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Late-Summer Crop Considerations

Late-Summer Crop Considerations

Be sure to start scouting for soybean aphids if you have not already started. There are some fields with very few aphids and others that have higher populations. Soybean aphids do not always reach levels high enough to warrant treatment so it is a good agricultural practice to only utilize insecticides only when treatment is necessary. The decision to spray or not spray is always difficult, but the decision can be determined after scouting soybean fields for the presence of soybean aphids. Remember that a neighboring field treated for pests does not necessarily warrant treatment on your field. Scouting for these pests is even more important due to variability in planting dates. Often aphids move from one field to another depending on the soybean crop maturity.

Soybean aphids have become a perennial pest for Minnesota soybean growers since 2002. Aphids are small (1/16” or less) and they are typically light green check for aphids in the soybean canopy. Signs of aphids include white skin casts of molting aphids, honeydew (sap excreted by aphids), or sooty mold (a black mold that grows on honeydew.

Bruce Potter, Integrated Pest Management Specialist based at the University of Minnesota, Southwest Research and Outreach Center, recently reported on soybean aphids. Activity with soybean aphid is picking up. Particularly be on the lookout in fields that tend to be infested first.  A great new U of MN Extension fact sheet on scouting for soybean aphids has been posted at:  z.umn.edu/speedscout. Topics discussed include scouting tips and procedures, speed scouting, what to count and what not to count, soybean stages, and the economic threshold.  Bruce Potter also recently posted a video on scouting for aphids which you can view at:  youtu.be/SW_oLAHUP24.    

A few key points from the fact sheet:  Remember, the economic threshold for soybean aphid is an average of 250 aphids per plant, with aphids on 80% of the plants, and the population increasing.  Note that reaching threshold does not mean you have experienced a yield loss.  Lead time to get out in the field and make an application before you experience a yield loss has been built into the threshold.  Fields where applications have been made to low aphid populations / populations below threshold are at higher risk for the need to make multiple pesticide applications (when possibly one or even none might have been called for).  Note that later planted soybeans will likely be very attractive to soybean aphids later in the season.  Keep on scouting through the mid R6 stage, regardless of calendar date.   

Crop production in the region has been a challenge. Livestock producers with prevented plant acres could use this opportunity for late-summer seeding on idle acres. The recommendation for late-summer seeding of alfalfa in Southern Minnesota is from August 1-15. Alfalfa needs at least six weeks of growth after germination to survive the winter. After six weeks, the alfalfa plant will have developed a crown prior to a killing frost. Be sure to control any weeds in the field prior to seeding and be sure that you have adequate fertility to ensure establishment and productivity.

Another consideration for livestock producers is to plant a winter cereal for grain/straw in 2015.  Following is some planting information from the University of Minnesota Extension Publication titled “Winter Wheat in Minnesota”. The optimum date for direct seeding winter wheat into standing stubble is from September 10-30 for locations South of I 94 and North of I 90. A delay in planting past the optimum seeding date increases the risk for winter kill and can reduce grain yield since the crowns will not be as well developed and the plant will have had less opportunity to store nutrients. Likewise, seeding too early can result in excessive growth in the fall, making plants more vulnerable to winter kill. Winter rye has similar planting dates like winter wheat if the crop is being planted for grain in 2015.

Feel free to contact either the McLeod or Meeker County Extension Offices if you have any particular crop production questions. The McLeod County Extension Office phone number is 320-484-4303 and the Meeker County Extension Office can be reached at 320-693-5275.
 

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