Effect of Aviation Spray Adjuvants on Defoliant Droplet Deposition and Cotton Defoliation Efficacy Sprayed by Unmanned Aerial Vehicles

Round  1

Reviewer 1 Report

GENERAL COMMENTS TO THE MANUSCRIPT:

The contents of manuscript are relevant and important information, for both farmer and scientific community, could be obtained. In general, the use of UAV for aerial spray application with relative resulting canopy deposition is a research hot-topic in precision agriculture all around the world, even if the manuscript focuses on particular application in cotton field. Although some lack and inaccuracy in M&M section are present the topic is interesting and suitable according the scope of journal.

I have detailed some comments that can help to apply them.

INTRODUCTION:

L75-77: Please delete the sentence “The use…application process.” and replace with the following text with a more comprehensive introduction view on adjuvants: “Nowadays, the equation, high efficacious/efficient spray application and reduced spray drift risk, could be concurrently balanced, adopting the appropriate direct measures to prevent drift at sources by giving preference to the most efficient application techniques [13]. Even if the nozzle type [14,15] as well as nozzle size [16] have the most important effect on droplet size and velocity, reducing substantially the spray drift [17-20], the composition of sprayed liquid is very important in relation to the application and use of pesticides as it influences the behavior of droplets as well as their persistence at the site of action [21]. A large number of materials (surfactants, oils, polymers and other macromolecules, etc.) have been recommended as “additives” to pesticides sprays to improve their performance in a variety of ways [22]. In particular, the use of spray adjuvants is one of the main approaches used to improve the spray application process [23].

Please, put also the references in the related section (line 407) using the properly formatting and changing all the references numbering in the following manuscript text.

15.   Balsari, P., Grella, M., Marucco, P., Matta, F., Miranda-Fuentes, A., 2019. Assessing the influence of air speed and liquid flow rate on the droplet size and homogeneity in pneumatic spraying. Pest Management Science 75, 366-379.

16.   Nuyttens, D., Baetens, K., De Schampheleire, M., Sonck, B., 2007. Effect of nozzle type, size and pressure on spray droplet characteristics. Biosystems Engineering 97(3), 333-345.

17.   Miranda-Fuentes, A., Marucco, P., Gonzalez-Sanchez, E.J., Gil, E., Grella, M., Balsari, P., 2018. Developing strategies to reduce spray drift in pneumatic spraying vineyards: Assessment of the parameters affecting droplet size in pneumatic spraying. Science of Total Environment 616-617, 805-815.

18.   Guler, H., Zhu, H., Ozkan, H.E., Derksen, R.C., Yu, Y., Krause, C.R., 2007. Spray characteristics and drift reduction potential with air induction and conventional flat fan nozzles. Transaction of ASABE 50(3), 745–754.

19.   Zande, J.C. van de, Holterman, H.J., Wenneker, M., 2008. Nozzle classification for drift reduction in orchard spraying: identification of drift reduction class threshold nozzles. Agricultural Engineering International: the CIGR Ejournal. Manuscript ALNARP 08 0013. Vol. X. May, 2008.

20.   Grella, M., Gil, E., Balsari, P., Marucco, P., Gallart, M., 2017. Advances in developing a new test method to assess spray drift potential from air blast sprayers. Spanish Journal of Agricultural Research 15(3), e0207.

21.   Balsari P, Marucco P, Tamagnone M, 2007. A test bench for the classification of boom sprayers according to drift risk. Crop Prot 26: 1482-1489

22.   Nuyttens D, Zwertvaegher IKA and Dekeyser D, Spray drift assessment of different application techniques using a drift test bench and comparison with other assessment methods. Biosystems Engineering 154:14–24 (2017).

23.   Combellack, J.H., 1982. Loss of herbicides from ground sprayers. Weed Research 22, 193-204.

24.   Hewitt AJ, Miller PCH, Bagley WE, 2001. Interaction of tank mix and nozzle design on spray performance and drift potential. ASAE Paper 01-011081.

25.   Spanoghe, P., De Schampheleire, M., Meeren, P. van der, Steurbaut, W., 2007. Influence of agricultural adjuvants on droplet spectra. Pest Management Science 63(1), 4-16.

L100: “…defoliants  and…” delete one space (double spaces) to read “…defoliants and…”.

MATERIALS AND METHODS

L121: “The inertval…” change to read “The interval…”

L127: “…one sortie was close…” change to read “…one nozzle output was around…”. The term sortie is completely wrong in this type of sentence.

L154: “…TableS1” describing weather parameters is not present. If it is presented as supplementary material, please move it within the text using a table. It will be the Table 2; please change and reorder the numbering of the following tables.

L160 Table 2: In order to avoid repetition, delete all columns related to the dosage of pesticide in each treatment (always the same and already explained in the text through the lines 156-159) al leave only with the dosage of six tested adjuvants. In the treatment 6 there isn’t the name of adjuvants; I suppose that it is the control without adjuvants. If yes, please delete this line in the table and explain in the text that the control treatment consists of spray mixture consist in pesticides mix without adjuvant.

L156: Delete “The experiment consisted of 6 treatments”

L164-165: Move the sentence at the beginning of section 2.2.1 to read “The experiment….blank control (Table 2).”

L165: change “…were tested.” to read “…were measured.”

L168: Change “We set…10-m buffer zones between…” to read “10-m buffer zones were set between…”. Make this type of change consistent throughout the text avoiding to use the first person (too colloquial).

