Written by Mark Ferguson

Introduction

There are many ways in agriculture to control and limit the damage done to crops by pests to increase crop yields. Pests include everything from insects to diseases to weeds, and therefore pest management practices will differ substantially depending on each specific pest. One of the approaches often used to manage pests is Integrated Pest Management (IPM). IPM goes beyond chemical pest controls and uses a variety of techniques to effectively maintain pests below economic thresholds. Using IPM allows farmers to make the most economical decision possible regarding controlling pests that affect their crops by giving them a system in which they can weigh the pros and cons of how and when to take action. IPM is used to limit the effects of all pests, no matter the type, and is very effective if done correctly (OMAFRA 2020). There are four steps to the IPM approach. The first is setting a threshold for the point at which to take action on any pests. The second is to monitor for and identify pests that are in the field. The third is prevention and techniques that can be used as preventative measures before pests become an issue. The final step is to initiate the control techniques once the level of a pest exceeds its economic threshold. IPM is dependent on the farmer or grower monitoring their crop for the prevalence of pests that are in the field (OMAFRA 2020).

The steps to be taken will depend on the type of pest as well as the time of year and the growth stage of the crop. Several techniques are used for weed management, insect management, and disease management. Organic agriculture focuses more on preventative and cultural controls as chemical controls are often prohibited.  This chapter will discuss IPM as a whole, and then take a closer look at two of the many strategies used in the IPM approach.

Integrated Pest Management (IPM)

Integrated Pest Management is a way of controlling pests in a farmer’s crop that considers all management options to keep the pest levels below the economic injury level (EIL) (EPA 2019). The economic injury level is the break-even point where the financial loss caused by the pest is equal to the cost that is associated with controlling said pest (Hunt 2015). Below the EIL, it would not be cost-effective to use controls on the pest population because it would mean that application of the controls would cost more that the damage caused by the pests (Hunt 2015). If the cost caused by the pests exceeds the cost of control, steps should be taken to reduce the damage caused by the pests resulting in greater economic gain. IPM uses steps to limit the need for control by implementing additional preventative measures into the system.

As mentioned above, IPM is initiated by setting action thresholds. These are thresholds for pest presence and determining when action should be taken to limit them. The threshold does not just depend on the presence of pests but also on the environmental conditions in the field (EPA 2019). The action threshold is therefore set at the EIL and, if the threshold is exceeded, action must then be taken or at the very least considered to ensure the crop maximizes economic gains (EPA 2019).

Integrated Pest Management incorporates monitoring and identifying the pests present because it is important to monitor the pest situation throughout the growing season to ensure the action threshold is not reached. This would mean that the farmer or someone hired by the farmer would have to regularly scout the crops. Crop scouting requires someone to walk the field and record observations.  The person scouting the crop is looking at the actual crop including abnormalities that may arise from causes such as diseases and insects, insect populations for both harmful and beneficial insects, and weed populations in the field (OMAFRA 2018). In this way, the farmer can closely monitor pest prevalence in the field and ensure that effective steps are taken to control them. Monitoring each field also allows the farmer to use an appropriate procedure to reduce the population of the pest to ensure that it is done effectively.

Prevention of pests is the first line of defense for the crops and if done effectively results in little to no need for other measures to be taken to reduce the effect of the pest on the crop (EPA 2019). Using preventative measures to avoid damage to crops from pests will also often decrease costs that are incurred, whether the cost comes from damage due to the pests or the cost of actually controlling the pests. Preventative measures include crop rotations, cover crops and choosing pest-resistant varieties (EPA 2019).

The fourth step of Integrated Pest Management is control, which becomes necessary once the pests present in the field have been identified and the preventative techniques are no longer effective, allowing the pest prevalence to exceed the threshold that was previously set (EPA 2019). In organic agriculture, pest control techniques can include weeding, trapping insects, planting covering crops, or applying organic compounds to the crop to ensure that the pest population is brought under control (EPA 2019).

A Closer Look At IPM Measures

Crop Rotation

Crop rotation techniques are helpful to control many diseases and insects. For crop rotation to be effective, the grower must know the life cycle of diseases and insects that are present (Mohler and Johnson 2009). Once this is understood, a rotation can be planned and followed to limit the prevalence of these pests. Crop rotations can be used effectively by understanding the life cycle of the pests and the plants they feed upon. If there is an increasing population of the pest in a specific crop, the field is then switched to another crop that the pest does not feed on (Mohler and Johnson 2009). For effective pest control, the field is usually switched to a new crop every year or every other year to keep pest levels below the economic threshold that has been set (Mohler and Johnson 2009). The effectiveness of crop rotation is dependent on how long the disease or insects remain active without the crop they thrive on (Mohler and Johnson 2009). The crop must not be included in the rotation for that amount of time before it is grown again in that field for the rotation to be effective. An effective rotation will result in much less damage to the crop because there are far fewer pests present in the soil and field to affect the crop.

Weed Management

There are many techniques that organic farmers can use to help control weed populations in their fields. These mainly include production practices, as well as mechanical controls. Production controls are usually decided before the seed is planted and tend to be a proactive approach to controlling the weeds. However, mechanical controls are used throughout the growing season and often take a more reactive approach to control weed populations.

