Managing A Challenging Rape Harvest

July 11, 2004 - Only a handful of the rape crops for which ProCam technical agronomist, Nick Myers is responsible are uniform this season, with many fields having flowered over at least a month if not two.

On top of this, he sees poor establishment and a relatively greater contribution from pods on the side-stems in many crops exacerbating in-crop maturity variations. And where establishment was good last winter, significant leaning and lodging in higher biomass varieties are presenting a further harvesting challenge.

"All in all, after several years of relatively easy OSR harvests, I’m convinced rape growers could be in for some serious difficulties this time around," he stressed. "They will have to manage their harvesting very carefully, indeed, if they are to avoid problems."

Swathing timing trials show harvesting oilseed rape crops when the pods aren’t sufficiently ripe reduces yields by 20-25% and oil contents by 5-10% while increasing glucosinolate levels by as much as 25%. Equally, harvesting too late can reduce yields by 10-15% primarily through pod shatter.

Extra moisture in the stem when cutting too early further means crops take longer to dry and, if harvesting is not sufficiently delayed, are slow and difficult to combine with less efficient grain separation.

"I’m really worried about swathing all but our most even crops this year," said Nick Myers. "Uneven crops dry very unevenly in the swath, and this will make really make timely and efficient combining difficult.

"The scale of the current crop variation will prove a challenge for desiccation, but I see it as far the most reliable option for all crops that aren’t too tall for direct combining."

At Masstock Arable, Clare Bend has seen every bit as much variation in this year’s crop and is equally in favour of desiccation wherever possible to even it out for the most efficient and timely harvesting.

"Pods at very different stages of ripeness mean Roundup has a greater edge over diquat than usual because it minimises shatter," she observed. "Which means you can afford to hold-off combining longer to allow the greener part of the crop to catch-up. Its systemic action is also better at coping with thicker areas of crop than the contact herbicide.

"With considerable weed growth in many crops adding to the desiccation challenge, I’d consider using Roundup Max at the higher 2 kg/ha rate this season in some cases, with Katalyst at 0.1% of the water volume; especially so in hard water areas and where the greatest speed of action is important.

"We employ a good Caramba regime to avoid forward crops leaning or lodging. But if there are a number of thicker or leaning areas, I’d use 250 litres/ha of water rather than the standard 100 litres for maximum coverage and penetration," she added. "And I’d be very careful to get both spraying and harvesting timings right."

Clare Bend stresses that the crop variation will make sampling pods from several areas of the field to check for overall ripeness to the standard Roundup protocol (panel) especially important this year.

She recommends spraying in the morning to ensure the best possible translocation within the plant. While pointing out that Roundup Max will achieve good desiccation in 12-18 days under normal conditions, she insists that crops should only be combined when inspection shows them to be ready.

"Particularly variable crops may need 21days or more before combining to give the less mature pods and greener stems a chance to catch-up," she noted. "This will be more likely with cool, overcast or unsettled weather."

Nick Myers agrees that successful harvesting this season will depend on using the right desiccant at the right rate and water volume and with the right timing. He too advises higher rates of water use to tackle areas of thick or leaning crop, and a good three week spraying to harvesting interval unless the weather is very hot and dry.

"Where crops have areas of different maturity that can be conveniently separated, a more flexible approach to desiccation and combining could be considered," he suggested.

"Leave the forward area of the field to ripen naturally and only desiccate the rest; desiccate the backward area a week ahead of the rest; or desiccate the whole field at the same time and delay the combining the backward area.

"This could mean a lot more hassle. But if it saves yield, quality and combining problems it could well prove very worthwhile."

Panel

Roundup Desiccation Timing Check

1. Pick a total of 20 pods at random from the middle of the main stem of a plant in the middle of the crop.
2. If at least two thirds of the seeds in at least 15 of these pods are brown rather than green, the crop it at its earliest correct stage for spraying.
3. Repeat this process in other areas of the crop to check the assessment applies across the field.
4. If the majority of the crop has reached the correct stage, spray within four days. If there is any doubt, wait and check again four days later.