Crop production often results in abundant agricultural residues, and organic crop production suffers from an overabundance of weeds. Scientists Perez-Ruiz et al. recently showed that several gritty-textured residues, particularly those derived from maize cobs and olive pits, could abrade weed seedlings when propelled by air. Their use can contribute to the non-chemical control of weeds requested by organic farming and offers a potential solution to address herbicide-resistant weeds.
Johnsongrass, one of the most competitive weeds in maize, is actually controlled by broadcast application of at least two herbicide treatment. Agronomists López-Granados et al. designed a high-resolution method to locate weeds using drones to take visible and near infrared pictures, then algorithms to map johnsongrass patches (light green) in maize rows (dark blue). They deduce that site-specific control would save up to 95% herbicides, which will be consistent with European and the Spanish legislations.
Cover crops reduce nitrogen pollution from croplands, but naturally occurring weeds may provide similar benefits during fallow periods. Agronomist Wortman shows that nitrogen loss is 60% lower in weedy fields than in bare fields. Cover crops are 26% more effective than weeds in reducing nitrogen loss, but given the issues of cover crop adoption, cultivation of fallow weeds looks promising.
Crop yield depends on atmospheric CO2 levels, temperature, drought and competition with weeds. There is therefore a need to forecast which plant traits are important to sustain yield under a changing climate. Agronomists Korres et al. review the effect of climate on crops and weeds to disclose resilient plant traits and cultivars.
In industrial agriculture weeds have been considered solely as undesired plant species that should be removed with pesticides. Now scientists have found that weeds could help farming by, e.g., pollination, preventing water and soil runoff, and attracting predators of crop pests. There is therefore a need of weed surveys across Europe. Agronomists Gerovitt and Hanzlik reviewed the methods of weed surveying in 43 surveys, mainly in Europe, covering up to 4423 fields.
A million-years old relationship has been established between bees and weed flowers. Weeds indeed provide food to bees in the form of tasty pollen, and bees carry pollen from plant to plant to ensure pollination, weed reproduction and diversity. This win-win relationship is endangered by industrial agriculture practices such as weed control and the use of insecticides. Scientists Rollin et al. review agricultural practices that modify weed-bee long-standing collaboration.
Industrial agriculture is killing bees and other pollinators, thus paradoxically threatening future crop production because 35% of world crops need pollination. In the USA honeybees have declined by 59 % in 61 years, and weed diversity by 50 % in 70 years. Bretagnolle and Gaba report the unexpected benefits of weeds for bees and crop production.
Industrial agriculture is a major cause of global warming due to greenhouse emissions of CO2 and N2O. Reducing the tillage is a potential solution because emissions are lower. However, in organic farming, the lack of herbicide should favour weed infestation. But are weeds really a problem for productivity? Armengot et al. compared the effect of reduced and conventional tillage on crop yields and weeds in a 2002-2011 field experiment under organic farming. They found that despite higher weed infestation by perennial species under reduced tillage, yields of wheat, sunflower and spelt were similar for both tillage systems. Therefore findings show that reduced tillage is a viable cropping system for organic farming.
Crop weeds are a major cause of economic loss. Recent changes such as global warming and pesticide-free cropping are changing weed patterns in agriculture. For example, thermophile weeds – weeds that like warm – such as tumbleweeb (Amaranthus retroflexus) have become more abundant in some cropping systems due temperature and precipitation changes. The review article by Peters et al. analyses the ecological mechanisms ruling weed migration.
Fostered by climate change the parasitic weed Phelipanche ramosa infests host crops such as tomato, hemp, tobacco and oilseed rape at an increasing rate. This weed can cause more than 80% yield loss of oilseed rape. To solve this issue knowledge on the way parasitic weeds infect oilseed rape is needed in order to design agroecological solutions. A report by Gibot-Leclerc et al. shows unexpectedly that the P. ramosa weed grows faster on slow-growing Brassicaceae – the oilseed rape family – than on fast-growing mouse-ear cress A. thaliana. This finding demonstrates for the first time that the growth of parasitic plants does not depend only of the growth speed of the host plant.