Crop Watch: Pest threat warning for oilseed rape

Our Crop Watch team have swung back into action to deal with the fallout from this season’s harvest and tackle the problems growers are facing across the country as the cutting begins to give way to planting.

Patrick Stephenson says that growers in the North would do well not to heed the advice of drilling as late as those further south, as their drilling window is much shorter.

Growers in the West with their eye on bumper maize crops need to cultivate afterwards to prevent soil erosion if not planting another crop this season, warns Giles Simpson.

Most of next season’s oilseed rape crop has been drilled already, but if you are planning to establish on the late, Kevin Knight has some top tips on getting plants out of the traps quickly.

See also: Video: Advice on autumn establishment and weed control

Those who already have rapeseed crops emerged need to keep a sharp eye out for turnip sawfly larvae, says Marcus Mann, as they need to be dealt with rapidly if present in large numbers.

North: Patrick Stephenson

Patrick Stephenson

Patrick Stephenson

AICC (Yorkshire)

Weed control in rape crops has changed considerably in recent years with many growers now using very early post-emergence applications for broad leaf weed control.

It is vital that this is carried out before the weeds get too big. Application of herbicides for broad-leaved weed control must be applied when rape plants are at early cotyledon stage to ensure good levels of activity.

I am very conscious that in the North of England we have a relatively short drilling window. Delaying drilling to late September is a “Fool’s Goal”, although I know the wise sages of blackgrass control will deride us for this practice.

Unfortunately, our experience is that crops drilled in October establish poorly, suffer greater herbicide damage and increase our blackgrass burden; it is far better to alter the rotation than try to drill in October.

Excuses out of the way and I can say that drilling of first wheat is well under way. All crops will be targeted with a range of pre-emergence herbicides based around flufenacet.

Seed-beds are good and moisture is plentiful, so control we hope will match last year’s excellent results.

Rotations under scrutiny

Second wheats have come under severe scrutiny for their below par performance. They will get drilled last and will receive latitude seed dressing in an attempt to minimise the impact of take-all.

As you read this, winter barley drilling will have commenced and a robust pre-emergence herbicide programme is essential for this crop, as the post-emergence grass weed control product is very limited.

Changes in the Greening requirements added to the problems of weed control, combined with harvest date and handling will all reduce the overall area of pulses.

On a positive note, the winter beans that have been harvested so far have produced good yields. In my experience, we can get better blackgrass control in winter beans than in either oilseed rape or spring beans. As a consequence, we will keep some beans in the rotation.

West: Giles Simpson

Giles-Simpson

Giles Simpson

Pearce Seeds (Somerset)

What started as a promising early harvest, turned out to be a very difficult wet one, with a lot of crop still left to cut.

The oilseed rape that has been drilled has germinated well; most crops have not suffered from flea beetle as we think they have probably been drowned.

Slugs, however, have been a problem but have been controlled by low dose rates of metaldehyde and Sluxx (ferric phosphate).

Under the new metaldehyde stewardship guidelines, we are using ferric phosphate on all headlands.

The pre-emergence sprays have all been applied and we are now spraying for volunteers and flea beetle.

There have been some crops not drilled due to the wheat and straw not cleared quick enough to get the rape in. These fields are now going to be drilled with winter barley, so they can go into oilseed rape next year.

Bumper maize harvest predicted

The maize harvest has just started in the early maturing varieties. Yields are going to be very good, with most crops looking to yield the highest they have for a number of years.

There is a little eyespot appearing in crops now, but only certain varieties. The early harvest that we were all expecting has been delayed due to the inclement weather in August; a nice dry period now is what we all need.

Some of the later maturing varieties are still two to three weeks away from harvest. Most fields are destined for another crop after the maize has been harvested but the ones that aren’t need to be cultivated in some form to prevent soil erosion.

The grass reseeds that have been drilled have emerged quickly and evenly along with the weeds. These are now being sprayed out; slugs have only been a problem where grass has followed grass.

It’s too early to say if frit fly or leather jackets are going to be a problem; let’s hope not as we have no chemical control available now.

South: Kevin Knight

Kevin Knight

Kevin Knight

Zantra (Kent)

Last year good yields came from the later established rape, but September was warmer, so with soil temperatures around 4C lower this year, if you are still drilling rape make sure it gets the best start possible.

Create a fine, consolidated seed-bed, roll as soon as you’ve drilled and make sure the emerging crop has adequate nutrition.

Autumn sulphur will ensure that applied nitrogen is effective, improving early growth and final yield. Follow this with a multi-nutrient foliar feed at two to three leaves to give the crop a boost.

Take out volunteers early if they’re competing with the crop and monitor slug populations before cereal drilling – applying pellets if needed.

Remember to follow metaldehyde stewardship guidelines, ensuring that no pellets fall within a minimum of 10m from any field boundary or watercourse using ferric phosphate over this area.

Frankly, it’s my “pellet of choice” due to its persistence. Emerging crops may need a top up six to 10 days after emergence.

Re-registrations of familiar insecticides have resulted in tighter restrictions such as arthropod buffer zones; check the label closely as width can vary between crops.

Big blackgrass flush

In spite of forecasts of high dormancy in seed shed this summer, I’m seeing a much bigger early blackgrass flush than last year.

I’m just pleased to get the chance to take out a more significant chunk of the population before drilling – who knows, we may get a chance for another stale seed-bed flush yet.

Grassland weeds are particularly susceptible to herbicides at this time of year as they take nutrients down to the roots and the actives along with them.

With the revocation of flupyrsulfuron products (Lexus, Excalibur etc) it leaves me wondering whether we’ll have anything effective to use for oat weed control next autumn other than stale seed-beds.

East: Marcus Mann

Marcus-Mann

Marcus Mann

Frontier (Essex)

After a rather slow wet harvest, the new cropping year began with winter oilseed rape being drilled during August.

Overall establishment has been very good and the early drilled crops certainly had ideal conditions with moisture and warmth, with early nitrogen helping give crops large cotyledons and sufficient vigour to overcome flea beetle damage.

One pest which does appear to still be causing a problem this year is the turnip sawfly, with adults being seen in large swarms.

The adult causes no harm. It is the larvae that will hatch within a week that cause damage. If the adults are spotted, keep a close watch for emerging black caterpillars because in high numbers they can very quickly strip the leaves.

Blackgrass has emerged within the winter oilseed rape, which makes the timing of the early herbicides important.

If using clethodim, make sure the blackgrass is large enough to take up a large dose to be toxic and add a water conditioner. The efficacy has certainly improved when adding a water conditioner to prevent the lock up to cations in harder water.

Integrated drilling strategy essential

Winter cereal drilling will soon be upon us and on lighter soils has already begun. It is now understood that a fully integrated strategy is the approach for controlling grassweeds.

Ensuring the residuals are applied to good seed-bed conditions as well as using angled nozzles and higher water volumes to encourage better coverage remains an essential part of getting the most from the pre-emergence stack.

Flufenacet remains the base on which to develop the programme. A minimum of 240g/ha pre-emergence is required for “difficult” grass weed situations, followed by a decision as to if or when to top the rate up to 360g/ha.

Again this will be decided on conditions at time of drilling. Tri-allate helps the efficacy of the flufenacet base in difficult blackgrass regions.

A similar approach to blackgrass control is required for the control of ryegrass. However the addition of prosulfocarb, flurtamone and picolinafen has added greater efficacy.

Ryegrass is much more predictable in its emergence timing, making late winter cropping more effective than spring cropping.