Effect of anaerobic soil disinfestation amendment type and C:N ratio on Cyperus esculentus tuber sprouting,growth and reproduction

Anaerobic soil disinfestation (ASD) is a cultural technique primarily targeted for control of soilborne plant pathogens, but can also impact weed propagules. A repeated pot study was conducted to evaluate ASD treatment impact on sprouting and growth of introduced Cyperus esculentus (yellow nutsedge) tubers using dry molasses‐based and wheat bran‐based amendment mixtures at four carbon‐to‐nitrogen (C:N) ratios (from 10:1 to 40:1) and compared with a non‐amended control. The mean percentage of sprouted tubers recovered after ASD treatment was lower for wheat bran‐based (42%) than dry molasses‐based (65%) amendments, and tuber production was 1.6‐fold higher in dry molasses‐based than wheat bran‐based treatments. The highest percentage of sprouted tubers (79%) and the highest mean production of large tubers (threefold higher than wheat bran‐based and 1.7‐fold higher than molasses‐based amendments) were observed for the non‐amended control. Tuber sprouting was significantly lower from all ASD treatments (regardless of amendment C:N ratio) compared with the non‐amended control at a 15 cm burial depth. New tuber production was lowest at C:N ratios of 10:1 and 20:1 and more than twofold higher in the non‐amended control. Wheat bran‐based amendments reduced above‐ground C. esculentus biomass compared with the non‐amended control and ASD treatments with molasses‐based amendments, and reduced below‐ground biomass compared with molasses‐based amendments. Above‐ground biomass was highest at amendment C:N ratio of 10:1, and below‐ground biomass was highest at amendment C:N ratio of 40:1 and the non‐amended control. ASD treatment with wheat bran‐based amendments at lower C:N ratios reduced tuber sprouting and reproduction compared with the non‐amended control, but not at rates high enough to use as a primary weed management tactic.     

Differential sensitivity of Atriplex patula and Chenopodium album to sugar beet herbicides: a possible cause for the upsurge of A. patula in sugar beet fields

In the last decade, the prevalence of Atriplex patula as a weed in the Belgian sugar beet area has increased. Possible reasons for its expansion in sugar beet fields, besides a poor implementation of the low‐dose phenmedipham/activator/soil‐acting herbicide (FAR) system, might be low sensitivity or evolved resistance to one or more herbicides used in sugar beet. Dose – response pot bioassays were conducted in the glasshouse to evaluate the effectiveness of five foliar‐applied sugar beet herbicides (metamitron, phenmedipham, desmedipham, ethofumesate and triallate) and three pre‐plant‐incorporated herbicides (metamitron, lenacil, dimethenamid‐P) for controlling five Belgian A. patula populations. Local metamitron‐susceptible and metamitron‐resistant populations of Chenopodium album were used as reference populations. Effective dosages and resistance indices were calculated. DNA sequence analysis of the photosystem II psbA gene was performed on putative resistant A. patula populations. Overall, A. patula exhibited large intraspecific variation in herbicide sensitivity. In general, A. patula populations were less susceptible to phenmedipham, desmedipham, ethofumesate and triallate relative to C. album populations. Two A. patula populations bear the leucine‐218 to valine mutation on the chloroplast psbA gene conferring low level to high level cross‐resistance to the photosystem II inhibitors phenmedipham, desmedipham, metamitron and lenacil. In order to avoid insufficient A. patula control and further spread, seedlings should preferentially be treated with FAR mixtures containing higher‐than‐standard doses of metamitron and phenmedipham/desmedipham and no later than the cotyledon stage.     

