Good points Dr Ali....but an eye should be kept on soil microbial population and its natural diversity...

Dear Mohammed...

Practically, it will be easier to apply herbicides pre-emergent, and their side effects on the growing field crops will be less.

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..??

It will depends on situation like type of weeds, infestation pattern, weed ecology, soil biology, exiting vegetation etc.

It depends on many factors such as

Plants, soil quality and environment

Thanks all for your answers.

Can you recommend some references about that topic??

In general, post-emergent herbicides are more compatible with recurrent farming practices like no till farming.

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

Good points Dr Ali....but an eye should be kept on soil microbial population and its natural diversity...

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

Dr. Ali and Dr. Shrivastava sir elaborate very clearly about use of pre and post emergence herbicides.

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.

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.

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

I am about developing a potential herbicide based on light activation. Photosensitizers like cationic porphyrins are good candidates. they have post-emergent photosensitive effects on Arabidopsis thaliana (a weed-like plant).

If you are interested you can refer to my last publication:

Issawi et al, 2018. Responses of an adventitious fast-growing plant to photodynamic stress: comparative study of anionic and cationic porphyrin effect on Arabidopsis thaliana. Physiologia Plantarum.

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.

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).

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)

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.

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.

This is an interesting information, Mr. Issawi.

If you specify the type of plant, this question can be answered better! It is vary greatly depending on the type of plant.

We do pre. in our experiments !

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.