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3/12/2012 - 3/18/2012

Options for Soybean Aphid Host Plant Resistance

By Michael McCarville, Erin Hodgson, and Matt O’Neal, Department of Entomology

Host plant resistance for soybean aphid is the newest management tool for farmers. In 2010, a single gene expression, called Rag1, was commercially released in the North Central Region. Aphids feeding on Rag1 plants do not live as long or produce as many offspring compared to feeding on susceptible plants. In small plot evaluations of the Rag1 gene, there is a dramatic decrease in the seasonal accumulation of soybean aphid compared to susceptible varieties.

The entomology department at Iowa State University recently released a new publication, Soybean aphid-resistant varieties for Iowa, that lists currently available soybean seed with resistance to soybean aphid. The list is intended to assist farmers wanting to adopt this new management tactic for soybean aphids, a sporadic pest that can reduce yield by as much as 40 percent. The listing includes varieties in late maturity group 0 and maturity groups 1, 2 and 3. 

The list contains 16 varieties from 10 companies. Seed companies provided varietal information including relative maturity, herbicide resistance, source of aphid resistance and resistance to other pests. Two items of interest to farmers will be:

  1. Four varieties with resistance to both the soybean aphid and soybean cyst nematode (SCN).  The SCN is a pervasive and serious pest of soybean in Iowa. Farmers with SCN infested fields are encouraged to select an SCN-resistant variety.
  2. One variety carrying two different genes for soybean aphid resistance. Varieties containing two soybean aphid resistance genes provide significantly better aphid control than varieties containing a single resistance gene.

The publication also contains Iowa State University recommendations for considering soybean aphid-resistant varieties. For more information on soybean aphid management consult: Soybean Aphid Management Field Guide 2nd edition. Additional information about insecticides is found in the most recent soybean aphid insecticide efficacy evaluation. This publication was funded in part by the Soybean Checkoff and the Iowa Soybean Association.

 

Michael McCarville is a Department of Entomology graduate student; he can be reached at 515-294-8663 or by email at mikemcc@iastate.edu. Erin Hodgson is an assistant professor of entomology with extension and research responsibilities. She can be contacted by email at ewh@iastate.edu or phone 515-294-2847. Matt O'Neal is an associate professor in the Department of Entomology with teaching and research responsibilities. He can be reached at oneal@iastate.edu or at 515-294-8622.

Mild Winter for Bean Leaf Beetle

By Erin Hodgson, Department of Entomology, and Adam Sisson, Integrated Pest Management

Most Iowa winters are harsh on overwintering bean leaf beetles. Typical statewide overwintering mortality ranges from 60-99 percent (see a 20-year historical record of predicted bean leaf beetle mortality in central Iowa.) A combination of cold winter temperatures and the high adoption of insecticidal seed treatments have drastically curbed bean leaf beetle populations throughout much of the state.

Bean leaf beetle adults are susceptible to cold weather and will die when the temperature is below -10 degrees C, but they have adapted to winter by protecting themselves in leaf litter and insulating snow cover. An overwintering survival model was developed by Lam and Pedigo from Iowa State University in 2000, and is helpful for predicting winter mortality based on accumulated subfreezing temperatures. Figure 1 is a map of predicted mortality in Iowa for the 2011-2012 winter.

In general, Iowa experienced a warm winter, with predicted mortality ranging from 30-53 percent. The predicted mortality estimates are the lowest since the overwintering model was developed. Many areas in the state had less than normal accumulated snow cover, which could increase actual adult mortality. A recent ICM News article discusses the implications for warm winters, lack of snow cover and insect survival. 


Figure 1. Predicted overwintering mortality of bean leaf beetle based on accumulated subfreezing temperatures during the 2011-2012 winter (1 October 2011 – 8 March 2012).

Overwintering adults are strongly attracted to soybean and will move into fields with newly emerging plants (Fig. 2). Early-planted fields should be monitored closely this year, given the predicted likelihood of adult overwintering survival. Other fields of concern include food-grade soybean and seed fields where reductions in yield and seed quality can be significant. Information about managing bean leaf beetle and bean pod mottle virus is available on the Iowa State entomology website. 
 

Figure 2. Overwintering bean leaf beetles can defoliate young soybean plants and vector bean pod mottle virus

Bean leaf beetle is easily disturbed and will drop from plants and seek shelter in soil cracks or under debris. Sampling early in the season requires you to be sneaky to estimate actual densities. Although overwintering beetles rarely cause economic damage, their presence may be an indicator of building first and second generations later in the season.

 

Erin Hodgson is an assistant professor of entomology with extension and research responsibilities; contact at ewh@iastate.edu or phone 515-294-2847. Adam Sisson is an Integrated Pest Management program assistant. Sisson can be contacted by email at ajsisson@iastate.edu or by calling 515-294-5899.



This article was published originally on 3/19/2012 The information contained within the article may or may not be up to date depending on when you are accessing the information.


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