Sensitivity of Echinochloa crus‐galli populations to maize herbicides: a comparison between cropping systems

Echinochloa crus‐galli is an important maize weed with significant variation in herbicide sensitivity. This differential response may reflect differences in selection pressure caused by years of cropping system‐related herbicide usage. The herbicide sensitivity of E. crus‐galli populations from three divergent cropping systems was evaluated in dose–response pot experiments. Populations were collected from sandy fields with (i) a long‐term organic cropping system, (ii) a conventional cropping system with maize in the crop rotation or (iii) a conventional cropping system with long‐term monocropping of maize. Each cropping system was represented by six E. crus‐galli populations. The effectiveness of three foliar‐applied maize herbicides (nicosulfuron, cycloxydim and topramezone) and two soil‐applied maize herbicides (S‐metolachlor and dimethenamid‐P) was tested at three doses and two runs. Foliar‐applied herbicides were applied at the three true leaves stage. Soil‐applied herbicides were applied immediately after sowing. The foliage dry weight per pot was determined 4 weeks after treatment. Plant responses were expressed as biomass reduction. Herbicide sensitivity was consistently lowest for populations from maize monocropping systems. Compared with populations from organic cropping systems, populations from monocropping systems showed 6.9%, 9.8% and 29.3% lower sensitivity to cycloxydim, topramezone and nicosulfuron respectively. Populations from the conventional crop rotation system showed intermediate sensitivity levels, which did not significantly differ from sensitivity levels of populations from the other cropping systems. Sensitivity to dimethenamid‐P and S‐metolachlor was not affected by cropping system. Environmental conditions influenced herbicidal response . This study indicated that integrated weed management may be necessary to preserve herbicide efficacy over the long term.     

Morphological and genetic variability of local Echinochloa accessions and the link with herbicide sensitivity

Echinochloa crus‐galli and Echinochloa muricata are common weeds in Belgian maize fields. Both species are morphologically difficult to distinguish and exhibit high morphological variability. Their response to herbicides varies from field to field. This study investigated whether the considerable morphological polymorphism found among Belgian Echinochloa accessions has a genetic background and whether it is consistently associated with differences in sensitivity to maize herbicides. For this purpose, accessions of E. crus‐galli and E. muricata were compared for morphological and genetic resemblance and tested for herbicide sensitivity. All accessions were planted in the field to examine the morphological traits. A cluster analysis was conducted to assess them for morphological diversity. DNA of leaf material was used for amplified fragment length polymorphism analysis to cluster the accessions genetically. Dose–response pot experiments were conducted in the glasshouse to assess the effectiveness of an acetolactate synthase (nicosulfuron), acetyl‐CoA carboxylase (cycloxydim) and 4‐hydroxyphenyl phosphate dioxygenase (topramezone) inhibiting herbicide. The genetic and morphological clusters were compared with the effective doses obtained from the dose–response bioassays. Morphological variation significantly correlated with genetic variation, but the relation with herbicide sensitivity was weak. Spikelet size and biomass characteristics are reliable discriminating characteristics for (sub)species classification. Intraspecies identification does not seem essential for optimisation of chemical control of E. crus‐galli and E. muricata in the field.     

Sensitivity of recently naturalised Digitaria spp. populations to 4‐hydroxyphenyl pyruvate dioxygenase‐ and acetolactate synthase‐inhibiting herbicides in maize

Until recently, Digitaria aequiglumis var. aequiglumis, native to South America, and Digitaria ciliaris subsp. nubica, native to Northeast Africa, were completely overlooked in Belgium due to their close morphological resemblance to Digitaria sanguinalis and Digitaria ischaemum. One of the possible reasons for their expansion in maize fields, besides for example the lack of crop rotation, might be a lower sensitivity to post‐emergence herbicides acting against panicoid grasses. Dose – response pot experiments were conducted in the glasshouse to evaluate the effectiveness of four foliar‐applied HPPD‐inhibiting herbicides (mesotrione, sulcotrione, tembotrione, topramezone) and two foliar‐applied ALS‐inhibiting herbicides (foramsulfuron, nicosulfuron) for controlling Belgian populations of D. aequiglumis and D. ciliaris subsp. Nubica, as well as local D. sanguinalis and D. ischaemum populations. In another dose–response pot experiment, the influence of growth stage at time of herbicide application on efficacy of topramezone and nicosulfuron for Digitaria spp. control was evaluated. In general, D. aequiglumis and D. ciliaris subsp. nubica populations were less sensitive to HPPD inhibitors than D. ischaemum and D. sanguinalis populations, except for D. aequiglumis treated with topramezone. Contrary to other herbicides tested, topramezone adequately controlled all D. aequiglumis populations at doses well below maximum authorised field dose. All species tested showed a progressive decrease in sensitivity to topramezone and nicosulfuron with seedling age. A satisfactory post‐emergence control of Digitaria species in the field will require appropriate choice of herbicide and dose, as well as more timely application.     

