Spanish orchard weeds now shrug off six major herbicides
Rojano-Delgado A, Sohrabi S, Gherekhloo J, Domínguez-Valenzuela JA, Palma-Bautista C
Invasive Species
If you've ever wondered why the weeds in a neighbor's orchard or along a farm road keep coming back no matter how much herbicide gets sprayed, this study shows it's not bad luck, it's evolution working exactly as expected under decades of chemical pressure.
Researchers checked weeds growing in olive and citrus orchards in southern Spain and found that many of them have become resistant to several different weed killers at once, including glyphosate. Some weeds, like ryegrass and Johnson grass, have even developed internal chemical defenses that break down herbicides before they can work, similar to how overused antibiotics stop working on bacteria. The upshot is that farmers are spraying more chemicals for less effect, which raises concerns about pollution building up in the soil.
Key Findings
Ten dominant weed species across 11 orchards were screened against six herbicides (atrazine, 2,4-D, glyphosate, oxyfluorfen, quizalofop-ethyl, tribenuron-methyl) and showed widespread multiple and cross-resistance
Amaranthus albus, A. viridis, Conyza bonariensis, and Solanum nigrum resisted atrazine, glyphosate, and tribenuron-methyl simultaneously
Lolium rigidum and Sorghum halepense showed broad-spectrum resistance via target-site changes plus enhanced metabolic detoxification, partially reversed by the P450 inhibitor malathion
chevron_right Technical Summary
Weeds in Spanish citrus and olive orchards have evolved resistance to multiple herbicides after decades of chemical use, making common weed killers like glyphosate and atrazine increasingly ineffective and pushing farmers toward even heavier chemical use.
Abstract Preview
Original paper
Evolution of multiple resistance under long-term herbicide exposure reshapes Mediterranean perennial agroecosystems.
Decades of intensive herbicide use in perennial cropping systems have imposed substantial environmental pressures and accelerated the evolution of herbicide-resistant weed populations. In Andalusia...
open_in_new Read full abstractAbstract copyright held by the original publisher.
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Amaranthus albus is an annual species of flowering plant native to the Americas. Its common names include common tumbleweed, tumble pigweed, tumbleweed, prostrate pigweed, pigweed amaranth, white amaranth and white pigweed.