L170-171: Change “…deposition characteristics…droplet size.” To read “deposition characteristics: i) coverage, ii) number of spray impacts/stains and iii) impact/stains dimension. Please avoid to talk about droplet dimension measured on WSP! You can estimate the spray quality from impacts/stains dimension measured on WSP but you cannot measure the droplet size spectra. Droplet size spectra parameters (VMD, D10, D90 and V100) can only be measured in laboratory or field trials using laser scan (Malvern, PDPA, etc.) Make consistent this type of change throughout the text taking care that spray quality, droplet deposition and spray deposit parameters are evaluated based on impacts/stains measurements and could be related to the droplet size spectra produced by nozzles but the droplet size spectra cannot be measured on WSP.

L184-185: Please avoid to use Dv50 because it is not correct. See the previous comment. You can leave talking about the average impacts/stains dimension without referring to the droplet spectra parameters.

L180-L191: Replace the term droplet by impact or stain. It is more appropriate, because it is well known that any spot size measurements made on WSP can be affected by spots that were touching or overlapping.

RESULTS AND DISCUSSION

L244: Change “…on defoliant droplet size, droplet density, and coverage rate of the cotton canopy.” to read “…on defoliant cotton canopy spray quality parameters, namely droplet impacts dimension, density and surface coverage.”

L246: “…which reduce droplet formation, …” what are you meaning? Are you meaning that reduce the volume fraction characterized by smallest droplets (lower than 100 µm –V₁₀₀ %-)? If yes please specify and clarify in the text.

L247: change “…the droplet density…” to read “…the average number of impacts…”.

L248-L250: If Nuyttens et al., found 75µm the most investigated threshold and commonly used in spray application technology is 100 µm.

Many researchers have considered droplets smaller than 75 μm (Hobson et al., 1990; Hobson et al., 1993; Miller and Hadfield, 1989), 100 μm (Bode, 1984; Byass and Lake, 1977; Grover et al., 1978), 150 μm (Combellack et al., 1996; Yates et al., 1985) or 200 μm (Bouse et al., 1990) to be the ones most prone to drift. Spray particles under 50 μm in diameter remain suspended in the air indefinitely or until they evaporate (Zhu et al., 1994). Although there is no specific droplet size range that is liable to drift under all conditions, droplets by diameters less than 100 µm are considered highly driftable. A lot of authors, mainly explain the relation between the drift and the droplet size linked to the V100 indicator (Arvidsson et al., 2011; Baetens et al., 2008; Bode, 1984; Bouse et al., 1990; Combellack et al., 1996; Gil et al., 2015; Nuyttens et al., 2007; 2010; 2011).

Please add some references and discuss deeply your results using the above suggested literature.

L253: Sometimes you talk about wettability. Have you assessed the wettability using a test protocol? The assessment of leaf wettability is a complex procedure that foresee a complex trials (He et al., 2019). Please, explain clearly in which way you have assessed the wettability. If you don’t have evaluated the wettability with a scientific approach, please avoid the discussion about wettability.

L253-254: Change “…droplet density…” to read “…impact density…” or “…average number of impacts…”.

L262: Change “…Dv50…” to read “…mean impacts dimension…”.

L264-265: You state “The defoliant droplets were greatly affected by the gravity and formed larger droplet size”. On what of your results this statement is based? Please specify and clarify adding also relevant literature showing similar results.

L266 table caption: Change “…, droplet density, and Dv50…” to read “…number and mean impacts dimension…”.

L266 in the table head column: Change “(droplets number/cm²)” to read “( number of impacts/cm²)”

L266 in the table head column: Change “Dv50 (µm)” to read “mean impacts dimension (µm)”

L267: What are you meaning with “..had not been converted”? Please clarify.

L268 -269: The sentence “The data…on the leaves.” does not belong to a footnote. It seems a comment/discussion and it is not clear what are you meaning.

L267-271: Where is the end of table footnote? I can presume at the end of line 269. If yes, start a new line.

L291-295: Please add in the manuscript table containing the weather conditions at the time of application. You are discussing about the influence of weather conditions on both coverage and number of impact measured; are you referring to wind speeds, to the RH, to the temperature or both? What kind of analysis have you performed to state that the environmental condition influences your results? Between the lines 278-282 you mention the influence of UAV rotors; can you prove that the difference that you attribute to the weather conditions are not due to the effect of UAV rotors that are very close to the cotton canopies at the time of spray application? Furthermore, use also some weather data in the text to discuss your results variability; as it is your statements are not proved.

L320: Start a new line to divide Figure caption and manuscript text.

L386: Please avoid expression like “...we used…” because are too colloquial. Change to read “WSP was used to measure…”. Check this type of colloquial form throughout the text and change those in appropriate way to make consistent the form along whole manuscript.

L386: change “….droplet parameters…” to read “…spray quality parameters…”.

L391-392: “…were consistently affected by environmental factors, …” this statement have to be proved by the analysis of your data. You can assert this only if you are able to demonstrate that the influence of environmental factors is higher than the influence of winds/air currents generated by UAV rotors. In your results there isn’t this type of data analysis (see also my previous comment).

L407: the “reference” section has to be adequately changed and numbered adding the suggested relevant and international references. This suggestion has to be strictly considered to reach international readers and increase the interest in your research (a lot of your references are in Chinese language).

Author Response

Dear reviewer 1, We are so grateful for the excellent suggestions and the detailed revising from you. We have benefited greatly by the revision. Now we explain your questions firstly point by point, and then made modification accordingly. 

