Soybeans: Defoliating Insects

Excerpt from Agronomy Guide for Field Crops (Chapter 4)

OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Introduction
2. Standard Damage Thresholds for Soybean Insect Defoliation - Table 4-20
3. Defoliating Insects
   • Bean Leaf Beetle
   • Japanese Beetle
   • Grasshoppers
4. Updates on Soybeans: Defoliating Insects
5. Related links....

Introduction

Soybeans are able to compensate for large amounts of foliage loss due to insect feeding, and often little effect on yield is observed. However, the most critical stage for soybeans is bloom to pod-fill, when seed development is highly dependent on photosynthesis. Should large amounts of defoliation occur at this stage, yield can be affected and, therefore, control may be necessary.

To estimate damage thresholds for leaf-feeding insects on soybeans, the percentage of defoliation occurring in each soybean field must be determined. In 10 areas of the field, pick trifoliate leaves from 5 plants that are newly and fully expanded from the center of the plant canopy. Discard the least and most damaged leaflets from each trifoliate collected. Compare the leaflets that are left with Figure 4-5, Defoliation Chart for Soybean Leaf-Feeding Insects and determine the average percentage of defoliation.

Figure 4-5. Defoliation Chart for Soybean Leaf-Feeding Insects

Source: University of Illinois and Purdue University, 1982

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Once the percentage of defoliation in each field has been established, general damage threshold guides can be used to determine whether control is necessary, depending on the stage of the crop, Table 4-20, Standard Damage Thresholds for Soybean Insect Defoliation.

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Updates on Soybeans: Defoliating Insects

• Field Crop Protection Guide - Publication 812
  • Bean Leaf Beetle

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Related links...

• Insects
• Soybeans

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