Weed Seeds Research Articles

Assessment of Common Ragweed (Ambrosia Artemisiifolia L.) Seed Predation in Crop Fields and Their Adjacent Semi-Natural Habitats in Hungary

Ambrosia artemisiifolia has turned into a noxious weed species in agricultural fields and landscapes in Europe. Durable control options are still needed to limit the abundance of this species. Weed seed consumption by naturally occurring seed predators is a key ecosystem service in agricultural areas. Seed predation levels of common ragweed were examined in wheat and maize fields and adjacent semi-natural habitats (SNHs). To evaluate the weed seeds’ exposure to invertebrate seed predators, 20 cards each were set on the soil surface inside the crop field and in SNHs with four replications. Twenty seeds of ragweed were attached to sandpaper. Seed removal was assessed every 24 h of exposure for 5 days in June and November 2019, October 2020, and June 2021. The seed consumption level was measured according to the number of removed seeds from the seed cards. High consumption rates of ragweed seeds were found in all sampling rounds in both seasons and habitats. The seed predation rates in 2019 were stronger within crop fields in summer than in autumn with a slight difference between SNHs and inside fields. Our results demonstrate the possibility of seed predation contributing to Integrated Plant Protection (IPM) of common ragweed in rural areas.

Grassland restoration on linear landscape elements – comparing the effects of topsoil removal and topsoil transfer

Artificial linear landscape elements, including roads, pipelines, and drainage channels, are main sources of global habitat fragmentation. Restoration of natural habitats on unused linear landscape elements can increase habitat quality and connectivity without interfering with agricultural or industrial development. Despite that topsoil removal and transfer are widely applied methods in restoration projects, up to our knowledge these were previously not compared in the same study system. To address this knowledge gap, we compared spontaneous vegetation recovery after the elimination of positive (embankments) and negative landscape scars (drainage channels) in lowland alkaline landscapes in South Hungary. The novelty of our study is that we compared the fine-scale and landscape-scale results of both methods. At the fine scale, we monitored the spontaneous vegetation development on the created open surfaces in the first, second and fourth year after restoration in 160 permanent plots per year. For characterizing the habitat changes on the landscape scale, we prepared habitat maps and assigned naturalness scores to each patch before and after the restoration activities. Both restoration methods resulted in a rapid vegetation recovery at the fine scale, progressing toward the reference state. In the topsoil removal treatment, a large part of the soil seed bank was removed; therefore, the colonization of the bare surface was a slower process. Seeds of halophytes, including the endemic and protected Suaeda pannonica, were probably present in the deeper soil layers, and these species became established in the restored surfaces, despite being absent in the surrounding vegetation. For restoring vegetation cover, topsoil transfer was a more rapid option; however, vegetation closure and competition by generalist species and weeds hampered the establishment of target species. The removal of the landscape scars by both methods made the sites accessible for grazing. At the landscape scale, the two methods had different effects: there was a slight increase in the habitat naturalness in the topsoil removal site, and a slight decrease in the topsoil transfer site because of weed encroachment. Spreading an upper layer of nutrient-poor soil with low amounts of weed seeds, direct propagule transfer, and targeted grazing regimes could enhance restoration success.

The Potential of Deleterious rhizobacteria to Control Primary Weed <i>Echinochloa </i>sp. on Rice

Deleterious rhizobacteria (DRB) is one of the rhizobacteria that can be used as a bioherbicide and can stimulate plant growth. The objectives that can be obtained from this study are to determine the potential of DRB on the growth of weeds Echinochloa crusgalli and Echinochloa colona on rice. Variables observed in this study were identification of secondary metabolites, measurement of weed sprouts, percentage effectiveness of bacterial isolates against weed seeds, normal sprouts, abnormal sprouts, fresh seeds that did not grow and dead seeds. The aim of this study is to explore biological agents that can be used to control the main weeds of rice crops. This candidate could be a recommendation for environmentally friendly controls. Exploration of the DRB group was obtained by collecting soil samples around the roots of rice crops. Then isolate it, identify as morphologically and physiologically, and test it in vitro studies. The results showed that DRB had the potential to control weed growth and could stimulate the growth of rice. The application of PFA and PFB isolates had a significant effect on inhibiting the length of weed roots and buds, the average percentage of control effectiveness > 80-90%. Novelty in this study could be found as candidate groups of DRB bacteria with specific locations to control the weed Echinochloa sp. on rice crops. For society, this research could be an alternative to reduce dependence on synthetic herbicides . DRB has the potential to be formulated into a bioherbicide to control weeds.

