Protoporphyrinogen oxidase inhibitor herbicide effects on pythium root rot of sugarcane, pythium species, and the soil microbial community

ABSTRACT The effects of three protoporphyrinogen oxidase inhibitor herbicides, azafenidin, flumioxazin, and sulfentrazone, on Pythium root rot of sugarcane and the soil microbial community were evaluated in greenhouse experiments. Herbicides were applied as foliar and soil treatments. There were no consistent effects on plant growth or disease parameters. However, some herbicide treatments affected the relative frequency of isolation of Pythium spp. from roots and reduced colonization by the pathogenic species Pythium arrhenomanes. A comparison of sole carbon source utilization profiles indicated that soil-applied herbicides altered the functional diversity of the soil microbial community, with some variation depending on herbicide used. All three herbicides inhibited the in vitro mycelial growth of P. arrhenomanes, P. aphanidermatum, and P. ultimum. Active ingredients were less inhibitory than formulated product for azafenidin and flumioxazin but not for sulfentrazone.     

黑龙江省大豆疫霉根腐病调查与病原分离

１９９６年对黑龙江省东部和中部大豆产区２３个市、县的大豆苗期疫霉根腐病进行了调查、研究,应用ＰＢＮＩＣ疫霉选择性培养基分离大豆疫霉根腐病病原菌,从牡丹江、穆棱、林口和佳木斯豆田具疫霉根腐症状的大豆植株上分离到大豆疫霉根腐病菌,并从根腐病株上单独或与大豆疫霉菌同时分离到终极腐霉菌,研究进一步证实我国黑龙江省有大豆疫霉根腐病。调查发现,大豆疫霉根腐病和终极腐霉根腐病主要发生在土质粘重、土壤含水量高或易积水的田块。     

Interactions between the root pathogen Rhizoctonia solani AG-8 and acetolactate-synthase-inhibiting herbicides in barley

BACKGROUND: The widespread acceptance of reduced‐tillage farming in cereal cropping systems in the Pacific Northwest of the United States has resulted in increased use of herbicides for weed control. However, soil residual concentrations of widely used imidazalone herbicides limit the cultivation of barley, which is more sensitive than wheat. In addition, increased severity of the root rot disease caused by Rhizoctonia solani is associated with reduction in tillage. Many crops exhibit altered disease responses after application of registered herbicides. In this study, the injury symptoms in barley caused by sublethal rates of two acetolactate synthase (ALS)‐inhibiting herbicides, imazamox and propoxycarbazone‐sodium, were assessed in factorial combinations with a range of inoculum concentrations of the root rot pathogen Rhizoctonia solani AG‐8. RESULTS: Both herbicides and pathogen had negative impacts on plant growth parameters such as root and shoot dry weight, shoot height and first leaf length, and interactions between pathogen and herbicide were detected. CONCLUSIONS: The results suggested that sublethal rates of herbicides and R. solani could alter severity of injury symptoms, possibly owing to the herbicide predisposing the plant to the pathogen. Copyright © 2012 Society of Chemical Industry     

Shoot zone uptake of soil-applied herbicides in some legume species

Localized placement of prometryne, linuron and diuron in the soil at the first or second shoot internodes of dwarf broad bean (Vicia faba L.) equally reduced aerial plant growth, whereas simazine and atrazine had no effect. Growth reduction also occurred when the first shoot internode of scarlet runner bean (Phaseolus multiflorus L.) in the soil was treated with all five herbicides, especially with diuron. Localized placement of these herbicides at the first or second shoot internodes of vetch (Vicia sativa L.) in the soil equally reduced aerial plant growth. Foliar injury to vetch due to placement of these herbicides in the shoot zone of the soil was markedly reduced by simultaneous treatment with trifluraiin or nitralin which prevented adventitious root development on the shoot without otherwise affecting plant growth. This lack of root development on the shoots treated with trifluraiin was associated with a marked decrease in ¹⁴C-labelled atrazine uptake, which probably accounted for the reduction in atrazine phytotoxicity. A similar explanation may account for the reduced phytotoxicity of the other herbicides in the presence of trifluraiin or nitralin.     