Reconstructing the invasion of Cyperus esculentus in Central Europe

Cyperus esculentus (yellow nutsedge) is a serious weed in agriculture worldwide and observational data suggest that it has recently started to spread rapidly in Central Europe. We studied its spatiotemporal invasion pattern, rate of spread and habitat affiliation in Austria, Germany and Switzerland, using retrospective distribution data from various sources and a method that accounts for sampling bias. In total, we found 265 records of C. esculentus since 1900. Multiple accidental introductions, coupled with subsequent regional radial expansion, describe the spatiotemporal range expansion of C. esculentus in the study area. Cumulative number of records and of the number of invaded grid cells showed a continuous increase, but spread has become more pronounced recently (>2005). Invasion hotspots were located in the warmest regions of the study area, as well as in regions with an oceanic climate. On average, the rate of spread within these invasion hotspots ranged between 3.1 and 5.7 km per year. Cyperus esculentus was primarily found on arable land, while other habitats have been rarely invaded. The integration of different data sources improved the cover of distribution data and was useful for reconstructing the incipient and recent invasion phase of C. esculentus. The data suggest that control may be best achieved by preventing long‐range dispersal and containing or eradicating incipient infestations of C. esculentus.     

Herbicide efficacy for aquatic Alternanthera philoxeroides management in an early stage of invasion: integrating above‐ground biomass,below‐ground biomass and viable stem fragmentation

Alternanthera philoxeroides is a problematic invasive plant in many regions of the world that is difficult to control once naturalised. It poses a threat to agricultural productivity, biodiversity and social amenity values of aquatic environments. Significant research has been conducted internationally, regarding the efficacy of different herbicides for control of A. philoxeroides. However, no studies have looked at key aspects of control for effective management in an early stage of invasion of aquatic environments, hindering eradication and control programmes. This study evaluates the efficacy of herbicides and surfactants on key A. philoxeroides response metrics, including control of above‐ground biomass, below‐ground biomass and production of viable stem fragments. This study concluded that glyphosate (isopropylamine salt) minimises viable stem fragment production post‐herbicide application, compared with imazapyr and metsulfuron, thus reducing the potential for dispersal throughout catchments and waterways. In contrast, imazapyr and metsulfuron provided more effective control than glyphosate for A. philoxeroides growing on exposed embankments. We propose that an effective management strategy for early invasion of aquatic A. philoxeroides, using herbicides, would be to conduct initial applications of glyphosate to control overwater biomass and limit dispersal of viable stem fragments. Once infestations have been forced back to the embankment, imazapyr or metsulfuron treatments will provide longer term control.     

Effects of selective cutting and timing of herbicide application on growth and development of Cirsium arvense in spring barley

Recently, a new implement for controlling weeds in cereals (CombCut) has been developed. It cuts weeds in growing cereals without damaging them by using the physical differences (in height, stem thickness, straw stiffness and branching pattern) between crops and weeds. To evaluate and compare the effects of selective cutting with different timings of herbicide application on Cirsium arvense in spring barley, a randomised block experiment was conducted in Sweden in 2015–2017, in a field with a naturally occurring C. arvense population. Treatments consisted of control (C), herbicide application at 4–5‐leaf stage of C. arvense (H1), herbicide application at 8–10‐leaf stage (H2) and selective cutting at 10‐leaf stage (S). The treatments were performed in 2015 and repeated in 2016 in the same plots, and a final evaluation was performed in 2017. Compared to the control, S, H1 and H2 were equally efficient in reducing above‐ground biomass production of C. arvense and increasing spring barley grain yield per unit area. The number of C. arvense shoots per area was, however, higher in S compared to H1 and H2. No differences in control effects on shoot number were observed between H1 and H2. Our study indicates that (i) selective cutting (S) reduces C. arvense equally efficient as herbicide application and (ii) early herbicide spraying is as efficient as spraying later in the season.     

