Sunflowers (Helianthus annuus L.) occur in various forms in the landscape. There is the wild sunflower, which is a widespread ruderal plant in North America and has been introduced into some European countries. There is the hybrid sunflower, which is cultivated in the fields, and the volunteer sunflower, which originates from seeds lost during a previous harvest. However, there are also weedy sunflowers. These are morphologically distinct from the cultivated sunflower and the volunteer sunflower.

The main characteristics of the weedy sunflowers are the following: strong branching, the production of many small flower heads and heights of individuals of up to over 300 cm, reddish pigmentation, a longer flowering phase and patchy seed shedding. Weedy sunflowers are very competitive and can cause high yield losses and can therefore be a problem for farmers.

The study by Follak et al. (2024) showed, that weedy sunflowers occur in Austria and may cause harvest losses locally.

Follak, S., Glaser, M., Griesbacher, A., & Essl, F. (2024). Crops gone wild – weedy Helianthus annuus L. in Austria. 13(3), 565–576.

Horse nettle (Solanum carolinense) is native to North America. The species is a major problem in agriculture because it is very competitive and poisonous. The plant has an extensive root system consisting of a taproot, which in turn forms several meters long, horizontally growing lateral roots with numerous regenerative buds. This means that large areas can be colonized by horse nettle in a few years. Successful mechanical or chemical control is therefore very difficult.

In south-eastern Austria, horse nettle is spreading and is mainly found in crops such as soybean, maize and oil pumpkin. A species distribution model shows that although only a relatively small part of Austria is currently climatically suitable, most of it is used for agriculture. Climate change will further increase the potential distribution area in Austria. This underlines the need to take effective measures to stop the further spread of horse nettle and avoid yield losses.

The study by Follak et al. (2023) investigated the current occurrences of the horse nettle in Austria and its spread potential: Follak S. Chapman D., Schwarz M., Essl F. (2023): An emerging weed: rapid spread of Solanum carolinense in Austria. BioInvasions Records 12, 649–658, https://www.reabic.net/journals/bir/2023/3/BIR_2023_Follak_etal.pdf

Climate change affects many aspects of agriculture, from altered planting and harvesting times to herbicide efficacy. Rising temperatures can directly reduce the effectiveness of herbicides while favoring the growth of weeds from warmer regions. Increased CO2 concentrations, the driving force behind climate change, also have a fertilizer-like effect on some weeds. In short, climate change can make weeds more competitive and cause herbicides to become less effective.

As environmental changes due to climate change accelerate, farmers need to be informed about how to adapt their practices. AgriWeedClim aims to communicate the often complex findings from climate and biodiversity research more clearly, through articles in agricultural journals and on the project’s homepage.

Ziska et al. (2016) showed that climate change can significantly reduce the efficacy of certain herbicides by altering plant physiology.

Ziska, L. H. (2016). The role of climate change and increasing atmospheric carbon dioxide on weed management: Herbicide efficacy. Agriculture, Ecosystems and Environment, 231, 304–309. https://doi.org/10.1016/j.agee.2016.07.014

In Europe, species such as Japanese Knotweed (Fallopia spp.), Himalayan Balsam (Impatiens glandulifera), and Common Ragweed (Ambrosia artemisiifolia) have become significant invasive weeds. In many areas, they damage not only agriculture but also local biodiversity, making their control even more important. This primarily involves curbing new populations to prevent further spread.

Early detection and control of these invasive weeds are critical to stopping their expansion. Measures such as mechanical removal or the use of biological control methods offer sustainable solutions. Early detection is also the most cost-effective control method in the long run, both for invasive species and for weeds.

Vilà et al. (2011) have extensively documented the impacts of invasive species on ecosystems, showing that they can have significant negative effects on biodiversity and agriculture.

Vilà, M., et al. (2011). Ecological impacts of invasive alien plants: a meta-analysis of their effects on species, communities, and ecosystems. *Ecology Letters*, 14(7), 702-708. Link to summary: https://onlinelibrary.wiley.com/doi/10.1111/j.1461-0248.2011.01628.x

Early weed monitoring can help control weeds before they become a problem. In its simplest form, it involves regular field inspections—documenting with photos can help keep track of the population development of new weeds. Recently, drones and artificial intelligence have been used to assist with this task. These technologies enable more precise and efficient weed control, benefiting both the environment and the economy.

