Round 1

Reviewer 1 Report

Comments to authors

 General comments – the paper is very interesting and valuable contribution to the best practices on weed management. The authors do a good job and in my opinion this manuscript meets the standard criteria required by Forests.

I have only a few comments/questions, listed below:

 I would suggest shortening Treatment applications p.2.2. lines 182-197 due to the same information in Table 2.1. and difficulty in reading of long description of consumption rates for selected method of weed management. Moreover, data on depth of mulch application can be added to Table 2.1 to facilitate  comprehension of experiment.

Table 2.9. It seems curiously that mean phytotoxicity for Allegan White pine for mix Clopyralid + Oxyfluorfen + Glyphosate (73,13) has the same letter (a) as other treatment in column and mean phytotoxicity are not significantly different at p<0.05level with all treatment except mulch and control (letter b), the same in Table 2.10 and for table 2.11 (even in Table 2.11 no difference between  all treatments and control although mean phytotoxicity for pesticide mix is 79.13 and control is 0%.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The topic is super relevant and systematic testing across sites and species very important. The methodology of the study is strict and very well described including the chemicals used and their way of operating. Data are well analyzed - in detail by site, but I was tempted to suggest some overall analyses. This might help to be a little more precise about he conclusions and the general findings. Furthermore, I think it is important to address the growth results, which actually are showing quite some reduction due to chemical treatment.

The design has confounding effects of site and tree species – which to some extent is confusing, sometimes site is referred and sometimes species at the specific site. Conformity would help the reader.

It is a bit difficult to get hold of the main results having 30-60 and 90 DAT results, and the confounding effects of site and species. One could ask – do species really interact with the effectiveness of the weed control issues? In case not, sites could, despite different tree species, be treated as “plain” sites and an overall across site analyses could be carried out, also for the factorial combinations evaluating the weed control effect. Some interaction with site is expected, but it might be a way to get an overview of the results across all locations, and help desiccate the overall picture. Average performance regarding weed control across all sites for the treatments – maybe it is of value to add average across all sites to table 2.3 to 2.8 (if limited site x treatment interaction is present, or even despite the interaction).

This “across site” approach might also be used for growth – despite of species. An additional question is if 30 and 60 DAT growth are interesting (potentially add to supplementary material – but I might have missed some important details). A grower might think the final height after the growing season is the main goal – meaning focus analyses on 90 DAT results, and maybe also use top and side branch growth as two traits?

However, the most striking paradox in the results are the expectation/hypothesis of weed control to improve height and Christmas tree production, and based on the results, all the chemical weed control efforts simply show a negative effect on growth in the magnitude up to 30% reduction – that’s a lot J. I think this result i.e. growth-reduction needs and deserves more discussion. Are we by habit using chemicals improving weed control, but for what benefit? Trees are growing slower?  How much weed control is actually acceptable? The results are from one year, are results normally changing across years?

Some specific comments:

L26-27 Tree growth were diminished by use of chemicals

L160 Map is not easy to read – simplified map might be better

L175-203 maybe consider to simplify – there is very thorough text and table 2.1 adds a lot of the same information. I think table 2.1 is very informative

L322 table 2.3 is one decimal sufficient – I think so.

L428 Table 2.16. If I understand correctly – the analyses is based on average across 30,60 and 90 DAT or made as an analyses of repeated measurements? I think growth after 90 DAT intuitively is most interesting.

L429 the nice factor analyses is missing/omitted for growth? I think these results of diminished growth is very interesting

L486 I have not read the reference, but the wording "will likely be washed out" is to unprecise. A product can also be decomposed to other products when absorbed into the soil, and thereby glyphosate will not make it to the groundwater. There are examples of very persistent herbicide product that can be found in groundwater reserves, in example, Velpar and Atrazin. Either don’t get in to this discussion or add more and be more clear. But its not part of the objectives, so maybe skip this issue.

L538-542 Grower observations? Results from this study shows that growers strategy comes with a strong reduction in growth. What is really needed – any studies available? Is it only growth or do excessive weed impact quality, not so far mentioned?

L548 I suggest also some more discussion on mulch – it looks great in response to weed and growth, but N-content, although not significant, indicate issues to be handled, N content is decresing in needles, but is that only first year, and released later on for te benefit of the trees?