GENERAL COMMENTS TO THE MANUSCRIPT: The contents of manuscript are relevant and important information, for both farmer and scientific community, could be obtained. In general, the use of UAV for aerial spray application with relative resulting canopy deposition is a research hot-topic in precision agriculture all around the world, even if the manuscript focuses on particular application in cotton field. Although some lack and inaccuracy in M&M section are present the topic is interesting and suitable according the scope of journal. Response: Thanks for the great suggestion. I have detailed some comments that can help to apply them. INTRODUCTION: L75-77: Please delete the sentence “The use…application process.” and replace with the following text with a more comprehensive introduction view on adjuvants: “Nowadays, the equation, high efficacious/efficient spray application and reduced spray drift risk, could be concurrently balanced, adopting the appropriate direct measures to prevent drift at sources by giving preference to the most efficient application techniques [13]. Even if the nozzle type [14,15] as well as nozzle size [16] have the most important effect on droplet size and velocity, reducing substantially the spray drift [17-20], the composition of sprayed liquid is very important in relation to the application and use of pesticides as it influences the behavior of droplets as well as their persistence at the site of action [21]. A large number of materials (surfactants, oils, polymers and other macromolecules, etc.) have been recommended as “additives” to pesticides sprays to improve their performance in a variety of ways [22]. In particular, the use of spray adjuvants is one of the main approaches used to improve the spray application process [23]. Please, put also the references in the related section (line 407) using the properly formatting and changing all the references numbering in the following manuscript text. 15.   Balsari, P., Grella, M., Marucco, P., Matta, F., Miranda-Fuentes, A., 2019. Assessing the influence of air speed and liquid flow rate on the droplet size and homogeneity in pneumatic spraying. Pest Management Science 75, 366-379. 16.   Nuyttens, D., Baetens, K., De Schampheleire, M., Sonck, B., 2007. Effect of nozzle type, size and pressure on spray droplet characteristics. Biosystems Engineering 97(3), 333-345. 17.   Miranda-Fuentes, A., Marucco, P., Gonzalez-Sanchez, E.J., Gil, E., Grella, M., Balsari, P., 2018. Developing strategies to reduce spray drift in pneumatic spraying vineyards: Assessment of the parameters affecting droplet size in pneumatic spraying. Science of Total Environment 616-617, 805-815. 18.   Guler, H., Zhu, H., Ozkan, H.E., Derksen, R.C., Yu, Y., Krause, C.R., 2007. Spray characteristics and drift reduction potential with air induction and conventional flat fan nozzles. Transaction of ASABE 50(3), 745–754. 19.   Zande, J.C. van de, Holterman, H.J., Wenneker, M., 2008. Nozzle classification for drift reduction in orchard spraying: identification of drift reduction class threshold nozzles. Agricultural Engineering International: the CIGR Ejournal. Manuscript ALNARP 08 0013. Vol. X. May, 2008. 20.   Grella, M., Gil, E., Balsari, P., Marucco, P., Gallart, M., 2017. Advances in developing a new test method to assess spray drift potential from air blast sprayers. Spanish Journal of Agricultural Research 15(3), e0207. 21.   Balsari P, Marucco P, Tamagnone M, 2007. A test bench for the classification of boom sprayers according to drift risk. Crop Prot 26: 1482-1489 22.   Nuyttens D, Zwertvaegher IKA and Dekeyser D, Spray drift assessment of different application techniques using a drift test bench and comparison with other assessment methods. Biosystems Engineering 154:14–24 (2017). 23.   Combellack, J.H., 1982. Loss of herbicides from ground sprayers. Weed Research 22, 193-204. 24.   Hewitt AJ, Miller PCH, Bagley WE, 2001. Interaction of tank mix and nozzle design on spray performance and drift potential. ASAE Paper 01-011081. 25.   Spanoghe, P., De Schampheleire, M., Meeren, P. van der, Steurbaut, W., 2007. Influence of agricultural adjuvants on droplet spectra. Pest Management Science 63(1), 4-16. Response: Thanks for the great suggestion. We had revised those sentences. L100: “…defoliants  and…” delete one space (double spaces) to read “…defoliants and…”. Response: I am very sorry for the mistake. We had revised it. MATERIALS AND METHODS L121: “The inertval…” change to read “The interval…” Response: I am very sorry for the spelling mistake. We had revised the “inertval” as “interval”. L127: “…one sortie was close…” change to read “…one nozzle output was around…”. The term sortie is completely wrong in this type of sentence. Response: Thanks for the great suggestion. We had revised that sentence. L154: “…TableS1” describing weather parameters is not present. If it is presented as supplementary material, please move it within the text using a table. It will be the Table 2; please change and reorder the numbering of the following tables. Response: We had uploaded the weather information in “Supplementary Materials”. L160 Table 2: In order to avoid repetition, delete all columns related to the dosage of pesticide in each treatment (always the same and already explained in the text through the lines 156-159) al leave only with the dosage of six tested adjuvants. In the treatment 6 there isn’t the name of adjuvants; I suppose that it is the control without adjuvants. If yes, please delete this line in the table and explain in the text that the control treatment consists of spray mixture consist in pesticides mix without adjuvant. Response: Thanks for the great suggestion. We had revised those sentences. L156: Delete “The experiment consisted of 6 treatments” Response: We had deleted that sentence. L164-165: Move the sentence at the beginning of section 2.2.1 to read “The experiment….blank control (Table 2).” Response: Thanks for the great suggestion. We had revised that sentence. L165: change “…were tested.” to read “…were measured.” Response: Thanks for the great suggestion. We had revised that sentence. L168: Change “We set…10-m buffer zones between…” to read “10-m buffer zones were set between…”. Make this type of change consistent throughout the text avoiding to use the first person (too colloquial). Response: Thanks for the great suggestion. We had revised that sentence. L170-171: Change “…deposition characteristics…droplet size.” To read “deposition characteristics: i) coverage, ii) number of spray impacts/stains and iii) impact/stains dimension. Please avoid to talk about droplet dimension measured on WSP! You can estimate the spray quality from impacts/stains dimension measured on WSP but you cannot measure the droplet size spectra. Droplet size spectra parameters (VMD, D10, D90 and V100) can only be measured in laboratory or field trials using laser scan (Malvern, PDPA, etc.) Make consistent this type of change throughout the text taking care that spray quality, droplet deposition and spray deposit parameters are evaluated based on impacts/stains measurements and could be related to the droplet size spectra produced by nozzles but the droplet size spectra cannot be measured on WSP. Response: Thanks for the great suggestion. We had revised that sentence. L184-185: Please avoid to use Dv50 because it is not correct. See the previous comment. You can leave talking about the average impacts/stains dimension without referring to the droplet spectra parameters. Response: Thanks for the great suggestion. We deleted the sentence “Dv50 indicates the droplet size corresponding to the cumulative volume fraction of 50%.”