Effect of Forced Aeration and Turning Method on Manurial Value of Cattle, Goat and Poultry Manure Compost

Composting is the transformation of organic material through decomposition in to a biologically humus rich substance suitable for growing plants. The good management of those wastes would be an effective means of organic matter restoration through carbon restitution to the depleted soils through organic amendments. A properly managed composting process can destroy weed seeds, plant pathogens and human pathogens. The main goal of composting is carbon sequestration and enhances soil quality. Compost analysis assures buyers of bulk compost in addition to receiving good value for their money and safe organic fertilizer. Composting has four phases viz., mesophilic (21-45℃, thermophilic (45-68℃), mesophilic-II (<45℃) and maturation phase (Papale et al., 2021). The mesophilic phase also called hot phase, during which heterogeneous group of microorganisms were metabolically active and degrade the soluble compounds like sugars. The second phase is thermophilic phase/curing phase. Mesophilic organism was replaced by thermophilic organism and complex organic matter are degraded at this stage. High temperature in compost destroys the pathogenic organisms and contaminants. Composting is one of the methods used and among this forced aeration and turning method helps to improve the manurial value of compost. The present study is conducted to evaluate the effect of forced aeration and turning method in manurial value of cattle, goat and poultry manure compost.

Germination Biology of Three Cyperaceae Weeds and Their Response to Pre- and Post-Emergence Herbicides in Paddy Fields

(1) Background: Cyperaceae weeds have become a major type of weed in local paddy fields in China. (2) Methods: We assessed the impact of environmental factors, including temperature, light, salinity, water stress and soil depth, on the germination and emergence of three dominant Cyperaceae weeds: Cyperus difformis L., C. iria L. and Fimbristylis littoralis Gaudich. Using the dish dipping method, the performances of the pre- and post-emergence herbicides commonly used in paddy fields on three Cyperaceae weeds were evaluated using the pot method. (3) Results: The seeds optimally germinated at 35 °C in constant conditions and 25 °C/40 °C in alternating conditions. The seeds of the three Cyperaceae weeds were sensitive to light and could not germinate under dark conditions. The germination rate of the three weeds decreased with the increase in the NaCl concentration and water potential; the three weeds could not germinate at a 320 mmol·L−1 NaCl concentration and −0.1 MPa water potential. When the pH levels were 4 to 9, the germination rates of the three weeds were all greater than 80%. The burial depths to inhibit 50% of the emergence of C. difformis, C. iria and F. littoralis were 0.27, 1.06 and 0.42 cm, respectively. The control efficacy of the pre-emergence herbicides of pretilachlor, butachlor and oxyfluorfen on the three weeds were all above 90% at the recommended dose in the field. Halosulfuron-methyl, florpyrauxifen-benzyl and bentazone could effectively control the three Cyperaceae weeds; their performances on the three weeds at the 3- to 4-leaf stage were all above 82%. (4) Conclusions: The three Cyperaceae weed seeds have a strong adaptability to temperature, water potential, salinity and soil depth, and these weeds are sensitive to most pre- and post-emergence herbicides. Therefore, taking Cyperaceae weed seeds into the deep soil layer by tillage or selecting appropriate herbicides according to their growth stages can effectively control Cyperaceae weeds in rice fields.

