Crop growers loathe pigweed because its biology and resistance to herbicides render it extremely difficult to control. With the appearance first identified in South Africa in 2018, this well-known weed has a negative impact on regional food production.
Ingrid Boshoff, technical lead of herbicides at Syngenta South Africa, explains how early, quick, and effective action may be performed in order to control and remove this weed.
What is pigweed?
Amaranthus palmeri is an aggressive competitor that grows fast and propagates extremely effectively. The weed is dioecious, with separate male and female plants. Under favourable growing conditions, it can maintain a growth rate of up to 6cm per day, and it is possible for a single female plant to produce up to 600 000 tiny, easily dispersible seeds. The weed can also reproduce vegetatively through regrowth from stalks left behind in fields.
“Palmar amaranth or amaranthus palmeri is a type of pigweed that is rapidly spreading throughout the world. Since its establishment in the USA, it has become our country’s most troublesome weed. The reason why it is so problematic is because it’s become very difficult to control,” explains Boshoff.
“Not only is palmar amaranth very good at spreading and establishing itself but it has an incredible ability to develop resistance. Worldwide it has developed herbicide resistance to more herbicide groups than any other weed.”
Impact on crops
According to a study on herbicides that was done in South Africa in 2022, nine of the 17 herbicide groups were confirmed internationally. In South Africa, resistance to two groups out of the 17 groups was reported.
“An academic paper was published last year about the South African population in Douglas and it confirmed resistance within these two groups or modes of action. Group 2 is the acetolactate synthase (ALS) inhibitor and contains a multitude of commonly used herbicide actives.
In this episode, Boshoff also discusses:
- How to identify pigweed among crops;
- Steps to successfully control weeds; and
- Advice to farmers.
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