Choose a variety with appropriate vigour, get your seedbed preparation right and pay attention to achieving the right plant population if you’re drilling into September, says Sarah Hawthorne of DSV UK Ltd.
“It’s an over simplification to think just in terms of low and high vigour when it comes to how oilseed rape grows, particularly with regard to how it responds to potentially low soil temperatures and heat units when growing later in the season,” she points out.
“Hybrids generally have better early vigour but they’re not all the same.
“The ideal variety for later sowing is one that shows a very strong early response to soil moisture and temperature and grows vigorously for the first 30 days, then vigour flattens to a lower threshold of growth before dropping down significantly for the Winter.
“Oilseed rape grows from its roots rather than its leaves and the tap root’s development in the first 30 days is critical and actually dictates the crop’s final yield potential.
“Unchecked early growth of roots is essential so the plant establishes rapidly and the leaves develop before it then hunkers down for the Winter.”
With lower temperatures and the change in daylight length stimulating growth hormones less when drilling later, this ‘quick, flat, slow’ profile is key. Hybrids like DSV Duplo and DSV Dolphin are specifically developed to achieve this, she says.
“DSV Duplo shows particularly rapid establishment even in very late drilled situations with a growth habit that keeps cotyledons close to the ground and a rapid increase in leaf area and ground cover before effectively ‘switching off’.
“DSV Dolphin is another high yielding variety with very similar vigour and early growth properties but with the added benefit of DSV’s new PowerfulPods technology to minimise seed loss later in the season and at harvest.
“Strong early growth is particularly important in September drilling as poor root development will reduce yields and plants that don’t establish quickly are susceptible to pest attack.
“Good ground cover deters pigeons from landing and early vigour helps the plant grow through attack by pests including slugs. But too much subsequent growth allows the pests back in and gives problems with crops being too forward through the winter.
“In fact, a lot of the problems with some well known varieties lodging in recent years have been down to their genetics causing them to actually grow too much and develop weak stems so they can not support the quickly developing canopies in the Spring.”
Cultivations for later drilled crops should be focused on helping the tap root develop to its optimum potential and to allow free drainage, Sarah Hawthorne adds.
“Cold, waterlogged and compacted soils are where the potential problems lie with late drilling so you’ve got to take all precautions to avoid this – soil temperature has more of an influence on seed establishment than air temperature.
“If you’re direct drilling, make sure you use a subsoiler to break any pans and choose your fields carefully. Straw, trash levels and soil type are critical factors in these decisions.”
“Rhizotrons developed by DSV to study how cultivation method affects root growth show a consistent 50 - 60% increase in root mass in open, free draining soils compared to heavier or compacted soils.
“Around 15% more root growth is seen in hybrids in the first 30 days compared to conventional varieties.
Plant population is key and seed rates should be geared to achieving around 25 -35 plants per square metre for over-wintering, she stresses.
“ADAS trials have shown late drilled crops with 25 plants per square metre yield bettter than crops sown at higher densities. This holds true even if the plant has just 3 - 4 true leaves through the winter.
“Oilseed rape is generally tough and a good hybrid will only really be unable to compensate if it is very patchy and plant numbers drop to less than about 5 -10 plants per square metre. Conventionals, however, generally reduce from about 20 plants per square metre.
“In many ways you’re better off planting rape later, but a lot of people are very worried this year because of last season. In truth, it’s field conditions and variety choice that are more important than the actual date.”
"Follow the basics and your late-drilled crop of DSV Duplo or DSV Dolphin will soon catch up with other earlier drilled varieties and go on to produce strong, well-structured plants in the spring with a very high yield potential."