DIFFERENTIAL PHOTOSYNTHETIC RESPONSES TO GLUFOSINATE AMMONIUM IN TWO GRASS WEEDS: Lolium multiflorum AND Echinochloa crus-galli.

Weed control poses a significant challenge in modern agriculture, especially as herbicide-resistant populations become more common. Two problematic species, Lolium multiflorum and Echinochloa crus-galli, have been reported to develop resistance to glyphosate. As an alternative, glufosinate ammonium has gained attention for its potential effectiveness against these weeds.

However, its efficacy may differ based on the weed species and their photosynthetic metabolism. This study aimed to assess the differential sensitivity of ryegrass (C3) and barnyardgrass (C4) to ammonium glufosinate by examining physiological responses linked to leaf senescence and photosystem II activity.

The researchers analyzed visual injury, chlorophyll fluorescence, and ammonium accumulation to determine the impact of glufosinate ammonium on both weed species. The results showed a clear distinction in the response between barnyardgrass and ryegrass. Barnyardgrass exhibited earlier symptom onset and a more significant reduction in the quantum yield of photosystem II (ΦPSII), whereas ryegrass demonstrated a slower senescence process.

These differences suggest that barnyardgrass is more sensitive to glufosinate ammonium, likely due to its C4 photosynthetic metabolism.

The findings conclude that the effectiveness of glufosinate ammonium varies depending on the photosynthetic metabolism and each species' ability to withstand herbicide-induced oxidative stress. By understanding these differential responses, farmers can optimize the use of glufosinate ammonium and develop management strategies to delay the emergence of herbicide resistance in these weeds.