Harvest weed seed control
by Dr. Charles Geddes
It is possible to reduce the number of weed seeds that hit the ground in a field using Harvest weed seed control (HWSC).
During harvest, most farmers set their combines to select for a clean grain sample and limit dockage due to the presence of weed seeds. This exclusion of weed seeds causes weed seed dispersal by the combine and ultimately additional weed seed inputs into the soil seedbank, contributing to weed management problems in subsequent years.
Harvest weed seed control aims to manage weed seeds during harvest as they are expelled from the back of the combine. It is effective only on the portion of weed seeds that enter the combine at harvest; meaning that weed species prone to seed shatter (like wild oat) can evade HWSC quite effectively. However, it could be very effective for weeds like kochia or green foxtail that tend to hold on to seed until later in the growing season.
HWSC came to Canada decades ago; however it’s seen limited adoption to date. Some of these weed management tools include narrow windrow burning, collecting chaff in chaff carts and removing it from the field or bailing straw and chaff resulting in complete removal of crop and weed biomass.
Limited options for management of herbicide-resistant weeds (like annual rye grass) in Australia created the need for HWSC adoption by many Australian farming operations and also the development of new, more sustainable, tools for it. Examples of these new tools include the Harrington Seed Destructor (HSD), Seed Terminator, or chaff decks. The HSD consists of a cage mill either pulled behind or integrated into the back of the combine that pulverizes weed seeds into a fine powder and then disperses the mixture back on to the field (for more information see: www.ihsd.com; a quick internet search for this machine can yield an abundance of valuable information).
Breanne Tidemann, a Research Scientist working with Agriculture and Agri-Food Canada in Lacombe, AB, began testing the HSD for weed control in western Canadian production systems. Preliminary results ( https://ahri.uwa.edu.au/spoiled-rotten-the-sequel/) look promising and indicate that the HSD can destroy between 95% and 99% of weed seeds that enter the machine during harvest. Seed size, seed species, crop (chaff) species, and chaff volume had minimal influence on the efficacy of the HSD. There are, however, some limitations to this weed management tool; the largest is the current price point (about $200,000 CAD). Recent integration of the HSD into the back of combines helped alleviate many of these limitations, making this tool a viable option for many farmers.
Overall, Australia has a high adoption rate of HWSC where about 43% of Australian growers use these weed management tools. Adoption in Canada could also increase soon as herbicide-resistance continues to threaten crop production systems. HWSC can be an effective tool for weed management and can help mitigate selection pressure for herbicide-resistance when it’s part of an integrated weed management program.