Phenazines are Involved in Biocontrol of Pythium myriotylum on Cocoyam by Pseudomonas aeruginosa PNA1

Root rot of cocoyam (Xanthosoma sagittifolium) caused by Pythium myriotylum is the most devastating disease of this important tropical tuber crop with yield reductions of up to 90%. Bioassays were conducted in vitro and in sterile volcanic soil artificially infested with Pythium myriotylum, isolate CRPm, to test whether Pseudomonas aeruginosa PNA1 can control the cocoyam root rot disease. P. aeruginosa PNA1 (wild type) produces phenazine-1-carboxylic acid and phenazine-1-carboxamide (oxychlororaphin), while its tryptophan auxotrophic mutant FM13 is phenazine negative and secretes anthranilate in vitro. PNA1 and FM13 have previously been shown to control Pythium debaryanum and Pythium splendens on lettuce and bean. PNA1 and FM13 significantly inhibited growth of P. myriotylum in dual cultures, while their supernatants highly reduced mycelial dry weight in potato dextrose broth. However, in the presence of tissue culture derived cocoyam plantlets, only strain PNA1 strongly reduced root rot disease severity. Soil experiments involving strain PNA1 in comparison to phenazine-deficient mutants suggested that the biocontrol activity of PNA1 against P. myriotylum may involve phenazines. Phenazine involvement was further strengthened by the fact that FM13 fed with exogenous tryptophan (so that phenazine production is restored) significantly reduced disease severity on cocoyam. The efficiency of PNA1 to control P. myriotylum on cocoyam was significantly improved when the strain and the pathogen were allowed to interact for 24 h prior to transplanting cocoyam plantlets, while doubling the inoculum density of the pathogen negatively affected its efficiency.     

Root Rot of Miniature Roses Caused by Pythium helicoides

Miniature roses growing in an ebb-and-flow watering system developed dieback during the summer growing season of 1996 in Gifu Prefecture. The main diagnostic symptoms were chlorosis of leaf followed by blight, and a brown, water-soaked root rot followed by dieback. Pythium isolates were recovered from the rotted root. The isolates form proliferous ellipsoidal papillate sporangia, spherical smooth oogonia, elongate antheridia, and aplerotic oospores. The optimum temperature for hyphal growth was 35°C with a growth rate of 34 mm/24 hr. Optimum temperature of zoospore formation (25-30°C) was lower than that of mycelial growth, and zoospores were produced even at 10°C. The isolates were identified as P. helicoides on the basis of these characteristics. In pathogenicity tests disease severity was highest at the highest tested temperature (35°C) at which the disease naturally occurred in summer. Four days after inoculation, the leaves turned yellow and the roots had a water-soaked rot, followed by leaf blight and root dieback after 7 days. The disease transmission test showed that diseased plants were found throughout the bench after 10 days. Received 4 July 2001/ Accepted in revised form 10 October 2001     

The influence of two herbicides on the antifungal activity of some fungicides against Pythium butleri and Rhizoctonia solani causing damping-off of cowpea

The herbicides fluchloralin and alachlor applied to soil altered the effectiveness of fungicide treatments to seed and soil for controlling cowpea damping-off. These herbicides also modified the in-vitro toxicity of the fungicides to the mycelial growth of Pythium butleri and Rhizoctonia solani in a nutrient medium. Both herbicides reduced the toxicity of 2-methoxyethylmercury chloride (MEMC) and propamocarb to the growth of P. butleri, and of carbendazim to the growth of R. solani, but enhanced the toxicity of captafol and quintozene to P. butleri and R. solani, respectively. In pot tests, quintozene gave better control of R. solani damping-off in soil treated with fluchloralin or alachlor than in untreated soil, whereas disease control by carbendazim was decreased in similarly treated soils. Both herbicides attenuated the effectiveness of MEMC and captafol to control the damping-off caused by P. butleri; the efficacy of propamocarb was increased by alachlor but was decreased by fluchloralin. The implications of herbicide-fungicide interactions are discussed in the context of fungicidal control of root diseases in herbicide-treated soil.     

