Farmers urged to join the fight against pigweed

The Palmer amaranth ( Amaranthus palmeri), commonly known as pigweed, is making serious inroads into South Africa’s croplands, Ingrid Boshoff, Syngenta’s technical lead for herbicides, has warned.

“This weed was first identified in the Douglas region of the Northern Cape in 2019,” Boshoff told Farmer’s Weekly. “In 2020, it was also identified in the Limpopo Valley near Pafuri and Mapungubwe, as well as near Howick in KwaZulu-Natal. Most recently, it was identified near Potchefstroom, North West.”

Boshoff said that pigweed was a serious concern for crop farmers and a great challenge to manage effectively. “Of even greater concern with Palmer amaranth is the fact that it quickly becomes resistant to herbicides, particularly glyphosate.

“Over a prolonged period, this weed could make it impossible to farm certain crops, while farming crops such as maize will become very complicated.”

According to the US Department of Agriculture, this type of pigweed had been found to cause yield losses of up to 91% in maize and 79% in soya bean. Farmers therefore needed to be proactive in identifying and managing it.

“Palmer amaranth is the number-one weed in the US, and that country is still struggling to control it effectively,” Boshoff said. “We don’t know how it came to South Africa, but currently that shouldn’t be our top priority. We need to learn from the US’s mistakes. They have very few pesticides left that are still effective against this weed.”

Boshoff said the most important lesson to learn was to protect South Africa’s herbicides, and ensure that resistant populations did not get out of hand.

“Farmers should prevent a pigweed plant from shedding seeds. A single female plant can produce up to 600 000 seeds, which makes this a huge distribution risk.”

Boshoff encouraged farmers to sanitise all implements, equipment, clothing and shoes to ensure that the spreading of the plants was kept to a minimum.

Producers were also advised to follow a proper herbicide programme to protect their crops.

“We advise farmers to practise deep tillage where infestations are found.”

All plants had to be uprooted and destroyed by burning them, Boshoff said.

Despite fears about their farms being placed under quarantine, it was crucial for farmers to seek help as soon as they discovered plants that might be Palmer amaranth, she stressed. – Susan Marais

SYNGENTA The leaf stem of Palmer amaranth ( Amaranthus palmeri) is larger than the leaf blade. Hairs can be seen at the ends of the leaves.