Crop Watch: Oilseed rape crops struggle after larval damage

Oilseed rape looks like being the problem crop to manage this spring with many fields badly damaged by cabbage stem flea beetle larvae and agronomists scratching their heads about how to manage  patchy fields.

There is growing concern that these larval attack will lead to a long and protracted flowering which may heighten the risk of sclerotinia disease attacks and lead to disappointing harvested yields.

Winter wheat crops are approaching the T1 fungicide timing with leaf threes being frustratingly slow to emerge while is some concern about the gap between T1 and T2 sprays being stretched.

South

Iain Richards

Agrii (Oxfordshire)

Iain Richards

Iain Richards

Much-needed rain in the first week of the month has done a world of good all round – helping our winter crops move ahead and getting our spring plantings going.

Decidedly cool temperatures continuing into mid-April, though, have been far more of a mixed blessing.

Along with an early plant growth regulator mix at T0, they’ve certainly helped calm down some earlier-drilled wheats which were looking worryingly thick and leggy.

But they’ve also given us the slowest run into oilseed rape flowering we’ve had for many years, which is just what our flea beetle-affected crops could have done without.

The cooler conditions have been valuable too in containing early mildew and brown rust infections, holding back competition from any surviving grassweeds, and preventing our wheats cantering ahead in their development.

Although leaf 3 is our T1 target, we’re always more driven in its timing by spray intervals. Above all, we don’t want to go in too early and leave a gap or more than three weeks before T2; especially as we’re getting so little kick-back from fungicides on septoria these days.

Our T1s will likely to be applied from the last week of the month, and be based firmly around an SDHI again this year, simply because we always get better results from a joint T1 and T2 approach.

In most cases, we’ll be employing bixafen partnered with prothioconazole at T1, adding the balance of our wheats’ plant growth regulation to match our programme as well as we can to crop need.

While wheat management has been fairly plan sailing so far, the same cannot be said of oilseed rape. Some crops are coming into flowering nice and evenly.

Others are all over the place. It all depends on the level of damage they’re carrying from flea beetle larvae.

This hasn’t been helped by stop-start growth which has seen them take a good four weeks to go from first yellow bud to 10% flowering. 

It looks like being a prolonged flowering with a heightened sclerotinia risk in many cases.

East

Sean Sparling

AICC/SAS Agronomy (Lincolnshire)

Sean Sparling

Sean Sparling

With some 99.2mm of rain from Christmas Eve to 19 April, crops are supposed to be growing like billy-o, but this lack of moisture is becoming a cause for concern.

Main nitrogen doses on winter cereals are largely complete. Many decided to get the job done while we wait for leaf 3 and some rain.

But with day degrees and phyllochron governing leaf production, leaf 3 is frustratingly slow to emerge.

Yellow rust is widespread in Diego, Lili, Kerrin, Leeds, Skyfall and others, while septoria is easy to find everywhere including Graham, Barrell, Zyatt, Siskin and even Extase.

Timing fungicides and plant growth regulators will be complicated – another season when the calendar date is irrelevant!

In oilseed rape, our AICC cabbage stem flea beetle spring survey has highlighted the true scale of larval infestation and the subsequent crop effects we’re still dealing with.

There is widespread bud abortion and many fields seem painfully slow to get to flower, so one wonders how much is due to continuing larval activity.

Only the combine will tell us the answer, and it may not make good viewing – either for us or the future oilseed rape crop.

Still, at least we got rid of those pesky neonicotinoids for no good reason after all – phew!

 

There is more wheat bulb fly than we’ve seen in recent years, particularly in spring barley on brashy soils after sugar beet – reliance upon luck, early nitrogen and the rolls will be our only defence from next year, now that the geniuses have banned Austral Plus.

Sugar beet emerged into frost after frost, but at least it’s too cold for polygonums to germinate, so gently does it with herbicides.

Peas and beans are growing faster than the sluggish weevils can damage them, there is no sign of flea beetle in emerged linseed yet and potato planting is as sluggish as the weevils.

There will be many over the coming weeks evangelically touting the benefits of their snake oils and miracle elixirs to save our fading drought-affected crops.

But well structured soils beneath and a welcome rain from above will do more good than any of them.

Even the swallows seem reluctant to come home to Blighty this spring.

North

Helen Brown

Hutchinsons (Cumbria)

Agronomist Helen Brown

Helen Brown

A warm winter in Cumbria has left winter cereals thick and tall with huge yield potential.

However, warm and wet weather over the past month has provided a “perfect storm” scenario for wet weather diseases septoria in wheat and rhyncosporium in barley, which are now evident in most crops.

Our regional trial site near Carlisle shows massive differences in disease levels between varieties, highlighting how variety choice can ease disease management in spring, which is crucial with increased pressure to consider integrated crop management.

Winter cereals with high disease and lodging pressure have received a T0 fungicide alongside a plant growth regulator.

In general, winter herbicide applications have done an excellent job and cereals are clean. However, where spring weeds are abundant, herbicides have been applied as well as wild oat sprays where necessary.

A field of winter wheat

Crops are now approaching or at T1 and it is essential to dissect plants to see true growth stage, as the large canopies produced this winter can be misleading and recent cold winds and frosty nights have slowed down growth over the past couple of weeks.

Spring cereals in Cumbria are usually planted around Grand National time, and this year is no exception. A wet March and snow in early April delayed drilling. However, they are mostly now in the ground and will be emerging soon.

Grassland is growing fast, and this is a perfect time to assess fields for management.

Key things I’m looking for are weeds, nutritional problems and, importantly, percentage of sown species in the sward to decide which fields require re-seeding or over-seeding, in order to manage accordingly this summer.

Chickweed and docks are the most common grassland weeds around Cumbria and fluroxypyr-based products are the basis of my control.

The mild winter means docks are well established. However, it is important to spray healthy new leaves, not overwintered leaves for good control.

West

Stephen Harrison

Avon (AICC/Southwest Agronomy)

Stephen Harrison

Stephen Harrison

The middle of the week should see a return to warmer weather and milder nights, and surviving oilseed rape crops could well be entering a critical period for sclerotinia control.

Monitor prediction tools and be prepared to treat in advance to coat petals. CSFB continues to dominate conversations. Scarily, even what appear to be fresh green side shoots contain larvae. 

I was shocked to see a client’s photo of a charlock plant infested with the pest. In the 1980s Adas looked at continuous oilseed rape, and it was insect pests and not disease which finished off the crop. I feel we really are at a watershed with this crop.

An expensive crop in the early part of its life, it is a huge pest risk and 12 months or more to wait for any payment hardly seems an attractive proposition.

Of concern in cereal crops is the continuing incidence of mosaic virus diseases. We are seeing Barley Yellow and Barley Mild Mosaic in varieties which have resistance.

Unfortunately, this resistance does not apply to all strains of mosaic viruses. Soil-borne Cereal Mosaic Virus is also being detected in a handful of wheat crops.

Currently only Zulu, Claire and Cordiale are resistant.

I look after two commercial crops of Extase which is generating a lot of interest due to its high septoria score.

It certainly looks well but it is extremely fast developing and definitely not for early sowing. It is the only variety on my books which had leaf 3 out a week ago.

Crop growth stages are well ahead of last season. I believe that last year was exceptionally late, whereas this is a more normal season. 

We have avoided the dryness of further east and septoria is easily detectable in most wheat except late drilled tolerant varieties.

Tip of the week

Oilseed rape crops could well be entering a critical period for sclerotinia control so monitor prediction tools and be prepared to treat in advance to coat petals.

Stephen Harrison

 

See more