3. Limitations of Conventional and Non-Conventional Weed Control Strategies
Apart from the advantages of using herbicides for weed control, there are also disadvantages, mainly due to limitations of the conventional spraying technologies
[4]. Continuous use of the same group of herbicides over a period of time on the same piece of land leads to ecological imbalance in terms of weed shift, herbicide resistance in weeds and environmental pollution
[15]. Indeed, the overuse of herbicides with the same mode of action may lead to the development of herbicide-resistant weed populations
[9]. As a result, agricultural landscapes now tend to be dominated by a few weed species that are difficult to control and that provide a poor resource for farmland biodiversity
[33]. For example, cutleaf evening primrose (
Oenothera laciniata Hill) has become resistant to glyphosate and paraquat
[27]. Herbicides can also have negative side effects, such as surface and ground water contamination, as well as leaving herbicide residues in the food chain
[9][34]. In addition, chemical herbicides can substantially decrease the soil microbial communities and earthworm populations, and the persistent effects of weed suppression can lead to the reduction of nutrient availability and soil biodiversity
[14].
In the same way, the excessive use of tillage results in substantial harmful effects on the soil quality parameters, including biological diversity, soil structure and water storage capacity. Tillage reduces the supply of carbon and nitrogen nutrients to microorganisms
[14]. Soil erosion and soil degradation, inherent in tillage-based systems, increase the environmental pollution from agricultural chemical inputs, such as fertilizers and pesticides, compromising the sustainability of crop production and ecosystem services, as well as threatening global food security in the long run
[35]. Moreover, the operation may face limitations owing to adverse weather conditions. There are also potential problems associated with minimum tillage or non-tillage. The bulk density and compaction of the topsoil increases, and the phytosanitary situation worsens with a higher spread of fungal diseases and the weed infestation of crops
[36]. Furthermore, farmers using reduced tillage may choose to rely increasingly on herbicides and pesticides to deal with these threats
[21] and, as a result, the phytotoxicity of the soil increases.
Ground cover methods, flaming or livestock grazing for weed control also have a few limitations. For example, mulching is cost intensive on a large scale, can promote changes in the soil due to the continuous use of the same mulching material and some of the organic mulches have allelopathic effects on crops
[37]. In addition, many types of organic mulching, such as grass and straw, contain seeds which could allow weeds to grow and acidify the soil
[38]. Cover crops incur expenses for novel equipment, more complicated management practices and time spent seeding and eliminating cover crops instead of managing cash crops
[39]. Living mulches can reduce main crop growth and yield due to competition for water and nutrients, increase pest populations and the risk of diseases. Moreover, living mulches can also promote allelopathy
[40]. Soil solarization induces high temperatures that can be lethal to bacteria and fungi. In some species, if the lethal temperature is not reached, dormancy can be broken, allowing an emergence of a new flush of weed seedlings. This can occur along the topsoil layer
[27]. Solarization tends to result in a flush of nutrients which should be managed by immediately establishing the crop after plastic removal to prevent nutrient loss
[23]. In a flaming strategy, fuel and water consumption can be high, and the flame has restrictions for use during the summer from a fire prevention standpoint. However, smaller, more portable units are now available and provide another tool for the spot control of escape weeds or around sheds and other pieces of infrastructure
[16]. Finally, weed control via livestock grazing can cause damage to the soil structure and non-target species, lead to the spread of weed seeds in feces or on wool, hair or hooves, or even cause the loss of animal condition or liveweight
[41].
Some of the limitations described above can be mitigated or even eliminated when technology associated with precision weed management (PWM) is integrated. The use of the internet, the various types of sensors, artificial intelligence or machine learning can provide potential improvements to integrated weed management (IWM).