. L180-L191: Replace the term droplet by impact or stain. It is more appropriate, because it is well known that any spot size measurements made on WSP can be affected by spots that were touching or overlapping. Response: Thanks for the great suggestion. We had revised that sentence. RESULTS AND DISCUSSION L244: Change “…on defoliant droplet size, droplet density, and coverage rate of the cotton canopy.” to read “…on defoliant cotton canopy spray quality parameters, namely droplet impacts dimension, density and surface coverage.” Response: Thanks for the great suggestion. We had revised that sentence. L246: “…which reduce droplet formation, …” what are you meaning? Are you meaning that reduce the volume fraction characterized by smallest droplets (lower than 100 µm –V100 %-)? If yes please specify and clarify in the text. Response: Thanks for the great suggestion. We had revised “formation” as “surface tension”. L247: change “…the droplet density…” to read “…the average number of impacts…”. Response: Thanks for the great suggestion. We had revised that sentence. L248-L250: If Nuyttens et al., found 75µm the most investigated threshold and commonly used in spray application technology is 100 µm. Many researchers have considered droplets smaller than 75 μm (Hobson et al., 1990; Hobson et al., 1993; Miller and Hadfield, 1989), 100 μm (Bode, 1984; Byass and Lake, 1977; Grover et al., 1978), 150 μm (Combellack et al., 1996; Yates et al., 1985) or 200 μm (Bouse et al., 1990) to be the ones most prone to drift. Spray particles under 50 μm in diameter remain suspended in the air indefinitely or until they evaporate (Zhu et al., 1994). Although there is no specific droplet size range that is liable to drift under all conditions, droplets by diameters less than 100 µm are considered highly driftable. A lot of authors, mainly explain the relation between the drift and the droplet size linked to the V100 indicator (Arvidsson et al., 2011; Baetens et al., 2008; Bode, 1984; Bouse et al., 1990; Combellack et al., 1996; Gil et al., 2015; Nuyttens et al., 2007; 2010; 2011). Please add some references and discuss deeply your results using the above suggested literature. Response: Thanks for the great suggestion. We had revised that sentence. L253: Sometimes you talk about wettability. Have you assessed the wettability using a test protocol? The assessment of leaf wettability is a complex procedure that foresee a complex trials (He et al., 2019). Please, explain clearly in which way you have assessed the wettability. If you don’t have evaluated the wettability with a scientific approach, please avoid the discussion about wettability. Response: In order to avoid ambiguity, we had deleted the sentence “Organic silicone adjuvant Y-20079® has good wettability.” L253-254: Change “…droplet density…” to read “…impact density…” or “…average number of impacts…”. L262: Change “…Dv50…” to read “…mean impacts dimension…”. Response: Thanks for the great suggestion. We had revised those sentences. L264-265: You state “The defoliant droplets were greatly affected by the gravity and formed larger droplet size”. On what of your results this statement is based? Please specify and clarify adding also relevant literature showing similar results. L266 table caption: Change “…, droplet density, and Dv50…” to read “…number and mean impacts dimension…”. L266 in the table head column: Change “(droplets number/cm2)” to read “( number of impacts/cm2)” L266 in the table head column: Change “Dv50 (µm)” to read “mean impacts dimension (µm)” Response: Thanks for the great suggestion. We had revised those sentences. L267: What are you meaning with “..had not been converted”? Please clarify. Response: Those data was based on the analysis of WSP, without any conversion. L268 -269: The sentence “The data…on the leaves.” does not belong to a footnote. It seems a comment/discussion and it is not clear what are you meaning. Response: In order to avoid ambiguity, we had deleted the sentence “The data…on the leaves.” L267-271: Where is the end of table footnote? I can presume at the end of line 269. If yes, start a new line. Response: I am very sorry for the mistake. We had revised it. L291-295: Please add in the manuscript table containing the weather conditions at the time of application. You are discussing about the influence of weather conditions on both coverage and number of impact measured; are you referring to wind speeds, to the RH, to the temperature or both? What kind of analysis have you performed to state that the environmental condition influences your results? Between the lines 278-282 you mention the influence of UAV rotors; can you prove that the difference that you attribute to the weather conditions are not due to the effect of UAV rotors that are very close to the cotton canopies at the time of spray application? Furthermore, use also some weather data in the text to discuss your results variability; as it is your statements are not proved. Response: Weather conditions have a significant impact on UAV spraying. We were just here to tell the reader to pay attention to the weather when working with UAVs. L320: Start a new line to divide Figure caption and manuscript text. Response: I am very sorry for the mistake. We had revised it. L386: Please avoid expression like “...we used…” because are too colloquial. Change to read “WSP was used to measure…”. Check this type of colloquial form throughout the text and change those in appropriate way to make consistent the form along whole manuscript. Response: Thanks for the great suggestion. We had revised those sentences. L386: change “….droplet parameters…” to read “…spray quality parameters…”. Response: Thanks for the great suggestion. We had revised that sentence. L391-392: “…were consistently affected by environmental factors, …” this statement have to be proved by the analysis of your data. You can assert this only if you are able to demonstrate that the influence of environmental factors is higher than the influence of winds/air currents generated by UAV rotors. In your results there isn’t this type of data analysis (see also my previous comment). Response: In order to avoid ambiguity, we had deleted the sentence “Polymer and silicone adjuvants were considerably affected by environmental factors, and the synergistic effect with those factors was insignificant.” L407: the “reference” section has to be adequately changed and numbered adding the suggested relevant and international references. This suggestion has to be strictly considered to reach international readers and increase the interest in your research (a lot of your references are in Chinese language). Response: Thanks for the great suggestion. We had added more international references. Kind regards, Xiaoqiang Han & Wei Fu 2019.4.22