Investigation of the Allelopathic Effects of Different Faba Bean (Vicia faba L.) Genotypes Against Various Weeds

Many allelopathic crops are cultivated in agricultural fields, and these plants can influence the growth of other plants in the cultivation environment with their phytotoxic compounds. One of these plants is the faba bean. In this study conducted under the ecological conditions of Sakarya/Arifiye, the allelopathic effects of Eresen-87, Salkim, Bilecik, and Sakarya faba bean genotypes on weeds such as Johnson grass (Sorghum halepense L.), curly dock (Rumex crispus L.), purslane (Portulaca oleracea L.), and wild mustard (Sinapis arvensis L.) were investigated. Weed seeds used in the experiment were collected from agricultural fields in the Sakarya province. Extracts from dried plant parts of faba bean genotypes were prepared and applied to petri dishes containing weed seeds at concentrations of 5% and 10%, with four replications. At the end of the research, it was observed that all faba bean genotypes at all application doses caused a decrease in germination rate (%), root length (cm), and shoot length (cm) parameters in the four weed species tested. The best results were determined as Eresen-87 and Bilecik at 10% concentration. When the activities of fresh and dry extracts of faba bean genotypes was compared, it was determined that dry application had a higher allelopathic effect.

Weed Seeds in Marketed Wheat and their Identification

Weed seeds of fifteen species representing 12 genera and 7 families have been observed, contaminated in wheat samples available in Calcutta ration shops. A key has been prepared for identification of these seeds.

Method of corn contamination decreasing after later harvesting predecessors under energy-storage soil maintenance system in irrigation landscapes

The research was carried out at Agrofirm Chokh of the Gunibsky district in the Kizilyurt transhumance zone of the Republic of Dagestan on light chestnut soil. The humus content in the arable layer is 2.77%, P2O5 – 2.21, K2O – 32.8 mg/100 g of soil, the density of the arable layer is 1.24 g/cm3, the lowest moisture capacity (MC) of the soil layer 0–0.6 m is 29.2%. We studied the influence of two corn predecessors: sunflower and corn itself during the main tillage for corn based on plowing to a depth of 28–30 cm without skimmers and with skimmers. During the autumn period, after harvesting the predecessors, the soil was not cultivated, and in the spring, upon the onset of its physical ripeness, two treatments were carried out in a layer of 0–15 cm with disk cultivators to crush the plant residues of the previous crop and plowing to 28–30 cm with a PLN-4-35 plow when physical ripeness of the soil in this layer. It has been established that a radical way to reduce the weediness of corn crops and increase its yield in the irrigated conditions of the Western Caspian region when placed after late-harvested predecessors, including repeated sowings in the same field, is to carry out basic tillage and moisture-recharging irrigation in the spring of the year of sowing. To chop the plant mass remaining after harvesting the predecessor, double processing with disc implements should be carried out before plowing. Plowing is carried out with skimmers, which ensure uniform distribution of weed seeds in the surface layer and their simultaneous germination at a later date than when plowing without skimmers. Subsequently, their life activity is limited to vegetative corn plants. The infestation of corn crops with such soil treatment is reduced three times, the corn yield for the predecessor corn increases by 1.12 t/ha of grain (16.3%), after sunflower – 1.32 t/ha (17.8%).

Allelopathic Effects of Corn Straw and Its Water Extracts on Four Weed Species and Foxtail Millet.