Influence of multiple herbicide resistance on growth in Amaranthus tuberculatus

Plant defence traits, such as herbicide resistance mutations, may incur a fitness cost to plants that become evident when the trait is not needed. However, individuals with multiple herbicide resistance traits may decrease fitness beyond that of plants with a single herbicide resistance mutation. Multiple herbicide‐resistant (MHR) Amaranthus tuberculatus populations are becoming more prevalent in Midwest United States agroecosystems. The objective was to determine whether selected MHR A. tuberculatus populations express differential development when grown in a herbicide‐free environment. The hypothesis was that MHR A. tuberculatus populations become increasingly less fit when additional herbicide resistances evolve. Multiple herbicide‐resistant and herbicide‐susceptible A. tuberculatus populations were grown in a herbicide‐free field for 20 weeks for two seasons. Differences (P < 0.001) in apical growth were detected 5 and 7 weeks after transplanting for all populations in 2016 and 2017 respectively. Gender and population influenced (P < 0.001) flowering date, with males flowering up to 1.5 weeks earlier than females, but did not cause pollination asynchrony. Shoot biomass was not different (P = 0.84) across A. tuberculatus populations, but there were differences (P < 0.001) for gender and year. Seed production was different amongst A. tuberculatus populations (P = 0.001), but was not influenced by the number of MHR traits. Conversely, a negative quadratic relationship between seed mass and the number of MHR traits was observed (r² = 0.32; P < 0.001). The experiment results demonstrate that MHR in A. tuberculatus populations is not incurring a fitness penalty that will remove the populations in the immediate future.     

Reduced translocation is involved in resistance to glyphosate and paraquat in Conyza bonariensis and Conyza canadensis from California

Resistance to glyphosate and paraquat has evolved in some populations of Conyza spp. from California, USA. This study evaluated whether herbicide absorption and translocation were involved in the mechanism of resistance to both herbicides. Three lines of each species were used: glyphosate‐paraquat‐susceptible (GPS), glyphosate‐resistant (GR) and glyphosate‐paraquat‐resistant (GPR). Radiolabelled herbicide was applied to a fully expanded leaf, and absorption and movement out of the treated leaf were monitored for up to 24 h for paraquat and 72 h for glyphosate. Plants treated with paraquat were incubated in darkness for the first 16 h and then subjected to light conditions. More glyphosate was absorbed in C. bonariensis (52.9–58.3%) compared with C. canadensis (28.5–37.6%), but no differences in absorption were observed among lines within a species. However, in both species, the GR and GPR lines translocated less glyphosate out of the treated leaf when compared with their respective GPS lines. Paraquat absorption was similar among lines and across species (71.3–77.6%). Only a fraction of paraquat was translocated in the GPR lines (3% or less) when compared with their respective GPS or GR lines (20% or more) in both species. Taken together, these results indicate that reduced translocation is involved in the mechanism of resistance to glyphosate and paraquat in C. bonariensis and C. canadensis.     

Multiple herbicide‐resistant Lolium rigidum (annual ryegrass) now dominates across the Western Australian grain belt

Lolium rigidum (annual or rigid ryegrass) is a widespread annual weed in cropping systems of southern Australia, and herbicide resistance in L. rigidum is a common problem in this region. In 2010, a random survey was conducted across the grain belt of Western Australia to determine the frequency of herbicide‐resistant L. rigidum populations and to compare this with the results of previous surveys in 1998 and 2003. During the survey, 466 cropping fields were visited, with a total of 362 L. rigidum populations collected. Screening of these populations with the herbicides commonly used for control of L. rigidum revealed that resistance to the ACCase‐ and ALS‐inhibiting herbicides was common, with 96% of populations having plants resistant to the ACCase herbicide diclofop‐methyl and 98% having plants resistant to the ALS herbicide sulfometuron. Resistance to another ACCase herbicide, clethodim, is increasing, with 65% of populations now containing resistant plants. Resistance to other herbicide modes of action was significantly lower, with 27% of populations containing plants with resistance to the pre‐emergent herbicide trifluralin, and glyphosate, atrazine and paraquat providing good control of most of the populations screened in this survey. Ninety five per cent of L. rigidum populations contained plants with resistance to at least two herbicide modes of action. These results demonstrate that resistance levels have increased dramatically for the ACCase‐ and ALS‐inhibiting herbicides since the last survey in 2003 (>95% vs. 70–90%); therefore, the use of a wide range of integrated weed management options are required to sustain these cropping systems in the future.     