Biocompost from sugar distillery effluent: effect on metribuzin degradation, sorption and mobility

BACKGROUND: Metribuzin (4-amino-6-tert-butyl-4,5-dihydro-3-methylthio-1,2,4-triazin-5-one) is weakly sorbed in soils and therefore leaches easily to lower soil profiles and results in loss of activity. Soil amendments play an important role in the management of runoff and leaching losses of pesticides from agricultural fields. Therefore, the effect of biocompost from sugarcane distillery effluent on metribuzin degradation and mobility was studied in a sandy loam soil.RESULTS: Metribuzin was more persistent in biocompost-unamended (T-0) flooded soil (t(1/2) - 41.2 days) than in non-flooded (t(1/2) - 33.4 days) soil. Biocompost application at the rate of 2.5 and 5.0% (T-1 and T-2) in non-flooded soils increased metribuzin persistence, but no significant effect was observed on persistence in flooded soils. Freundlich adsorption constants (K(f)) for treatments T-0, T-1 and T-2 were 0.43, 0.64 and 1.13 respectively, suggesting that biocompost application caused increased metribuzin sorption. Leaching studies in packed soil columns indicated that biocompost application affected both metribuzin breakthrough time and maximum concentration in the leachate. Leaching losses of metribuzin were drastically reduced from 93% in control soil (T-0) to 65% (T-1) and 31% (T-2) in biocompost-amended soils.CONCLUSION: Biocompost from sugarcane distillery effluent can be used effectively to reduce downward mobility of metribuzin in low-organic-matter sandy loam soil. Copyright (c) 2008 Society of Chemical Industry.     

Soybean Brown Stem Rot, Phytophthora sojae, and Heterodera glycines Affected by Soil Texture and Tillage Relations

ABSTRACT Investigations were conducted to determine whether the effects of tillage practices on the prevalence of brown stem rot of soybean (caused by Phialophora gregata), Heterodera glycines, and Phytophthora sojae were confounded by soil texture in samples collected in the fall of 1995 and 1996. Soil and soybean stem samples, along with tillage information, were collected from 1,462 randomly selected fields in Illinois, Iowa, Minnesota, Missouri, and Ohio in collaboration with the National Agricultural Statistics Service. The incidence of brown stem rot was determined from 20 soybean stem pieces collected from each field in a zigzag pattern. The detection frequency of P. sojae (expressed as percent leaf disks colonized) and population densities of H. glycines were determined from soil cores also collected in a zigzag pattern. The soil samples were grouped into various textural classes, and the effect of soil texture and tillage relations on the activities of each pathogen were determined. Both tillage and soil texture affected the incidence of brown stem rot; however, there was no interaction between tillage and soil texture. Conservation tillage had a greater (P < 0.05) incidence of brown stem rot in clay loam and silty clay loam than did conventional tillage. The detection frequency of P. sojae was not affected by tillage, but a tillage x texture interaction (P = 0.013) indicated that the effect of tillage depended on soil texture. There was a greater (P < 0.05) detection frequency of P. sojae in conservation tillage than in conventional tillage in silt loam and loam soils. However, in sandy loam, the detection frequency of P. sojae was greater (P = 0.0099) in conventional tillage than in conservation tillage. Population densities of H. glycines were significantly affected by both tillage and soil texture, but overall, there was no tillage x texture interaction. There was an inverse relationship between population densities of H. glycines and percent clay (r = -0.81, P = 0.01) in no-till fields, but little or no change in nematode densities was observed with increasing clay content in tilled fields. Population densities of H. glycines were less (P < 0.05) in no-till fields than in tilled fields in silty clay loam and clay soils. There was no difference in H. glycines densities between the tillage categories in soils sandier than silty clay loam or clay. The findings emphasize the need for cautious interpretation of the effects of tillage practices on diseases and pathogens in the absence of information on soil texture.     

Effects from simulated rainfall on shoot-zone uptake of herbicides

In glasshouse experiments, atrazine, simazine, lenacil and linuron applied to the soil surface were phytotoxic to turnip seedlings which had emerged from a depth of 1–5 cm when 3 mm artificial rainfall was applied at the time of seedling emergence or shortly afterwards. When rainfall was applied on 2 or 3 consecutive days, the herbicides were in general more phytotoxic. As the delay between emergence and commencement of surface watering increased, however, the response of the seedlings decreased. Studies with [¹⁴C]-atrazine showed that at emergence the seedlings contained a small amount of herbicide which increased considerably with surface watering. Relatively high concentrations were attained when rainfall was applied while the seedlings were small, but as the interval between seedling emergence and rainfall increased, the same uptake resulted in lower shoot concentrations, Atrazine extraction from the soil showed little movement from the surface 1.0 cm, suggesting uptake via the stem. The observed responses of the other three herbicides are explained by assuming the same pattern of uptake as that recorded for atrazine.     

