Editing Weed control (section)

==== Herbicides ====
{{main|Herbicide}}
[[File:LPCC-733-Aplicació d'herbicides en arròs.jpg|thumb|A tractor spraying herbicide onto a field of crops]]
The above described methods of weed control use no or very limited chemical inputs. They are preferred by [[Organic gardening|organic gardeners]] or [[Organic farming|organic farmers]].

However weed control can also be achieved by the use of herbicides. Selective herbicides kill certain targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often based on plant [[hormone]]s. Herbicides are generally classified as follows:{{citation needed|date=December 2022}}

* '''Contact''' herbicides destroy only plant tissue that contacts the herbicide. Generally, these are the fastest-acting herbicides. They are ineffective on perennial plants that can re-grow from roots or [[tuber]]s.
* '''Systemic''' herbicides are foliar-applied and move through the plant where they destroy a greater amount of tissue. [[Glyphosate]] is currently the most used systemic herbicide.
* '''Soil-borne''' herbicides are applied to the soil and are taken up by the roots of the target plant.
* '''[[Preemergent herbicides|Pre-emergent]]''' herbicides are applied to the soil and prevent germination or early growth of weed seeds.

In [[agriculture]] large scale and systematic procedures are usually required, often by machines, such as large liquid herbicide 'floater' sprayers, or [[aerial application]].

These are thought to likely have several substantial detrimental impacts (e.g. on soils, health and insects)<ref>{{cite journal |last1=Sánchez-Bayo |first1=Francisco |title=Indirect Effect of Pesticides on Insects and Other Arthropods |journal=Toxics |date=30 July 2021 |volume=9 |issue=8 |pages=177 |doi=10.3390/toxics9080177|pmid=34437495 |pmc=8402326 |doi-access=free }}</ref><ref>{{cite journal |last1=Bourdineaud |first1=Jean-Paul |title=Toxicity of the herbicides used on herbicide-tolerant crops, and societal consequences of their use in France |journal=Drug and Chemical Toxicology |date=4 March 2022 |volume=45 |issue=2 |pages=698–721 |doi=10.1080/01480545.2020.1770781|pmid=32543998 |s2cid=219726947 }}</ref><ref>{{cite journal |last1=Meena |first1=Ram |last2=Kumar |first2=Sandeep |last3=Datta |first3=Rahul |last4=Lal |first4=Rattan |last5=Vijayakumar |first5=Vinod |last6=Brtnicky |first6=Martin |last7=Sharma |first7=Mahaveer |last8=Yadav |first8=Gulab |last9=Jhariya |first9=Manoj |last10=Jangir |first10=Chetan |last11=Pathan |first11=Shamina |last12=Dokulilova |first12=Tereza |last13=Pecina |first13=Vaclav |last14=Marfo |first14=Theodore |title=Impact of Agrochemicals on Soil Microbiota and Management: A Review |journal=Land |date=23 January 2020 |volume=9 |issue=2 |pages=34 |doi=10.3390/land9020034|doi-access=free |hdl=2158/1364313 |hdl-access=free }}</ref> – which may partly explain the development of alternatives described here – and there are also systematic procedures using herbicides that have lower impacts such as robots and machines that apply low amounts [[precision agriculture|with high precision]].<ref>{{cite web |title=Verdant Robotics launches multi-action agricultural robot for 'superhuman farming' |url=https://roboticsandautomationnews.com/2022/02/23/verdant-robotics-launches-multi-action-agricultural-robot-for-superhuman-farming/49471/ |website=Robotics & Automation News |access-date=17 November 2022 |date=23 February 2022}}</ref><ref>{{cite magazine |title=Small Robot Company Tom, Dick, and Harry farm robots: The 200 Best Inventions of 2022 |url=https://time.com/collection/best-inventions-2022/6225155/small-robot-company-tom-dick-and-harry/ |magazine=Time |access-date=17 November 2022 |language=en}}</ref>