Crop Watch: Rising aphid threat to OSR and cereals

A mild autumn has seen crop growth accelerate in recent days, with oilseed rape and cereals growing away from the threat of slugs and flea beetle.

Disease pressure remains low and the forecast map for light leaf spot in oilseed rape is showing the lowest average risk for the past five seasons.

However, this weather has favoured mildew in northern barley crops, as well as wheat. In most cases, treatment is not required but is something to keep an eye on.

West: Giles Simpson

Pearce Seeds

Agronomist Giles Simpson

Giles Simpson

Cereal drilling has all but finished. There was just a little drilled this week as the weather held out and people took advantage of good conditions and drilled a little extra into mainly maize stubbles or grassland that had not recovered.

In general, all the cereals look well, although I’m always hesitant to say that as it always comes back to bite you. Seed-beds were all good and emergence has been quick and even.

Most of my crops were treated with residual herbicides and it looks as if they have done a good job, although there has been some bleaching of crops.

The crops that weren’t treated pre-emergence will now have a herbicide, aphicide and manganese. It’s unusual to be able to travel so well at this time of year and even the crops that received a pre-emergence and had a Deter (clothianidin) dressing will now receive an aphicide and manganese where needed.

Grass leys

Grass reseeds have struggled over the past month and it’s mainly down to a lack of moisture. Many have come up uneven and in places where drilling took place in late August or early September they have been redrilled.

Most now are up, but they are not really growing away. Even the short-term Italians are struggling and dare I say it, moisture is needed. Thankfully there has been very little frit fly damage.

The autumn’s fine weather has allowed many farmers over the past couple of weeks to make another cut of grass, which will, hopefully, ease the forage situation a little. Many farmers will need an early spring with plenty of grass growth, as forage stocks will be very low by then.

Looking ahead, spring cereal seed maybe short due to poor yields at this year’s harvest.

Also maize growers are advised to talk to their seed supplier as Mesurol (methiocarb) seed dressing is being banned and treated seed supplies may become short later in the spring, which may well lead to increased bird damage.

The delivery of maize seed may also be affected by, dare I say it, Brexit or no Brexit by then. I’ll leave you to your own thoughts on that one!

East: Marcus Mann

Frontier

Agronomist Marcus Mann

Marcus Mann

It has certainly been an easier, more open autumn period to complete cereal drilling this year and so far, conditions have been ideal for good establishment. Warmer weather with damper mornings has led to quick emergence, which has helped get crops past the slug-susceptible stages.

Residual herbicides appear to have had reasonable activity, however where blackgrass is being found, peri-emergence top-ups are being applied. It is important to apply flufenacet-based top-ups at the one true leaf stage of blackgrass.

Keep a watch on aphids, as significant numbers of key barley yellow dwarf virus (BYDV) vectors have been observed in crops and in national suction traps. Crops not treated with an insecticide seed treatment have already been sprayed and will be monitored closely over the next few weeks.

Seed treated with Redigo Deter (prothioconazole + clothianidin) will generally be protected for up to eight weeks depending on seed rate and soil conditions.

Next year without the use of Deter seed dressing, varieties such as KWS’s Amistar with bred tolerance to BYDV may become an important strategy to early-drilled crops.

Oilseed rape

The milder autumn has helped oilseed rape grow away from the worst effects of adult flea beetle grazing, however, the true impact in-terms of the number of larvae per plant is still to unfold. 

Milder weather has also brought in further peach potato aphids. The yield impact from turnip yellows virus remains uncertain in commercial crops, but has had up to 30% impact in trials.

Aphids on a leaf

© Blackthorn Arable

Data would suggest that earlier insecticide applications will be more effective at reducing virus spread. Where this is necessary, apply non-resistant insecticides in the form of pymetrozine, thiacloprid or flonicamid.

Disease pressure still remains low. The dry and warm weather means infections are likely to be later this year.

Similarly, the light leaf spot forecast map is showing the lowest average risk for the last five seasons with the traditional areas of Scotland and the North West seeing the highest pressure.

With this in mind, fungicides are now more likely to be added to propyzamide later on, once the disease pressure increases.