The influence of tillage on the weed flora in a succession of winter wheat crops on a clay loam soil and a silt loam soil

Weed populations were monitored for 4 years on two experiments designed to compare the effect of different primary tillage treatments on winter wheat (Triticum aestivum L.) cropping. Ploughing was compared with deep and shallow tine cultivation and with no tillage on both a clay loam and a silt loam over chalk. Soil-acting residual herbicides were used to control weeds, especially Alopecurus myosuroides Huds. and Avena fatua L. Dicotyledonous weeds were uncommon on the clay loam but on the silt loam, in a year when no residual herbicide was used, they were most numerous where the soil was disturbed most. In other years there was little difference in the number emerging. Six species were reduced in number by reduced cultivation or no tillage, whilst four species, including two grasses, were increased. At both sites, A. myosuroides was more numerous on direct drilled and tine cultivated plots than on ploughed. Herbicides gave good control on the silt loam but failed to control the weed on the clay loam. On the clay loam, A. fatua was most numerous on tine cultivated plots and a combination of herbicides and roguing produced a decline in the population.     

Soil persistence studies with bromoxynil, propanil and [14C]dicamba in herbicidal mixtures

The persistence of bromoxynil (3,5-dibromo-4-hydroxybenzonitrile), [¹⁴C]dicamba (3,6-dichloro-2-methoxybenzoic-7-¹⁴C acid) and propanil [N-(3,4-dichlorophenyl)propionamide] at rates equivalent to 1 kg ha^?1, were studied under laboratory conditions in a clay loam, a heavy clay and a sandy loam at 85% of field capacity and at 20±1°C, both singly and in the presence of herbicides normally applied with these chemicals as tank-mix or split-mix components. The degradation of bromoxynil was rapid with over 90% breakdown occurring within a week in the heavy clay and sandy-loam soils, while in the clay-loam approximately 80% of the bromoxynil had broken down after 7 days. In all three soils degradation was unaffected by the presence of asulam, diclofop-methyl, flamprop-methyl, MCPA, metribuzin or propanil. Propanil underwent rapid degradation in all soil treatments, with over 95% of the applied propanil being dissipated within 7 days. There were no noticeable effects on propanil degradation resulting from applications of asulam, barban, bromoxynil, dicamba, MCPA, MCPB, metribuzin or 2,4-D. The breakdown of [¹⁴C]dicamba in a particular soil was unaffected by being applied alone or in the presence of diclofop-methyl, flampropmethyl, MCPA, metribuzin, propanil or 2,4-D. The times for 50% of the applied dicamba to be degraded were approximately 16 days in both the clay loam and sandy loam, and about 50 days in the heavy clay.     

The phytotoxicity of various herbicides in two sandy loam soils and the effect of liming

The phytotoxicity of five soil-acting herbicides was investigated in two sandy loam soils and that of a further five herbicides in one of these soils. The effect of liming on phytotoxicity was also examined. Metoxuron, fenuron, metribuzin and fluometuron were more active in Boddington Barn soil than in Bledington soil. Prometryne was similar in effect in both soils. Liming significantly increased the effect of metoxuron in Boddington Barn soil and metoxuron, atraton, difenoxuron and metribuzin in Bledington soil. Monolinuron was less toxic in limed Bledington soil. Reasons for these differences have not been determined.     