Straw covering is a protective tillage measure in agricultural production, but there is relatively little research on the allelopathic effects of corn straw on weeds and foxtail millet. This experiment studied the allelopathic effects of corn straw on four weeds (Chenopodium album, Setaria viridis, Echinochloa crus-galli and Amaranthus retroflexus) in foxtail millet fields, and also measured the growth indicators of foxtail millet. The study consisted of Petri dish and field experiments. Five treatments were used in the Petri dish experiment: clear water as control (0 g/L, TCK) and four types of corn straw water extracts. They were, respectively, the stock solution (100 g/L, T1), 10 X dilution (10 g/L, T2), 50 X dilution (2 g/L, T3), and 100 X dilution (1 g/L, T4) of corn straw water extracts. Additionally, seven treatments were set up in the field experiment, consisting of three corn straw covering treatments, with covering amounts of 3000 (Z1), 6000 (Z2) and 12,000 kg/ha (Z3), and four control treatments-one treatment with no corn straw cover (CK) and three treatments involving the use of a black film to create the same shading area as the corn straw covered area, with black film coverage areas of 50% (PZ1), 70% (PZ2), and 100% (PZ3), respectively. The results showed that the corn straw water extract reduced the germination rate of the seeds of the four weeds. The T1 treatment resulted in the allelopathic promotion of C. album growth but the inhibition of S. viridis, E. crus-galli, and A. retroflexus growth. Treatments T2, T3, and T4 all induced the allelopathic promotion of the growth of the four weeds. The order of the effects of the corn straw water extracts on the comprehensive allelopathy index of the four weed seeds was as follows: C. album > S. viridis > A. retroflexus > E. crus-galli. With an increase in the corn straw mulching amount, the density and total coverage of the four weeds showed a gradual downward trend, whereas the plant control effect and fresh weight control effect showed a gradual upward trend. All indices showed the best results under 12,000 kg/ha of mulching and returning to the field. Overall, corn straw coverage significantly impacted the net photosynthetic rate and transpiration rate of foxtail millet and increased the yield of foxtail millet. Under coverages of 6000 and 12,000 kg/ha, the growth of foxtail millet is better. Based on our findings, we recommend a corn straw coverage of 12,000 kg/ha for the allelopathic control of weeds in foxtail millet fields.

Influence of cultivation methods on the soil aggregate state in the context of weed development in winter wheat plantations

Weed control in winter wheat crops is an important issue. There is a risk of increasing populations of certain weed species that are resistant to some of herbicides used for winter wheat crops. This could be controlled by a combination of agronomic, mechanical, chemical, and biological methods. After introducing winter wheat into the rotation and improving tillage, the weediness of regular black soils with perennial root and emerged weeds were significantly reduced. The formation of nodal and rudimentary roots had a significant effect on the productivity of winter wheat under different soil moisture conditions. The highest yield of winter wheat was obtained when sown at the optimum time, with higher stem density and ear productivity due to better grain fullness. We studied what effects did the tillage methods have on the aggregate state of the soil in relation to weed development in winter wheat crops, finding that the structural and aggregate composition of the soil played an important role in winter wheat crops, influencing both the development of the crop root system and the water-physical balance of the chernozem, as well as naturally influencing the course of erosion processes in the experimental plots, and having a universal dynamic in terms of adaptation of aggregation and disaggregation processes. Prolonged mechanical stress on soil can cause destruction of its structure. For instance, continuous ploughing or moldboardless tillage with little or no manure application may permanently reduce soil fertility by increasing humus mineralisation. Subsequently, these factors may cause a significant decline in the soil's structural and aggregate composition, resulting in larger amounts of dusty particles smaller than 0.25 mm and cloddy particles larger than 10–12 mm. The soil's structural condition before sowing winter wheat in early September, on average for 2011–2016, indicates increased dispersion of the tilth layer (0–10 cm) in the experimental variants where shallow disc tillage of 10–12 cm was applied. Increase in the number of clods larger than 10 mm in the areas where moldboardless tillage had been applied can be attributed to significant soil drainage. The soil's aggregate state was rated as good, with 8.7% in the 0–10 cm soil layer and 1.7% of clods > 10 mm in the 0–30 cm layer. In 2014–2016, it was rated as satisfactory, with 7.4% and 9.8% of clods > 10 mm, respectively. Shallow disc cultivation resulted in slightly worse indicators: 6.6% and 8.3% of clods > 10 mm in soil layer 0–10 cm and 0–30 cm, respectively, in 2011–2013; and 7.2% and 6.9% of clods > 10 mm, respectively, in 2014–2016. In general, the parameters of optimal structural condition were positive. The tillage method used had a considerable effect on weed growth and development, particularly for those with a root and rhizome structure. It also affected the prevalence and development of pests and diseases in winter wheat. Agrotechnical methods of weed control do not guarantee complete destruction of weeds. Mechanical moldboardless tillage to the depth of 14–16 cm and disc tillage to the depth of 10–12 cm left the fields with 4.1 to 8.8 annual weeds per square meter and 1.3 to 3.3 specimens of harmful root weeds such as Convolvulus arvensis, Lactuca tatarica and Cirsium arvense. Mechanical moldboardless tillage to the depth of 14–16 cm and disc tillage to the depth of 10–12 cm left the fields with 4.1 to 8.8 annual weeds per square meter and 1.3 to 3.3 specimens of harmful root weeds such as Convolvulus arvensis, Lactuca tatarica and Cirsium arvense. Post-harvest residues (4–5 t/ha) can provide almost complete protection against weeds by covering the soil surface. However, pests and diseases may spread more easily due to preservation of fungal spores on the surface of plant residues and preservation of pest larvae in the straw and soil. The distribution of weed seeds in the soil was altered when the rotational tillage of common chernozems in winter wheat cultivation technology had been replaced with energy–saving minimum tillage (shallow flat-cutting disc tillage). This resulted in the concentration of most of the weed seeds (85–90%) in the upper soil layer (0–10 cm).

