Farmer Forum Recap: How to Optimize Threshing Settings for Harvest Weed Seed Control

In GROW’s fourth Farmer Forum of the season, Australian combine experts took a deep dive into combine settings for threshing and separating grain. 

Why? When a seed impact mill (also known as a weed seed destructor) such as the integrated Harrington Seed Destructor (iHSD) or Redekop Seed Control Unit (SCU) is added to a combine, a lot changes.

Chaff that previously flew easily out of the back of the combine is now funneled into a mill unit that is attempting to grind it all up. Making sure a combine is threshing grain as efficiently as possible becomes more important than ever, to avoid overloading a combine’s sieves and ultimately, the weed seed destructor, with too much chaff residue. 

In this Forum, American farmers shared their 2022 harvest experience with weed seed destructors in corn, soybeans, rice and even sunflowers, before Australian presenters discussed how to adjust their combine threshing and separator settings to minimize overloaded sieves and clogged seed impact mills, while also optimizing weed seed destruction. 

Here is a breakdown of the video’s content:

00:00:00 – Start
00:00:40 – Introduction of Australian presenters
00:01:50 – Michael Flessner shares Virginia operation Shockley Farms’ experience with Redekop SCU in soybeans, wheat and corn harvests
00:06:05 – Virginia farmer Kenton Moyer shares experience with iHSD in corn and soybean harvest
00:11:28 – Sarah Chu shares Texas operation Wiese Brothers Farm’s experience with iHSD in rice harvest
00:16:01 – Texas farmer Rodney Schronk shares experience with iHSD in wheat, corn and sunflower harvests
00:20:16 – Introduction by Peter Broley on terminology & purpose of this Forum
00:22:28 – Introduction of this Forum’s topic: Threshing & Separation combine adjustments for optimized harvest weed seed control
00:24:25 – Brief recap of importance of header set-up to reduce weed and grain losses
00:26:26 – Begin discussion of combine grain threshing, sieve loading and air flow
00:35:13 – Why putting a seed impact mill on a combine requires learning about how a combine works internally
00:38:39 – Separator baffle angle and positioning
00:40:28 – Concave and rotor settings can optimize threshing and not overload sieves
00:50:28 – How to test and check thresher/separator settings and sieve loss in the field
00:56:28 – Specific concave and rotor modifications for better threshing and less rotor loss in cereals and soybeans
01:04:56 – Why lower rotor speed is better for grain threshing
01:11:09 – How volume of crop material affects air flow
01:15:11 – How to avoid sieve loading and blockages from green material

GROW’s Farmer Forum series is connecting harvest weed seed control experts from Australia and Canada with U.S. farmers who are working to adopt the technology – namely chaff lining and seed impact mills, also known as weed seed destructors. 

The next Farmer Forum is scheduled for November 29. For more details on how to attend that upcoming session, contact Emily Unglesbee at

Text by Emily Unglesbee, GROW; Video editing by Claudio Rubione, GROW.