Western Australian research investigating whether it is economic to reseed a canola crop that has established poorly suggests that in many cases it might not be worthwhile.
Department of Agriculture and Food (DAFWA) researcher Mark Seymour said trial results showed that sticking with low plant numbers sown early appeared to be an acceptable approach.
“However, weeds could be a problem in canola crops that have low plant numbers as a result of poor crop establishment,” he said.
As part of the ‘Tactical break crop agronomy project’, funded by the Grains Research and Development Corporation (GRDC), Mr Seymour conducted trials last year aimed at determining the point at which reseeding a low density canola crop was worthwhile.
“Canola is often the first crop sown each autumn, but as the seed is small it is best suited to shallow seeding, making it susceptible to drying soil conditions,” he said.
“If growers don’t get a good break or follow-up rains they may have to consider reseeding two to three weeks later.
“The big question for growers is whether they should leave their low density crop – fewer than 10 plants per square metre – alone or reseed it.”
The trials assessed sowing canola before or at the break of the season at plant densities of five, 10, 15 and 30 plants per square metre, compared with plots resown at 30 plants/m² over the top of five and 10 plants/m² and plots sown normally (not resown) at later dates at five to 60 plants/m².
Mr Seymour said one of the trials saw the canola variety Pioneer 43Y23RR sown in the Northern Agricultural Region on April 29, with about 90 per cent of plants establishing.
The second time of sowing at this site was May 16 when conditions were drier and less favourable, resulting in about 40 per cent of plants establishing.
The resown plots involved the use of offset rows and seed was ‘tickled in’ to reduce damage to the earlier sown plants, with only 13 per cent of these plants establishing.
“As expected, the April sown plots out-yielded plots sown in May, at every comparable plant density,” Mr Seymour said.
“In addition, April plots that had only five to 10 plants/m² produced equal or higher yields than later sown plots at higher densities.
“It is often difficult to reseed without damaging the plants that are already established, which suggests that in many cases it may not be economically viable to reseed low density canola crops under these conditions.
“These results are consistent with previous trials over a number of years which have shown that canola produces 60 to 80 per cent of its maximum yield at about 5 plants/m² and 80 to 90 per cent at 10 plants/m².”
Mr Seymour said that while sticking with low plant numbers sown early appeared to be an acceptable approach, weed control could be compromised at these densities.
“In a plant density trial conducted by DAFWA at the Liebe Group trial site in 2013, we observed more annual ryegrass in triazine tolerant (TT) canola when the crop density was below 20 plants/m², but plant density had no effect on ryegrass numbers in the Roundup Ready® hybrid plots,” he said.
“This indicates that if you have a competitive variety such as a RR hybrid and effective herbicides such as glyphosate, low crop densities will be less of an issue than for less competitive crops such as TT canola combined with, in this instance at least, a less effective herbicide system.”
Caption: Trial results have provided information about whether it is worth reseeding canola that has established poorly, like this plot with fewer than 5 plants/m² (right) at Salmon Gums.
Mark Seymour, DAFWA
08 9083 1143
Natalie Lee, Cox Inall Communications
08 9864 2034, 0427 189 827
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