Harvest Weed Seed Control (HWSC) is the practice of preventing weed seeds from entering the soil seed bank by mechanically collecting seeds encountered at harvest time.
Studies show that in many weed species a significant proportion of seeds are retained harvest time, in some species of weeds up to 90% of seeds pass through the combine harvester. HWSC targets those weed seeds in a way that allows them to be devitalised, rather than be spread across the field with harvest trash. So, depending species of weed plant targeted HWSC can have a significant impact on weed numbers in following years.Beyond the immediate benefit of reducing the number of weed seeds that enter the soil seed bank, the main benefit of HWSC is that weed plants encountered at harvest are more likely to have developed resistance to herbicide treatments. HWSC is non-selective to herbicide resistant weed populations, and so provides the farmer a broadscale means by which to control herbicide reistant weeds, or to control weeds without the use of herbicides in the case of organic farmers.
Another benefit of HWSC applies the addage "This years crop is next years weed.." Volunteer seeds are controlled with HWSC preventing, for example, round-up ready wheat from passing to the next crop in the farm's rotation, which needs selective treatment to eradicate.
To succed with HWSC the operation should maximise the opportunity to collect weed seeds during harvest. This can be done by:
Cutting low. This maximises the collection of mature weed plants and weed plant heads encountered standing in crops, therefore maximising the number of weed seeds collected by the combine harvester.
Combine Harvester Setup. Configure the harvester to ensure that weed seeds pass through the rotor and over the sieves to exit with the chaff.
Swathing (aka windrowing). This, like grain, holds weed plant heads above the ground on interlaced straw. Swathing can be done up to 3 weeks ahead of direct heading, so may be used to target weed seeds that would be otherwise shed before harvest.
There is an abundance of good material on the internet concerned with HWSC. For a detailed explaination of HWSC by highly regarded Australian experts, we recommend referring to Weedsmart as a starting point. Some of their latest YouTube publications are higlighted below: