 are recommended for land under tomato cultivation that has been contaminated with broomrape.     

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.     

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.     

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.     

Orobanche ramosa L. (broomrape) control in tomato (Lycopersicon esculentum Mill.) with chlorsulfuron, glyphosate and imazaquin

Chlorsulfuron, giyphosate and imazaquin were evaluated in pot and field studies for their efficacy in controlling broomrape (Orobanche ramosa L.) in tomato (Lycopersicon esculentum Mill.) in Northern Greece. All herbicides were applied four to five weeks after tomato transplanting, when the crop was at early flowering stage and broomrape had started to develop underground attachments. The number of emerged broomrape shoots and underground attachments were less affected by herbicide treatments than the dry weight, suggesting that the herbicides suppress the growth of broomrape rather than kill its underground organs. In the pot experiments, chlorsulfuron applied at 5 g AI ha^?1 was the most effective treatment for broomrape control and the least toxic to the crop. Imazaquin and glyphosate applied at 37 and 180 g AI ha^?1, respectively, controlled broomrape but imazaquin reduced crop yield. In the field, similar rates of glyphosate and higher rates of imazaquin were not toxic to the crop but were less effective on broomrape. Chlorsulfuron applied at 10 g AI ha^?1 controlled broomrape emergence by 88%. When the herbicide was applied twice (5+10 g AI ha^?1), it gave complete control of broomrape but delayed crop maturity. The yield of tomato was not increased as a result of these treatments because of low broomrape infestation and a short competition period.     

Non-target effect of herbicides: I. effect of glyphosate and hexazinone on soil microbial activity. Microbial population,and in-vitro growth of ectomycorrhizal fungi

The effects of two herbicides, glyphosate (as a 359 g litre^?1 SL) and hexazinone (as a 50gkg^?1 granule) on soil microbial population, carbon dioxide evolution, and in-vitro growth of five species of ectomycorrhizal fungi were investigated. Glyphosate at 0–54 and 3.23 kg a.i. ha^?1 and hexazinone at 1. 2 and 8 kg a.i. ha^?1 did not reduce soil microbial population or carbon dioxide evolution in the long term (6 months). However, there was a significant short-term (2 months) effect of glyphosate on both fungal and bacterial counts at the 0.54 kg ha^?1 treatment. In in-vitro tests, Cenococcum graniforme. Hebeloma crustuliniforme and Laccaria laccata were more susceptible to both herbicides than was Suillus tomentosus. which was, in turn, more susceptible than Paxillus involutus. The growth of all five ectomycorrhizal fungi was significantly reduced when subjected to concentrations above 50 μl formulation litre^?1 (glyphosate) or 50 μg formulation litre^?1 (hexazinone).     

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.     

Abscisic acid as a protectant of Avena fatua L. against diclofop-methyl activity

The imposition of water stress before or al the time of spraying diclofop-methyl reduced efficacy against wild oat (Avena fatua L.). Similar reductions in herbicide performance were obtained by application of 20 μg of the methyl ester of abscisic acid (ABA) to plants with three to four leaves before spraying with I kg ha^?1 diclofop-methyl. Application of 40–100 μg ABA per plant effectively protected plants against damage from diclofop-methyl applied at 1 5–2 0 kg ha ^?1. The application of 20 μg ABA induced rapid stomatal closure and a reduction in leaf extension rate, which were sustained for 7–8 days after treatment. These changes were associated with an overall reduction in shoot growth. ABA-treated plants that were additionally sprayed with diclofop-methyl sustained ABA symptoms, but no additional weight loss or leaf chlorosis. The mechanism of the protective action of ABA on diclofop-methyl has not been determined.     

Uptake and phytotoxicity of chlorsulfuron in Zea mays L. in the presence of 1,8-naphthalic anhydride

The sites of uptake of chlorsulfuron in maize (Zea mays L.) were investigated at three different growth stages. Exposure of seedling roots, or shoots separately, to herbicide-treated sand over 4 days resulted in inhibition of both roots and shoots. Exposure of seedling roots to chlorsulfuron-treated soil over 21 days severely inhibited both roots and foliage, while separate shoot exposure also reduced both foliage and root growth. After plant emergence, exposure of the crown root node, growing point and lower stem to treated soil reduced foliage and root growth, but exposure of the shoot above the growing point caused only slight inhibition of foliage and had no effect on roots. The herbicide safener 1,8-naphthalic anhydride (NA) applied as a dust (10 g kg^?1 seed weight), or as a 50 mg 1^?1 suspension in water to maize seeds, reduced the root inhibition by chlorsulfuron in 4-day-old seedlings. NA completely prevented both foliage and root injury when chlorsulfuron was placed in soil in the shoot zone before emergence, or in the shoot zone below the soil surface after plant emergence. NA slightly decreased injury to foliage, but not to roots when chlorsulfuron was placed in soil in the root zone before emergence. NA seed treatment protected both roots and foliage against injury from foliarly applied chlorsulfuron. Plants were also protected when a suspension of NA in water was sprayed on the foliage seven days before chlorsulfuron. When a mixture of NA and chlorsulfuron was applied to foliage, root injury was reduced more than foliage injury.     

