Herbicide management in canola rotations

Careful planning of weed management is essential when introducing canola to a crop rotation system. Adama's Hardus van Vuuren spoke to Glenneis Kriel about achieving effective weed control and preventing herbicide-related crop damage.

- Glenneis Kriel

Canola has come a long way since it was first introduced as a rotation crop in winter cereal production systems in the 1990s.

Initially, it was primarily used to manage and reduce the risk of herbicide resistance by allowing farmers to use herbicides with different modes of action to those traditionally used on wheat, barley, and oats. Today, however, canola is seen as a commercially viable crop, with prices per ton being higher but yields per hectare lower than with wheat production.

While canola still assists in the management of herbicide resistance, careful planning is necessary to achieve good weed control and avoid plant-back constraints, which are defined by the minimum amount of time that must pass between applying a pesticide and planting another crop.

HERBICIDE MANAGEMENT

Hardus van Vuuren, marketing and technical manager for crop protection company Adama in the Western Cape, says herbicide options in canola are limited, raising the possibility of residual injury, especially on irrigation farms when farmers introduce canola to their rotation systems for the first time.

For instance, canola is highly sensitive to sulfonylureas, for which the withholding period can range from nine months to two years, depending on the product.

Using an acetolactate synthase (ALS) inhibitor (Group 2), such as a sulfonylurea, in a summer maize crop may constrain the follow-up winter canola crop, while using a herbicide-like clopyralid (Group 4) on canola may impact follow-up legumes.

For this reason, farmers should familiarise themselves with the chemical history of a field before deciding on which new crop to plant.