Application of defoliants alters leaf growth and gas exchange parameters for cotton defoliation

The goal of the current study was to determine how different chemical defoliants and application timing affected defoliation in cotton variety CO 17. The studies were conducted using a split-plot design with three applications at three different times as the main plot and seven defoliants as the subplot. Thidiazuron + Diuron (0.03%) defoliant reduced the gas exchange parameters, photosynthetic rate, transpiration rate and stomatal conductance by reducing plant growth parameters, leaf area, leaf area index, specific leaf weight which significantly increased the defoliation percentage. The negative correlation of cotton growth and gas exchange parameters with defoliation percentage was observed in correlation studies. In conclusion, Thidiazuron + Diuron (0.03%) defoliant was found to be superior in action for improving leaf defoliation and its associated parameters. And also it may be a cost-effective cotton defoliant for aiding the mechanical picking of cotton bolls

Development of New Cotton Defoliation Sprayer Using Unmanned Ground Vehicle and Pulse Width Modulation Technology

Chemical spraying is one of the most important and frequently performed intercultural agriculture operations. It is imperative to utilize appropriate spraying technology as a selection of ineffective one leads to waste of agrochemicals to the non‐target area. Several precision technologies have been developed in the past few decades, such as image processing based on real‐time variable‐rate chemical spraying systems, autonomous chemical sprayers using machine vision and nozzle control, and use of unmanned aerial and ground vehicles. Cotton (Gossypium hirsutum L.) is an important industrial crop. It is a perennial crop with indeterminate growth habit; however, in most parts of the United States, it is grown as an annual crop and managed using growth regulators. Cotton defoliation is a natural physiological phenomenon, but untimely and/or inadequate defoliation by natural processes necessitates the application of chemical defoliants for efficient harvest. Defoliation is a major production practice influencing harvester efficiency, fiber trash content, cotton yield, and fiber quality. Currently, defoliant spraying is done by conventional ground driven boom sprayer or aerial applicator and both systems spray chemical vertically downwards into the canopy, which results in less chemical reaching the bottom of the canopy. Thus, a new autonomous ground sprayer was developed using robotics and pulse width modulation, which travels between two rows covering the whole canopy of the plant. Field research was conducted to evaluate the (i) effect of duty cycles (20%,40%, and 60%) on droplet characteristic (droplet distribution, deposition, and drift potential), defoliation cotton fiber and (ii) effect of duty cycles on cotton yield and II fiber quality. Droplet characteristics (droplet distribution, density, and potential droplet drift) were non-significant across the treatments and results from the water‐sensitive paper field test showed adequate penetration with low flow rates. Therefore, a 20% duty cycle was sufficient to defoliate based on the result of the field experiment. Likewise, the defoliants could be applied safely at the duty cycles tested without influencing fiber quality except for nep/gm, length (Ln), L (5%), short fiber content (SFCn), trash content in field 1 and micronaire, nep size, length (Ln), span length (5%), SFC, and fiber fineness in field 2 which were significant. However, the 20% duty cycle significantly reduced the amount of defoliant and would be a good choice for the autonomous cotton defoliation. This is a significant development as there is a huge potential to save on the cost of applying defoliant chemicals and the environment

The relations of leaf area index with the spray quality and efficacy of cotton defoliant spraying using unmanned aerial systems (UASs)

Leaf area index influences on the spray quality and efficacy, and has relationships with the spray quality and efficacy in agricultural spray application. The aim of the present study was to sought the relations of LAI with the spray quality and efficacy of cotton defoliant spraying using unmanned aerial systems (UASs). A TRAC-II instrument was used to measure the LAI of cotton plants. Three different types of UASs with different spray volume rates (48 L·ha, 72 L·ha and 96 L·ha), flight altitudes (1.5 m, 2.0 m and 2.5 m), and flight speeds (1 m·s, 2 m·s and 3 m·s) were tested. Results showed the following: (1) There were exponential relationships between LAI and droplet deposition at volume rates of 48 L·ha, 72 L·ha and 96 L·ha. There were cubic relationships between LAI and cotton defoliation rate at volume rates of 48 L·ha, 72 L·ha and 96 L·ha. (2) The multiple regression model between LAI and volume rate, and droplet deposition was D = −0.02896 − 0.08055 L + 0.01226 V, the R and RMSE values of the training and test sets were 0.81 and 0.08, and 0.83 and 0.07, respectively. The multiple regression model between LAI and volume rate, and cotton defoliation was C = 100.8524 − 4.0617 L + 0.05482 V, the R and RMSE values of the training and test sets were 0.72 and 0.17, and 0.75 and 0.06, respectively