The effect of temperature and exposure time on redroot pigweed (Amaranthus retroflexus) and yellow foxtail (Setaria pumila) seed mortality in the natural soil seedbank

Abstract Heat disinfection of soil can be used to reduce the content of the soil seedbank. However, species differ in the lethal temperature needed for seed destruction and mortality. Laboratory research was conducted on the seeds of two weed species, redroot pigweed (Amaranthus retroflexus L.) and yellow foxtail [Setaria pumila (Poir.) Roem. & Schult]. The soil samples were collected at the experimental station Šašinovečki Lug, Zagreb, Croatia (45.850289°N, 16.180465°E), and exposed to linearly increasing constant temperatures of 40, 50, 60, 80, 100, and 120 C and exposure times of 30, 60, and 90 min in a laboratory oven. Weed seeds were then extracted from the soil using the sieve separation method and survival was measured by germinating seeds on filter paper. Germination counts were converted into percentages of mortality compared with untreated seeds. The results show that both temperature and exposure time significantly affected seed mortality of both weed species. Amaranthus retroflexus shows a greater susceptibility to high temperatures than S. pumila. A fitted three-parameter sigmoid model was used to define the relationship between temperature and exposure time needed for 50% (LT50) and 90% (LT90) seed mortality. The estimated LT50 values for A. retroflexus are 58.89 to 46.08 C over the 30- to 90-min exposure times; the estimated LT90 values were 113.36 to 65.72 C for the same durations. The estimated LT50 values for S. pumila over the 30- to 90-min exposure times ranged from 91.33 to 75.15 C; the estimated LT90 ranged from 98.79 to 90.32 C over the same durations. The research results contribute to the knowledge about the thermal sensitivity of seeds. Estimating efficacy of soil-heating treatments is essential when comparing the environmental, economic, and social costs of alternatives to conventional weed control methods.

IMPACT OF SOIL STERILIZATION FROM DIFFERENT LOCATIONS, WHEAT SEEDS CLEANING AND THEIR INTERACTIONS ON WEED CONTROL, AND YIELD AND YIELD COMPONENTS

IMPACT OF SOIL STERILIZATION FROM DIFFERENT LOCATIONS, WHEAT SEEDS CLEANING AND THEIR INTERACTIONS ON WEED CONTROL, AND YIELD AND YIELD COMPONENTS

Mechanisms of seed persistence in blackgrass (Alopecurus myosuroides Huds.)