L559 “extremely important” yes, but the results show it  is not in the “traditional way” ? I think this study opens an interesting discussion, which might not have a clear answer right away, but need further studies.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

This manuscript entitled “Developing integrated strategies to address emerging weed management challenges in christmas tree production” is subjected to the weed control efficacy of organic mulch and herbicide combinations. For this purpose, three herbicides and their combinations were dosed to farms of Christmas tree, and combination with organic mulching was also applied. As a result, multi combined herbicides suppressed weed growth better than using each herbicide alone, and multi herbicides with organic mulching was also effective in suppressing weeds. However, some herbicides dose caused phytotoxic symptoms in early stage of Christmas tree sapling. In present study, weeding control did not affect growth and leaf nitrogen content. Although experiment was generally well designed, and achievements would useful for Christmas tree production, I consider that careful discussion is needed to properly evaluate the results of this study.

Major problems

The amount of each herbicide applied was the same as in the single-use treatments, and hence the total amount of herbicide applied in the multiple-use herbicide treatments was higher than in the single-use treatments. This study showed that multi combination of herbicides were more effective in weed control than the single use of each herbicide.  However, it is still unclear whether this result due to the combination of the herbicides or due to large amount applications of herbicides.  The amounts of applied herbicides were the highest labeled rates, but were they sufficient amounts to maximize the control of weed growth?  The ANOVA result, in which the interactions between herbicides were few observed implies that the applied amount effect is more important for weed control than herbicide combination. Therefore, effectiveness of combination use of herbicides should be carefully considered. Additionally, the effects of mulching were not detected as statistically significant in the ANOVA, and this should also be taken into account in Discussion.

In the Result section of this manuscript, generally single observation results were presented in the text (the results at 90 DAT for Weed control and Growth Indices, and the result at 30 DAT for Phytotoxicity). In contrast, the tables showed the results of all observations. I consider this to be information overload. Table 2.4, 2.5, 2.7, 2.8, 2.10, 2.11, 2.13, and 2.14 should be removed or be treated as supplemental data.

Specific Remarks

Abstract

I consider that in Abstract, more weight should be given to results and conclusion.

Materials and Methods

P8L251-257 (Growth Indices): If possible, the data about height and crown width of saplings should also be presented as supplemental information.

P8L272-274: Does it mean the blocks have spatial auto correlation each other?

P8L274-276: I recommend the authors to apply GLMM (GLIMMIX procedure) with error distribution rather than normal distribution instead of transformation of dependent valuables.

Results

P9L310 “36% greater…”: I could not find this result in Tables (Table 2.3?).

P12L370-371 “At 60 DAT…”: I could not find this result in Tables (Table 2.10?).

P12L371-372 “At 90 DAT…”: I could not find this result in Tables (Table 2.11?).

P12L372-377 “At DAT…”: This result does not seem to match the Table 2.12.

P15L432 “1.76%”: “1.77%” in Table 2.17.

Discussion

P16L449-450 “generally mulch combined with herbicides provided the best weed control”: This sentence contradicts to the result of ANOVA (Table 2.6) that the mulch effect was statistically significant in only two of the five farms.

P16L465-466 “Mulch consistently improved…”: Is this based on the result of this manuscript or on others (see above comment)?

P16L478-479 “In our study, mulch was…”: Strictly speaking, significant mulch effect was observed only at Horton and Sidney blue spruce farms (and the significant effect was not observed at other farms).

Tables and Figures

I recommend that not only the mean values are provided, but also the range of variability of the data (i.e., standard error or standard deviation).

Table 2.5 and 2.9 subscript “**”: “*” in correct?

Table 2.11 subscript “f” in 6th row of Sidney Blue Spruce: “a” in correct?

Table 2.11 subscript “a” in 11th row of Sidney Fraser fir: “c” in correct?

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

I accept all the revised parts of this manuscript and have no further comments.

However, some formatting issues need to be checked in the supplemental Data (bolding “mean” in legend of Table S3, insert blank lines between Table S3 and S4, S5 and S6, S7 and S8, insert space between numbers and letters in table S6 and S7).