Major emerging alien plants in Austrian crop fields

Globalisation and increasing trade have led to the introduction of alien plants that are highly competitive and difficult to control in agriculture in central Europe. Our study set out to analyse the invasion process and agricultural impact of the six emerging alien plants Abutilon theophrasti, Ambrosia artemisiifolia, Cyperus esculentus, Datura stramonium, Panicum schinzii and Sorghum halepense in Austria, based on a large distribution data set (694 occurrence records in crop fields). We found that all study species have increased in abundance and range, especially after the year 2000. The rate of spread was highest for A. artemisiifolia and lowest for C. esculentus. At present, records of the study species were largely associated with areas of high summer crop concentration in eastern, southern and north‐western Austria. Based on the CORINE land‐cover data set, we found that the agricultural area at risk of being invaded increased over time. At present, it ranges between 45 500 and 168 000 ha (approximately 2.4% and 8.7% of the total agricultural area) depending on the species. The invasion success of the study species is probably associated with frequent human‐mediated dispersal, specific crop‐dominated rotations and herbicide use. Our results suggest that the study species will successfully spread further. We conclude that these emerging alien species will cause substantial impacts on crops in Austria and probably in other countries of central Europe.     

Mechanisms of resistance to acetyl‐coenzyme A carboxylase‐inhibiting herbicides in a Hordeum leporinum population

A failure of acetyl‐coenzyme A carboxylase (ACCase)‐inhibiting herbicides to control a population of Hordeum leporinum Link (barleygrass) occurred following eight applications of these herbicides in both crops and pastures. This population was 7.6‐fold resistant to fluazifop‐P‐butyl compared with standard susceptible populations. The population was between 3.6‐ and 3.8‐fold resistant to other ACCase‐inhibiting herbicides, except butroxydim to which it was susceptible. ACCase extracted from resistant plants and assayed in the presence of herbicides in vitro was susceptible to fluazifop acid and other aryloxyphenoxypropanoate herbicides, but was 4‐fold less sensitive to sethoxydim compared with ACCase from susceptible plants. Resistant plants metabolised fluazifop acid about 1.3‐fold more rapidly compared with susceptible plants; however, sethoxydim was metabolised equally in both populations. Resistance to fluazifop‐P‐butyl and other aryloxyphenoxypropanoate herbicides may be the result of increased herbicide detoxification, whereas resistance to sethoxydim appears to be due to a modified target enzyme. Herbicide resistance in this population is unusual in that different mechanisms appear to confer resistance to the aryloxyphenoxypropanoate and cyclohexanedione herbicides. © 2000 Society of Chemical Industry     

Improved chemical control of Conyza bonariensis in wheat limits problems in the following fallow

Conyza bonariensis is a major weed infesting zero‐tilled cropping systems in subtropical Australia, particularly in wheat and winter fallows. Uncontrolled C. bonariensis survives to become a problem weed in the following crops or fallows. As no herbicide has been registered for C. bonariensis in wheat, the effectiveness of 11 herbicides, currently registered for other broad‐leaved weeds in wheat, was evaluated in two pot and two field experiments. As previous research showed that the age of C. bonariensis, and to a lesser extent, the soil moisture at spraying affected herbicide efficacy, these factors also were investigated. The efficacy of the majority of herbicide treatments was reduced when large rosettes (5–15 cm diameter) were treated, compared with small rosettes (<5 cm diameter). However, for the majority of herbicide treatments, the soil moisture did not affect the herbicide efficacy in the pot experiments. In the field, a delay in herbicide treatment of 2 weeks reduced the herbicide efficacy consistently across herbicide treatments, which was related to weed age but not to soil moisture differences. Across all the experiments, four herbicides controlled C. bonariensis in wheat consistently (83–100%): 2,4‐D; aminopyralid + fluroxypyr; picloram + MCPA + metsulfuron; and picloram + high rates of 2,4‐D. Thus, this problem weed can be effectively and consistently controlled in wheat, particularly when small rosettes are treated, and therefore C. bonariensis will have a less adverse impact on the following fallow or crop.     

