A list of SCN-resistant soybean varieties for use in Iowa is compiled and made available every fall as ISU Extension publication PM 1649. The updated list recently has been made available online. Overall there are fewer SCN-resistant soybean varieties than in past years, but there are varieties from more brands (27) in this year’s publication. Most importantly, there are 47 varieties with Peking SCN resistance in the 2022 list, which is 13 more than were in the list in 2021. Soybean varieties with Peking SCN resistance are highly valued because they limit reproduction of Iowa SCN populations much more than varieties with the common PI 88788 resistance.
Integrated Crop Management News
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With harvest winding down, one weed that made harvest more frustrating for some is burcucumber. Consequently, there have been many questions on how to better manage this weed to prevent those frustrations.
Iowa State conducts soybean cyst nematode (SCN) experiments in fields rented from farmers in all of Iowa’s crop reporting districts. Spring soil samples from each study area are used to test the SCN population in the field for levels of reproduction on soybean breeding lines with SCN resistance genes. The results of testing in 2022 revealed some SCN populations with 75% to 90% reproduction on PI 88788, the source of SCN resistance genes present in almost all of the soybean varieties available in Iowa. This high level of reproduction makes complete loss of effectiveness of PI 88788 SCN resistance seem possible within several years. The number of varieties with more effective Peking SCN resistance is increasing every year, but the rate of increase is not keeping pace with the increase of reproduction of SCN populations in Iowa fields on PI 88788 resistance. An active, integrated approach to managing SCN in Iowa is more important than ever.
With harvest in full swing and while conditions have generally been good for in-field drying this fall there are still some corn fields in areas of the state with moisture levels in the low to mid 20s.
Getting fields sampled for SCN is a task that should be on every farmer’s to-do list this fall. SCN soil samples can be collected from corn fields after harvest to determine what levels of the nematode are present to infect the 2023 soybean crop. Results of soil samples collected from fields of harvested soybeans this fall will show if SCN was present and reveal what effect the nematode might have had on soybean yields in 2022. Reproduction of SCN is greatest in dry years, and SCN egg numbers in the soil are expected to be high in soybean fields this fall. This article outlines guidelines for sampling fields for SCN, gives information on where to send SCN soil samples, and provides guidance on managing fields that are infested with SCN.
October began dry across most of Iowa except for some areas in southern and southeast Iowa. These conditions are allowing for rapid harvest progress. The outlook for the rest of the month calls for lower than normal rainfall. Below normal rainfall since August until the soil sampling time may result in lower than expected soil test results for phosphorus (P), potassium (K), and pH. Therefore, farmers and crop consultants should interpret those soil test results with caution.
While Iowa weed communities change constantly, it is rare that a species new to the region is discovered. Asian copperleaf (Acalypha australis) was first discovered in Iowa in 2016 in a corn field near Cedar Falls. Prior to this discovery, the only documented infestation in North America was within New York City. The plant was recently found in a soybean field in Grundy County, nearly 30 miles from the original infestation (Figure 1).
Recent rainfalls are likely to result in the establishment of winter annual weeds. Many fields may have dense stands of these weeds going into winter (Figure 1). It is often difficult to achieve timely burndown of these species in the spring, so farmers with persistent problems should consider making a fall burndown application to control winter annuals.
Fall is one of the best times for managing perennial and biennial weeds found in pastures or other areas maintained in perennial grass. As perennials prepare for the upcoming winter, they move energy reserves from shoots to their perennial vegetative reproductive structures (e.g. rhizomes, perennial rootstocks).