AbstractSeed dormancy is the key factor determining weed emergence in agricultural fields and there is growing interest in weed seeds as a target for weed management. A foremost limitation to this approach is the lack of molecular insight into the mechanisms regulating dormancy in weed seeds. Alopecurus myosuroides (blackgrass) seeds were collected from a wheat field in the UK. At low temperatures, dormant (D) and after‐ripened (AR) seeds germinate similarly and at warm temperatures dormancy is enforced. RNAseq analysis at both temperatures for D and AR seeds demonstrated distinct mechanisms, involving abscisic acid and gibberellin signalling, are involved in after‐ripening and cold‐induced dormancy release. Exogenous application of selected plant growth regulators provided further insight into the phytohormone processes involved in seed dormancy in blackgrass. An untargeted analysis of the transcriptome revealed dormancy‐related processes beyond the regulation of germination, such as seed defence processes, which may have potential as targets for weed seedbank management. Our findings suggest that dormancy breaking can occur via multiple independent but connected hormone‐mediated mechanisms and provide a case study for the use of next‐generation sequencing to uncover the mechanisms involved in seed dormancy in weed and non‐model species.

Effect of Black Soldier Fly Larvae and Food Substrates on Weed Seed Emergence

Black soldier fly larvae (Hermetia illucens; BSFL) composting is biotechnology used for organic waste management and an alternative to traditional composting. We designed a two-phase experiment to evaluate the effect of BSFL composting on the emergence of the following six weed species: barnyardgrass (Echinochloa crus-galli), common ragweed (Ambrosia artemisiifolia), giant foxtail (Setaria faberi), ivyleaf morningglory (Ipomoea hederacea), redroot pigweed (Amaranthus retroflexus), and velvetleaf (Abutilon theophrasti). The first experiment phase was in the laboratory (laboratory composting phase), which consisted of 100 seeds of each weed species subjected to five composting treatments [two controls (nontreated and standard Gainesville diet alone) and three types of substrates (standard Gainesville diet, vegetable waste, food waste) + BSFL]. Live pupa weighed 179 mg with the standard Gainesville diet + BSFL and 205 mg with the food waste diet + BSFL. Dry pupa weighed 68 mg and 70 mg, respectively. The BSFL in the vegetable waste + BSFL treatment did not pupate. During the second experiment phase, the composting treatments were placed in a greenhouse to evaluate weed emergence. Emergence in the nontreated control was 62% for barnyardgrass, 38% for common ragweed, 26% for giant foxtail, 66% for ivyleaf morningglory, 3% for redroot pigweed, and 69% for velvetleaf. Compared with the nontreated control, all treatments with BSFL reduced the emergence of each weed species to ≤1%, except for velvetleaf. This study suggests that BSFL composting may effectively reduce weed seed emergence of many weed species and could be a safe alternative to conventional composting processes to minimize weed pressure in compost. However, efficacy may vary by weed species and may be dependent on seed characteristics, such as an impermeable seedcoat.

Laser weed seed control: challenges and opportunities

Farmers are greatly interested in reducing weed seeds in their fields to avoid unnecessary weed infestation. Autonomous vehicles equipped with plant recognition systems and lasers can be used to control weed plants and may therefore be used to replace or supplement herbicides and mechanical weed control. However, less is known about the ability of laser to control weed seeds. In this study, seeds of weeds (Alopecurus myosuroides, Anisantha sterilis, Avena fatua, Centaurea cyanus, Silene noctiflora) and crops (wheat (Triticum aestivum), maize (Zea mays)) were exposed to increasing dosages of laser energy. The species represented dicots and monocots with different seed sizes and morphology. We used a thulium-doped 50 W fiber laser with a wavelength of 2 µm and a diameter of 2 mm developed for weed control. The seeds were exposed to laser directly on the seed surface or after been covered with soil (2.5 and 5 mm). Small doses of energy (0.4 J mm−2 and 0.8 J mm−2) affected the germination ability of small seeds (S. noctiflora and C. cyanus) when the seeds were irradiated directly on the seed surface, and they were completely burned at the high doses (8.0 J mm−2 and 15.9 J mm−2). However, there was not a clear relationship between seed size and sensitivity to laser dose. Additionally, increasing the laser dose on the seed surface resulted in increasing infection of fungi. Seeds covered with soil were not affected by the laser treatments except C. cyanus seeds. Controlling large seeds on the ground while weed seedlings are controlled with laser robots seems realistic in the future. However, dosages higher than 50 J (~15.9 J mm−2) is necessary to control large seeds.

