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As of October 14, 2018, Iowa soybean harvest was only about 20% complete, making it the latest soybean harvest on record. This was caused by the prolonged heavy rains in September and early October. As a result, field losses, abnormally high harvest moisture content and moldy/weathered soybeans are all issues this year.
Above normal rains in September have slowed field crop dry-down. Coupled with early season drought in South Central and Southeast Iowa and above-average rainfall in the Northwest, there is high risk of reduced grain quality. Corn and soybeans remaining in the field are currently exposed to excessive moisture that encourages the growth of ear molds. Moldy kernels are counted in total damage, thereby affecting the overall grade of the corn. Additionally, if the fungus is capable of producing mycotoxins, affected grain may be subject to marketing restrictions.
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.
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.