VERTICAL DISTRIBUTION OF HERBICIDES IN SOIL AND THEIR AVAILABILITY TO PLANTS: SHOOT COMPARED WITH ROOT UPTAKE

Summary. Turnip, lettuce and ryegrass seedlings showed toxicity symptoms following shoot exposure to atrazine, linuron and aziprotryne at soil concentrations less than would be obtained from normal field applications. Responses following shoot exposure to simazine and lenacil were much less. Root exposure to all five herbicides caused seedling death at concentrations lower than those required for 'shoot-zone' toxicity. Pronamide and chlorpropham were tested against ryegrass only and at the concentrations examined were toxic only when localized in the shoot zone. Root exposure suppressed root growth, but the shoots were able to grow normally if the soil was kept sufficiently moist. Shoots contained more ¹⁴C-atrazine at emergence after shoot exposure compared with root exposure, but there was little subsequent uptake from the shoot zone. There was extensive uptake from the root zone after emergence. In the shoot-zone treatments, concentrations in the plant were high at emergence but were rapidly diluted by plant growth, whereas with root exposure, they increased throughout the experiments. The possible significance of these results to herbicide bebaviour under field conditions is discussed.
La distribution verticale des herbicides dans le sol et leur disponibilité pour les plantes: absorption comparée par la partie aèrienne et par les radnes     

SELECTIVE ACTION OF DIPHENAMID AND NAPROPAMIDE IN PEPPER (GAPSICUM ANNUUM L.) AND WEEDS

Summary. A comparison was made between diphenamid and napropamide with regard to phytotoxicity to pepper and weeds under glasshouse and field conditions. Diphenamid was considerably less phytotoxic than napropamide in inhibiting root elongation and shoot growth of pepper seedlings. Plant growth was reduced when the roots were exposed to either one of the herbicides, but growth of the shoot through treated soil was not adversely affected. Since diphenamid was found to be more leachable into soil, it might become more available to the roots and damage the crop plants. Graminaceous weeds were very sensitive to both herbicides, whereas several dicotyledonous weeds were more susceptible to napropamide. Selectivity of both herbicides at a late pre-emergence application to direct-seeded pepper was found satisfactory in two field experiments on different soil types.
Action sélective de la diphénamide et de la napropamide sur le piment et les mauvaises herbes     

Cyclic Lipopeptide Surfactant Production by Pseudomonas fluorescens SS101 Is Not Required for Suppression of Complex Pythium spp. Populations

ABSTRACT Previously, the zoosporicidal activity and control of Pythium root rot of flower bulbs by Pseudomonas fluorescens SS101 was attributed, in part, to the production of the cyclic lipopeptide surfactant massetolide A. The capacity of strain SS101 and its surfactant-deficient massA mutant 10.24 to suppress populations and root infection by complex Pythium spp. communities resident in orchard soils was assessed on apple and wheat seedlings and on apple rootstocks. Both strains initially became established in soil and persisted in the rhizosphere at similar population densities; however, massA mutant 10.24 typically was detected at higher populations in the wheat rhizosphere and soil at the end of each experiment. Both strains effectively suppressed resident Pythium populations to an equivalent level in the presence or absence of plant roots, and ultimately suppressed Pythium root infection to the same degree on all host plants. When split-root plant assays were employed, neither strain suppressed Pythium spp. infection of the component of the root system physically separated from the bacterium, suggesting that induced systemic resistance did not play a role in Pythium control. Strain SS101 only marginally suppressed in vitro growth of Pythium spp. and growth was not inhibited in the presence of mutant 10.24. When incorporated into the growth medium, the cyclic lipopeptide massetolide A significantly slowed the rate of hyphal expansion for all Pythium spp. examined. Differences in sensitivity were observed among species, with Pythium heterothallicum, P. rostratum, and P. ultimum var. ultimum exhibiting significantly greater tolerance. Pythium spp. populations indigenous to the two soils employed were composed primarily of P. irregulare, P. sylvaticum, and P. ultimum var. ultimum. These Pythium spp. either do not or rarely produce zoospores, which could account for the observation that both SS101 and mutant 10.24 were equally effective in disease control. Collectively, the results showed that (i) Pseudomonas fluorescens SS101 is very effective in controlling diverse Pythium populations on different crops grown in different soils and (ii) production of the cyclic lipopeptide massetolide A does not play a significant role in disease suppression. Other, as yet undefined mechanisms appear to play a significant role in the interaction between P. fluorescens SS101 and soilborne Pythium spp. communities.     

