Soybean aphids prove to be major pests for soybeans
Information from Purdue University Web site
Insect pressure and unfavorable weather are two culprits that will steal any grower’s soybean yields long before harvest.
Although growers can’t predict what Mother Nature has in store for the 2009 growing season, they can protect their fields from sucking and chewing pests, such as soybean aphids, bean leaf beetles and Japanese beetles.
“Aphid infestations that peak at the R1–R2 growth stage of the host may cause stunted plants with reduced pod and seed counts, resulting in lower yields,” according to a North Central Pest Management Center “Soybean Aphid Regional Pest Alert” posted on the Purdue University Indiana Cooperative Agricultural Pest Survey Program Web site.
Yield loss isn’t the only problem insects can bring. Soybean aphids are “capable of transmitting a number of viruses present in the United States that naturally infect soybeans,” according to the alert.
University researchers have set the aphid threshold at 250 aphids per plant on 80 percent of the plants scouted.
To find out more from Purdue University on the soybean aphid, click here.
Rapid Population Increases in Soybean Aphids
Information from University of Minnesota Extension
Soybean aphids increase at such a rapid rate that the females are essentially cloning themselves. The University of Minnesota Extension Web site explains that females give birth to live young nymphs at a rate of three to five per day. The female nymphs then mature in five to seven days and then begin producing their own young.
This speedy life cycle stresses the importance of scouting early and often because in an experiment when temperatures ranged from the mid 70s to early 80s – ideal conditions for aphids – populations doubled in as little as two days.
A 2001 study held in Houston, Minn., demonstrated the dynamics of soybean aphid populations. The field was colonized with soybean aphids when the plants reached the V1 to V2 stage (first and second trifoliate). Within four weeks, the entire field had been colonized and the populations increased dramatically. Just one week later, the densities reached five times the injury level at 5,000 per plant.
For more information on this population growth study from the University of Minnesota, click here.
Threshold Critical in Application Timing
Information from University of Wisconsin Extension Integrated Pest and Crop Management Newsletter
With the ever-changing commodity price of soybeans, many questioned whether the threshold number would change for numerous pests including soybean aphids. The North Central Extension entomologists reviewed the threshold in the summer of 2008 and decided to keep the recommendation at 250 aphids per plant.
The University of Wisconsin Extension Web site notes that growers should base scouting on a sample of 20 to 30 plants throughout the field. These plants are usually at R1 to R5 growth stages, (beginning bloom, first flower to 1/8″ seed in top four nodes).
This threshold level provides a seven-day window to treat fields before the economic yield loss occurs at 1,006 aphids per plant.
For more timely insect management information from the University of Wisconsin, click here.
Understanding Aphid Thresholds
Information from Iowa State University Extension Web site
When scouting soybeans for aphids, it’s important to understand the threshold numbers.
Currently, according to Iowa State University, threshold is 250 aphids per plant on 20 to 30 plants sampled throughout the field when aphid populations are on an active increase. (more…)
