Results of the study of the weed-field flora of Primorsky Territory in 2016-2020

The results of the study of the weed component of soybean, early grain crops and maize agrocenoses in Primorsky Territory are presented. In total, 111 species of weeds belonging to 35 families were found during the period from 2016 to 2020. Compared with the results of crop surveys conducted in 2006-2015, the total number of species detected has increased by 23. The largest number of species belongs to the families Asteraceae (24), Poaceae (15), Polygonaceae (11), Fabaceae (9), Brassicaceae (8), Caryophyllaceae (7) and Lamiaceae (5). The remaining 26 families were represented by 1-3 species each. For the first time weeds-representatives of the families Scrophulariaceae, Violaceae, Lythraceae, Onagraceae, Asclepiadaceae and Boraginaceae have been discovered. The floristic composition of soybean agrocenoses was the highest with 108 weed species from 31 families. In cereal and maize crops, weed diversity was less significant, with 75 species in 22 families and 72 species in 25 families, respectively. Weed vegetation in all the above crops is represented by 62 species of 19 families. The main weed species that grew on 97-99% of the surveyed territory with a sufficiently high average density of standing (21-61pcs/m2) were Asian copperleaf, cockspur grass and common ragweed. Also, more than half of the surveyed crops of soybeans, cereals and corn were hairy cupgrass, perennial sow thistle, common couch-grass, common lamb’s quarters, wormwood species, field horsetail, yellow thistle, dayflower and yellow foxtail. Practical measures to protect against weeds on the Primorsky Territory should be primarily aimed at controlling these species.

Seed viability of common ragweed (Ambrosia artemisiifolia L.) is affected by seed origin and age, but also by testing method and laboratory

Common ragweed (Ambrosia artemisiifolia L.) is an annual Asteraceae species native to North America which is highly invasive across Europe and has harmful impacts, especially on human health and agriculture. Besides its wide ecological range, particularly its high reproductive power by seeds is promoting its spread to various habitats and regions. To prevent further spread and to control the plant, the European Commission funded projects and COST-Actions involving scientists from all over Europe. A joint trial was set up comprising eight different laboratories from Europe to study seed viability variation in different seed samples. Three different testing methods (viability test with 2,3,5-triphenyltetrazolium chloride (TTC), a germination test combined with a subsequent TTC test and a crush test) were tested within the EU-COST-Action SMARTER network to four different seed origins. The viability test results from different laboratories were compared for variation amongst tests and laboratories. The main aim was to optimise the reliability of testing procedures, but results revealed not only significant effects of seed origin and seed age on seed viability, but also considerable differences between the output of the individual testing methods and furthermore between laboratories. Due to these significant differences in the results of the testing labs, additionally a second test was set up. Twelve Austrian ragweed populations were used for TTC testing to obtain a precise adjustment of the testing method as well as a tight guideline for interpreting the results, particularly for the TTC state “intermediate” since a proper classification of TTC-intermediate coloured seeds is still a challenge when determining viability rates.

Grain trade between China and the United States shapes the spatial genetic pattern of common ragweed populations in East China cities

Common ragweed (Ambrosia artemisiifolia L.) is an invasive alien species (IAS) that can cause severe allergies among urban residents. Understanding its invasion pathways is critical for designing effective control programs. However, studies on the invasion of common ragweed normally skip urban areas. Results from a few studies based on analyzing occurrence records contain high uncertainties. We attempted to address this knowledge gap through a case study in East China cities by combining the population genetic method with the occurrence records. We first collected leaf samples of 37 common ragweed populations from 15 cities. We then quantified the spatial genetic pattern of common ragweed populations by analyzing genomic and chloroplast DNA extracted from the leaf samples. Combined with the analysis of occurrence data and trade data, we discovered that multiple introductions have impacted the spatial genetic pattern of common ragweed populations in East China Cities. We inferred that the modern-day grain trade between the United States and China could be the primary invasion source while the bridgehead introduction passage through Japan played a minor role. Among the studied cities, Nanjing and Shenyang dispersed more gene flows than other cities. The two cities' central roles in transportation and grain importation might explain the observed pattern. Based on our findings, we suggest that invasive species control programs should consider the potential role of cities as landing points and dispersal hubs of common ragweed in invaded countries.

Weed Response to Co-Application of Herbicides and Acephate in Cotton

Determining compatibility of pesticides is important in developing effective management practices and adjusting to outbreaks of pests in cotton (Gossypium hirsutism L.). Field experiments were conducted in 2013 and 2014 to determine the effect of chloroacetamide herbicides with residual activity only and acephate with foliar activity against thrips (Frankliniella spp.) on control of emerged weeds by glyphosate, glufosinate, and a mixture of these herbicides. The residual herbicides acetochlor and S-metolachlor as well as the insecticide acephate did not affect control of emerged common ragweed (Ambrosia artemisiifolia L.) and Palmer amaranth (Amaranthus palmeri Watts.). Results from these trials indicate that weed control will not be compromised with co-application of glufosinate, glyphosate, and glufosinate plus glyphosate with acetochlor or S-metolachlor applied alone or with acephate.

