Shattercane (Sorghum bicolor (L.) Moench Subsp. Drummondii) and Weedy Sunflower (Helianthus annuus L.)—Crop Wild Relatives (CWRs) as Weeds in Agriculture

Shattercane (Sorghum bicolor (L.) Moench subsp. drummondii) and weedy sunflower (Helianthus annuus L.) are two examples of crop wild relatives (CWRs) that have become troublesome weeds in agriculture. Shattercane is a race belonging to a different subspecies than domesticated sorghum (Sorghum bicolor (L.) Moench subsp. bicolor). Weedy sunflower populations are natural hybrids between wild and domesticated sunflower (Helianthus annuus L.). Both species have key weedy characteristics, such as early seed shattering and seed dormancy, which play an important role in their success as agricultural weeds. They are widely reported as important agricultural weeds in the United States and have invaded various agricultural areas in Europe. Shattercane is very competitive to sorghum, maize (Zea mays L.), and soybean (Glycine max (L.) Merr.). Weedy sunflower causes severe yield losses in sunflower, maize, soybean, pulse crops, and industrial crops. Herbicide resistance was confirmed in populations of both species. The simultaneous presence of crops and their wild relatives in the field leads to crop–wild gene flow. Hybrids are fertile and competitive. Hybridization between herbicide-tolerant crops and wild populations creates herbicide-resistant hybrid populations. Crop rotation, false seedbed, cover crops, and competitive crop genotypes can suppress shattercane and weedy sunflower. Preventative measures are essential to avoid their spread on new agricultural lands. The development of effective weed management strategies is also essential to prevent hybridization between sorghum, sunflower, and their wild relatives and to mitigate its consequences.

Agricultural Weed Assessment Calculator: An Australian Evaluation

Weed risk assessment systems are used to estimate the potential weediness or invasiveness of introduced species in non-agricultural habitats. However, an equivalent system has not been developed for weed species that occur in agronomic cropland. Therefore, the Agricultural Weed Assessment Calculator (AWAC) was developed to quantify the present and potential future adverse impact of a weed species on crop production and profitability (threat analysis), thereby informing or directing research, development, and extension (RDE) investments or activities. AWAC comprises 10 questions related primarily to a weed’s abundance and economic impact. Twenty weed species from across Australia were evaluated by AWAC using existing information and expert opinion, and rated as high, medium, or low for RDE prioritization based on total scores of 70 to 100, 40 to <70, or <40, respectively. Five species were rated as high (e.g., Lolium rigidum Gaud.), eight were rated as medium (e.g., Conyza spp.), and seven were rated as low (e.g., Rapistrum rugosum L.). Scores were consistent with the current state of knowledge of the species’ impact on grain crop production in Australia. AWAC estimated the economic or agronomic threat of 20 major or minor agricultural weeds from across Australia. The next phase of development is the testing of AWAC by weed practitioners (e.g., agronomists, consultants, farmers) to verify its utility and robustness in accurately assessing these and additional weed species.

Hyptis alata (clustered bushmint).

Hyptis alata is a perennial herb native to the Americas that grows as a weed in pastures and disturbed sites, forming dense thickets that render affected areas unproductive. Several Hyptis species behave as weeds and have become naturalized principally in savannas, disturbed sites and agricultural systems in warmer and wet regions of the world. A total of 19 Hyptis species are already included in the Global Compendium of Weeds, listed as agricultural weeds, environmental weeds and invasive species.

What Makes a Weed a Weed? How Virus-mediated Reverse Genetics Can Help to Explore the Genetics of Weediness

Reverse genetics investigates what a gene does by testing how the plant responds when the specific gene is changed. These techniques have been in use for decades to assess whether a given gene underpins interesting phenotypes and gain insight into the function of gene networks and families. Weed science has only recently entered the "genomic era" in which genomic and reverse genetics approaches are used to address hypotheses. This review focuses on two reverse genetic techniques used on a variety of plants including agricultural weeds, virus-induced gene silencing (VIGS) and virus-mediated overexpression (VOX), explaining the biology behind them and highlighting how these tools may be used for gene function validation in weed species for which no other transgenic approaches have been developed.

Functionality and efficacy of Franklin Robotics’ Tertill™ robotic weeder

Agricultural weeds remain an important production constraint, with labor shortages and a lack of new herbicide options in recent decades making the problem even more acute. Robotic weeding machines are a possible solution to these increasingly intractable weed problems. Franklin Robotics’ Tertill™ is an autonomous weeding robot designed for home gardeners that relies on a minimalistic design to be cost-effective. The objectives of this study were to investigate the ability of the Tertill to control broadleaf and grass weeds, and based on early observations, experiments were conducted with and without its string-trimmer–like weeding implement. Tertill demonstrated high weed-control efficacy, supporting its utility as a tool for home gardeners. Weeds were best controlled by the combined effect of soil disturbance caused by the action of the robot’s wheels and the actuation of the string trimmer. Despite the regrowth potential of an annual grass due to its meristem location, Tertill maintained low densities of millet in an experimental arena. The simple and effective design of the Tertill may offer insights to inform future development of farm-scale weeding robots. Weed density, emergence periodicity, robot working rate, and robotic weeding mechanisms are important design criteria regardless of the technology used for plant detection.