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors did great improvement of the paper quality since the first submission. However the conclusion should be improved to better highlight the work that have been done during this research. A conscientious proof-reading should be done to correct the remaining grammar mistakes in the text. 

Specific comments / grammar:

#Line 121: inertval 

#Line 166: m area should be m2 area (same on lines 167-169, 211)

#Line 184: what is 5h3?

Author Response

Dear reviewer 2,

We are so grateful for the excellent suggestions and the detailed revising from you. We have benefited greatly by the revision. Now we explain your questions firstly point by point, and then made modification accordingly.

Reviewers' comments:

The authors did great improvement of the paper quality since the first submission. However the conclusion should be improved to better highlight the work that have been done during this research. A conscientious proof-reading should be done to correct the remaining grammar mistakes in the text. 

Response: Thanks for the excellent suggestion on our manuscript. We had rewrote the “Conclusions” section.

Specific comments / grammar:

#Line 121: inertval 

Response: I am very sorry for the spelling mistake. We had revised the “inertval” as “interval”.

#Line 166: m area should be m2 area (same on lines 167-169, 211)

Response: Thanks for the great suggestion. We had revised the “135 × 215 m area” as “135 m × 215 m area”, (same on lines 167-169, 211).

#Line 184: what is 5h3?

Response: I am very sorry for the mistake. We had deleted the “5h3”.

Kind regards,

Xiaoqiang Han & Wei Fu

2019.4.22

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round  1

Reviewer 1 Report

GENERAL COMMENTS TO THE MANUSCRIPT:

The contents of manuscript are relevant and important information, for both farmer and scientific community, could be obtained. In general, the use of UAV for aerial spray application with relative resulting canopy deposition is a research hot-topic in precision agriculture all around the world, even if the manuscript focuses on particular application in cotton field. Although the topic is interesting and suitable according the scope of journal, a relevant lack and inaccuracy in M&M section have to be reported; these lacking are reflected on all subsequent sections.

Although I’m not qualified to judge about the English language, I carefully suggest to do an extended language review by a native English speaker.

I have detailed some comments that can help to improve the manuscript.

INTRODUCTION

GENERAL COMMENT: The information contained are quite adequate to the contents of manuscript. However, sometimes sentences are disconnected decreasing the flow of text. Even if manuscript is focused and relevant for Asia region, I suggest to extend a little bit the introduction investigating the UAV spray application in Europe and America providing also further relevant references.

MATERIALS and METHODS

L90-L96: You have reported a long list of chemical products without any explanation about use. The text is not organic.

L97: You have listed the adjuvants in Table1. Why don’t put also the chemical in a Table?

L100-107: Also in this case you have reported a long mixed list of equipment and instruments used. In some cases, important information are missed (e.g. technical specification of centrifugal nozzles together with producer and position on UAV). What about droplet spectra (VMD, D10, D90 and V100) produced by centrifugal nozzle used at 800rpm? These are fundamental information related to the droplet deposition? At least technical specification provided by nozzle producer have to be reported.

L118: “…the leaf area index were uniform within each farm.” Please put the value of measured LAI together with method used to determine it (it is enough put references about methodology used avoiding long explantion).

L119: “[22]” why are you using reference in the sub-title?

L120: “Defoliation is an important management practice of cotton production”. This information belong to the introduction; please, move it.

L123-124: This information is redundant. You have already explained the hand held weather station used in the section 2.1.2. I suggest to move the information contained in the sections 2.1.1 and 2.1.2 throughout the text where needed avoiding long list that make the reader lost.

L125-130: More information about weather measurements and conditions at the time of application are required? What was the weather station frequency of records? The most influent weather parameters during spray application are the wind speed and direction that vary continuously: at least 1Hz frequency is required to characterize adequately the weather conditions at the time of application.

L130: “Table S1”: Tabe S1 describing weather parameters is not present!

L132-133: “Cotton defoliant spraying was carried out on September 15, 2018 and September 22, 2018.” Please avoid repetition. Information showed between lines 125-127.

L134: Table 3 is not clear. Are you meaning that in each treatment adjuvants was mixed with Thidiazuron, alkil ethyl sulfonate and Ethephon and each treatment was repeated in two periods (15 and 22 September)? If yes, please give a clear explanation in the text and reorganize the table adequately.

L143: “The WSP was collected and bagged individually” information repeated in the line 146 “Alll WSP was quickly removed and placed in zip-lock bags…”. Please avoid repetitions.

L146-148: Information not relevant for the paper.

L150: Please, provide a more detailed and technical draw in order to understand exactly the position of WSP in the field and canopy height and depth.

