Dear Durgesh

I think the ''Efficacy'' means effectiveness, i.e. the ability of something, e.g. a herbicide to produce the results you want (proper control the weeds).

But

the ''Efficiency'' means ability to do something well without a waste of time or money.

Efficacy is the effectiveness of the product. It is the number of pests killed by the application (= percent mortality).

Efficiency is the level of waste in an application. In the laboratory I find that I get 100% mortality if I apply 1 ug of toxicant to a plant. I go to the field and spray 100 grams per hectare. From pre-application scouting I found 100 target weeds per hectare. With this many weeds a 100% efficient application would require 100 ug, but I applied much more pesticide.

One can find that an application sufficient to kill all the target pests 800 times over was less effective than an application sufficient to kill all the pests 1500 times over. Exactly how dead must something be before it can be considered "dead?"

If a pesticide application is viewed in this light field trials of pesticide efficacy are not dose-response trials but efficiency-response trials. Every increase in applied dose increases efficacy by a small amount. However, you have already applied more pesticide than needed to kill all the targets many times over. You have simply reduced efficiency to gain increased efficacy.

Herbicide that drifts, degrades, applied to soil, or contacts non-target plants are all contributors to reduced efficiency. Pesticide application is inherently wasteful because we have not figured out how to more efficiently target individual pests. In some cases, machine vision and neural net analyses have been used to more effectively target weeds.

Timothy A Ebert explained it very well, I think. Here is a link to another source that might also help clarify the terms. https://writingexplained.org/efficacy-vs-efficiency-difference

Efficacy means level of effectiveness of some thing to produce the desired results e.g herbicide to manage weed in the field, while efficiency means level of ability to do some thing well without wasting time and money.

Efficacy is about whether or not something can be done anything......Means capacity or ability of any one to do work.

Efficiency is about how something is done and if it minimizes waste.

The ability of a medicine, insecticide or a method of achieving something, to produce the intended result.

Efficiency is the ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without waste.

Agreed - Efficacy is about the results, whereas Efficiency is about waste when achieving the results. Something could be said to have good efficacy but poor efficiency, if it was effective but comparatively costly or wasteful. Likewise, something could be considered to show good efficiency but poor efficacy, if it only is moderately effective, but isn't particularly wasteful in the process.

Efficacy means effectiveness, i.e. the ability of something, and Efficiency means ability to do something well without a waste of time or money,

thanks to everyone for giving the knowledge.

Dear Durgesh,

In pesticide science, efficacy means the ability to produce a desired or intended result, such as control pest population and don't let it go up into EIL (Economic Injury Level).

Efficiency means the state or quality of being efficient. The Rendement is its French synonym.

Kind regards, Homayoon.