Canola Damage from Clethodim

Group A “dim” herbicides such as Clethodim have a narrow safety margin on canola, especially at higher rates and later application timings. Trials conducted in South Australia by Michael Zerner and Rob Wheeler from SARDI during 2013 at Hart and Yeelanna, showed interesting results in canola’s tolerance to Clethodim, especially at later application timings.

The trials showed that Clethodim applied at 0.5 L/ha and 1.0 L/ha to ATR Gem, AV Garnet and Hyola 474 CL at the 4-leaf stage, had no impact on the crop yield. However when applied at the 8-leaf stage, the 1.0 L/ha rate resulted in a 10 to 25% yield reduction with variation between varieties.

Later applications of both the 0.5 L/ha and 1.0 L/ha rates at bud initiation, caused significant yield loss up to 52%. AV Garnet appeared to suffer less yield loss at the differing rates and timings compared to the other two varieties.

Identifying crop growth stage is critical, so that Clethodim is applied at the correct time. Stressed plants may be at a more advanced growth stage than they visually appear and therefore more susceptible to herbicide damage.

Clethodim damaged plants are paler green in colour. Flower buds become distorted and club like, plus fail to open, leading to poor pod development and reduction in grain yield.

When applying Clethodim, it is important to identify the appropriate canola growth stage for the rate intended to be used. Plants should be actively growing and frosty conditions avoided, especially after application. A water rate of at least 70 L/ha with medium droplets should be used.

There is evidence to suggest that higher Clethodim rates give superior control of annual ryegrass. A compromise may need to be made when determining the Clethodim rate required, taking into account crop growth stage and other conditions (variety, weather), to minimise the risk of crop damage while achieving satisfactory weed control.