When using the widely accepted treatment threshold of 250 aphids per plant and 80% of the plants with these levels, the response from people who will do the field scouting is less than enthusiastic. No one wants to count all those aphids. What happens is that people tend to streamline the process, “training” themselves to recognize what 250 soybean aphids per plant looks like.

The Speed Scouting method is referred to as binomial sequential sampling plan. The binomial refers to two outcomes or classifications. The sequential sampling aspect refers to the process of keeping track of what is and isn’t infested and then being able to conclude, often times quickly, that the number of plants needed to make a decision with high levels of reliability have been sampled.

The protocol for a binomial sequential sampling plan for soybean aphid was developed by researchers at the University of Minnesota. A discussion about the procedure can be found at:

http://www.soybeans.umn.edu/crop/insects/aphid/aphid_sampling.htm

Here is a quick overview:
After collecting data from commercial soybean in southern and central Minnesota, entomologists at the University of Minnesota developed a binomial sampling plan, called Speed Scouting for Soybean Aphid. The recommendation is to use this sampling plan through the pod set stage.

A ‘binomial’ plan refers to two choices; sometimes it means a presence/absence count or, as in this case, a pre-set cut-off number where counting can be stopped. For this procedure, the binomial sampling cut-off point is 40 aphids per plant. If a plant has less than 40 aphids, consider it non-infested; however, if the plant has 40 or more aphids (remember, counting additional aphids is not necessary after 40), consider the plant infested.

The field scout keeps track of the plants and how they are classified. A worksheet really is a must in order to keep track. Eventually, enough plants (the minimum number of plants is 11) will have been checked to start making some decisions. The statistical models these decisions are based on will allow you to make one of three decisions with a high degree of reliability (the model has been set at 75% reliability). Those decisions are:

1. Do not treat that field,
2. Treat that field, and
3. Resample that field in 3 to 4 days

The binomial sampling plan can improve the cost (especially in time commitment) of sampling because every insect no longer needs to be counted. Though not perfect, the model has attempted to balance reliability with cost of scouting. When fields are close to threshold levels, more plants are typically required to make a decision. However, when fields are clearly not at threshold or easily over threshold, decisions are made quickly and reliably.

An copy of the worksheet and directions for the procedure are provided in this document. You can also obtain an electronic copy of the worksheet on the web page previously mentioned. In addition, there are sample worksheets to illustrate decisions with the three different outcomes:

     
Examples of completed worksheets

You understand the process, now you just want a
pocket size field card so you can carry
the worksheet easily into the field.

Here is a simple "print and cut" pocket size
speed scouting worksheet

Modifications for 2006:
After field validation during 2005, results revealed that the procedure can prematurely reach treatment decisions, typically ca. 160 aphids per plant rather than the threshold of 250 aphids per plant. To ensure the population is actually increasing, we recommend that the field be re-checked in 3 to 4 days.

Reference
Hodgson, E. W., E. C. Burkness, W. D. Hutchison, and D. W. Ragsdale. 2004. Enumerative and binomial sequential sampling plans for soybean aphid (Homoptera: Aphididae) in soybean. J of Econ. Entomol. 97(6): 2127-2136.