Oscillations of Leaves of Abutilon theophrasti (Velvetleaf) and their Sensitivity to Bentazon in Relation to Low and High Humidity

The upper leaf surfaces of velvetleaf (Abutilon theophrasti Medic.) contain trichomes which facilitate the adhesion of droplets of solution, even when the leaves are oriented in a vertical (night) position. Leaves of plants subjected to conditions of high relative humidity were more injured by bentazon (3‐isopropyl‐1H‐2,1,3‐benzothiadiazin‐4(3H)‐one 2,2‐dioxide) than leaves under low soil moisture and relative humidity. Although a significant 24‐h oscillation in the sensitivity of leaves to bentazon was sometimes evident under both high and low humidity conditions, it was definitely more evident in the latter. Generally, the second leaves of plants in the three leaf stage were more consistent for displaying oscillations in sensitivity than the first. The youngest leaves were the most sensitive to bentazon but generally did not display pronounced daily oscillations. The abscission of cotyledons appeared to have possible merit as a bioassay for monitoring leaf injury.