High Phenotypic Plasticity in a Prominent Plant Invader along Altitudinal and Temperature Gradients

Studies on plant growth and trait variation along environmental gradients can provide important information for identifying drivers of plant invasions and for deriving management strategies. We used seeds of the annual plant invader Ambrosia artemisiifolia L. (common ragweed) collected from an agricultural site in Northern Italy (226 m. a.s.l; Mean Annual Air Temperature: 12.9 °C; precipitations: 930 mm) to determine variation in growth trajectories and plant traits when grown along a 1000-m altitudinal gradient in Northern Italy, and under different temperature conditions in the growth chamber (from 14/18 °C to 26/30 °C, night/day), using a non-liner modeling approach. Under field conditions, traits related to plant height (maximum height, stem height, number of internodes) followed a three-parameter logistic curve. In contrast, leaf traits (lateral spread, number of leaves, leaf length and width) followed non-monotonic double-Richards curves that captured the decline patterns evident in the data. Plants grew faster, reaching a higher maximum plant height, and produced more biomass when grown at intermediate elevations. Under laboratory conditions, plants exhibited the same general growth trajectory of field conditions. However, leaf width did not show the recession after the maximum value shown by plants grown in the field, although the growth trajectories of some individuals, particularly those grown at 18 °C, showed a decline at late times. In addition, the plants grown at lower temperatures exhibited the highest value of biomass and preserved reproductive performances (e.g., amount of male inflorescence, pollen weight). From our findings, common ragweed exhibits a high phenotypic plasticity of vegetative and reproductive traits in response to different altitudes and temperature conditions. Under climate warming, this plasticity may facilitate the shift of the species towards higher elevation, but also the in situ resistance and (pre)adaptation of populations currently abundant at low elevations in the invasive European range. Such results may be also relevant for projecting the species management such as the impact by possible biocontrol agents.

A high diversity of mechanisms endows ALS-inhibiting herbicide resistance in the invasive common ragweed (Ambrosia artemisiifolia L.)

Ambrosia artemisiifolia L. (common ragweed) is a globally invasive, allergenic, troublesome arable weed. ALS-inhibiting herbicides are broadly used in Europe to control ragweed in agricultural fields. Recently, ineffective treatments were reported in France. Target site resistance (TSR), the only resistance mechanism described so far for ragweed, was sought using high-throughput genotyping-by-sequencing in 213 field populations randomly sampled based on ragweed presence. Additionally, non-target site resistance (NTSR) was sought and its prevalence compared with that of TSR in 43 additional field populations where ALS inhibitor failure was reported, using herbicide sensitivity bioassay coupled with ALS gene Sanger sequencing. Resistance was identified in 46 populations and multiple, independent resistance evolution demonstrated across France. We revealed an unsuspected diversity of ALS alleles underlying resistance (9 amino-acid substitutions involved in TSR detected across 24 populations). Remarkably, NTSR was ragweed major type of resistance to ALS inhibitors. NTSR was present in 70.5% of the resistant plants and 74.1% of the fields harbouring resistance. A variety of NTSR mechanisms endowing different resistance patterns evolved across populations. Our study provides novel data on ragweed resistance to herbicides, and emphasises that local resistance management is as important as mitigating gene flow from populations where resistance has arisen.

Weed Management in White Bean With Pre-plant Incorporated Herbicides

Five field experiments were conducted in Ontario Canada during 2018-2020 to determine the level of crop injury, weed control and white bean yield with up to four-way mixtures of herbicides applied preplant incorporated (PPI). The trials were arranged in a factorial design: Factor 1 was “Grass herbicide” including no grass herbicide, trifluralin, S-metolachlor and trifluralin + S-metolachlor and Factor 2 was “Broadleaf herbicide” including no broadleaf herbicide, halosulfuron, imazethapyr and halosulfuron + imazethapyr. At 2 and 4 weeks after emergence (WAE), there was minimal (≤ 4%) white bean injury. At 8 weeks after herbicide application (WAA), trifluralin, S-metolachlor or trifluralin + S-metolachlor averaged across Factor 2 controlled velvetleaf 69, 71 and 62%, respectively; halosulfuron, imazethapyr and halosulfuron + imazethapyr averaged across Factor 1 controlled velvetleaf 75, 95 and 97%, respectively. At 8 WAA, trifluralin, S-metolachlor and trifluralin + S-metolachlor controlled pigweed 93, 90 and 97%, respectively, and halosulfuron, imazethapyr and halosulfuron + imazethapyr controlled pigweed 97, 79 and 98%, respectively. At 8 WAA, trifluralin, S-metolachlor and trifluralin + S-metolachlor provided poor (≤ 32%) control of common ragweed while halosulfuron, imazethapyr and halosulfuron + imazethapyr controlled common ragweed 86, 53 and 87%, respectively. The 4-way tankmix of trifluralin, S-metolachlor, halosulfuron + imazethapyr controlled common ragweed 95%. At 8 WAA, trifluralin, S-metolachlor and trifluralin + S-metolachlor controlled common lambsquarters 81, 38 and 91%, respectively, and halosulfuron, imazethapyr and halosulfuron + imazethapyr controlled common lambsquarters 94, 97 and 99%, respectively. At 8 WAA, trifluralin, S-metolachlor and trifluralin + S-metolachlor provided poor (≤ 46%) control of wild mustard while halosulfuron, imazethapyr and halosulfuron + imazethapyr provided excellent (≥ 97%) wild mustard control. At 8 WAA, trifluralin, S-metolachlor and trifluralin + S-metolachlor controlled barnyardgrass 70, 85 and 94%, respectively, and halosulfuron, imazethapyr and halosulfuron + imazethapyr controlled barnyardgrass 9, 50 and 59%, respectively. At 8 WAA, trifluralin, S-metolachlor and trifluralin + S-metolachlor controlled green foxtail 89 to 98% and halosulfuron, imazethapyr and halosulfuron + imazethapyr controlled green foxtail 19, 69 and 67%, respectively. Weed interference reduced white bean yield 76%. Generally, white bean yield reflected the level of weed control. Based on these results, the 2- and 3-way tankmixes of herbicides evaluated generally provide similar weed control as the 4-way tankmixes.

