IPM is not a static concept but has been evolving over the past years and it is still changing as new experiences are used to fine-tune the concept.
The Economic Threshold Level (ETL) used to be part of IPM many years ago, but in modern IPM it has been replaced by Agro-Ecological System Analysis (AESA) where farmers take decisions based on a larger range of observations.
Unfortunately, even today, there are still many “specialists” who still recommend ETLs to farmers, presenting this as an IPM method. But there are many reasons for not using an ETL.
One of the problems of the ETL is that it is based on parameters that are changing all the time, and that are often not known. An ETL is calculated from:
- the management cost (cost/area)
- the price of the farm produce (cost/kilo)
- expected damage or yield losses (kilo/area)
Management cost could be estimated, but when the crop is still in the field, it is usually not possible to know what the price per kilo will be at harvest time.
The damage or losses caused by a certain density of insects can not be predicted at all. It depends on many other factors, such as crop variety, weather conditions, availability of water and nutrients, plant stage, etc. It also depends on the availability and performance of natural enemies. There is a big difference between “a bean plant with 20 aphids” and “a bean plant with 20 aphids and 1 hover fly larva”.
This is why ETLs that are “recommended” in all kinds of manuals for farmers can never be applied in a farmer’s field. Farmers cannot base their decisions on just a simple count of pests. They will have to consider many other aspects of the crop (crop ecology, growth stage, natural enemies, weather condition, etc.) and their own economic and social situation before they can make the right crop management decisions.
Another important consideration is that good crop management does not only depend on controlling pests, but even more on the prevention of pests. Over a period of time, IPM specialist have realized the limitations of ETLs and gradually developed the Agro-Ecosystem Analysis (AESA) as a much more flexible tool to make crop management decisions.
| Economic Threshold Level (ETL) | Agro-Ecosystem Analysis (AESA) |
|---|---|
🙁
|
🙂
|
The AESA drawing shows all the observations that were made by the farmers.