Production practices include measures such as selecting crops or varieties of crops that form a canopy rapidly (Delate and Hartzler 2003). This crowds out weeds and gives the crop a competitive advantage over the weeds, essentially inhibiting the sunlight and nutrients that they would need to thrive (Delate and Hartzler 2003). Another production technique that works similarly would be increasing crop density or decreasing row spacing to increase competition for weeds (Delate and Hartzler 2003).

One production technique that can be effective depending on the conditions is using cover crops. Cover crops can be inter-seeded within a crop or grown when there is no crop in the field to prevent weeds from taking over a field when it is not growing a crop (Delate and Hartzler 2003). The cover crops also essentially crowd out the weeds, preventing them from growing and competing with the crop (Delate 2003). Rye is an excellent example of an effective cover crop: it is grown before crimping and the main crop is no-till planted into the mat of crimped rye. The rye acts as a mulch over the field and prevents weeds from shooting up through the soil while letting the main crop thrive. The layer of crimped rye also helps keep moisture in the soil and promotes water infiltration as it slows water movement when it rains, helping it to be absorbed into the soil rather than becoming runoff. This is particularly important in areas that may experience dry weather and not have access to irrigation as it will help keep the moisture in the soil for the main crop to access.

Mechanical controls are used before, during, or after the growing season and require some sort of physical effort from the farmer whether they are using a machine or doing it by hand. The primary type of mechanical control would be cultivation. Mechanical cultivation involves using a tractor and some sort of implement or using hand tools to kill the weeds that are in the field. Before planting in the spring, field cultivators are used to kill the weeds and prep the soil for planting. As the growing season progresses and the weeds need further control, a row cultivator is often a good option (Delate and Hartzler 2003). Then, once the crop is harvested, a disc plow, chisel plow, or Marlborough plow are good options to use to not only kill any remaining weeds but also to incorporate the organic matter into the soil. This allows the organic matter to better decompose into the soil and increase soil health.

There are other options if the farm does not have adequate equipment. Depending on the acreage and area that needs to be weeded, the farmer may opt to hire workers and do the weeding by hand with hand tools such as a hoe. This makes more sense for smaller farms that may not already have the necessary equipment for machine weeding and would therefore be more cost-effective. Another alternative that is used for certain crops, especially corn, is propane flame burning (Delate and Hartzler 2003). This process burns any weeds off of the field at specific growth stages of the corn crop to ensure there is no damage to the plant. The first stage is at corn emergence from the soil and the second is at the 30-45 cm growth stage (Delate and Hartzler 2003). This is the point at which the growth point is protected and ensures that the crop is not damaged, which could decrease crop yield (Delate and Hartzler 2003).

Conclusion

In the organic farming community, pest control is a hot topic because it is critical to the success of an organic farm. Since organic farms cannot use conventional pest control methods such as pesticides and synthetic fertilizers, organic farmers must come up with alternatives to combat damage that is caused by the many pests that may occur in the fields. Integrating a pest management system effectively as well as using all the correct controls at the correct time can help ensure farmers maximize their profits year in and year out. IPM helps ensure that the crop is grown in the most economical way possible and considers the costs and benefits of all possible actions the farmer takes to manage the crop.

For the IPM system to be effective, the farmer must identify an action threshold at which point control actions must take place to limit the damage that pests may inflict on the crop yield. The crops must be closely monitored for the pests as well as how the prevalence of these pests is fluctuating. If the prevalence of the pests is increasing the farmer should keep a close eye to ensure they are under control and not approaching the action threshold. Also if the prevalence of the pests is decreasing following a control action but the level is still above the action threshold, the farmer may want to wait before more action is taken as the pest population may continue to decrease without any further control actions taken against them. The third step that needs to be taken is preventative measures which aim to reduce the pests so that control actions are not needed. This can include activities such as cover crops, crop rotations, and production changes. If these measures do not work, the farmer must implement the appropriate control measures once the action threshold is surpassed so that the pests do not damage the crop and decrease the yields.

References

Delate K, Hartzler R. 2003. Weed management for organic farms.  Iowa University Extension Services, Organic Agriculture series.   Accessed March 05, 2021, from http://www.extension.iastate.edu/Publications/PM1883.pdf.

EPA. 2019. Integrated pest management (IPM) principles. Accessed March 03, 2021, from https://www.epa.gov/safepestcontrol/integrated-pest-management-ipm-principles.

Hunt, T., 2015.  The economic injury level and economic threshold in IPM.  University of Nebraska-Lincoln Institute of Agriculture and Natural Resources Crop Watch.  https://cropwatch.unl.edu/economic-injury-level-and-economic-threshold-ipm

Mohler C, Johnson S. 2009.  Editors; Crop rotations on organic farms, SARE, Maryland, USA. Accessed March 04, 2021, from https://www.sare.org/wp-content/uploads/Crop-Rotation-on-Organic-Farms.pdf.

OMAFRA. 2018. How to scout. Retrieved March 03, 2021, from http://www.omafra.gov.on.ca/IPM/english/ipm-basics/how-to-scout.html.

OMAFRA. 2020. What is IPM? Retrieved March 02, 2021, from http://www.omafra.gov.on.ca/IPM/english/ipm-basics/what-is-ipm.html.