Previous sections in these documents discussed some agricultural practices and their effects on ecosystems, and introduced the Green Revolution and some pros and cons associated with it.
In the following sections, we will focus on a single issue that is also intimately connected to modern agriculture; the use of pesticides in agricultural systems. Many (most) of the concepts discussed here concerning pesticides in agriculture could, however, be generalized to their use in other kinds of ecosystems as well, such as forests. Before discussing pesticide use and impacts:
Pesticide is a general term referring to a chemical, physical, or biological agent that kills organisms that we classify as pests, such as insects, rodents or fungi. They are sometimes also called "biocides." The term includes fungicides, insecticides, and agents effective against other disease organisms, such as bacteria. Most uses include herbicides (agents that kill plants) as a kind of pesticide, and we will do so as well.
We will focus here on chemical pesticides, as opposed to physical or biological agents, which will be discussed when we talk about sustainable agriculture.
Each year, pests consume or destroy 20-48% of the world's food production [UN FAO]! ("Pests" here includes insects, mammals and birds, bacteria, fungi, virus, and weeds. Technically, agents of disease, such as fungi and bacteria, are considered "pathogens" rather than pests, but we will use the term "pest" more inclusively.)
Highest rates of loss are in tropical and subtropical areas, as farmers often grow more than one crop each year on the same field, which can allow large build-ups of pest populations. In addition, pests in tropical and subtropical areas are not faced with winter setbacks.
However, even in nations like the US, losses to pests are huge. For the US:
preharvest losses are about 34% of production
post harvest losses take about 9% of what is left
The result is that about 2/5 of the US annual crop production is lost to pests and diseases (about 37%).This translates to about $9 bill/year worth of human and animal food.
And, amazingly, these losses occur despite U.S. pest control efforts costing about $4.1 bill /year!
In a world with so much hunger, and so much land degradation and other environmental problems caused by our intense efforts to grow food, losses of this magnitude pose an immense problem.
Pest control has always been important in agriculture, but green revolution style agriculture often requires more pesticide inputs than did traditional agricultural systems. Why should this be? A brief listing is given below, with details to follow.
(1) As we have seen, green revolution style agriculture typically involved the planting of genetically homogeneous monocultures over wide areas both within one year and across years (i.e. lack of rotation). These practices make crops more vulnerable to pests, as we will see .
(2) The altered growing conditions often required in green revolution style agriculture (increased moisture , fertilizer , planting density, etc.) often make conditions more favorable for certain pests.
(3) In many cases, the new green revolution crop varieties are not as widely resistant to each local pest as were the traditional varieties.
Modern commercial agriculture uses:
Crop management practices, including timing of planting, density of planting, choice of varieties to plant, crop rotation, and so forth
Genetic improvements in crop plant resistance to the pests [including the use of genetically-modified ["engineered"] crops]-- and natural resistance to pests and diseases; in fact,most plants are naturally resistant to most insects and diseases!
Synthetic organic chemicals
Biological control agents, some of which are native and some of which are introduced. (Native biological control agents are an example of "ecosystem services " that the farmer may often not even be aware of.)
The next section (">>" at the bottom of the page) reviews briefly the history of pesticide development, focusing on DDT as a case study. For reminders on how to navigate within and among these pages, click "Navigate " here.