Increased foliar activity of clodinafop‐propargyl and/or tribenuron‐methyl by surfactants and their synergistic action on wild oat (Avena ludoviciana) and wild mustard (Sinapis arvensis)

Surfactants can improve postemergence herbicide efficacy and reduce the amount of herbicide required to obtain weed control. The effect of surfactants on the efficacy of herbicides is complicated and depends on the interaction among the plant, surfactant, and herbicide. The effects of surfactants on the efficacy of clodinafop‐propargyl and/or tribenuron‐methyl on wild oat (Avena ludoviciana) and wild mustard (Sinapis arvensis) under greenhouse conditions were investigated. In addition, the surface tension of aqueous solutions of the surfactants and surfactants + herbicides was determined. Significantly lower surface tension values were obtained with the aqueous solutions of citofrigate (Citogate plus Frigate) alone and with the herbicides used in this study. The citofrigate surfactant lead to the greatest enhancement of clodinafop‐propargyl and/or tribenuron‐methyl efficacy and the effect was species‐dependent. The efficacy of clodinafop‐propargyl and/or tribenuron‐methyl in the presence of surfactants in controlling wild oat was higher than for wild mustard. The foliar activity of the tested herbicides rose with increasing surfactant concentrations. The tank mixture of clodinafop‐propargyl and tribenuron‐methyl showed a synergistic effect in controlling wild oat and wild mustard. The synergistic effect in controlling wild mustard was greater than for wild oat.     

Growth and reproduction of Cyperus esculentus L. and Cyperus rotundus L.

The growth of both species (as characterized by their total dry weight, inflorescence dry weight, root and rhizome dry weight and number of shoots per pot) was similar, but they differed in the manner in which the dry weight was partitioned to reproductive structures. Each species partitioned less than 2% of its dry weight into floral formation. However, yellow nutsedge (Cyperus esculentus L.) partitioned only 28% of its dry weight to tubers, whereas purple nutsedge (C. rotundus L.) partitioned 50% of its dry weight to fewer and larger tubers. The allocation of dry weight to reproductive structures was related to changes in day-length. Yellow nutsedge tuber formation increased as day-length decreased from 14.5 to 12.5 h, while floral formation did not begin until the day-length dropped below 14 h. Purple nutsedge formed inflorescences earlier and production continued throughout the remainder of the study, but tuber formation was curvilinear and accelerated as the day-length decreased.     

Continuous non‐destructive monitoring of Cyperus rotundus development using a minirhizotron

A new method for non‐destructive monitoring of the subsurface development of Cyperus rotundus (purple nutsedge) is described. A minirhizotron (MR) system was adopted for use to observe vegetative growth of the weed in a net‐house and under field conditions. In particular, the key stages of tuber production and sprouting were monitored and quantified. The MR system allowed non‐destructive repeated measurements of the key stages in C. rotundus subsurface development, serving as a both quantitative and qualitative tool in the study of C. rotundus. A comparison between the MR method and a destructive method revealed that the former reduces experimental variance, thus providing a more accurate prediction of the sprouting process. The techniques presented in the current study offer advanced methodologies for continuous monitoring of C. rotundus development under the soil surface. The novelty of this method lies in its simplicity and efficiency, allowing continuous observation of specific organs of this noxious weed and potentially of other geophytes.     