A first survey for herbicide resistant weeds across major maize growing areas in the North Island of New Zealand.

Weeds are increasingly documented with evolved resistance to herbicides globally. Three species have been reported as resistant in maize crops in New Zealand: Chenopodium album to atrazine and dicamba, Persicaria maculosa to atrazine and Digitaria sanguinalis to nicosulfuron. Despite knowledge of these cases, the distribution of these resistant biotypes is unknown. This study aimed to determine the prevalence of known resistant weeds in major maize growing areas in New Zealand, and to pro-actively screen other species for resistance. Weed seeds of broadleaf and grass species were collected from 70 randomly selected maize growing farms in the North Island in 2021-2022. Seeds were grown and treated with herbicides at recommended field rates. Atrazine-resistant C. album were recorded in a third of surveyed farms and nicosulfuron-resistant D. sanguinalis in a sixth. Half of Waikato farms and a quarter of Bay of Plenty farms (no Hawkes Bay or Wellington farms) had atrazine-resistant C. album. Dicamba-resistant C. album were not detected, nor were atrazine-resistant P. maculosa. Nicosulfuron resistant D. sanguinalis was recorded in 19% of Waikato farms, 6% of Bay of Plenty farms and 9% of Hawkes Bay farms (no Wellington farms). Amaranthus spp., Fallopia convolvulus, Persicaria spp., Solanum spp., Echinochloa crus-galli, Panicum spp. and Setaria spp. were not resistant to any of the herbicides tested. Twenty-nine to 52% of maize farms in the North Island are estimated to have herbicide resistant weeds. Resistance is common in maize farms in Waikato and western Bay of Plenty. Resistance is rare in southern regions, with only one instance of nicosulfuron-resistant D. sanguinalis and no resistant C. album. Most annual weeds in maize are not resistant to herbicides; although atrazine resistant C. album is widespread, it is currently controlled with alternative herbicides. Resistant D. sanguinalis appears to be an emerging problem.

Adaptations in wild radish (Raphanus raphanistrum) flowering time, Part 2: Harvest weed seed control shortens flowering by twelve days

AbstractHarvest weed seed control (HWSC) is an effective technique for managing wild radish (Raphanus raphanistrum L.), a weed that retains its seed until harvest. However, earlier flowering time (leading to increased seed shedding before harvest) is a risk to HWSC effectiveness. This study investigated the effects of repeated HWSC on the evolution of R. raphanistrum flowering dates, using two methods: an adaptation of the SOMER model that included flowering genes (called SOMEF); and a mathematical calculation of the endpoints of flowering date evolution utilizing the relevant life-history equations. In weed management systems with highly effective herbicides, the additional use of HWSC predicted R. raphanistrum population extinction. Low weed numbers and rapid extinction meant that any gradual evolution in days to first flower (DFF) was insufficient to lead to HWSC evasion. In alternative management systems with less vigorous herbicide control and using HWSC, modeling predicted a maximum 2- to 3-d reduction in DFF. In contrast, mathematical calculations of the phenotypes maximizing seeds returned to the seedbank predicted an endpoint to evolution of 12-d earlier flowering, which matched field observations. However, genetic change postulated by the mathematical calculations was not hampered by a restriction to changing DFF allele frequencies. Unknown accompanying genetic changes could affect germination dates or flowering triggers.Simulation modeling that included only flowering genes failed to predict the magnitude of an observed 12-d reduction in DFF. Differences between the 12 d observed in the field (and predicted using mathematical calculations) and the modest changes demonstrated in this field-based modeling study are postulated to be due to unaccounted evolutionary changes in R. raphanistrum.