Population Genomic Approaches for Weed Science

Genomic approaches are opening avenues for understanding all aspects of biological life, especially as they begin to be applied to multiple individuals and populations. However, these approaches typically depend on the availability of a sequenced genome for the species of interest. While the number of genomes being sequenced is exploding, one group that has lagged behind are weeds. Although the power of genomic approaches for weed science has been recognized, what is needed to implement these approaches is unfamiliar to many weed scientists. In this review we attempt to address this problem by providing a primer on genome sequencing and provide examples of how genomics can help answer key questions in weed science such as: (1) Where do agricultural weeds come from; (2) what genes underlie herbicide resistance; and, more speculatively, (3) can we alter weed populations to make them easier to control? This review is intended as an introduction to orient weed scientists who are thinking about initiating genome sequencing projects to better understand weed populations, to highlight recent publications that illustrate the potential for these methods, and to provide direction to key tools and literature that will facilitate the development and execution of weed genomic projects.

Honeybee dietary neonicotinoid exposure is associated with pollen collection from agricultural weeds

Neonicotinoid insecticides have been linked to bee declines. However, tracking the primary exposure route for bees in the field has proven to be a major logistical challenge, impeding efforts to restore pollinator health in agricultural landscapes. We quantified neonicotinoid concentrations and botanical species composition in 357 pollen samples collected from 114 commercial honeybee colonies placed along a gradient of agricultural intensity between June and September. Neonicotinoid concentrations increased through the season, peaking at the end of August. As a result, concentrations in pollen were negatively associated with collection from woody and crop plants that flower early-mid season, and positively associated with collection from herbaceous plants that flower mid-late season. Higher clothianidin and thiamethoxam residues were correlated with samples containing a greater proportion of pollen collected from agricultural weeds. The percentage of agricultural land within 1500 m was positively correlated with thiamethoxam concentration; however, this spatial relationship was far weaker than the relationship with the proportion of pollen collected from herbaceous plants. These results indicate that both plant species identity and agricultural dominance are important in determining honeybee neonicotinoid exposure through the pollen diet, but that uncultivated plants associated with agriculture are the source of the greatest acute exposure.

The role of willowherbs (Epilobium) in the recovery of vegetation cover a year after use of herbicide: a case study from Central Lithuania / Ožkarožių (Epilobium) vaidmuo atsikuriant augalijai praėjus metams po herbicido panaudojimo: tyrimas centrinėje Lietuvos dalyje

Several species of willowherb (Epilobium) are considered as agricultural weeds and their prevalence has become an increasing problem in agriculture. The aim of this study was to investigate the role of willowherb plants in the initial stage of vegetation succession a year after the use of glyphosate. The study was based on the examination of thirteen willowherb specimens collected in the apple orchard of 0.2 ha area in August 2008, one month after glyphosate treatment, and vegetation field investigations in the same orchard in July 2009. The coverage of herb layer, the abundance and life stages of Epilobium plants in twenty plots of 1 m2 in size were investigated. The specimens of willowherbs, which survived the glyphosate application in 2008, were identified as Epilobium ciliatum and E. tetragonum. A year after the glyphosate treatment, the willowherb plants prevailed in the vegetation. One alien (E. ciliatum) and three native (E. hirsutum, E. parviflorum and E. tetragonum) species of willowherb were found. E. ciliatum was the most abundant. This species was characterized by the highest number of reproductive and virginile plants. E. parviflorum and E. tetragonum plants were abundant with a very high proportion of reproductive plants. Only pre-reproductive plants of E. hirsutum occurred in the study plots. The reproductive plants represented more than one third of the total number of willowherb plants. The distribution patterns of willowherb species in the plots were very variable.

Additions to vascular plant flora of the Western Suwałki Lakeland, north-eastern Poland / Suvalkų ežeringojo krašto vakarinės dalies (Šiaurės Rytų Lenkija) induočių augalų floros papildymai

The present study provides a floristic list of twenty vascular plant species recorded in 2015-2016 in the Western Suwałki Lakeland, north-eastern Poland, by using the ATPOL cartogram method. Attention is drawn to the species Camelina sativa, Geranium columbinum, Rubus corylifolius aggr., Salix ×mollissima and Vicia pannonica, which are new to the regional flora. Through this study, the distribution status of Allium vineale and Erigeron acris subsp. serotinus in the region has changed from the category of very rare taxon to the category of rare taxon. Two newly recorded species, Camelina sativa and Vicia pannonica, may become established in the Western Suwałki Lakeland in the future as agricultural weeds.