When I hear the phrase “Dog Days of Summer,” my mind often wanders to thoughts of shade trees, watermelon, cold lemonade and soybean aphids (Figure 1). During the heat of late July and August, I would rather be enjoying the first items mentioned, yet my time is often taken up scouting fields for the latter. Closely monitoring your soybean fields for the presence and potentially increasing population of soybean aphid can mean the difference between a potentially high-yielding soybean field and just an average yield. Mild temperatures along with dry conditions can increase the potential for the development of a soybean aphid infestation and population growth.
Aphid populations should be monitored and documented every four to seven days as populations can increase quickly. Control is warranted when 80% of the plants have 250 aphids per plant and the population is increasing. Populations of naturally occurring predator insects should also be noted as they can help control low to moderate aphid populations (Figure 2). For this reason, it is recommended to not include an insecticide in with a midseason herbicide application when aphid populations are below threshold. Insecticides can clean the field of beneficial insects as well as aphids, and can open the field up for potentially worse aphid infestations later in the summer. Soybean aphids have a great ability to move over large distances by way of general wind patterns and may repopulate the field very quickly.
Normally, aphid infestations start at the top (newest trifoliate leaves) of the plant and can be more easily found by looking in this specific area (Figure 3). However, under hot conditions, aphid populations may develop in the mid-canopy of the plant where temperatures are more moderate. Aphids found in the mid-canopy are typically smaller and lighter green in color.
To aid in aphid scouting, the “speed scouting” method, developed by the University of Minnesota, should be used. This scouting method can greatly reduce field evaluation time. There is an app developed for speed scouting in the field, just search the Apple App Store or Google™ Play for Aphid Speed Scouting (University of Nebraska).
Following is a good YouTube video by the Entomological Society of America on how to speed scout: https://www.youtube.com/watch?v=n_WmCQA0OHs
Two-spotted spider mites may also be present in some soybean fields. Some of the aphid insecticides may flare the mite population. Know if mites are present before spraying for aphids, and check the insecticide label for mite control if they are present.
As you are scouting for soybean aphids, also be on the lookout for other pests including stink bugs, Japanese beetles and bean leaf beetles. These additional pests can also lower soybean yields if left unchecked. Additional information on these pests can be obtained from the Channel.com Agronomy Library.
Glogoza, P. Soybean aphid speed scouting: An overview. University of Minnesota. https://www.extension.umn.edu/agriculture/crops-research/north/2015/docs/2015-soybean-aphid-speed-scouting.pdf
Koch, R. 2016. Soybean aphid in Minnesota. University of Minnesota Extension. https://www.extension.umn.edu/agriculture/soybean/pest/soybean-aphid/.
Soybean aphid. Agronomy ADVICE. Channel.com. http://www.channel.com/agronomics/Documents/AgronomicContentPDF/Soybean%20Aphid%20-%20Channel.pdf.
Soybean aphid speed scouting – How to? 2012. Enotmological Society of America. YouTube https://www.youtube.com/channel/UCOsDdSStbdt7ZebC0cMxcBg.