Question
Asked 3rd Feb, 2018

Pre-emergent vs post-emergent herbicides?

Pre-emergent herbicides kill weeds before emergence from soil whereas Post-emergent ones eradicate weeds that have already emerged from soil.
What is better herbicide to use? pre-emergent or post-emergent herbicide?

Most recent answer

7th Jan, 2021
A. S. Tayade
National Institute of Abiotic Stress Management
Both pre and post emergence herbicides are having their exceptional weed control efficiencies. Now a days early post emergence herbicide are available. We can not evaluate the effectiveness of herbicides as such on their time application only. The efficacy of any herbicide can be evaluated by working out its WCE and weed index. Rather I can say that both pre and post emergence herbicides are complementary to each other and can be one strategy for the integrated weed management as a whole. I would like to quote the best example of weed management in Sugarcane. In sugarcane pre emergence application of atrazine gave a good weed control upto early 30 to 40 days , whereas 2,4-D and Metribuzine tank mixed post emergence application found more suitable and selective for the management of weeds 50 days after planting.

Popular answers (1)

7th Jan, 2021
Omar Aljubouri
University of Mosul
11 Recommendations

All Answers (35)

3rd Feb, 2018
Ayoob Obaid Alfalahi
University of Anbar
Dear Mohammed...
Practically, it will be easier to apply herbicides pre-emergent, and their side effects on the growing field crops will be less.
4th Feb, 2018
Anoop Kumar Srivastava
ICAR-Central Citrus Research Institute ( Formerly National Research Centre for Citrus)
I will go a step further, how much weightage , do you give to the soil ecology while deciding the type of herbicide to be used..??
2 Recommendations
4th Feb, 2018
Prosanta Kumar Dash
Khulna University
It will depends on situation like type of weeds, infestation pattern, weed ecology, soil biology, exiting vegetation etc.
4th Feb, 2018
Mohammad R. Sahib Alsabri
University of Kentucky
It depends on many factors such as
Plants, soil quality and environment
4th Feb, 2018
Mohamad Issaoui
University of Limoges
Thanks all for your answers.
Can you recommend some references about that topic??
4th Feb, 2018
Mohamad Issaoui
University of Limoges
In general, post-emergent herbicides are more compatible with recurrent farming practices like no till farming.
5th Feb, 2018
Ali Alhayany
University of Diyala
Firstly i object on the use of the statement " eradicate weeds " because we cann,t eradicate all types of weeds in field conditions , but we can use this statement for the use of Non-selective herbicides to clear industrial sites, waste ground, railways and railway embankments.Secondly ,to determine which group of herbicides we advice to use .This depend on what is the nature of plants cultivated in the field? Is it herbaceous, shrubs ,or trees .Is it annual ,or perennial .According to my experience my advice is to combine pre and post emergence herbicides to control weeds growth (especially in the case of fruit trees ),where per-emergence herbicides killed new emerged weeds and post- emergence herbicides (especially selective ones),in order to control perennials and emerged other weeds.
accept my best regards
Alhayany
2 Recommendations
5th Feb, 2018
Anoop Kumar Srivastava
ICAR-Central Citrus Research Institute ( Formerly National Research Centre for Citrus)
Good points Dr Ali....but an eye should be kept on soil microbial population and its natural diversity...
3 Recommendations
5th Feb, 2018
Ali Alhayany
University of Diyala
Thank you Dr.Anoop. The wise application of many pre-emergence herbicides may have a good returns on soil microbial organisms especially when we add it as a soil incorporated material in perennial crops fields like fruit crops where the application lay near the soil surface and had little or no hazard effects on soil organisms populations.I used Simazine and Atrazine herbicides in Golden Delicious apple nursery ,i find that Nitrogen content in seedlings leaves raised in low concentration of both herbicides .I am interpreting this case due to the decomposition of herbicides by microorganisms presented in the soil.
Regards
3 Recommendations
5th Feb, 2018
Prashant Balasaheb Pawar
Mahatma Phule Krishi Vidyapeeth
Dr. Ali and Dr. Shrivastava sir elaborate very clearly about use of pre and post emergence herbicides.
2 Recommendations
5th Feb, 2018
Suresh K Malhotra
Ministry of Agriculture & Farmers Welfare
Pre-emergent herbicides are only effective on weeds that annually sprout from new seeds. These herbicides do not effectively treat perennial plants . This type of weed killer is used once the initial spring season has begun and plants have started to grow. Once a plant has started to grow it is too late to utilize the germination prevention of a pre-emergent herbicide and it is time for you to apply a post-emergent herbicide.