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.     

Residualwirkung von Chlortriazin-Herbiziden im Boden an drei rumänischen Standorten. II. Prognose möglicher Folgekulturen bei Atrazinrükständen im Boden

Residual effects of chlorotriazine herbicides in soil at three Rumanian sites. II. Prediction of the phytotoxicity of atrazine residues to following crops Total and plant-available atrazine residues in the top 10 cm soil were measured 120 days after application of 3 kg ai ha^?1 to maize (Zea mays L.) at three sites in Rumania. At one site, similar measurements were made 3?5 years after application of 100 kg ai ha^?1. Plant-available atrazine residues were estimated by extraction of soil samples with water, and by bioassay using Brassica rapa as the test plant. It was calculated that between 30 and 120μg atrazine 1^?1 was potentially available to plants in the different soils. Dose-response relationships for atrazine and the most important rotational crops with maize in Rumania—sunflower, winter wheat, soybean and flax—were determined in hydroponic culture using herbicide concentrations corresponding with the plant-available fractions measured in the different soils. ED₅₀ values were determined by probit analysis and the results showed that sunflower (ED₅₀, 22μg 1^?1) was the most sensitive crop, and soybean (ED₅₀, 78μg 1^?1) was the least. The residual phytotoxicity of atrazine to succeeding crops in the different soils was predicted using the appropriate availability and phytotoxicity data, and the results showed good agreement with those observed. The results suggest that measurements of plant-available herbicide residues afford a rapid method of assessing possible phytotoxicity to following crops.     

Effects of dose and application timing on the seed production of three weed species treated with MCPA or tribenuron-methyl

The seed production of Fallopia convolvulus (L.) A. Love, Galium spurium L, and Thlaspi arvense L., treated with MCPA or tribenuron-methyl, was studied in a pot experiment. The herbicides were applied in doses from 1/16 to 1/l of a full dose at five different growth stages. The largest reduction of seed production was observed on plants treated when one true leaf had developed (F. convolvulus, both herbicides) or at the beginning of the generative phase (G. spurium treated with tribenuron-methyl and T. arvense treated with either herbicide). Tribenuron-methyl (0.375 g a.i. ha^?1) or MCPA (0.1875 kg a.i. ha^?1) applied at bolting stage was enough to reduce the seed production of T. arvense by 83% and 100%, respectively. The seed production of F. convolvulus, treated with 0.75 kg MCPA at the cotyledon stage, was reduced by 70%. Plants of G. spurium with 5–9 axillary shoots, treated with 3 g tribenuron-methyl, produced 45% fewer seeds than the control. Both herbicides (at least at the highest doses) reduced seed production of all three species more than shoot dry matter.     

Eleven years of integrated weed management: long‐term impacts of row spacing and harvest weed seed destruction on Lolium rigidum control

Long‐term research aimed to determine whether narrow row spacing and harvest weed seed destruction, in combination with herbicide use, would be sufficient to drive a Lolium rigidum population to extinction. A trial was run from 1987 to 2013, with treatments including crop row spacings of 9, 18, 27 or 36 cm and crop residue burning or retention. Herbicides were applied to reflect regional practices. The initial trial design was randomised, but treatments were maintained in each plot over the following years. Lolium rigidum seed production at harvest was assessed from 2003 to 2013. Average crop yield was higher in the unburnt plots (1638 kg ha^?1) than the burnt plots (1530 kg ha^?1) and greater at narrow row spacing, with an average yield of 1658, 1637, 1548 and 1492 kg ha^?1 in the 9‐, 18‐, 27‐ and 36‐cm spacings. Lolium rigidum seed at harvest was reduced in the burnt plots (57 seeds m^?2) compared with the unburnt plots (297 seeds m^?2) and was reduced at narrow row spacing, with an average of 58, 78, 223 and 333 seeds m^?2 in the 9‐, 18‐, 27‐ and 36‐cm row spacings. By 2013, L. rigidum seed production was reduced to an average of 0 seeds m^?2 in the narrow row spacing, burnt plots.     

Diclofop-methyl antagonism by broadleaf weed herbicides: the importance of leaf expansion rate