Alachlor placement in the soil as related to phytotoxicity to maize (Zea mays L.) seedlings*

Growth chamber studies were conducted to investigate the effects of alachor (2-choloro-2′,6′-diethyl-N- (methoxymethyl) acetanilide) on emerging seedlings of maize (Zea mays L.) planted 2.5 and 8.0 cm deep in a Plano silt loam soil. Alachlor was localized in the shoot zone, in the root zone, and in the shoot and root zones. Four days after emergence, seedlings were harvested and total shoot and root lengths used as measures of herbicidal effectiveness. The herbicide applied at a rate of 2.5 kg/ha caused a severe reduction in seedling height when placed in the shoot zone of seeds planted at the shallow depth. This injury was prevented when seeds were planted at the deeper level. When alachlor was placed in the root zone, there was no inhibition of shoot growth. When both shoot and root zones were exposed to the herbicide, severe growth inhibition again occurred. Roots were less sensitive to alachlor. A simple technique involving use of sand and activated charcoal barriers to effectively separate the shoot and root zones is described.     

Use of activated carbon to protect tomato against metribuzin

Protection of tomato (Lycopersicon esculentum Mill., cv. UC 134) against metribuzin was increased by placing a small quantity of activated carbon near each seed position before pre-emergent application of the herbicide. The most protective location of the carbon was the surface of the soil, immediately above the seed. In this location, 0.10 g of activated carbon protected tomatoes from the phytotoxic effects of 0.700 kg metribuzin ha^?1 whereas, without the activated carbon, 0.175 kg metribuzin ha^?1 killed both tomato and blackberry nightshade (Solanum nigrum L.). Placing plastic discs in this location did not reduce the phytotoxicity; however, a barrier that prevented lateral invasion by the herbicide, of the zone of soil through which the plumule emerged, partially protected the plains from 0.350 kg metribuzin ha^?1, showing that metribuzin entered the plants in substantial quantities via the plumule as well as the roots. This result suggests that activated carbon maintained a lower metribuzin concentration in the plumule/root zone than the bulk concentration. It also explains way the soil surface was the most protective carbon location. These findings provide the basis for extending the use of preemergent herbicides to situations in which previously they could not be used safely or economically.     

Phytotoxic activity of pethoxamid in soil under different moisture conditions

The phytotoxic activity of soil-applied pethoxamid [2-chloro- N -(2-ethoxyethyl)- N -(2-methyl-1-phenyl-1-propanyl) acetamide], (TKC-94), on the plant growth of rice ( Oryza sativa cv. Kiyohatamochi ) seedlings as an assay plant in soil was investigated under different soil moisture conditions. The phytotoxic activity of pethoxamid mixed with soil on the shoot and root growth of rice seedlings was uppermost under the highest soil moisture condition and it decreased with declining soil moisture content, while the inhibition was greater on the root growth than the shoot growth. The amount of pethoxamid adsorbed on soil solid and the concentration of pethoxamid in soil water from soil applied with this herbicide were not influenced by the soil moisture content. In addition, the phytotoxic activity on the growth of rice seedlings in sea sand culture applied with the soil water from the herbicide-applied soil was not influenced by the soil moisture content. In the sea sand culture, the phytotoxic activity of pethoxamid was significantly reduced in negative water potential as the concentration of polyethylene glycol-6000 added to the water increased. It is suggested that the phytotoxic activity of pethoxamid in the soil primarily depends on the concentration in soil water, but the phytotoxic activity was affected by soil moisture through the effect on absorption of this herbicide by rice seedlings.     

Transport to ground‐water of six commonly used herbicides: a prediction for two Italian scenarios

In Italy suitable standard scenarios for pesticide risk assessment based on computer models are lacking. In this paper we examine the use of the VARLEACH model to assess the potential danger of ground‐water pollution by six herbicides (alachlor, atrazine, cyanazine, linuron, simazine and terbuthylazine) which are used to protect irrigated (maize) and non‐irrigated (sorghum) crops in the Po Plain, one of the most important agricultural lands in Italy. Two extreme scenarios are taken: real worst case (sandy soil) and real best case (clay loam soil). The simulation suggests that cyanazine, linuron and terbuthylazine can be safely used in clay loam soil in both non‐irrigated and irrigated crops, while alachlor, atrazine and simazine can be safely used only in non‐irrigated crops. On the other hand, the application of all the herbicides tested should be avoided in sandy soil, with the exception of linuron in non‐irrigated crops. © 2000 Society of Chemical Industry