Regarding propyzamide applications, most soils are experiencing soil moisture deficit, which at present is the largest limiting factor on timing of propyzamide this year rather than soil temperature.

South: Kevin Knight

Zantra (Kent)

Agronomist Kevin Knight

Kevin Knight

The winter wheat area seems to be up from last year, although there is still a fair amount to be drilled.

The lack of moisture in the southeast has been limiting the effectiveness of stale seed-beds, though significant flushes of blackgrass followed the odd shower three weeks ago and again last weekend into this week.

If you’re planting a winter wheat into blackgrass ground – hold your nerve. It’s tough, but not as tough as facing a lawn that needs spraying off along with several hundred pounds worth of germinated C1 wheat among it.

Pre-emergence herbicides are working surprisingly well so far given the dry conditions, with the odd barley crop showing a transient headache as it came through. The pre-emergences are now being topped up with some additional flufenacet and pendimethalin where required.

Aphids

Earlier drilled winter cereals are receiving an aphicide now, and a second one will soon be due where non-Deter (clothianidin) treated seed was used.

Flea beetle pressure in rape has subsided from earlier significant levels, though slug pressure remains high and a top-up of pellets has gone on where needed this week.

Forward oilseed rape crops are showing significant numbers of aphid in places, and phoma levels are approaching threshold so an aphicide will be included with the autumn fungicide scheduled for next week. These will be based around prothioconazole + tebuconazole on smaller crops, with an increase in tebuconazole rates or metconazole used where crops are more forward.

The winter bean area is up – partly due to the dire performance of spring beans last season for many, and because they offer more opportunities for grassweed control (carbetamide, pendimethalin, propyzamide and clomazone all feature in my programmes).

No doubt bruchid beetle will be as big a challenge as ever next summer – but that’s a long way off!

North: Patrick Stephenson

AICC (Yorkshire)

Agronomist Patrick Stephenson

Patrick Stephenson

In my part of the world, the rainfall for 2018 to date has been a meagre 361mm and with only two months to go it looks like one of the driest years on record.

This brings me round to the traditional agronomist’s ceremony of “Casting of the Boot”. This age-old event is when the ground becomes too wet for boots and its wellies only. I have never known a year when we have got through to November without wellies being essential, until this year.

Autumn has been unbelievably good, from harvest through to the completion of drilling. I appreciate that oilseed rape establishment was a battle for most growers in my area, but that aside, the countryside is turning green remarkably evenly and fast.

Oilseed rape crops are now starting to grow rapidly, and the change to cooler temperatures has just come at the right time. Phoma lesions are very rare, and with the dry weather persisting the risk of spraying is quickly disappearing.

Even the need to spray for light leaf spot in the autumn can be questioned, as many of the varieties sown have high resistance ratings.

The lack of continuous wet leaves for the disease to spread has been noticeably absent. I appreciate that many manufacturers and distribution companies have data on the benefits of an autumn spray, but surely this year is different?

Residual herbicides

The next action for my rape growers will be the application of propyzamide. I know it is too warm now, but if we wait for soils to hit 8C, then you can bet that there will be a foot of snow on the ground. My target is the first week of November for neat propyzamide, and a bit earlier for Astrokerb (aminopyralid + propyzamide).

Winter barley crops are tillering well and have unfortunately taken up quite a bit of diflufenican. I know this will grow out, but it looks very dramatic at the moment.

Unfortunately, this lovely weather has certainly favoured mildew in the barley crops. In most cases, treatment is not required, but if the mildew is on the emerging leaves then a low rate of mildewicide will be applied.

Top-up sprays of flufenacet have been applied and as applicable manganese and an aphicide. Aphids can be found in early drilled cereal crops. In the north of England, the main vector for barley yellow dwarf virus is grain aphid. We only have the pyrethroid range of insecticides and unfortunately there will be some aphids with resistance.

If you find that the insecticide of your choice has not worked, send a sample of live surviving ones to Rothamsted for testing. Walking fields and seeing the sheer number of spiders in the crop canopy, I feel that maybe they will be the best line of defence!