Leaf water content and physiological recovery influence glyphosate efficacy in drought‐stressed and re‐watered weeds
Tasawer Abbas, Naila Farooq, Muhammad Adnan, Asad Shabbir, Ali Ahsan BajwaAbstract
BACKGROUND
Glyphosate efficacy is highly dependent on plant physiological processes that are sensitive to drought stress. Leaf water content (LWC) can be used as a proxy to indicate drought stress and improve herbicide efficacy. A greenhouse study was conducted to understand the relationship between LWC, physiological processes, and glyphosate efficacy in two weed species, Parthenium hysterophorus (C₃) and Setaria faberi (C₄) under high soil moisture [90–100% water holding capacity (WHC)], re‐watering at 21 days after weed emergence (DAWE), re‐watering at 25 DAWE, and low soil moisture (40–50% WHC).
RESULTS
Soil moisture stress caused significant reduction in LWC (27–32%), stomatal conductance (81–84%), photosynthetic rate (76–82%), chlorophyll content index (46–55%) and shikimic acid accumulation (55–57%) in both species. Both re‐watering treatments recovered LWC to well‐watered levels; however, significant recovery of other physiological traits occurred only in the re‐watering at 21 DAWE (5‐day recovery period), where glyphosate efficacy remained high (94% mortality) in both species. Re‐watering at 25 DAWE (1‐day recovery period) failed to recover stomatal conductance and photosynthesis, resulting in significantly reduced glyphosate efficacy (81% and 69% mortality for P. hysterophorus and S. faberi , respectively). The LWC showed strong correlation with glyphosate efficacy for all moisture regimes except for the re‐watering at 25 DAWE.
CONCLUSION
The time allowed for physiological recovery after re‐watering is critical. Therefore, LWC with the advantage of real‐time remote estimation, can be used as a practical proxy for scheduling glyphosate applications, but the history of drought‐breaking irrigation must be considered to ensure that weeds are physiologically susceptible. © 2026 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.