L154: “Dv50 indicates the droplet size corresponding to the cumulative volume fraction of 50%.” You are right that the Volume median diameter (VMD) or Dv50 is the diameter for which a volume fraction of 50% is made up of drops with diameters smaller than this value (expressed in μm). However, it is not possible obtain this value from WSP analysis based on measurements of droplets impacts/stains dimension. It is well known that any spot size measurements made on WSP can be affected by spots that were touching or overlapping; even if this phenomenon is more consistent with coverage greater than 20%, it cannot be excluded in other cases. Measurements of droplet spectra characteristics (D50, D10, D90 and V100) could be obtained only through laser measurements. The WSP stains dimension could provide indications about spray quality (very fine, fine, coarse, etc…) used during pesticide application, it is not possible derive the Dv50 from WSP stain dimension measurements.

L161: “[22]” why are you using reference in the sub-title?

L172: “[22]” why are you using reference in the sub-title?

L184: In the Table 4 what are the three columns 1, 2 and 3 of Recovery rate %?  Not explained in the text. Please, clarify explaining in the text the contents of table.

L186-188: Please, specify and describe adequately the methodology used to determine yield characteristics and fiber quality, also using references.

L190-195. This description belongs to other sections of M&M; the information contained are not related to the statistical analysis.

L197: Excel is not a statistical program. For sure you can use it for some statistical calculation but it is not “ad hoc” designed for statistics.

L198-201: Please specify when you use one-way ANOVA, LSD post hoc and the purposes. You have to describe adequately all analysis done; the reader must be able to understand what analysis has been done and what is the purpose. The description provided is too general and not adequate.

RESULTS

L211: You cannot refer to the Dv50 as already explained in my previous comment. You can show the difference in terms of impact/stains dimension that reflect the droplet size spectra sprayed. For sure the droplet size spectra are influenced by adjuvants but the Dv50 value can be obtained only through laboratory laser diffraction measurements.

L225: In Table 5 I’m not able to distinguish the groups, within which the letters mean differences. The statistical analysis is not adequately explained in this paragraph neither in the statistical analysis paragraph belonging to M&M section.

GENERAL COMMENT: The section is very confused and due to the very lack M&M section some results and statistical analysis are difficult to understand and adequately interpret.

DISCUSSION

GENERAL COMMENT: This section is a long and mixed list of references without link to your experimental results. I suggest to discuss the results using a joined section “Results and discussion” avoiding a dedicated “Discussion” section. This strategy could help you avoiding repetitions and increase at the same time the text flow.

CONCLUSIONS

GENERAL COMMENTS: The conclusion has to be completely revised based on suggested changes.

Author Response

Dear reviewer1,

We are so grateful for the excellent suggestions and the detailed revising from you. We have benefited greatly by the revision. Now we explain your questions firstly point by point, and then made modification accordingly.

GENERAL COMMENTS TO THE MANUSCRIPT:

The contents of manuscript are relevant and important information, for both farmer and scientific community, could be obtained. In general, the use of UAV for aerial spray application with relative resulting canopy deposition is a research hot-topic in precision agriculture all around the world, even if the manuscript focuses on particular application in cotton field. Although the topic is interesting and suitable according the scope of journal, a relevant lack and inaccuracy in M&M section have to be reported; these lacking are reflected on all subsequent sections.

Response: Thanks for the excellent suggestion on our manuscript. We had added more details in all sections.

Although I’m not qualified to judge about the English language, I carefully suggest to do an extended language review by a native English speaker.

Response: The manuscripthad used the English language editing service provided by MDPI. The text had been checked for correct use of grammar and common technical terms.

I have detailed some comments that can help to improve the manuscript.

INTRODUCTION

GENERAL COMMENT: The information contained are quite adequate to the contents of manuscript. However, sometimes sentences are disconnected decreasing the flow of text. Even if manuscript is focused and relevant for Asia region, I suggest to extend a little bit the introduction investigating the UAV spray application in Europe and America providing also further relevant references.

Response:We had added the UAV spray application in Europe and Americain “Introduction”.

MATERIALS and METHODS

L90-L96: You have reported a long list of chemical products without any explanation about use. The text is not organic.

Response: We had listed the dosages of all chemical products (defoliantsand adjuvants) in Table 3.

L97: You have listed the adjuvants in Table1. Why don’t put also the chemical in a Table?

Response: The main purpose of this paper is screeningspray adjuvantsfor UAV spraying defoliants, so we put thedetail information of spray adjuvantsin the Table 1.

L100-107: Also in this case you have reported a long mixed list of equipment and instruments used. In some cases, important information are missed (e.g. technical specification of centrifugal nozzles together with producer and position on UAV). What about droplet spectra (VMD, D10, D90 and V100) produced by centrifugal nozzle used at 800rpm? These are fundamental information related to the droplet deposition? At least technical specification provided by nozzle producer have to be reported.

Response: We added more detail of centrifugal nozzles in manuscript, and deleted the Table 2.

L118: “…the leaf area index wereuniform within each farm.” Please put the value of measured LAI together with method used to determine it (it is enough put references about methodology used avoiding long explantion).

Response: In order to avoid ambiguity,we had deleted the sentence “The heights, growing ways and leaf area index were uniform within each farm.”

L119: “[22]”why are you using reference in the sub-title?

Response: We had deleted the “[22]” in the sub-title.

L120: “Defoliation is an important management practice of cottonproduction”. This information belong to the introduction; please, move it.

Response: We had deleted the sentence “Defoliation is an important management practice of cotton production”.

L123-124: This information is redundant. You have already explained the hand held weather station used in the section 2.1.2. I suggest to move the information contained in the sections 2.1.1 and 2.1.2 throughout the text where needed avoiding long list that make the reader lost.

Response: In order to avoid ambiguity,we had deleted “The meteorological data during the deposition measurement were collected with kestrel 5500 digital meteorograph (Loftopia, LLC, USA).”

