Many Southland and Otago farmers were sold the wrong seed and have inadvertently grown crops linked to the deaths of hundreds of dairy cows in 2014.
PGG Wrightson Seeds general manager New Zealand David Green said swedes sown two or three months ago, which had started to mature, were last week seen in a paddock in Southland and "we noticed that the bulb colour was, in fact, white as opposed to yellow''.
That prompted an investigation by the company that showed "we had made an error in our supply chain and the wrong line of seed had been processed''.
"Straight human error" led to 556 farmers with the wrong crops in the ground. Farmers who assumed they had bought a new seed variety, Hawkestone yellow-fleshed Cleancrop swede, were sold a white-fleshed swede, HT-S57, that was linked to dairy cows suffering from liver disease, photosensitivity and dying three winters ago.
The HT-S57 swede variety was discontinued last year.