CANOLA growers buoyed by recent rain and thinking about whether to reseed a crop that has established poorly should carefully consider whether it is worth the cost.
Trials by the Department of Agriculture and Food, funded by the Grains Research and Development Corporation, have shown the number of plants per square metre was critical to making a decision about such an investment.
Department senior research officer Mark Seymour said the research had shown there were little yield gains to be made from reseeding a crop if there were more than seven to 10 plants per square metre.
"Canola has an amazing ability to bounce back and branch from the bottom of the plant," Mr Seymour said.
"The results showed that crops with 7-10 plants/m2 can still achieve 60-80 per cent of their potential yield, while crops with 10-15 plants/m2 will yield 80-90pc.
"Taking into account the cost of the seed - more than $40 per kilogram for some hybrid varieties - growers may not get enough of a yield boost to recover the cost of reseeding."
The research also showed there was a risk of damaging existing plants, which could compromise yields.
"Sometimes it's an easy decision to reseed - like a crop that has established so poorly there are large bare areas that need ground cover - but it's the paddocks where you 'umm and ahh' about the decision where not doing anything may pay off," Mr Seymour said.
While low plant density may not have a large effect on yield, it is likely to compromise weed control.
For growers with low plant densities of less than 10 plants/m2, Mr Seymour said to consider the weed burden and herbicide system carefully before investing in more seed.
"Growers who have sown Roundup Ready hybrids into paddocks with low weed competition would be likely to achieve a more positive response than other growers who have sown varieties with a less effective herbicide system," Mr Seymour said.
"Low plant densities also tend to be associated with a patchy crop establishment so for growers in this situation, particularly in low rainfall areas, the decision will be easy - it's not worth the investment."
p For information about reseeding canola visit www.agric.wa.gov.au and search for canola agronomy trials.