Rain events during September and October have created challenging conditions not only for timely harvest of corn and soybean crops but also for the impact harvest will have on the soil. These wet conditions coupled with a drop in air temperature will slow harvest operations. Soils are too wet for traffic from heavy equipment, making them susceptible to compaction during harvest operations. When soils are near saturated conditions, heavy equipment loads weaken soil structure where water works as lubricant, leading to the collapse of soil aggregates.
Integrated Crop Management News
Links to these articles are strongly encouraged. Articles may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If articles are used in any other manner, permission from the author is required.
This year continues the chain of years with unusual harvest conditions driven by rapid weather changes in the latter part of the growing season. In mid August, crops were significantly ahead of schedule in terms of maturity. Heat and moisture in May and June accelerated the pace of development, to the point that signs of maturity were evident by the 15th of August.
There have been flooded fields with water over the grain in Southwest, Northwest and East Central Iowa this year. This was caused by intense rains over Labor Day and the following weekends. Poor stalk strength causing downed corn has increased the amount of grain covered by flood waters. Grain submerged by uncontrolled flood waters is considered adulterated under the Food Drug and Cosmetic Act. This policy dates to 2008 when grain storage in Cedar Rapids were inundated and has been applied to several situations since then.
Cases of tar spot in corn have been reported over recent weeks in 12 Iowa counties. Iowa State University Extension and Outreach plant pathologists have been able to confirm the presence of tar spot in four counties via the Iowa State University Plant and Insect Diagnostic Clinic. Agronomists and collaborators have confirmed the remaining cases throughout the state. The current counties with confirmed tar spot presence include: Jones, Jackson, Johnson, Muscatine, Fayette, Clayton, Black Hawk, Buchanan, Delaware, Dubuque, Clinton, Scott, Grundy and Chickasaw counties.
Harvest is just around the corner for many Iowa farmers and now is a good time to consider options to reduce movement of weed seed between fields with harvest equipment. While we may not think of it during harvest time, combines are extremely effective at transporting seed from field to field. A few precautions leading up to harvest and during harvest can help manage any escaped problem weeds.
Perceptions about SCN in Iowa have changed over the decades - from grave concern over severe damage in the 1980s, to proactive testing of fields for SCN in the 1990s, to routine management of SCN in the 2000s. What about now? Soybean varieties with SCN resistance have been the foundation of effective SCN management, but resistance is mostly losing effectiveness. The widespread and long-lived nature of SCN requires sampling fields to monitor numbers and using a broad-based management program. The SCN Coalition recommends: Take the Test, Beat the Pest - What’s your Number?
Since early August, farmers and consultants have been reporting what they believed were potassium (K) deficiency symptoms in soybean leaves located in the middle or upper canopy. This is not surprising in fields or portions of fields with soil-test values in the very low or low K interpretation categories. Moreover, K deficiency symptoms could develop at these growth stages with drought conditions, even in fields with adequate soil-test K levels. Sometimes symptoms occur in late summer with rainfall events after a dry period.
I have been reluctant to provide estimates of soybean acres damaged from dicamba applied to Xtend soybean due to the difficulty in developing a realistic number of affected acres. While there has been a significant number of acres damaged by dicamba, I am sure it is less than five percent of Iowa’s nearly 10 million soybean acres. Due to this relatively small number of acres affected (in relation to total soybean acres), dicamba injury will not significantly impact Iowa’s productivity in 2018.
Iowa State University Extension and Outreach field agronomists have reported the appearance of frogeye leaf spot in soybeans as much of the crop across Iowa enters the R3-R5 growth stage.
Soybean aphid is the most important insect pest of soybean in Iowa. Foliar insecticides, mostly pyrethroids and organophosphates, have been the primary management tactic for soybean aphid in Iowa since 2001. Regular scouting and timely treatments will protect yield. Our research and extension program at Iowa State University (ISU) is focused on evaluating insecticide efficacy for soybean aphid on a wide range of products. We are also screening soybean aphid populations for pyrethroid resistance in northern Iowa.