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Weed Seed Destruction in Soybean Harvest Residue

Harvest weed seed control [HWSC] is a nonchemical weed control tool that is being considered and touted for control of problematic weeds is crops. The premise behind this concept is that a reduction in the number of viable weed seed that are harvested with the crop and returned to the field with the chaff will reduce the soil weed seedbank, thus significantly reducing the number of seed that will produce a new crop of weeds in a following crop. Click HWSC and soil weed seedbank for White Papers that discuss these weed seed control measures and how they might be used to combat problematic weeds, especially in the current environment of herbicide-resistant [HR] weeds.

One of the technologies discussed in the above HWSC article is the destruction of harvested weed seed by the Harrington Seed Destructor or HSD [Walsh et al., Crop Sci., Vol. 52, May-June 2012]. The original HSD was towed behind the combine, whereas the integrated Harrington Weed Seed Destructor [iHSD] is an adaptation of this unit that is integrated into the harvester. The premise behind the iHSD is that weed seed mixed with the chaff that comes out the rear of the combine can be physically altered so that they are no longer viable. Thus, they will not be available to replenish the soil weed seedbank.

Research results reported in an article titled “Efficacy of the Integrated Harrington Seed Destructor on Weeds of Soybean and Rice Production Systems in the Southern United States” [Crop Sci., Vol. 57, Sept.-Oct. 2017] provide support for the potential use of this machine as a useful tool for HWSC in the Midsouth. Details about and results from this research follow.

   The following premises guided the direction of the research. 1) HR weeds are becoming increasingly problematic in Midsouth crop production. 2) Reduction in the soil weed seedbank is deemed an important component of long-term weed management. 3) The soil weed seedbank allows for long-term persistence of weeds in crop fields. 4) Harvested weed seeds are mostly expelled from the rear of a combine harvester, and thus are dispersed across the field during crop harvesting. 5) Many weed species that escape in-season control measures retain a large percentage of their seed at time of crop harvest, and these mature seed will replenish the soil weed seedbank through dispersal from the combine harvester.

   The objective of the research was to determine the effectiveness of the iHSD in soybean and rice production systems for reducing the number of viable weed seeds that are returned to the field during crop harvesting.

   Three experiments were conducted using an iHSD mill and soybean harvest residues. 1) Efficacy of the iHSD was evaluated on seeds of 12 weed species (broadleaf and grass species varying in seed size, weight, and density) that are common in Midsouth soybean production systems by incorporating them into crop residue resulting from harvest. 2) Soybean harvest residue feeding rates were tested to determine their effect on the amount that could be processed without interfering with weed seed destruction [Palmer amaranth and morningglory species only]. 3) Soybean chaff moisture levels were varied to determine how high moisture content of chaff may affect iHSD effectiveness.

   Number of emerged seedlings expressed as a percentage of germination of seeds that were not processed by the iHSD was used to estimate seed mortality caused by the iHSD.

   Weed seed destruction ranged from 99.8% to 100% [except for common cocklebur which was 97.5%] in soybean residue. There was no significant difference in mortality among the 12 weed species tested.

   Destruction of Palmer amaranth and morningglory seeds was not significantly affected by the residue feeding rates used in the study.

   Residue moisture levels used in the study [8, 12, 16, 20, and 24%] did not significantly affect destruction of Palmer amaranth and morningglory weed seeds by the iHSD. However, the results from their experiments indicate that efficacy in a commercial application likely would decline or the equipment would not operate properly as a result of clogging when residue moisture content is ≥16%.

The authors concluded from the results of these studies that the iHSD has potential to improve weed management in Midsouth soybean production systems by destroying weed seeds at crop harvest, thereby reducing replenishment of the soil weed seedbank. However, they recognize that the iHSD should be further evaluated as a combine-fitted system that will be operated in commercial soybean production fields.

Composed by Larry G. Heatherly, Sept. 2017, larryheatherly@bellsouth.net