Integrated Pest Management and Ecosystems

Smart Choices Improve Production


Integrated Pest Management is a system for reducing crop losses from insects, weeds and plant diseases. IPM uses all available control practices such as crop rotation (changing what's grown in a field), selecting resistant varieties (plants resistant to pests), mechanical cultivation, changing planting and harvesting times, biological control (using other living organisms to control pests), and chemical control.

Using several methods of control is usually more effective than relying on a single pest management practice. One goal of IPM is to reduce pest damage to an acceptable level and minimize the risks of pesticides to human health and the environment.

Scouting fields for pests and basing treatment decisions on economic thresholds is an important part of IPM. The principle of using economic thresholds is that pests are not controlled until they reach a level that is economically damaging. The predicted loss from insects, weeds, or plant disease must be more than the cost of control. If the number of pests are not high enough to cause an economic yield loss, control is not recommended. In some cases, this means that pests are allowed to remain in the field.

Economic thresholds are based on how much damage a pest may cause if not controlled, the predicted crop yield, the estimated selling price, the cost of control, and other factors.

Activity 1: Is Herbicide Necessary?

Use economic thresholds to decide if a herbicide application is necessary.

Table I shows three different weeds and the effects they can have on soybean yield if they are not controlled.

Steps to Follow in Activity

1. Count the average number of weeds per 100 feet of a soybean row.

2. Refer to Table 1 to find the estimated yield loss for that number of weeds.

3. Estimate the potential crop yield for the field.

4. Multiply the estimated yield loss by the predicted crop yield. This equals yield loss if weeds are not controlled.

5. Multiply yield loss by expected cash price per bushel.

6. Determine cost of herbicide application.

7. Subtract the cost of herbicide treatment from the cost of yield loss to determine if herbicide treatment is economical.


You scout a soybean field and find an average of 8 giant ragweeds per 100 feet of row. Should you apply a herbicide to control these weeds?

Weed | Number of weeds in 100 feet of row

Giant ragweed
% of yield reduction


(For example: 4 pigweed plants in 100 feet of row will reduce soybean yield by 2%)

  • Expected Yield: 50 bushels/acre
  • Expected cash price per bushel: $5.00
  • Cost of herbicide application: $15.00

Step 1: 8 giant ragweed
Step 2: 8% yield loss (from Table 1)
Step 3: 50 bushels/acre
Step 4: (0.08) X 50 bushels = 4 bushels
Step 5: 4 bushels X $5.00/bushels = $20.00
Step 6. $15.00/acre
Step 7. Net gain or loss: $20.00 - $15.00 = $5.00/acre

Decision: Apply a herbicide to control weeds

Activity 2: Scouting Fields

You scout a soybean field and find an average of 10 pigweed plants per 100 feet of row.

  • Expected Yield: 40 Bushels/acre
  • Expected cash price per bushel: $5.00
  • Cost of herbicide application: $15.00
  1. Should you apply a herbicide to control these weeds?
  2. If the price for soybeans goes up to $8.00/bushel, should you control the weeds?
  3. If the cost of herbicide application drops to $10.00/acre, should you control the weeds?

Follow-up Questions
How do ecosystems benefit from using an Integrated Pest Management program?(Chemicals are used in a responsible manner, lowering the possibility of excess chemicals reaching water supplies.)

IPM encourages using several different pest control methods, including BIOLOGICAL controls. This means using living organisms to control pests. Beneficial insects, like lady bugs and some types of parasitic wasps can be used to lower the number of insects causing damage. How does this imitate a natural ecosystem? (In a natural ecosystem, a balance is usually maintained between the number of insects and insect predators. If the number of one type of insect increases, predators of that insect such as other insects or birds will also increase, because they have more to feed on. When the food supply goes down, so will the number of predators. This principle also applies to wildlife.)