Pesticides, better described as crop protection agents because of their diversity, are one of the key elements in a modern, integrated pest management (IPM) approach to managing crop pests. They are particularly important as a means of preventing the breakdown of genetic resistance due to pests that develop their own ways around that resistance. First of all, it is important to understand that farmers have no economic or practical incentive to over use pesticides. These materials can be costly as can be the time, fuel and equipment wear involved in applying them. Against that background, a number of other principles guide a farmer in terms of what specific pesticides to use, when to use them and how to deliver them. I’ll touch briefly on some of those principles below:
- Action Thresholds (when to start spraying)
One of the central principles of IPM is monitoring the pest population to see when it is, in fact, important to make a pesticide application. It is not economically ideal to go to the expense of a spray for certain levels of pests and their damage, such as while the natural enemies of the pest have the best chance to keep it in check. This issue varies greatly depending on the type of pest involved. For some pests, the threshold for action must be low. This is particularly true for certain insects that vector (spread) damaging viruses or bacterial pests. In that case, the insect may not be causing significant damage through its own feeding activity, but the disease it is spreading can quickly become devastating. Growers of each crop in each region have to be particularly tuned into these issues to spend time and/or money on monitoring for the worst pest threats in their situation
- Protecting Beneficial Organisms
One of the six elements of IPM is fostering beneficial organisms. In many cases, these organisms are biologically similar enough to the targeted pests that they too may be killed by a pesticide. Fortunately, not all pesticides are alike in this regard and a farmer can often choose a particular crop protection product that is effective on the pest but relatively safe for beneficial organisms. These options are preferable whenever possible, and a good deal of guidance is available on this subject from State Cooperative Extension agencies and from private pest control advisors.
- Protecting Pollinators
Different crops are pollinated in different ways (e.g. by the wind or by birds), but in many cases crops are pollinated by an insect like a honeybee, a bumble bee, various other wild bees or other insects. During the period when these crops are blooming, a spray for an insect pest can hurt the pollinators. Different pesticides have different profiles in this regard. Some are quite safe for pollinators and others are safe as long as growers apply them at a time of day when the pollinators are not working.
Farmers must make careful choices during the bloom of their crops and need to be aware of when bees are being employed to pollinate a neighbor’s crop. In recent years, some general problems with bee populations have arisen and pesticides have been widely blamed as the culprit. The truth is that this is a complex issue that often has more to do with pests of the bees themselves, like the Varroa mite and the virus diseases that it spreads among bee colonies. Through making thoughtful choices with pesticide options and by good neighbor-to-neighbor communications, farmers can and are doing their part to protect pollinators.
- Targeted Delivery
The IPM ideal is not only to apply the right pesticide at the right time but also to apply it as specifically as possible to where it is needed. Depending on the crop and pest in question, growers can achieve the latter goal with considerable precision. Some pesticides can be injurious to fish or other aquatic organisms. In those cases, growers must usually follow formal limits on how close their application can be to bodies of water. For weeds growing in an orchard or a vineyard, it is possible to spray downwards at the ground with virtually no danger of the herbicide contacting the susceptible, leafy part of the crop. In some situations, it is possible to attract the first wave of a given pest to physical traps or to a trap crop which is not intended for harvest but planted along the edge of the field. Once the pests arrive at the trap crop, farmers can spray them there without need to spray the crop itself. This only works in certain situations but is another example of targeted delivery.
For annual crops, the time during seed germination and initial growth is critical within the crop cycle. When the plants are small, feeding by an insect or infection by a fungus can much more easily kill the seedling or severely stunt it in ways that the plant cannot fully overcome throughout the growing season. In recent decades, scientists have developed technologies to treat/coat seeds with protective fungicides and insecticides which are present specifically around the germinating seed and/or picked up through the plant roots to provide protection during this most vulnerable stage. When crop protection products are applied this way, the total quantity used per acre is a tiny fraction of what it would be with a drench or spray application. The levels of these pesticides declines as the season progresses so that by the time the crop is blooming and long before the crop is harvested, the pesticide has been broken down to harmless components.
One more example of targeted delivery is the use of modern machine vision systems to selectively spray only weeds while passing over a field.
- Good Neighbor Standards
The control of some pests doesn’t just depend on the outcome in a given field but rather on the balance with the IPM programs in neighboring fields. If the local populations of some pests gets too high, IPM principles like action thresholds and preserving beneficial organisms become too difficult to employ. With too much pest pressure, control strategies like mating disruption will no longer work.
To prevent an abundance of pest pressure, some growing regions have laws in place such that if a grower is allowing the population of particularly damaging pests to grow too much, then the county or state authorities have the ability to step in and control the pest at the owner’s expense. Fortunately, these incidents are quite rare within strong crop sectors. In some particularly difficult pest examples, even an untended backyard tree can compromise the commercial production within a certain radius. Good neighbors of all types need to be aware of these sorts of issues.
- Managing the Risk of Pest Resistance Development
Part of good pest management with pesticides is preserving the usefulness of the tools available, particularly the most beneficial ones in terms of safety and low risk to non-target species. Pests tend to go through many life cycles during each single season of crop growth, so their potential to evolve pesticide resistance is significant.
Starting in the 1980s, guidance has been available to farmers about how to mix and match modes of action in their choice of pesticides. Most modern pesticides work through rather specific effects on a target enzyme in the pest, which is how they can be effective as a pesticide and yet essentially non-toxic to other organisms, including humans. The downside of that kind of specificity is that a single mutation in the pest can render it resistant. That is why farmers are advised, and sometimes even required, to use pesticides with different modes of action either in combinations or in consecutive treatments, a strategy called resistance management. These practices prevent, or at least significantly delay, the development of pest resistance to the most desirable pesticide options.
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