Effects of Dosage and Spraying Volume on Cotton Defoliants Efficacy: A Case Study Based on Application of Unmanned Aerial Vehicles

Abstract

Plant protection unmanned aerial vehicles (UAVs) consist of light and small UAVs with pesticide spraying equipment. The advantage of UAVs is using low-volume spray technology to replace the traditional large-volume mass locomotive spray technology. Defoliant spraying is a key link in the mechanized cotton harvest, as sufficient and uniform spraying can improve the defoliation quality and decrease the cotton trash content. However, cotton is planted at high density in Xinjiang, with leaves in two adjacent rows seriously overlapped, making the lower leaves poorly sprayed. Thus, the defoliation effect is poor, and the cotton quality is degraded. To improve the effect of defoliation and reduce the losses caused by boom sprayer rolling, the effect of defoliant dosage on defoliation, boll opening, absorption and decontamination in cotton leaves and the effect of spraying volume on absorption and decontamination in cotton leaves sprayed by UAVs are studied. The pooled results indicate that plant protection UAVs could be used for cotton defoliants spraying with a twice defoliant spraying strategy, and the defoliant dosage has no significant effect on seed cotton yield and fiber quality in Xinjiang. The residue of thidiazuron in cotton leaves reaches the maximum at four days after spraying, the residue of diuron in cotton leaves reaches the maximum at one day after second spraying. The thidiazuron and diuron residues are increased with spraying volume at rang of 17.6-29.0 L/ha. When the spraying volume is less than 17.6 L/ha, the residue of thidiazuron and diuron is reduced. The research results could provide a reference for further optimization of the spraying parameters of cotton defoliant by plant protection UAVs.

Harvest-aid application strategy in different cotton planting densities by unmanned aerial vehicle

“…In this study, compared with the conventional high-volume and low-concentration spraying method, it is found that harvest aid dosage and the applications frequency by UAVs utilizing a low-volume and high-concentration spraying method do not affect lint cotton yield and fiber quality. The results of the effect of dosage on fiber quality and cotton yield are consistent with previous research by Xin et al [23] .…”

“…It is observed that harvest-aid chemicals do not have a negative influence on fiber quality [34] . UAVs applying harvest aids with low-volume and high-concentration spraying does not affect the fiber quality and cotton yield [14,22,23] . However, there are very few related reports on the effects of harvest aid dosage and the application frequency on cotton yield and fiber quality by low-volume UAV spraying.…”

“…It is reported that with single-round spraying by a multiple-rotor UAV, the achieved defoliation rate (91.5%) is lower than required (95%), and the achieved boll opening rate (89.4%) is lower than required (90%) as well [21] . It is observed that defoliant dosage has no significant impact on fiber quality and cotton yield in a dual-round spraying strategy by a UAV in the sparse-density planting area [23] . In high-density planting area, it is reported that the required defoliation rate is achieved when the spraying volume ≥18 L/hm 2 with flight velocity no more than 5 m/s [14] .…”

Effects of alkyl ethyl sulfonate dosage on cotton defoliation efficacy sprayed by UAV

“…As ground machinery, the boom sprayer spraying leads to problems, such as rolling cotton plants, hitting cotton bolls and pulling cotton branches, which reduce the yield and quality of cotton [10,11] . To adapt to this unique operating environment and improve the shortage of the defoliants spraying equipment supply, unmanned aerial vehicles (UAVs) have been rapidly developed in Xinjiang, China for pesticide application [12][13][14][15] . According to the statistics provided by the Ministry of Agriculture and Rural Affairs of the People's Republic of China, nearly 30,000 crop protection UAVs are used in the country [16,17] .…”

“…Wang et al [20] and Hu et al [21] screened the defoliants suitable for UAV spraying. Zhang et al [22] and Xin et al [14] reported that UAV spraying cotton defoliants could achieve efficient utilization of the defoliants. Hu et al [15] and Wen et al [23] found that the efficiency of UAV spraying cotton defoliant was significantly higher than that of electric air-pressure knapsack (EAP) and boom sprayer.…”