Herbicide resistance - Don’t wear out a single solution, mix it up!
Herbicide resistance is a challenge no farm advisor or grower can afford to ignore. The cost of resistance is well documented globally impacting not only on crop output but also reducing rotational choice, income and asset value. In New Zealand since 1979 twenty different weed species have developed resistance to one or multiple herbicide mode of action groups including glyphosate1, perhaps our most commonly used herbicide. While on a global scale this number is low (compared to 161 in the United States, 91 in Australia and 27 in the United Kingdom1), it also highlights that it is not too late for us to modify our weed management practices to maintain farming viability by ensuring essential herbicides such as glyphosate remain effective for longer. So how do we achieve this, well we simply mix it up, ensuring our weed control strategies are diverse and incorporate non-chemical as well as chemical control tools without reliance on any single solution.
Crop rotation broadens your herbicide control options, and this is just one example of non-chemical weed control. Other non-chemical measures you can use to reduce the impact of weeds include; increasing your seeding rates to increase crop competition, especially with cereals; not over grazing to ensure you maintain highly productive and competitive pastures; spray topping to reduce weed seed set in pastures the year prior to cropping and cultivation to deeply bury weed seeds prior to planting.
With herbicides it is important to not only use them at full label rates but to also ensure you rotate between herbicide mode of action groups and not just herbicide brand names (Fact: New Zealand has 90 glyphosate brands registered2 to 22 importers and they all belong to the same herbicide mode of action – Group G). To improve control and reduce weed escapes always target young, actively growing weeds. Make sure the correct adjuvants are used. When applying a knockdown herbicide always look to reducing weed resistance selection pressure by tank-mixing it with another herbicide. The ideal partner is one that not only represents a different mode of action but is also effective in its own right against target weeds. For me this is Sharpen®, it is fast-acting, broad-spectrum herbicide and being the only systemic Group E herbicide (this group includes carfentrazone) when applied in combination with glyphosate the tank-mix results in far less regrowth, across more weed species, than the alternatives.
While the development of resistance can’t be totally prevented or reversed, it can be forestalled, and its impact managed if we all take action now and incorporate the “mix it up” philosophy into our weed control strategies.
Source: 1. www.weedscience.org 2. ACVM Register