L125-130: More information about weather measurements and conditions at the time of application are required?What was the weather station frequency of records? The most influent weather parameters during spray application are the wind speed and direction that vary continuously: at least 1Hz frequency is required to characterize adequately the weather conditions at the time of application.

Response: The meteorological information during spraying had been upload as “Supplementary Materials”

L130: “Table S1”: Tabe S1 describing weather parameters is not present!

Response: I am very sorry for the mistake. We forgot to upload “Supplementary Materials”. We had upload the weather information in “Supplementary Materials”

L132-133: “Cotton defoliant spraying was carried out on September 15, 2018 and September 22, 2018.”Please avoid repetition. Information showed between lines 125-127.

Response: We had deleted the sentence “Cotton defoliant spraying was carried out on September 15, 2018 and September 22, 2018.” in L132-133.

L134: Table 3 is not clear. Are you meaning that in each treatment adjuvants was mixed with Thidiazuron, alkil ethyl sulfonate and Ethephon and each treatment was repeated in two periods (15 and 22 September)? If yes, please give a clear explanation in the text and reorganize the table adequately.

Response: We had added the explanation.

L143: “The WSP was collected and bagged individually”information repeated in the line 146 “All WSP was quickly removed and placed in zip-lock bags…”. Please avoid repetitions.

Response: We had deleted the sentence “The WSP was collected and bagged individually”.

L146-148: Information not relevant for the paper.

Response: We had deleted the sentence “and then transported to the Key Laboratory of Oasis Agricultural Pest Management and Plant Protection Resources Utilization for analysis.”

L150: Please, provide a moredetailed and technical draw in order to understand exactly the position of WSP in the field and canopy height and depth.

Response: We had redrawnthe Figure 2.

L154: “Dv50 indicates the droplet size corresponding to the cumulative volume fraction of 50%.”You are right that the Volume median diameter (VMD) or Dv50 is the diameter for which a volume fraction of 50% is made up of drops with diameters smaller than this value (expressed in μm). However, it is not possible obtain this value from WSP analysis based on measurements of droplets impacts/stains dimension. It is well known that any spot size measurements made on WSP can be affected by spots that were touching or overlapping; even if this phenomenon is more consistent with coverage greater than 20%, it cannot be excluded in other cases. Measurements of droplet spectra characteristics (D50, D10, D90 and V100) could be obtained only through laser measurements. The WSP stains dimension could provide indications about spray quality (very fine, fine, coarse, etc…) used during pesticide application, it is not possible derive the Dv50 from WSP stain dimension measurements.

Response: The droplet spectra measured by the laser measurements is a theoretical value, which is quite different from the actual spraying.Zhu et al. had reported the DepositScan could quickly analyzes distributions of spray deposits on collectors such as water sensitive papers or Kromekote® cards, which are widely used for determinations of pesticide spray deposition quality on spray targets.

Therefore, many studies obtained droplet spectra from WSP analysis based on measurements of droplets impacts/stains dimension.

Zhu, H.P.; Salyani, M.; Fox, R.D. A portable scanning system for evaluation of spray deposit distribution. Computers and Electronics in Agriculture, 2011, 76, 38–43

Garcerá, C.; Moltó, E.;Chueca, P. Factors influencing the efficacy of two organophosphate insecticides in controlling California red scale, Aonidiella aurantii (Maskell). A basis for reducing spray application volume in Mediterranean conditions. Pest Manag. Sci. 2014; 70: 28–38

Qin, W.C.; Qiu, B.J.; Xue, X.Y.; Chen, C.; Xu, Z.F.,; Zhou, Q.Q. Droplet deposition and control

effect of insecticides sprayed with an unmanned aerial vehicle against plant hoppers. Crop Prot. 2017, 85, 79-88.

Wang, G.B.; Lan, Y.B.; Yuan, H.Z.; Qi, X.X.; Chen, P.C.; Ouyang, F.; Han, Y.X. Comparison of Spray Deposition, Control Efficacy on Wheat Aphids and Working Efficiency in the Wheat Field of the Unmanned Aerial Vehicle with Boom Sprayerand Two Conventional Knapsack Sprayers. Appl. Sci. 2019, 9, 218;

Wang, G.B.; Lan, Y.B.; Qi, X.X.; Chen, P.C.; Hewitt, A.J.; Han, Y.X. Field evaluation of an unmanned aerial vehicle (UAV) sprayer: effect of spray volume on deposition and the control of pests and disease in wheat. Pest Manag. Sci. 2019, doi:10.1002/ps.5321

L161: “[22]”why are you using reference in the sub-title?

L172: “[22]”why are you using reference in the sub-title?

Response: We had deleted the “[22]” in the sub-title.

L184: In the Table 4 what are the three columns 1, 2 and 3 of Recovery rate %?Not explained in the text. Please, clarify explaining in the text the contents of table.

Response: That was the conventional formulation for pesticide residue analysis. “1,2,3” means three repetitions, followed by their average.We had added the explanation.

L186-188: Please, specify and describe adequately the methodology used to determine yield characteristics and fiber quality, also using references.

Response:Cotton yield and quality factors were determined by the Northwest Inland Region Key Laboratory of Cotton Biology and Genetic Breeding. We had added this information in manuscript.

L190-195. This description belongs to other sections of M&M; the information contained are not related to the statistical analysis.

Response: We had deleted that paragraph.

L197: Excel is not a statistical program. For sure you can use it for some statistical calculation but it is not “ad hoc”designed for statistics.

Response: Yes, Excel was used for some statistical calculation, and we rewrote the “Data Statistics and Processing” section.

