Extension

Several field days are happening across the state throughout the month of June. Hear from our faculty experts along with other faculty and Extension and Outreach specialists about a variety of crop and pest related topics.

June 20 at 9:00 am: Northern Research Farm Summer Field Day - Kanawha, Iowa

A season review from ag specialists Matt Schnabel and Brandon Zwiefel
Sulfur use - Dr. John Sawyer
Weed control - Dr. Bob Hartzler
Cereal rye for seed - Dean Sponheim & Jamie Benning
Crop production issues - Paul Kassel & Angie Rieck-Hinz

June 27 at 1:00 pm: Northeast Iowa Agricultural Experimental Association Annual Spring Field Day - Nashua, Iowa

Crop weather outlook - Dr. Elwynn Taylor
Strip till and no till research - Dr. Mahdi Al-Kaisi
Nitrogen fertility - Dr. John Sawyer
Insect scouting and tips - Brian Lang

Row spacing is a management decision that often comes up as a priority for achieving high-yielding soybean. Research across the Midwest over several years has consistently shown that soybean planted in narrow rows (<30 inches) has a yield advantage compared to wide rows (≥ 30 inches). The primary reason for this advantage is light utilization; canopy closure is approximately 15 days earlier in 15-inch rows compared to 30-inch rows. Canopy closure earlier in the growing season results in greater light interception and higher growth rates. 

Plant pathologists at Iowa State University and University of Kentucky have confirmed that isolates of Cercospora sojina, the pathogen that causes frogeye leaf spot of soybean, have shown resistance to quinone outside inhibitor (QoI, strobilurin) fungicides in Iowa.

Frogeye leaf spot (Fig. 1) occurs across the United States, and significant yield loss can occur when this disease is widespread within a soybean field. Plant pathologists estimate that this disease was responsible for more than 17.5 million bushels of lost yield, valued at $158.1 million, across the U.S. in 2015. 

In 2017, we tested several foliar fungicides on corn at six locations in Iowa: ISU Northwest Research and Demonstration Farm (NWRF), Sutherland; Northeast Research and Demonstration Farm (NERF), Nashua; Northern Research and Demonstration Farm (NRF), Kanawha; Southwest Research and Demonstration Farm (SWRF), Lewis; Southeast Research and Demonstration Farm (SERF), Crawfordsville; and the Ag Engineering and Agronomy (AEA) Farm, Boone.

The purpose of these trials was to help farmers determine if foliar fungicides should be incorporated into their production. Our objectives were:

In response to problems with off-target movement and injury associated with dicamba applications on dicamba-resistant (Xtend) soybean, the EPA made significant changes to labels of the new dicamba products.  While much of the discussion has focused on the Restricted Use designation and the requirement for applicators to receive dicamba-specific training, the EPA also clarified how downwind buffers and protections of susceptible crops are to be implemented.

In October 2017, the Environmental Protection Agency reclassified Engenia®, FeXapan™ herbicide Plus VaporGrip® Technology, and Xtendimax® With VaporGrip® Technology as Restricted Use products and added additional restrictions and requirements to their use. One of the additional requirements stated that anyone wishing to apply these products must attend a dicamba or auxin-specific training. Recently, the Iowa Department of Agriculture and Land Stewardship issued Sec. 24(c) Special Local Need labels for Engenia®, FeXapan™ herbicide Plus VaporGrip® Technology, and Xtendimax® With VaporGrip® Technology.

Marestail (Conyza canadensis) is one of the most difficult weeds to manage in no-till soybean.  While classified as a winter annual, the plant has significant emergence in both late summer/early fall and in the spring.  This extended emergence period greatly complicates management since the success of postemergence products is closely tied to plant size.  Attempting to control populations at the time of planting often results in control failures as fall-emerged plants are too large for acceptable control.

Soybean farmers have kept the soybean cyst nematode (SCN) “in check” for decades simply by growing SCN-resistant soybean varieties. Unfortunately, prolonged use of varieties with SCN resistance genes from a breeding line called PI 88788 has resulted in SCN populations building up increased reproduction on resistant varieties. Almost all (97%) soybean varieties available to grow in Iowa have SCN resistance genes from PI 88788. This situation has led to dramatic and often unnoticed increases in SCN numbers in fields.

Need to know specifics

Now more than ever, farmers need to know if their fields are infested with SCN and what the numbers are. The higher the number of SCN eggs in the soil, the greater the yield loss - even with resistant soybean varieties

When looking for soybean varieties, it is important to give as much thought to the process as you give to choosing corn hybrids. If you only choose one or two soybean varieties and do not take into consideration management and environmental factors of your operation, you are likely limiting yield potential.

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