Foreword
The proper management of pests can improve soybean quality and yield while reducing costs.  This guide is designed to help scouts and growers learn how to check for pests and to know when treatment is economically justified. No pesticide recommendations are included. Refer to the latest edition of the North Carolina Agricultural Chemicals Manual or contact your county Agricultural Extension agent for suggestions.

1 Soybean Pest Management  

Crop scouting has been used for many years to help identify pest problems and determine what action, if any, should be taken. However, scouting is only one part of an overall approach known as integrated pest management (IPM). The objectives of integrated pest management are to consider all appropriate methods of lowering pest levels (rather than relying solely on chemicals), to use pesticides only according to need, and to help produce crops more profitably.

One way to improve profitability is to lower costs. Pesticide costs may be reduced by applying chemicals only when necessary and using only the amount needed to control the pests. To know precisely when to take action against crop pests it is necessary to scout for pests regularly and systematically and to know how many pests must be present before they will cause economic damage to a crop. (This level is called the economic threshold). Some knowledge about the advantages and disadvantages of specific pesticides can be very helpful in selecting the best product and minimum application rate needed for control.
Growers are quick to recognize the profit-robbing potential of pests, but it is just as important to realize that using a pesticide when it is not needed can also cut profits. The use of proper scouting procedures and knowledge of economic thresholds can ensure that growers use pesticides properly and realize maximum returns for their investment.

Scouting

The purpose of field scouting is to obtain an objective summary of the pest situation. Some of the information obtained will be useful in making immediate pest control decisions. Other observations will help in knowing what to expect at a comparable time next year.
Scouting is basically the process of walking through a field and stopping at certain places to look for pests or pest damage. The number of stops to make depends on the size of the field. The following chart gives the suggested number of stops for various field sizes.

Field Size                     Number of Stops
(acres)                   Insects                  Weeds
up to 20                    5                             10
21-35                       8                             15
36-50                       10                           15
over 50                  Split into               Split into
                              two fields.             two fields.

Sampling locations in a soybean field should be chosen in such a way that they accurately represent actual pest conditions throughout the field. Specific sample sites should be selected on the basis of a predetermined random pattern, not chosen because the crop looks better or worse at particular spots than in the rest of the field. There are several points to remember when scouting a field:

1. Select stops on a representative basis. Walk a random pattern to ensure that the field is thoroughly covered (Figure 1). Do not fall into the habit of entering a field at the same place each week.
2. Be aware that pests can invade from field borders. Walk to within 50 feet of every border. If a pest problem is detected, try to determine whether it is isolated to the border area or is more widespread and uniform.
3. Randomly select the places where you stop to sample for pests. For example, you might select your next site by stopping in a spot that is 20 steps ahead (or to the left or right) of your present position.
4. As you take samples, observe the plants surrounding the sample site. Scan the field constantly while walking from one area to another.
5. After obtaining counts and estimates, refer to the pest descriptions in this guide to determine whether action is necessary.
6. If you find pests you do not recognize, take samples to your local county Extension agent for identification.

Economic Thresholds

Many soybean growers watch their crop closely and check regularly for pests. When they find a potentially damaging pest, they must decide whether it will pay to apply a treatment to control the pest. The number of pests or level of pest infestation it takes to justify spending money on a pesticide treatment is known as the economic threshold (or action threshold) for that pest. The threshold can help determine whether control measures will pay and when they should be applied.

One might think that if pests are present they must be damaging the crop or interfering with its growth, thus causing a loss. Actually, pest populations can sometimes build up to relatively large numbers before it pays to control them. For example, soybeans before they bloom can withstand 30 percent defoliation from insect feeding without a loss of yield. Similarly, a vigorous soybean crop may be largely unaffected by minor competition from weeds. Treating the crop to control a pest that will not reduce the quality or yield is a waste of money.

Another point to consider is that there are almost always natural control agents working against an increase in pest populations. In other words, even though a certain pest is found in a field, there is no guarantee that its population will ever reach damaging levels. There is no point in spending money to control a pest that may never build to damaging levels. Waiting to see if there will be enough pests to warrant treating the crop is one of the ways growers can save money using integrated pest management.

Keep in mind that although the thresholds given in this manual have worked very well, they were developed as guidelines to be used under average conditions. In unusual situations, such as during periods of drought stress or when multiple pests are present, lower thresholds should be used.
 

Deciding About Pesticide Applications

Once a pest has been found to exceed the economic threshold, the grower must determine the best and least expensive way to prevent unacceptable losses. If a pesticide treatment is needed, the pesticide and its rate and method of application must be "customized" to the pest. This is probably the surest way to save money. High pesticide rates are not needed if the correct pesticide is chosen and the method of application delivers the required amount of chemical to the pest.

To apply pesticides properly, sprayer pressure and volume must be correct; the right nozzle type, arrangement, and number must be used; and the sprayer must be accurately calibrated. When deciding on a pesticide, talk to your local Extension agent and consult the North Carolina Agricultural Chemicals Manual before talking to your chemical supplier. There are times when control may be achieved with substantially reduced rates.