Effect of the Vertical and Non-Vertical Spray of Flat Fan Nozzle Types on the Control Efficacy of Winter Wild Oat (Avena sterilis subsp. ludoviciana Durieu.) by Haloxyfop-R-methyl

Since the leaves of a grass species are perpendicularly oriented to the ground, spraying an ACCase inhibitor with a conventional hydraulic nozzle can not cause an adequate control. In such a situation, it is well established that a large endo-drift of the spray droplets can be occurred. Recently, a new spray technique, angled spray, has been introduced to maximize the deposition of spray droplets on a vertical target surface (i.e., grassy species). This technique is simple, inexpensive, and available to farmers. Therefore, it can be noteworthy to them. This reserech aimed to study the effect of many angled sprays by three flat fan nozzle types on the efficacy of haloxyfop-R-methyl against winter wild oat.

This study was conducted as dose-response bioassay at the research greenhouse of Bu-Ali Sina University in 2019. Haloxyfop-R-methyl at seven doses (0, 5.06, 10.12, 20.25, 40.5, 60.75, and 81 ml a.i. ha-1) were sprayed at 300 kPa spray pressure using three flat fan nozzle types having different atomization quality (standard (Fine: 144–235 µm), anti-drift (Medium: 236–340 µm), and air induction (Extremely Coarse: 503–665 µm)) in seven angled sprays (vertical spray and non-vertical sprays with 10, 20, 30, 40, 50, and 60° forward) on winter wild oat at the three-leaf stage. The haloxyfop-R-methyl dose required to give a 50% reduction in dry weight of winter wild oat (ED50) was detected.

The ED50 values were significantly affected by the nozzle type and the spray angle. With a vertical spray, the ED50 values of 32.51, 44.05, and 53.98 ml a.i. ha-1 was obtained from the flat fan nozzles of standard, anti-drift, and air induction, respectively. The best efficacy of haloxyfop-R-methyl was obtained using a 30° forward angled spray by standard flat fan nozzle (ED50 = 15.10 ml a.i. ha-1), a 40° forward angled spray by anti-drift flat fan nozzle (ED50 = 17.13 ml a.i. ha-1), and a 50° forward angled spray by air induction flat fan nozzle (ED50 = 17.61 ml a.i. ha-1).

From this experiment, the following points were obtained: 1) with a vertical spray, there is a negative correlation between the herbicide efficacy and the spray droplet size; 2) with a non-vertical spray, there is a neutral correlation between the herbicide efficacy and the spray droplet size; 3) when the droplets produced by a nozzle is larger, the more non-vertical spray is required to obtain maximoum herbicide efficacy.