Interaction Effect between Nozzle Type and Application Time of Day on the Efficacy of Paraquat to control Velvetleaf (Abutilon theophrasti Medicus.)

When a contact herbicide is applied in the dark time of a day than in the light time, better weed control will be observed. Velvetleaf is a typical example of weeds in displaying the phenomenon of foliar Nyctinasty. This feature causes the leaf surface of velvetleaf is perpendicularly oriented to the ground during the dark time of day. As a result, when a contact herbicide is applied in the dark time of the day by a single flat fan nozzle which generates a perpendicular motion of spray droplets to the ground, the leaf surface of velvetleaf cannot be covered well. Therefore, the foliar Nyctinasty in velvetleaf reduces the efficacy of contact herbicide applied in the dark time of day. The main hypothesis leading this study was that if the motion of spray droplets is not perpendicular to the ground, it is possible to wet the leaves of velvetleaf in the dark time of day. In this study, the effects of using twin flat fan nozzles which generates a non-perpendicular motion of spray droplets to the ground in comparison with single flat fan nozzle on the efficacy of Paraquat at the different times of day were investigated.

This study was conducted in outdoor conditions at Bu-Ali Sina University, Hamedan, Iran. Treatments consisted of five doses of Paraquat (0, 75, 150, 300, and 600 g a.i. ha-1) using three types of nozzles (single anti-drift flat fan, twin anti-drift flat fan 2020, and twin anti-drift flat fan 7030) in two nozzle sizes (110015 and 11002) at four times of day (before sunset at 20:00, after sunset at 22:00, before sunrise at 05:00, and after sunrise at 7:00) with four replications which were sprayed at the six-to-seven-leaf stage of velvetleaf. Two days after spraying at 7:00, the shoots of velvetleaf were harvested nearly 1 cm above the soil surface. The individual fresh: dry weight ratio was used to analyze as nonlinear regression using a four-parametric logistic model.

 At all four application times of the day, increasing the nozzle size of single anti-drift flat fan nozzle increased the dose of Paraquat required for the 90% desiccation of velvetleaf shoots. While, except at some application times of day (22:00 and 07:00 in the case of twin anti-drift flat fan nozzle 2020 and 5:00 in the case of twin anti-drift flat fan nozzle 7030), increasing the nozzle size of twin anti-drift flat fan nozzles decreased the dose of Paraquat required for the 90% desiccation of velvetleaf shoots. Except in some cases (11002 twin anti-drift flat fan nozzle 2020 and 110015 twin anti-drift flat fan nozzle 7030), when Paraquat was sprayed with any nozzle size at 20:00 and 07:00, there was no significant difference in its efficacy. When Paraquat was sprayed with any nozzle size at 20:00 and 07:00, there was no significant difference in its efficacy. But, when it was sprayed with any nozzle size at 22:00 and 05:00, a significant difference in its efficacy was observed. So, the dose of Paraquat required for the 90% desiccation of velvetleaf shoots at 22:00 was significantly lower than that at 05:00. Our principal hypothesis in this study was confirmed. As when Paraquat was applied with twin anti-drift flat fan nozzles in the dark time of day, it more effectively improved the desiccation of velvetleaf shoots.

The treatment of the application of Paraquat with 11002 twin anti-drift flat fan nozzle 7030 at 22:00 required the minimum Paraquat dose to create the same desiccation intensity as other treatments. Therefore, this treatment is recommendable.