By identifying problematic weeds early, targeted actions can be taken before they spread significantly and threaten crop yields. This is especially important for new weed species, as they may not be easily controlled with traditional methods, requiring adjustments in management.

Studies like that of Mahajan et al. (2020) show that using drone technology in combination with AI significantly improves the efficiency of weed monitoring.

– Mahajan, G., Singh, S., & Chauhan, B. S. (2020). Drone-integrated smart farming solutions for sustainable agriculture in post-COVID-19 era: global overview and research opportunities. Remote Sensing, 12(24), 4085. Article available here: https://www.mdpi.com/2072-4292/12/24/4085

The development of herbicide resistance poses a major challenge in modern agriculture. The excessive and repeated use of the same herbicides causes many weed species to develop resistance, meaning they respond less effectively to an active ingredient. This leads to a cycle of increasing herbicide use, which in turn creates even more resistant weeds, resulting in higher costs and greater crop losses.

Resistant weeds such as Waterhemp (Amaranthus tuberculatus) in the USA or Blackgrass (Alopecurus myosuroides) in Europe are examples of how quickly this problem can escalate. In Austria, recent cases of resistance have been found in Redroot Pigweed (Amaranthus retroflexus) and Lamb’s Quarters (Chenopodium album). A solution is to diversify weed control strategies, as applied in Integrated Weed Management.

In suspected cases of resistance, documenting all control measures, even those beyond herbicides, is crucial. This allows advisors to suggest more effective management adjustments and communicate the resistance regionally. Resistance cases are documented in databases such as the “International Herbicide-Resistant Weed Database”: https://www.weedscience.org/Home.aspx.

Powles und Yu (2010) haben gezeigt, dass der Einsatz von mehreren Mechanismen der Herbizidresistenz in einer Population zu einem schnellen Anstieg von Resistenzen führen kann, wenn keine ausreichenden Wechselstrategien angewendet werden.

Powles, S. B., & Yu, Q. (2010). Evolution in action: plants resistant to herbicides. Annual Review of Plant Biology, 61, 317-347. Link zur Studie: https://www.annualreviews.org/doi/10.1146/annurev-arplant-042809-112119

Rissel, D., Petersen, J., & Ulber, L., 2024. Ergebnisse des Herbizidresistenz-Verdachtsmonitoring 2022. Herbizidresistenz-Verdachtsmonitoring. Link zur Studie: https://doi.org/10.5073/20240710-110752-0.

Zwerger, P., Augustin, B., Becker, J., Dietrich, C., Forster, R., Gehring, K, et al. (2017): Integriertes Unkrautmanagement zur Vermeidung von Herbizidresistenz. Journal für Kulturpflanzen 69, 146–149 Link zur Studie: https://ojs.openagrar.de/index.php/Kulturpflanzenjournal/article/view/13252

Agricultural habitats cover nearly half of the EU-27 and make up the backbone of many European landscapes. They are essential for the provision of food and fiber and provide cultural/recreational ecosystem services but also vital functions for biodiversity. Over the last century agriculture has been influenced by climate change, land use change, increasing land use intensity, changes in market demands and economic systems. This has had pronounced effects on its unique plant species and communities. While an overall biodiversity loss seems certain, weeds still cause substantial damage to crops, livestock and/or humans. With species introductions showing no signs of stopping and climate change accelerating in the 21^st century, some newly introduced species are set to emerge as new weeds. These emerging weeds are the focus of AgriWeedClim and its research questions:

1. How has the weed flora in Central Europe changed during the past decades?
2. Which weed species have declined, which weed species have expanded or newly emerged? Which factors have driven these changes?
3. Which weeds will likely emerge as important weed species in the future?
4. What will the possible future trajectories of emerging weeds under different land-use and climate change scenarios be?
5. What will be the likely agricultural impacts of future spread of emerging weeds?
6. Which regions will be hotspots of emerging weeds under different land-use and climate change scenarios?
7. Which management options are available to reduce future spread and impacts of emerging weeds?

Our new homepage is out and we are filling it with content, to keep in touch and suggest interesting ideas for posts, please contact us at unkraut.agriweedclim2021@univie.ac.at!