12 June 1998

Desiccation is best bet but

with what..?

How will you prepare oilseed

rape for harvest this year –

swath, spray or leave it to

ripen naturally? Conditions

suggest desiccation will be

worth the extra cost.

Charles Abel provides some

timely advice

WIDESPREAD lodging and vigorous weed growth mean most rape crops will benefit from desiccation this season, claims a Leics-based distributor agronomist. But care is needed to get the best from the products available.

Making the most of good crop potential drives that advice, not just the chance to sell product, stresses Graham Edwards of national input supplier Profarma.

"Growers have got crops this far and potential looks good, so it is daft to jeopardise yield by choosing the wrong management.

"I wouldnt rule out direct harvesting or swathing, but with so many crops lodged desiccation looks the best bet. There just isnt enough stalk under lodged crops to lay a swath on and expecting the weather to dry lodged crops unaided is unrealistic."

Heavy rain and snow in April lodged many crops. "And the 50mm of rain we had after the dry spell in May has lodged even more and sent those already lodged down further. Wet conditions are also favouring weeds."

But product choice and appropriate use is not simple. "Youve got to get into the crop and see how it looks to make the right choice."

Mr Edwards preferred option this year is diquat (as in Reglone) mainly for its vigorous crop desiccation. "For anything that is laid, uneven or weedy it will be the best choice."

Where lodging is limited, the crop is even and couch needs controlling, a glyphosate formulation such as Roundup Biactive may be more appropriate. "It also gives more harvest flexibility, reducing the risk of pod losses. But unless the crop is very even and not looking like the North Sea the Roundup route is not ideal."

If crops are lodged and contain a lot of broad-leaved weed, particularly cleavers, glufosinate-ammonium (Harvest) is suitable.

For each product timing must be spot on. "That means getting out into the crop and checking the colour of seed. It isnt enough to look at crop colour alone. Select pods from the mid section of the main raceme of representative plants across the field."

"For glyphosate seeds need to be turning from green to brown in two-thirds of the pods. There is a little leeway after that for spraying – about three to four days."

Harvest needs to go on when the majority of seeds are reddish to dark brown. Diquat spray timing is usually four to five days later, coinciding with 90% of seeds being reddish brown, with some black and none green, says Mr Edwards.

"If you apply Harvest or Roundup too early youre onto a loser straight away. It may kill weeds, but could fail to desiccate the crop properly. Look what happens to volunteer rape on sprayed set-aside. Its waxy bloom keeps the spray out and they dont die. You need the crop to be turning for best results." Adding 1 litre/ha of Ethokem can improve plant uptake.

For Harvest time of day is also crucial. "Sprays need to go on in the afternoon, when the crop has dried out. This is vital for good efficacy. You also need to use 3-400 litres/ha of water and a medium/fine spray."

In badly lodged crops there is a risk that desiccation with Roundup or Harvest may be impaired due to broken or severely bent stems, he adds. If Reglone goes on too late the risk of pod shatter increases, making harvest timing absolutely critical, adds Mr Edwards.

Rate reductions are not an option with Reglone or Harvest, he notes, both requiring 3 litres/ha, with 100ml Agral non-ionic wetter in 100 litres of water for Reglone.

For a less dense crop with couch control the main goal Roundups 4 litre/ha rate could be cut to 3 litres/ha. For an even crop with minor lodging 2 litres/ha with 1 litre/ha Ethokem could be adequate.

Compared with contract swathing at £30-31/ha (£12/acre) Roundup can be cheaper, costing £18/ha (£7/acre) for the 3 litre/ha rate. "But thats only an option if youre not worried about storm losses, the crop is even and not laid," notes Mr Edwards.

Reglone will cost £33/ha (£13/acre) plus application cost. "A contractor applying Reglone in 3-400 litres/ha of water could charge £10/ha, which puts the overall cost ahead of swathing. But youve got to do whats right for the crop, and the market could squeeze Reglone down to £29/ha anyway."

DESICCATION CHOICES

&#8226 Reglone for uneven, heavily lodged weedy crops.

&#8226 Harvest if crop laid and broad-leaved weed control needed.

&#8226 Roundup if even crop, slight lodging and couch a worry. Less risk of pod shatter.

APPROVED PRODUCTS

&#8226 Diquat: Barclay Desiquat, Landgold Diquat, Reglone, Standon Diquat.

&#8226 Glufosinate-ammonium: Harvest.

&#8226 Glyphosate: Alpha Glyphogan, Barclay Gallup, Barclay Garryowen, Glyper, Helosate, IT Glyphosate, Landgold Glyphosate, MON 240, Roundup, Roundup Biactive, Roundup Biactive Dry, Stacato, Standon Glyphosate 360, Stefes Glyphosate, Stefes Kickdown.

Widespread lodging and weed growth mean desiccation is likely to be the best pre-harvest treatment for this years rape crops, says Leics-based agronomist Graham Edwards.