Avena saliva cv. Amuri and A. fatua were sprayed with diclofop methyl (1.0 kg a.i. ha^?1) alone and in combination with 2,4-D (1.1 kg a.i. ha^?1), bentazone (1.0 kg a.i. ha^?1), chlorsulfuron (15 g a.i. ha^?1) or dicamba (0.3 kg a.i. ha^?1). Effects of the herbicides on leaf extension rate during the first 8 to 10 days after spraying and subsequent growth (dry weight) after 57–75 days were determined by comparison with unsprayed plants. Diclofop-methyl applied alone did not cause a decrease in leaf extension rate of A. saliva or A. fatua until at least 4 days after spraying. All broadleaf weed herbicides in combination with diclofop-methyl caused a decrease in leaf extension rate of both species within 2 days of spraying. Ten days after spraying, leaf extension rates for plants sprayed with a broadleaf weed herbicide plus diclofopmethyl (all combinations) were lower than for unsprayed plants but greater than for plants sprayed with diclofop-methyl alone. With the exception of A. fatua sprayed with bentazone, long-term growth of plants sprayed with a broadleaf weed herbicide plus diclofop-methyl (all combinations) was lower than for unsprayed plants but greater than for plants sprayed with diclofop-methyl alone. Bentazone applied with diclofop-methyl caused a substantial decrease in leaf extension rate of A. fatua within 24 h of spraying but at harvest, dry weight of plants from this treatment was similar to or less than that for plants sprayed with diclofop-methyl alone. Application of diclofop-methyl with bentazone at a rate of 0.3 kg a.i. ha^?1 also caused a reduction in leaf extension rate of A. fatua within one day of spraying. At this rate of bentazone, dry weight of plants at harvest was intermediate to that of unsprayed plants and those sprayed with diclofop-methyl alone. It is proposed that decreased leaf expansion rate during the first few days afte spraying is the cause of broadleaf weed herbicide antagonism of diclofop-methyl.     

Morphological and physiological variability in black nightshade (Solanum spp.)

Plants from two black nightshade (Solanum spp.) seed sources were compared for differences in morphology at seedling and mature plant stages, flowering and physiological responses to pre-germination seed treatment, growth responses to temperature, and response to herbicides. Differences in the morphology of the two Solanum spp. were evident from seedling to maturity. The plants grown from the Michigan (MI) seed source had a deep purple abaxial leaf surface at the three to four-leaf stage, a yellow anther column, and toothed proximal half in the mature leaf, whereas the plants grown from the California (CA) seed source had no unusual abaxial coloration or toothed proximal margin and had a dark brown anther column. Differences in response to herbicides were seen between plants grown from the two seed sources following pre-plant-incorporated, pre-emergence, and post-emergence herbicide applications. The plants from the MI seed source were up to five times more susceptible to chloramben, applied pre-plant-incorporated at 1.68 kg ha^?1, and to ethalfluralin, applied preemergence at 1.12 kg ha^?1, than plants from the CA seed source. Plants from both seed sources have been described as Solanum nigrum L. The plants from MI have been identified elsewhere as Solanum ptycanthum Dun. and those from CA as Solanum scabrum Mill. This identification could resolve conflicting reports among researchers regarding chemical control measures.     

A new molecular method for the rapid detection of a metamitron‐resistant target site in Chenopodium album

BACKGROUND: Resistance to photosystem II inhibitors—triazines (atrazine) and triazinones (metamitron, metribuzin)—in Chenopodium album L. is caused by the serine 264 to glycine mutation in the D1 protein. This mutation has been detected in C. album collections from Belgium with unsatisfactory metamitron efficacy in the field and was confirmed in greenhouse resistance bioassays. Incomplete herbicide efficacy in practice can also be caused by reduced uptake due to environmental conditions. Hence, for reliable differentiation and resistance identification, a rapid method for mutation detection in the target gene psbA is required. RESULTS: Dose–response curves obtained in herbicide greenhouse assays with metamitron‐resistant and ‐susceptible reference biotypes showed that a dose of 2 L ha^?1 metamitron was suitable for discrimination. A psbA PCR‐RFLP was developed, based on the presence of a FspBI restriction enzyme recognition site, covering D1 codon 264 in susceptible genotypes. A paper‐based DNA extraction allowed direct processing of leaf samples already in the field. In order to detect the mutation even in mixed seed samples, a nested PCR‐RFLP was also developed. CONCLUSION: The method allows exhaustive surveys screening C. album leaf or seed samples for the occurrence of the D1 Ser264Gly mutation to confirm or disprove metamitron resistance in the case of unsatisfactory control. Copyright © 2010 Society of Chemical Industry     

Sugarbeet tolerance and weed control efficacy with split applications of phenmedipham plus desmedipham

Sugarbeet and weeds were treated with phenmedipham plus desmedipham either as single applications or as split applications in which 50% of the equivalent single application rate was applied at each application. Split application did not alter the phytotoxicity to the crop when environmental conditions did not predispose the Sugarbeet to injury by the herbicide. Split applications at 1-1 or 1-4 kg ha^?1 spaced from 0-5 to c. 5 days apart caused more injury to the crop than the respective single applications when environmental conditions were such that injury to the crop resulted from the single applications. Injury to Sugarbeet following application of 0-72 kg ha^?1 of phenmedipham plus desmedipham was always low, regardless of the type of application. Susceptible weeds were controlled by single applications of 1 1-1 ?4 kg ha^?1, but 0-72 kg ha^?1 did not reliably provide adequate control. Split applications c. 3-8 days apart gave improved control. Control achieved by 0-72 kg ha^?1 of the herbicide applied as split treatments equalled or exceeded that produced by single applications of 1-4 kg ha^?1. Improvement in the control of tolerant weed species by split applications of phenmedipham plus desmedipham was species dependent. Use of low-rate split applications of phenmedipham plus desmedipham thus resulted in reduced injury to the Sugarbeet, and the introduction of less herbicide into the ecosystem, while maintaining or improving the control of susceptible weeds.