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Targeting Weed Seed Destruction at Soybean Harvest

There has been considerable attention to and research with weed seed destruction methods at or immediately following soybean harvest, a technology known as Harvest Weed Seed Control (HWSC). Destroying weed seed at this time prevents them from entering the soil weed seedbank, and provides a potential non-chemical mechanism for control of herbicide-resistant (HR) weeds. The major tenets of this concept/practice are covered in a White Paper on this website.

The factors that will influence the potential success of HWSC methods are 1) the amount of seed retention by targeted weed plants at soybean harvest, and 2) the component of the harvest residue (straw or chaff) leaving the combine that contains the majority of the weed seeds. Information about these two components will determine the success of HWSC methods. Previous research has shown that several weed species such as Palmer amaranth do retain a large majority of their seed at soybean maturity. Thus, these seed are harvested with the mature soybean seed and will travel through the harvesting machine, potentially leaving the combine in the grain, straw, and chaff components. The weed seed that enter the grain bin with soybean seed will cause a decrease in harvested crop quality that leads to dockage at the elevator, but these weed seed are removed from the field and do not enter the soil weed seedbank. Conversely, those weed seed that leave the combine in the straw and chaff will enter the soil weed seedbank and be available for future germination and subsequent crop infestation.

For a mechanical method such as the integrated Harrington Seed Destructor (iHSD) to be effective at destroying weed seeds at harvest, it must be attached to the combine where it will encounter the residue component (straw or chaff) that contains the greatest amount of weed seed exiting the combine. Results from research conducted in Arkansas by Green, Norsworthy, and Walsh that are reported in an article titled “Distribution of Common Cocklebur and Palmer Amaranth Seed Exiting the Combine for Harvest Weed Seed Control in Soybean” (Crop, Forage, and Turfgrass Management–https://doi.org/10.1002/cft2.20064) address this issue. A summary of the research conduct and results follow.

•   The study was conducted for two years at the Univ. of Arkansas NE Res. and Ext. Center in Keiser, Arkansas (lat. 35°40').

•   The objective of the study was to determine where (grain, straw, or chaff) seed of Palmer amaranth (small-seeded) and common cocklebur (large-seeded) exit the combine during soybean harvest. Samples were collected from these three harvested components for analysis of their content of weed seed.

•   Averaged across years, the chaff component contained the majority (75% + 2.14%) of common cocklebur burs. The grain and straw fractions contained nearly equal amounts of burs (12 + 1.2% and 13 + 1.8%, respectively).

•   Across both years, the chaff component contained 85 + 3.7% of Palmer amaranth seed, while the straw and grain components contained 9 + 3.2% and 6 + 2.4%, respectively.

•   The above results, coupled with cited results from other studies, indicate that the majority of seed from both large- and small-seeded weeds will exit the combine in the chaff component of harvest residue.

•   These results indicate that targeting weed seed leaving the combine in the chaff component of harvest residue for destruction via HWSC methods such as the iHSD should have a profound impact on future weed management, and thus be of great value toward the control of HR weeds that have evolved resistance to previously efficacious herbicides.

The following articles on this website provide additional information about HWSC.

Harvest Weed Seed Control

Harvest Weed Seed Control–MSSOY White Paper

Soil Weed Seedbank–One Source of Weed Problems–MSSOY White Paper

Weed Seed Destruction in Soybean Harvest Residue

The preponderance of results from research in the cited/linked papers and articles is that HWSC can and likely should be incorporated into soybean weed management programs. This non-chemical technology appears to offer a path to reducing the viable seed of problematic HR weeds, and this should result in fewer weed plants that must be controlled in subsequent soybean crops.

Composed by Larry G. Heatherly, Oct. 2020, larryheatherly@bellsouth.net