Choose the right desiccant for the state of the oilseed rape crop, Agrovista agronomist Tim Bullock (pictured) told growers at the firm’s oilseed rape open day at Reading University Farm.

“You have three choices – if the crop is standing well and free from weeds then straight glyphosate does a good job. If it is upright but there are weeds that need controlling, such as sow thistles, then you’re better off using something like Thunderbolt, which contains a haulm desiccant.”

Containing pyraflufen-ethyl as well as glyphosate, it was more expensive than glyphosate, but gave quicker burn-down of weeds and would dry and desiccate the crop more quickly, he said.

The third situation was where the crop was laid or stems kinked. “If it is badly lodged glyphosate won’t translocate around the plant effectively so you need to use Reglone.”

Under sunny conditions Reglone (diquat) would desiccate crops in as little as three days, he said. But the downside to was the increased risk of pod shatter.

“It dries the crop out so much, and you don’t really get any pod sealing. I always suggest to growers they park the combine in the corner of the field when they spray with Reglone, so they’re ready to harvest as soon as it is ready.”

Adding an adjuvant, such as Companion Gold, could increase pod sealing, but it had more effect when used with glyphosate, he said. “We’ve seen 15% yield increases from reduced pod shatter when added to glyphosate.”

The product also helped reduce glyphosate lock-up in hard water and drift. That was particularly important when spraying near to Entry Level stewardship or cross-compliance strips, he stressed.

Timing, formulation and spray technique for desication success

Desiccating thick-stemmed plants in cool, overcast conditions with Roundup (glyphosate) relies on timing, using the right glyphosate formulation and appropriate spraying techniques, says Monsanto’s Manda Sansom.

“Crops must not be sprayed until average moisture content gets down to 30%. Going any earlier will not hasten ripening – in fact it can slow desiccation – especially if there is still plenty of moisture in the ground.”

This season’s variable crops will not make hitting that timing any easier, she points out. “It will be vital to sample a number of pods from different parts of the crop for the key green to brown seed colour change. Opening pods to inspect seed is essential since neither crop nor pod colour is an accurate indication of ripening.”

Glyphosate formulation is also important, she claims. In difficult weather, the waxy leaves of oilseed rape plants can prove a struggle for formulations with low surfactant and active ingredient loading.

“Specialist Roundup formulations are proven to perform 20-25% better under the sort of challenge oilseed rape crops can present. As a result desiccation is more thorough and reliable.”

Application techniques should also not be underestimated, she stresses. “Use 200-250 litres/ha of water to ensure good coverage and penetration of a thick canopy, and nozzles rated to produce a medium or coarse spray to minimise spray drift.”

A water conditioner is advisable in hard water areas to counter possible glyphosate lock-up, she adds, while the use of low drift nozzles or anti-drift agents can be valuable.

Roundup timing advice

1 Pick 20 pods randomly from middle of main stem

2 If two-thirds of seeds in at least 15 pods are changing from green to brown, the plant is at earliest correct stage for spraying

3 Repeat in other areas of field

4 If majority of crop at correct stage, spray within seven days