Thermal-Time Hazard Models of Seven Weed Species Germinability following Heat Treatment

Determining the amount of heat units required to kill weed seeds is a crucial aspect for the success of weed control through soil solarization. Lab experiments were designed to determine the duration of exposure for weed seeds that is required to suppress germination at temperatures (40, 45, 50, 55, and 60 °C) in the range of those typically achieved during soil solarization in California. The species tested were annual sowthistle (Sonchus oleraceus L.), bristly oxtongue (Picris echioides L.), nettleleaf goosefoot (Chenopodium murale L.), redroot pigweed (Amaranthus retroflexus L.), common purslane (Portulaca oleracea L.), little mallow (Malva parviflora L.), and redstem filaree (Erodium cicutarium L.). Germination tests were performed to assess the germinability of the weed seeds. The germination suppression by the lab-simulated solarization temperatures differed among the species based on their seasonality. The cool-season annuals S. oleraceus and P. echioides were more susceptible to the heat treatments than the warm-season annuals P. oleracea, A. retroflexus, and C. murale. The hard-seeded weed species M. parviflora and E. cicutarium were the least susceptible to the heat treatments. The germination rates of S. oleraceus, P. echioides, and C. murale were reduced at all of the temperatures that were tested. The germination rates for A. retroflexus and M. parviflora were not affected by temperatures below 40 °C. The germination rates for P. oleracea were not affected by temperature below 45 °C and the germination of E. cicutarium was not affected by any of the temperatures that were tested. The duration (hours) of exposure and percent of germination suppression of the weed seeds were used to create thermal-time hazard models for weed seeds using logistic regression.

Bird Feeder Explorers Are Not Attracted by the Seeds of Invasive Weeds in Winter

Bird Feeder Explorers Are Not Attracted by the Seeds of Invasive Weeds in Winter

Soil solarization as a non-chemical weed control method in tree nursery production systems of the Pacific Northwest, USA

IntroductionHerbicide application in tree nurseries is limited because of the potential for chemical injury to the large diversity of trees species grown, the lack of registered products, and increasing restrictions on herbicide use, necessitating the costly practice of hand weeding. Soil solarization can reduce the weed seedbank by trapping solar energy under clear plastic film, resulting in high soil temperatures lethal to imbibed weed seeds and seedlings. The objective of this study was to determine if soil solarization would be an effective weed management strategy in Pacific Northwest, USA, tree production systems.MethodsField studies were conducted at three commercial tree nurseries in Oregon and Washington over two years to test soil solarization in reducing the naturally occurring weed seedbank and the time required to hand weed fields. Further field and laboratory tests were conducted with five weed species: Poa annua, Polygonum pensylvanicum, Amaranthus retroflexus, Portulaca oleracea, and Cyperus esculentus. Weed seeds and tubers were buried in packets at 5 and 10 cm to determine their viability after 6 weeks of solarization. A laboratory study was conducted with all but C. esculentus to quantify the exposure time at 45, 50, and 55°C required for 90% death (T90).ResultsSoil solarization was particularly effective in reducing the emergence of naturally occurring weeds in the fall and winter, when weed emergence was reduced by 94-96%. Emergence was reduced 67-81% during the subsequent spring and early summer. Nine to ten months after solarization, solarized areas had a 52 – 69% reduction in hand weeding time compared to non-solarized areas. In field trials with buried seed and tuber packets, mortality differed by location and depth, with P. annua and P. pensylvanicum having the greatest percent seed mortality followed by A. retroflexus and variable results for P. oleracea and C. esculentus. In lab studies, seed mortality differed depending on species and temperature; however, at 55°C, there was a relatively rapid drop in seed viability for all species, and T90 values ranged from 1.2 to 41 h whereas at 45°C the range was 47 to > 3000 h. Similar to the field studies, P. annua and P. pensylvancium were more sensitive to heat, followed by A. retroflexus and P. oleracea.ConclusionSoil solarization can be an effective weed management tool in reducing the weed seedbank in Pacific Northwest tree nurseries and other fall-sown crops but may not work for certain, thermotolerant weed species such as C. esculentus.