Most people are aware of Palmer amaranth seed contamination in native seed mixes. These findings have led to questions about whether cover crop seed might also be a source of Palmer amaranth. We are not aware of any situations of cover crop seed used in Iowa being a source of Palmer amaranth, and have not heard of this situation in other Midwest states.
Integrated Crop Management News
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Discoveries of Palmer amaranth in conservation plantings have created the need to develop management plans to reduce the likelihood of movement of the weed into crop fields (Figure 1). Reducing or preventing Palmer amaranth seed production should be a high priority. The maturity of Palmer amaranth varies considerably in the fields we have observed. While it is likely that some viable seed is already present, the amount of seed produced can still be dramatically reduced with appropriate control measures.
Bacterial leaf streak (BLS) in corn was recently identified in Iowa. Bacterial leaf streak is a disease caused by Xanthomonas vasicola pv. vasculorum. The disease has been found on field corn, seed corn, popcorn, and sweet corn. Iowa State University Extension and Outreach has been working with the USDA, Iowa Department of Agriculture and Land Stewardship (IDALS), the Iowa Crop Improvement Association (ICIA) and surveying several counties in the state.
In the past, corn leaf aphid could be a problem during corn tasseling. This species aggregated around the ear and silks, and sometimes their honeydew production interfered with pollination. But natural enemies and the environment rarely let them persist past July. Therefore, economic thresholds for corn leaf aphid are targeted around VT-R1 and mostly for drought-stressed cornfields. Since 2010, aphids have been colonizing corn later in the summer and are building up to striking levels.
Palmer amaranth was first detected in Iowa in 2013 in Harrison County, and until recently the invasive weed had been found in four additional counties. About a month ago, two landowners (both professional agronomists) detected Palmer amaranth in fields planted in spring 2016 with native seed mixes for conservation purposes. In the time since those July detections, Palmer amaranth has been found in an additional five counties (multiple fields in several of the counties). We think it’s safe to say the calm before the storm has ended.
Information provided by Bob Hartzler, compiled and written by College of Agriculture Life Sciences and Iowa State University Extension and Outreach.
In April 2016, an ICM News article showed a prediction for higher survivorship of overwintering bean leaf beetles in Iowa. Not surprisingly, I have been finding more bean leaf beetles in my research plots and hearing about adults in commercial soybean this summer. Most people have reported minor defoliation from overwintering and first generation adults, but some scouts are wondering about the potential for second generation injury.
Palmer amaranth was first identified in Iowa in 2013. Currently, we know it is established in five Iowa counties, but we suspect it is more widespread than this (Fig. 1). This past weekend we were made aware of a new infestation of Palmer amaranth in Fremont County, distant from the initial infestation in this county. In addition, a suspicious looking Amaranthus species was found in Madison County – the owner is allowing a few plants to develop seedheads in order to make a positive identification.
This spring consisted of wet field conditions for many regions across Iowa during planting season. When soil moisture is at or exceeds field capacity, there is an increased potential for soil compaction, particularly at topsoil depths. Soil compaction at planting time can impact root growth and development for the rest of the growing season, and can be a serious problem for Iowa farmers. However, with proper field management, compaction can be minimized.
Most herbicide applications have ceased for the year, but it is not too late to evaluate how well the program worked and what changes might be necessary for next year. Rather than just falling back on old habits, analyze your program closely to look for improvements for future years.
Surviving weeds from this year will affect weed pressure in next year’s crops. Identifying this season’s management successes and failures will make weed management and herbicide purchase decisions easier this winter.