L198-201: Please specify when you use one-way ANOVA, LSD post hoc and the purposes. You have todescribe adequately all analysis done; the reader must be able to understand what analysis has been done and what is the purpose. The description provided is too general and not adequate.

Response: We had added more details in “Data Statistics and Processing”.

RESULTS

L211: You cannot refer to the Dv50 as already explained in my previous comment. You can show the difference in terms of impact/stains dimension that reflect the droplet size spectra sprayed. For sure the droplet size spectra are influencedby adjuvants but the Dv50 value can be obtained only through laboratory laser diffraction measurements.

Response:The droplet spectra measured by the laser measurements is a theoretical value, which is quite different from the actual spraying. Zhu et al. had reported the DepositScan could quickly analyzes distributions of spray deposits on collectors such as water sensitive papers or Kromekote® cards, which are widely used for determinations of pesticide spray deposition quality on spray targets.Therefore, many studies obtained droplet spectra from WSP analysis based on measurements of droplets impacts/stains dimension.

L225: In Table 5 I’m not able to distinguish the groups, within which the letters mean differences. The statistical analysis isnot adequately explained in this paragraph neither in the statistical analysis paragraph belonging to M&M section.

GENERAL COMMENT: The section is very confused and due to the very lack M&M section some results and statistical analysis are difficult to understand and adequately interpret.

Response:In order to make it more easylyto read, We hadadded extra barsin Table 5.

DISCUSSION

GENERAL COMMENT: This section is a long and mixed list of references without link to your experimental results. I suggest to discuss the results using a joined section “Results and discussion”avoiding a dedicated “Discussion”section. This strategy could help you avoiding repetitions and increase at the same time the text flow.

Response:Thanks for the excellent suggestion on our manuscript. We had joined section “Results section” and “Discussion section” as “Results and discussion”, and revised the manuscript.

CONCLUSIONS

GENERAL COMMENTS: The conclusion has to be completely revised based on suggested changes.

Response: We had rewrote the “Conclusions” section.

Kindregards,

Xiaoqiang Han & Wei Fu

Reviewer 2 Report

The global quality of the paper is good. Some specific points are discussed in the attached file.

Comments for author File: Comments.pdf

Author Response

Dear reviewer2,

We are so grateful for the excellent suggestions and the detailed revising from you. We have benefited greatly by the revision. Now we explain yourquestions firstly point by point, and then made modification accordingly.

Reviewers' comments:

Very significant improvement is required on the manuscripts grammar and presentation. The high frequency of grammatical errors makes the paper very difficult to follow and unreadable in places. The order in which ideas are presented does not follow a coherent structure, leaving the reader with no clear understanding of the objectives and conclusions of the work.

Response:The manuscripthadused theEnglish language editing service providedby MDPI. The text hadbeen checked for correct use of grammar and common technical terms.

General remarks:

#1 More details should be given about the nozzle for example; what is the initial droplet velocity(direction and value); what is the droplet size distribution produced by it with your parameters at 1250px?

Response:We added more detail of centrifugal nozzles in manuscript, and deleted the Table 2.

Specific remarks:

Line 60: “Hitting cotton bolls” is mentioned twice

Response:I am sorry for the writing error. We had deleted the repetitive phrases“Hitting cotton bolls”.

Line 72: To support your statement that adjuvants affect wetting properties of pesticide youcan include the following work which focus on the study of droplet outcomes according to thespray formulation.

“Massinon, M., De Cock, N., Forster, W. A., Nairn, J. J., McCue, S. W.,Zabkiewicz, J. A., & Lebeau, F. (2017). Spray droplet impaction outcomes for different plant speciesand spray formulations. Crop protection, 99, 65-75.”

Response:Thanks for the great suggestion. We hadread this article in detail and cited it.

Line 125: the hours should be 1-7 pm (same on line 127)

Response:We had revised it.

Line 160: I think that X^Barshould be the mean number of droplets per unit area

Response:I am sorry for the writing error. We hadadded the word “mean”.

Line 163: 4, 7, 12 and 15 d after spraying. Does “d” means days?

Response:Yes, the“d” means days. We hadchanged the “d” asdays.

Table 5: Extra bars should be displayed on the table in order to make it more easy to read.

Response:Thanks for the great suggestion. We hadadded extra barsin Table 5.

Line 373: Polymer is written twice

Response:I am sorry for the writing error. We had deleted the repetitive word“Polymer”.

Lines 349-354: Many factors, including adjuvants, pesticide formulations, and nozzle tips, affectspray droplet size [33]. Nuyttens et al. found that the larger the proportion of droplets with diameterless than 75 μm, the larger the drift index of droplets [34]. Gao et al.adopted wind tunnel tested thetype of adjuvants, concentration, wind speed, ambient temperature and relative humidity hadsignificant effects on droplet deposition, the droplets drift could be reduced by adding Beidatong®and Y-20079®[35,36,37,38].

To extend your literature review here are some interesting papers discussion on the effect ofthe droplet size on drift process which is mainly related to the droplet:

Al Heidary, M., Douzals, J. P., Sinfort, C., & Vallet, A. (2014). Influence of spraycharacteristics on potential spray drift of field crop sprayers: A literature review. Cropprotection, 63, 120-130.

De Cock, N., Massinon, M., Salah, S. O., & Lebeau, F. (2017).Investigation on optimal sprayproperties for ground based agricultural applications using deposition and retention models.Biosystems engineering, 162, 99-111.

Hilz, E., & Vermeer, A. W. (2013). Spray drift review: The extent to which a formulationcancontribute to spray drift reduction. Crop Protection, 44, 75-83.

Response:Thanks for the great suggestion. We hadread thosearticle in detail and cited them.

Kindregards,

Xiaoqiang Han & Wei Fu