Common Ragweed (Ambrosia artemisiifolia L.) Causes Severe Yield Losses in Soybean and Impairs Bradyrhizobium japonicum Infection

Ambrosia artemisiifolia L. (Asteraceae), known as common ragweed, is an annual herbaceous species native to North America that has become one of the most economically important weeds in arable fields throughout Central Europe. Its large ecological amplitude enables the species to become established in several types of environments, and management options to effectively contain its spread are limited due to a lack of efficacy, high cost, or lack of awareness. In the last decade, in particular, soybean fields have been severely affected by common ragweed invasion. However, until now, information on the yield-decreasing effects of the plant has been scarce. Therefore, the aim of this study was to evaluate the competition effects of common ragweed on (1) soybean growth (aboveground/belowground), (2) the yield of two different soybean cultivars, and (3) the nodulation potential. Based on a greenhouse and biennial field trial, we found that in plots with the highest common ragweed biomass, the soybean yield loss accounted for 84% compared to the weed-free control, on average. The number of nodules, in addition to the mean nodule weight, which are tightly correlated with soybean yield, were significantly reduced by the presence of common ragweed. Just one common ragweed plant per square meter reduced the number of nodules by 56%, and consequently led to a decrease in yield of 18%. Although it has been reported that the genus Ambrosia produces and releases several types of secondary metabolites, little is known about the influence of these chemical compounds on soybean growth and nodulation. Thus, there is substantial need for research to understand the mechanisms behind the interaction between common ragweed and soybean, with a view to finding new approaches for improved common ragweed control, thereby protecting soybean and other crops against substantial yield losses.

Climate Change Hastens Invasional Interference Between Two Notorious Invasive Plants, Common Ragweed (Ambrosia Artemisiifolia) and Redroot Pigweed (Amaranthus Retroflexus), in China

As multiple invaders co-occur in similar habitats, understanding the interactions between different invasive species is very important. Invasional meltdown and neutral and interference relationships have been reported. However, interspecific interactions may vary with environmental change due to the different responses of various invaders. To better understand the interaction of notorious invasive alien plants under global climate change, the growth characters of common ragweed (Ambrosia artemisiifolia) and redroot pigweed (Amaranthus retroflexus) were compared when they were planted in monoculture or mixed culture under four environmental treatments: elevated CO2, enriched N, elevated CO2 + enriched N and a control. The results showed that 1) the plant height, basal stem diameter, and shoot, root, and total biomass of common ragweed all consistently increased in response to the treatments, while the growth traits of redroot pigweed were all inhibited. A significant CO2×N interaction was found only for the shoot and total biomass of common ragweed. 2) Invasional interference between these two notorious alien invasive plants was discovered. Common ragweed consistently displayed an obvious competitive advantage over redroot pigweed regardless of treatment. 3) Elevated CO2 and enriched N obviously changed the seed mass frequency distribution of common ragweed: elevated CO2 increased the proportion of small seeds, while enriched N increased the proportion of large seeds. We conclude that common ragweed can outcompete redroot pigweed; moreover, elevated CO2 and N addition hasten this competitive advantage.

Ambrosia artemisiifolia (common ragweed).

A. artemisiifolia is an annual herb native to Central and Northern America. It has been accidentally introduced into a large number of countries as a contaminant of seed and grains. A. artemisiifolia typically colonises disturbed land where it produces a large number of seeds which can remain viable in the soil for 40 years or more. The pollen produced by species of Ambrosia is highly allergenic and can induce allergic rhinitis, fever, or dermatitis. As a result, high medical costs have been reported in areas with large infestations in both its native and introduced range. A. artemisiifolia can also invade agricultural land where it acts as a weed in a number of crops (in particular in sunflower, maize, soybean and cereals) and can cause significant decreases in yields.