News stories about the University of Copenhagen study on the nutritional value of organic foods may have left many people confused about what the difference really is between food grown “conventionally” or “organically” and if the increased price for organic food is really worth it. Although most people in the general public probably recognize the terms “conventional” and “organic” for agriculture, there are two other major terms that apply to agricultural practices: “integrated pest management” and “sustainable agriculture.”
If you were confused before, I’m sure you’re REALLY confused now, so the next several blog posts will attempt to focus on one type of farming practice and compare them to the others. This post is targeted to a general audience, so if you’re a professional in any of these areas, I’m sure that what will follow will appear much too simplified.
I’ll begin by explaining what “conventional” farming is, since it’s the baseline for comparison to all of the other practices. In most cases, “conventional” farming involves a scheduled regimen of fertilizer, pest control and irrigation. Fields are usually sprayed with pesticides on a timed schedule (such as once a month, once every two weeks, etc.) with little weekly monitoring of the field. Farmers using conventional practices base their treatment decisions on problems that they had last year that they expect may happen again, or pests that their neighbors have dealt with that they’d like to keep out of their field.
Before I continue, I want to clarify that conventional practices are not “bad,” as they are often characterized in some literature. They are practices that have been around for years, and farmers with large amounts of acreage use conventional practices because they are less time-intensive and may be less expensive in the short-term than the other practices.
Integrated Pest Management (IPM) is a little more involved than conventional pest control but is designed to be more effective and cheaper in the long-term because the farmer is targeting specific pests with the control. In addition, control is based on thresholds (see below), so the farmer is using only the amount of pesticides needed to manage the pest problem rather than spraying for an insect that may or may not be in the field.
I do, however, want to emphasize at this point that one of the reasons that IPM can be so confusing to people is that the definition of IPM often varies depending on the person defining it. Some groups say that IPM means using no pesticides at all. Other groups say that IPM means using pesticides only as a last resort, after all other options have been explored. Still other groups define IPM as a combination of tactics, including pesticides, used together throughout the season.
The problem is that none of these definitions are correct on their own, but each of them can be correct depending on the situation. So what does IPM actually mean? IPM means deciding what control measures need to be taken—and when—depending on the individual situation. So Farmer A may be able to save his tank of pesticides for an entire season because no insects ever entered the field, whereas Farmer B had to take measures to keep a nearby population of a devastating insect—that she discovered was close to her farm through a forecasting website—from destroying her crop. In short, IPM involves trying to prevent insects or diseases from either entering the field or from destroying the crop. IPM involves four principles: Prevention, Avoidance, Monitoring and Suppression (PAMS).
Still confused? Perhaps an example will help. Meet two farmers who grow tomatoes. One farmer uses conventional practices, and the other uses IPM. Both farmers buy healthy plants or seeds to begin with. The conventional farmer chemically treats the crop every month for a variety of insect pests and diseases that he anticipates will be a problem because he has seen them before and expects them again. Or perhaps one of the nearby farmers told him that his consultant expected a certain pest to be a problem this year. So the farmer treats his field monthly in anticipation of those pests, and assumes that since he doesn’t see the pests in the field that the spray is working (when the pest may not have been in the field to begin with).
The IPM farmer also sets a schedule, but her schedule is set to walk the field a few times a week looking for pests. Because she waits until she sees specific pests, when she chooses a control option, she is targeting only those pests because she already knows what pests and diseases she has. Often, this farmer will also use “thresholds” before treating a field (explanation is below). She may wait to put out an insecticide until she sees a certain number of that pest, or a certain number of plants infested before she treats for that insect. The difference is that she knows for sure that she is controlling a specific insect, and she knows WHAT that insect is.
The first step of IPM is at the nursery, when the IPM farmer is buying the plants. Not only does she check the plants carefully to make sure they’re healthy, but she also makes sure that there are no insects on any of the plants, and no weeds are in the pots. The farmer has done her best to prevent pests, diseases and weeds from even entering the farm.
But somehow a few tomato fruitworm moths enter the farm and lay eggs, so now the farmer moves on to the next stages of IPM: avoidance and monitoring. To avoid pest populations from doing significant damage, the farmer will have to monitor the populations. A number of options will do this: pheromone traps attract specific pests into a box with sticky paper so the farmer can keep track of the number of fruitworms. Or the farmer can check the plants every day and count the number of fruitworms he or she finds. Both options require the farmer to know two things: the economic threshold of tomato fruitworm (the minimum number of fruitworms that can be in the crop before economic loss occurs) and that tomato fruitworm is actually the pest that is in the field.
All four stages of the PAMS approach have one thing in common: knowledge. The farmer must be able to identify insects and diseases to know what is in the field, know the growth stages of the crop, know what economic thresholds can be used to justify treatment, and know what various control options are available.
For those of you who have seen me mention “threshold” thus far and want to know what it means, read on. However, the next few paragraphs will seem textbook-like.
The economic threshold and the economic injury level are the two principles that separate IPM from other pest management strategies. Both involve making treatment decisions based on the pest population (Radcliffe). The economic injury level (EIL) is defined as “the lowest population density that will cause economic damage” (Radcliffe). In other words, the EIL is the number of pests it would take to actually cause economic loss for the farmer. Typically the farmer wants to prevent that from happening, so most use the economic threshold as the deciding factor about when to start spraying or using another type of treatment (see below).
The economic threshold, or, as it is often called, the action threshold, is the number of pests that justify treatment in order to prevent the pest population from reaching the economic injury level (Radcliffe). Fortunately, the farmer does not need to figure out either population number; university researchers do field trials to determine those numbers, and extension specialists and agents work with farmers to show them what those numbers are, how to measure them, and treatment options if the numbers are reached.
The last PAMS step—suppression—is the treatment stage. When pest populations reach the economic threshold, farmers can choose control options, such as chemical treatments, biological control or other treatments. Chemical control, in this case, is not used as a last resort; the decision about control options is based on whatever is most effective at reducing the pest numbers based on the biology of the pest, and considerate of other issues that may be affected by the treatment. For instance, if the farmer’s neighbor is a beekeeper, and the farmer can get access to a non-chemical control (such as an insect predator), the farmer may decide to use the non-chemical control rather than a pesticide.
In short, the major difference between conventional practices and IPM in terms of pest control is the basis on which treatment decisions are made. Conventional practices use a schedule for pesticide sprays, while IPM relies on the results of regular monitoring before making decisions to spray and choose treatments best suited to the biology of the pest. When I compare IPM to sustainable agriculture and organic agriculture in the next post, you’ll find that those three practices have more similarities than differences, but each still has some unique features that differentiate it from the others.
Source: Pedigo, L.P. 2009. Economic Thresholds and Economic Injury Levels. In: E. B. Radcliffe, W. D. Hutchison & R. E. Cancelado [eds.], Radcliffe’s IPM World Textbook, URL: http://ipmworld.umn.edu, University of Minnesota, St. Paul, MN.