Leaf chlorophyll fluorescence discriminates herbicide resistance in Echinochloa species

Timely detection of herbicide resistance at an early stage of crop cultivation is essential to help farmers find alternative solutions to manage herbicide resistance in their fields. In this study, maximum quantum yield of PS II [F_v/F_m = (F_m – F_o)/F_m] was measured at the 4–5 leaf stage to discriminate between herbicide‐resistant and susceptible biotypes of Echinochloa species. The differences in F_v/F_m between herbicide‐resistant and susceptible Echinochloa spp. were consistent with the whole‐plant assay based on I₅₀ (herbicide doses causing a 50% inhibition of F_v/F_m) and GR₅₀ (herbicide doses causing a 50% reduction in plant fresh weight) values and R/S ratios (herbicide resistance index), regardless of the mode of action of the tested herbicides. A PS II inhibitor caused the fastest inhibition of F_v/F_m, compared with ACCase and ALS inhibitors, after herbicide treatment. The required time for discrimination between herbicide‐resistant and susceptible Echinochloa spp. was 64 h after PS II inhibitor treatment, much shorter than those of ACCase and ALS inhibitor‐treated plants, which required 168 and 192 h respectively. The leaf chlorophyll fluorescence assay provided reliable diagnostics of herbicide resistance in Echinochloa spp. with significant time savings and convenient measurement in field conditions compared with the conventional whole‐plant assay.     

Foliar absorption and translocation of nicosulfuron and rimsulfuron in five annual weed species

Ambrosia artemisüfolia L. (common ragweed) and Digitaria ischaemum Schreb. (smooth crabgrass) are not controlled by nicosulfuron and rimsulfuron at the highest recommended application rates, whereas Panicum miliaceum L. (wild proso millet), Amaranthus retroflexus L. (redroot pigweed) and Avena fatua L. (wild oat) are susceptible. The foliar absorption and translocation of ¹⁴C-nicosulfuron and ¹⁴C-rimsulf uron were studied in these weed species up to 48 h after treatment (HAT). Differences in herbicide uptake and translocation were not correlated with the species susceptibility. By 48 HAT, more than 50% of both herbicides remained on the treated leaf surface. Foliar absorption of rimsulfuron was greater than that of nicosulfuron in A. retroflexus, P. miliaceum and A. artemisüfolia. Most of the absorbed herbicide remained in the treated leaf of each weed species. Export of ¹⁴C–nicosulfuron ranged from 28 to 54% of that absorbed, in contrast to 15 to 39% for ¹⁴C–rimsulfuron. The absorption and translocation rates of both herbicides were highest within the initial 6 HAT, and decreased thereafter. Both herbicides showed approximately the same distribution pattern within each weed species.     

Root infection of potato by Spongospora subterranea: knowledge review and evidence for decreased plant productivity

Information is reviewed on root infection of potato by the plasmodiophorid Spongospora subterranea f. sp. subterranea. This pathogen has long been recognized as the cause of root galls (hyperplasia) and the economically important disease powdery scab on tubers (modified stolons). The significance for plant productivity of the zoosporangium stages of the pathogen in potato roots has only recently begun to be documented. Two experiments are described that assessed effects of S. subterranea root infection on potato plant root function and productivity. A greenhouse experiment measured root function and plant parameters for eight potato cultivars with markedly different susceptibilities to tuber powdery scab. Water uptake and plant growth were reduced by S. subterranea inoculation in all eight cultivars. The magnitudes of these negative effects, and intensities of root hyperplasia, differed among the cultivars, but were not related to respective susceptibilities to tuber powdery scab. A field trial assessed root function and plant productivity for a cultivar (Iwa) that is very susceptible to Spongospora tuber and root diseases. Soil water content beneath uninoculated plants was consistently less than for inoculated plants, indicating that inoculation reduced water uptake (root function). Inoculation reduced shoot and root dry weights, and reduced weight of tubers per plant by 42%. Spongospora subterranea causes three diseases of potato: root membrane dysfunction, root hyperplasia and tuber powdery scab. The root diseases caused by the pathogen are likely to be important both for powdery scab management and for deleterious effects on potato crop yields.