EFFECT OF DROUGHT STRESS ON VELVETLEAF (ABUTILON-THEOPHRASTI) AND BENTAZON EFFICACY

Greenhouse experiments were conducted to determine the effects of drought stress length and relief on velvetleaf growth and bentazon efficacy with crop oil concentrate (COC) and 28% urea ammonium nitrate (UAN). Drought stress caused leaf water and osmotic potentials to decline linearly over time. Leaf water potential (PSI(L)) declined 0.02 and 0.08 MPa day-1 for velvetleaf subjected to -0.03 and -0.4 MPa soil water potential (PSI(P)), respectively. Osmotic potential (PSI(O)) declined 0.02 and 0.21 MPa day-1 for velvetleaf subjected to -0.03 and -0.4 MPa PSI(P), respectively. Bentazon did not reduce drought-stressed compared to non-drought-stressed velvetleaf dry weight 21 d after treatment with either COC or no adjuvant but did decrease dry weight with UAN. Reduced velvetleaf dry wights in drought-stressed velvetleaf compared to non-drought-stressed velvetleaf could not be accounted for by increased bentazon penetration in the drought-stressed plants. Rewatering velvetleaf subjected to 7 d of -0.4 MPA PSI(P) caused them to be more sensitive to bentazon than velvetleaf subjected to -0.03 MPa PSI(P) except when UAN was the adjuvant.