Herbicide Resistance – Why Mechanical Weed Seed Control Becomes More Important

Herbicide resistance has become one of the most serious problems facing farmers across the globe. The evolution of resistant weeds is causing significant economic losses from reduced yield, crop quality and ineffective herbicides applications. In addition, the risk of losing effective weed management tools, like herbicides has farmers looking for new ways to manage weed resistance.

The keys to reducing the impact of herbicide resistant weeds are preventing their entry to new farms and fields, early detection, weed seed management and integrating more diverse management strategies to target weeds from multiple angles.

Conventional weed control (herbicide application, tillage, burning, etc.) remains an effective approach to weed control, but as herbicide resistant weeds spread and become more persistent, taking an integrated pest management by incorporating a combination of cultural, mechanical, biological, and chemical control measures is essential.

Enter Harvest Weed Seed Control (HWSC), a powerful non-herbicide weed control tool to tackle herbicide resistance. Also known as a form of mechanical weed seed control, HWSC is an excellent way to stop weeds in their tracks by collecting weed seeds at harvest and destroying them altogether. This reduces the spread of weed seeds (especially resistant weed species) and prevents them from residing in the soil weed seed bank, providing farmers with a clean weed-free seedbed the following season.

Benefits of Harvest Weed Seed Control

With a variety of mechanical weed control and weed seed management methods to choose from, the most effective, cost efficient and easy to manage is a weed seed impact mill.

Impact mills pulverise the entire chaff fraction, destroying the weed seeds that enter the mill. Simply adding an impact mill, like Redekop’s Seed Control Unit (SCU) can help farmers destroy up to 98% of harvestable weeds in a single pass operation at harvest.

Research has proven that a seed is no longer viable if is hit at least four times at a high enough velocity. The seed does not have to be crushed, sheared or ground up to be devitalized, which is why impact mills like the Redekop SCU are designed to provide that impact to weed seeds that pass through the combine.

Mechanical weed control works best on weeds that effectively retain most of their seeds until the crop is ready for harvest.¹ This makes HWSC an excellent management tool for common herbicide-resistant weeds like annual ryegrass, Palmer amaranth, waterhemp and wild oat.

Reducing weed seed bank deposits (dormant or actively growing weed seeds in the soil) to the soil by devitalizing seeds at harvest ultimately decreases weed pressure in future crops and sets the field up for success with a clean seedbed. Starting with a clean field means crops won’t have to fight for nutrients, moisture or sunlight, providing a better plant establishment that can help crops reach their yield potential.

Mechanical weed control pays off

According to weedscience.org, there are currently 530 herbicide-resistant weed biotypes around the world, weeds have evolved resistance to 21 of the 31 known herbicide sites of action and to 168 different herbicides. Herbicide resistant weeds have been reported in 100 crops in 72 countries.

The cost of managing these weeds adds up year after year as herbicide resistance spreads. In Australia, herbicide-resistant weed populations are increasing costs by about 27 percent per acre² because of increased herbicide resistance management costs and yield loss. In the US, growers are paying up to $150/acre for hand weeding where no control options exist. And in Canada, it’s estimated that herbicide resistance costs growers $1.1 to $1.5 billion annually due to increased herbicide use and decreased yield and quality.³

One of the greatest benefits mechanical weed seed control offers farmers is minimal investment required when compared to the cost savings that can add up from reduced reliance on other weed control options like fewer sprayer passes, labour, equipment depreciation and fuel.

When it comes to investing in an impact mill, the Redekop SCU’s unique design provides combines with a flexible and cost-efficient solution. Fully integrated into the combine residue, drive and display system, its optimized design is easy and safe to use, with low power requirements and running costs, and excellent residue distribution over the whole cutting width. Adding an impact mill to a farm’s integrated weed management system offers another strategy for controlling the toughest weeds.

Mechanical weed control not only saves dollars, but it makes sense when it comes to environmental stewardship. Integrating HWSC to effectively manage and reduce the emergence of herbicide resistant weeds will reduce overall herbicide applications and fuel consumption necessary for applications while ensuring sustainable crop production for the future.

Problem weeds

Using HWSC to manage these problem and herbicide resistant weeds can be effective for weed seed management – destroying weed seeds at harvest and preventing them from overwintering in weed seedbanks. Here’s a look at common, problem herbicide resistant weeds in North America.

Barnyard grass is one of the most successful weeds globally and the reports of herbicide resistance continues to increase, especially across the U.S. This problem weed easily adapts to a broad range of climates and has developed a hardy seed dormancy.

Herbicide-resistant kochia is one of the largest weed threats to crop production in Western Canada. An annual broadleaf noxious weed, kochia is difficult to control due to its ability to spread quickly and to thrive in challenging conditions such as heat, drought and high-saline soils. Kochia is also known to be resistant to multiple modes of action, or chemical groups.

Herbicide-resistant wild oats are a serious problem and resistance is on the rise in Western Canada. Wild oats can cause severe yield losses, increased dockage, cleaning costs, and lower grade and quality. Wild oats are also developing multiple resistance to chemistry groups, leaving growers with very limited herbicide control alternatives.

Herbicide-tolerant volunteer canola is a common problem in Western Canada, causing management problems in following growing seasons if the volunteers are resistant to the same herbicide being used in that crop. Herbicide-tolerant volunteer corn, soybeans and wheat are also common across North America.

Herbicide-tolerant volunteer weeds are derived from the seed of previous crops, and when those crops include herbicide-tolerant traits, the resulting volunteer weeds require management to prevent continued reproduction as they will threaten crop yield and quality if left uncontrolled.

Ryegrass is one of the most successful weed species in terms of herbicide resistance evolution and is known to exhibit resistance to multiple modes of action. Herbicide-resistant ryegrass is a serious problem for U.S. farmers, and those around the world. HWSC is proving to be a new solution to control ryegrass and reduce ryegrass seedbanks in many countries, including Australia.

Waterhemp is not only a prolific weed, with female plants producing more than one million seeds, but is also a serious herbicide-resistant weed for farmers across North America. Reported cases of single and multiple-herbicide resistance means this problem weed is getting harder to control. Prevention is key to managing waterhemp, making a clean seedbed and weed-free seedbank essential.

Integrated Pest Management

Integrating HWSC can significantly reduce weed pressure and offers another effective tool for managing herbicide resistant weeds. Impact mills offer mechanical weed control without tillage that fits well with organic and conventional farm practices.

An Integrated Management Approach, like adding a Redekop SCU to a combine can help farmers incorporate pre-emergent weed control, and repeated use of the SCU on a field over multiple harvests will have a significant impact on the size of a weed seedbank. Farmers can expect to reduce their reliance on other weed control options while saving time and money.

Learn more about how to integrate HWSC and the Redekop SCU to manage resistant weeds here.

¹Beckie, 2019 (https://www.researchgate.net/publication/333683956_Herbicide_Resistance_Management_Recent_Developments_and_Trends)

²Grains Development Research Corporation (2014 ‒ 2015).

³manageresistancenow.ca/weeds/