3 Recommendations
5th Feb, 2018
Ali Alhayany
University of Diyala
We can control annual weeds by both types of herbicides .Pre-emergence ones used early in spring before seeds emergence ,if we didn,t use it ,then we can use foliar applied ones even selective or non selective depending to the field situation.But if we have fields infested with annual and perennial weeds ,here i advice to use pre and post emergence herbicides inorder to have the benefits of both kinds of herbicides.
1 Recommendation
5th Feb, 2018
Mohamad Issaoui
University of Limoges
Thanks all for that valuable discussion
please if you have any interesting issue to discuss concerning the aspects of pre/post emergent herbicide application, let me know.
please provide some references if it is possible
9th Feb, 2018
Kulvir Singh
Punjab Agricultural University
Mohammad
I think the question you asked was in a different context with reference to responses received.
I think you simply wanted to know bettter among two options.
Rest assured every herbicide is having effect on soil flora/fauna but few one having large persistence do affect in a severe way.
Now coming to point, i think it is the situation which dictates you to go for a particular situation rather than giving vague accliams.
For example in case of pastures where you need to cut fodder, you can not go for post emergence application as the residue may be issue for milching animals.
Similarly in crops like rice,where puddling of water is necessary,stage of application will not allow you to go for post emergence appplication upto a certain limit,because of ease of operations in pre-emergence applications.
However, if the herbicide is only active through foilage and photosynthetic pathway is interupted as per mode of action at some point and is selective, you can not go for pre-emergence applications for chemicals like clodinafop in wheat .
So my point in reference to all the responses is that only situation specific and crop specific conditions will dictate you to go for any of the two options best suited for that particular crop/weed/agroecosystem .
But simply saying pre or post is better is not suffice.
let us invite opinions in this regard
best regards to all respondents.
1 Recommendation
9th Feb, 2018
HOUNGBO N. E.
National University of Agriculture of Porto-Novo, Benin Republic
No herbicide is good. For, when it is used, it kills both weeds and micro-organisms in the soil, what micro-organisms are useful for humus and clay-humic complex formation. In long term, it leads to soil degradation (chemically, biologically, and physically). It's more sustainable to use cover crops (such as Mucuna pruriens) and insect repellent plants (such as Hyptis suaveolens).
9th Feb, 2018
Mohamad Issaoui
University of Limoges
Dear Kulvir Singh
Concerning the first case of pastures, I completely agree with you because herbicide could be toxic for grazing animals.
Talking about rice-soil water-soaking I do not understand the relation between ease-to-use pre-emergent herbicides and waterlogged rice plants. Can you explain please?
(Thanks for your insightful answer)
9th Feb, 2018
Mohamad Issaoui
University of Limoges
Mr. Houngbo,
Not all herbicides are bad. Nowadays, herbicides are extensively used in horticulture and are beneficial.
The eco-friendly herbicide that is safe for micro-wildlife and biodegradable will not be harmful to microorganisms and ecosystem. You can refer to my article (mentioned above) to know about exogenous photodynamic molecules potentially holding herbicidal capacity. They are inactive under dark conditions (similar conditions in soil where the darkness prevails) hence they cannot harm microorganisms; moreover, they are photodegradable if we want to spray them in a crop field.
Best regards.
1 Recommendation
9th Feb, 2018
Mohammad Irfan
CCS Haryana Agricultural University
Pre-emergence- This type of herbicide kills weeds before they sprout. While they won’t prevent germination, they do keep the pests from breaking through the soil.
Post-emergence-These herbicides kill actively growing weeds that are already through the soil surface. This includes perennial and annual broadleaf weeds (those not resembling grass). Some products even work on grassy weeds (those that do look like grass). Use post-emergents only for existing weeds. They’re perfect for spot-treating individual pests.
10th Feb, 2018
HOUNGBO N. E.
National University of Agriculture of Porto-Novo, Benin Republic
This is an interesting information, Mr. Issawi.
10th Feb, 2018
Maryam Rahimi Jahangirlou
University of Tehran
If you specify the type of plant, this question can be answered better! It is vary greatly depending on the type of plant.
14th Mar, 2018
Kulvir Singh
Punjab Agricultural University
Mohammad Issawi
sorry for the delayed response.
This is with reference to my previous reply.
Rice/paddy is grown in puddled conditions/waterlogged field conditions.
In Indian context, most of herbicides are being used within 1-2 days of transplanting(manual) and later on with crop growth,tillering and standing water conditions,application of post-emergence herbicides become a difficult task.
Hence early applications are preferred.
16th Apr, 2020
Himanshu Verma
G. B. Pant University of Agriculture and Technology, Pantnagar
Pre emergence herbicides are are those herbicides which has to be applied over the soil surface just before emergence of weeds as well as crop immediately after sowing of the crop...
While post emergence herbicides are applied after emergence of the weeds even emergence of crops also over the foliage portion when weed got some definite height with its foliage surface..
In general, the concept behind pre as well as post emergence are same except , the pre emergence herbicides are applied over the soil surface, so it is clear that it will kill only weed propagates from which a weed plant will develop..it means it will kill underground weed seed and other multiplication profiles like rhizomes, tubers and many more...thats why for controlling grassy weeds which are largely propagated through their seeds and underground part, one should apply pre emergence herbicides like pendinethalin...This is in general, exceptions may be there...
While in case of post emergence herbicide, it is applied when weed attain some definite height and foliage, so it is clear when herbicide molecule is attached with weed leaf or foliage , it will move and circulate within the whole plant system, killing them...like 2, 4-D, which is generally applied to kill broad lead weeds...
17th Apr, 2020
Ofer Szyper
Independent Researcher
Thanks
20th May, 2020
Sandro Shanidze
Agricultural University of Georgia
Hello, there are some good insights here and I would like to add a question - when a crop is resistant to pre-emergence herbicide, can it be applied after the crop has sprout and is in the fist stages of growth, but the weeds have not yet?
I am referring to applying a PRE herbicide on soil in a winter crop in March, before the weeds are still dormant., but the crop already has a stand.
1 Recommendation
25th May, 2020
Sanjay Chavan
Dr. Balasaheb Sawant Konkan Krishi Vidypeeth
Premergence herbicide, better.
Possible to covered soil by use black plastic sheet it works.
1 Recommendation
6th Jun, 2020
Mehar Chand
CCS Haryana Agricultural University
It depends upon the growing condition, crop and crop duration. For rice preemergent herbicides are better. For short duration crop generally preemergent herbicides are better. Long duration crop crop requires both pre and post emergence herbicides.
3 Recommendations
7th Jan, 2021
Omar Aljubouri
University of Mosul
herbicides "Pre-emergent" Do they affect the micro-organisms present in the soil?
8 Recommendations
7th Jan, 2021
Mohammed Akram Alobaidy
University of Mosul
Both types are effective in eliminating weeds, but Pre-emergent kills the role only the weeds seed and post-emergent herbicid after killing the gestures...
1 Recommendation
7th Jan, 2021
Mohammed Akram Alobaidy
University of Mosul
Depends on the physiological system of the herbicid and the mode of action
1 Recommendation
7th Jan, 2021
Anoop Kumar Srivastava
ICAR-Central Citrus Research Institute ( Formerly National Research Centre for Citrus)
Long term application of either pre-emergence or post-emergence herbicides , they do affect the rhizosphere mciorbial population , therefor e, rhizosphere mciorbiology holds a key factor to be decissive on how long shall we use such herbicides...
2 Recommendations
7th Jan, 2021
Omar Aljubouri
University of Mosul
11 Recommendations
7th Jan, 2021
Omar Aljubouri
University of Mosul
10 Recommendations
7th Jan, 2021
Omar Aljubouri
University of Mosul
THANK YOU Mohamad Issaoui
11 Recommendations
7th Jan, 2021
A. S. Tayade
National Institute of Abiotic Stress Management
Both pre and post emergence herbicides are having their exceptional weed control efficiencies. Now a days early post emergence herbicide are available. We can not evaluate the effectiveness of herbicides as such on their time application only. The efficacy of any herbicide can be evaluated by working out its WCE and weed index. Rather I can say that both pre and post emergence herbicides are complementary to each other and can be one strategy for the integrated weed management as a whole. I would like to quote the best example of weed management in Sugarcane. In sugarcane pre emergence application of atrazine gave a good weed control upto early 30 to 40 days , whereas 2,4-D and Metribuzine tank mixed post emergence application found more suitable and selective for the management of weeds 50 days after planting.

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