Crop Watch: Moist conditions maximise residual efficacy

Seed-bed quality is uppermost in our agronomists minds this week, with the stop-start establishment season testing the patience of growers in the South. However, Richard Harding is pleased with the extra opportunity to control blackgrass.

While the moist conditions are hampering activity on heavy land, they are also providing optimum conditions for expensive residual herbicides to work at their best for eastern growers, says Marion Self.

In the West, Antony Wade is also hoping for good performance from post-emergence chemistry. He is particularly interested in  a new oilseed rape herbicide for broad-leaved weed control.

See also: Autumn micronutrient sprays help to raise wheat yields

Our thoughts are with growers in northern Scotland who are still battling to harvest crops from last season, says Mary Munro. She warns growers not to let the plough get too far ahead of the drill in these wet conditions.

antony wadeWest: Antony Wade

Hillhampton Technical Services (Herefordshire/Shropshire)

Drilling opportunities have been grabbed on farms where there is not extreme grassweed pressure, mainly wheat after oilseed rape and seed-beds have generally been good.

I had hoped this would reduce the slug risk sufficiently, but early indications are that these will need treating with pellets to ensure establishment.

Growers are gaining confidence in using ferric phosphate, so are accepting the slight additional cost that this pellet brings or enduring the risk of untreated metaldehyde headlands.

Wheat planted after potatoes poses less of a slug risk, not least because of the amount of work to the soil the crop entails, plus with good lifting conditions so far, seed-beds have been good.

September-drilled wheat and barley are a must for residual herbicides for grassweed control, mainly based on flufenacet, diflufenican and pendimethalin combinations.

The loss of flupyrsulfuron as an active will be a loss for specific weeds in wheat and barley, but more concerning is that it has been a mainstay for grassweed control in oats.

This has been in the form of Absolute under an extension of authorisation for minor use, leaving options very sparse after this season.

With plenty of moisture in the seed-beds, I had expected oilseed rape to emerge rapidly, but it was strangely slow in getting to the rows visible stage.

I can only put this down to cooler-than-normal soil temperatures in early September, but in the past two weeks crops have really picked up and are now at between two and four leaves.

Volunteer cereals have enjoyed the moisture with a strong flush requiring graminicide inclusion where residual herbicides were delayed to post-emergence, or will be sprayed at the next opportunity on others.

Although I am hopeful, with sufficient moisture at application, of good broad-leaved weed control from the residuals.

I will also be evaluating the newly approved Parish (phenmedipham) in oilseed rape where we have an early flush escaping ahead of later residual applications.

Richard HardingSouth: Richard Harding

Procam (Sussex)

Cereal drilling is now under way on the Downs, but it has been a stop-start affair, much like this year’s harvest.

Any delay to drilling has several advantages, giving the opportunity to take out blackgrass and ryegrass with glyphosate before drilling and better pre-emergence herbicide efficacy achieved by spraying in cooler conditions.

Cereal pre-emergence herbicides based on flufenacet, diflufenican, picolinafen and prosulfocarb are lined up and ready to be applied as conditions allow.

Slug numbers are particularly high in oilseed rape stubbles this season and ferric phosphate will be used where needed in the following cereal crop.

With plenty of moisture around, oilseed rape has established well, albeit slightly later than planned again due to the wet weather.

The flea beetle pressure has been lower this year, however, some later-drilled crops are still at, or have just reached, the expanded cotyledon stage.

These crops are showing clear signs of damage. A timely application of lambda-cyhalothrin will be used if damage begins to exceed threshold levels of 25% plants affected in these slower-growing crops.

Conditions recently have created a high risk for phoma infection on oilseed rape, which is now starting to appear in crops.

Plants with no more than two true leaves are showing signs of the disease. The smaller crops infected are at higher risk as the mycelium has a much shorter route to get into the stem of the plant.

However, the levels have not yet reached the 10% of plants infected threshold needed before an intervention with a fungicide such as difenoconazole is required.

Cover crops are growing well and producing pleasing levels of biomass. Mixes containing peas and beans are showing good levels of nodulation.

This season a higher proportion of oilseed rape than last year has been sown with a companion cover crop.

This technique looks very promising as a lower-risk method of establishing oilseed rape.

The aim has been to choose non-frost-tolerant species, as the companion which will either die or can be removed later with a selective herbicide, provided there is a viable plant population of rape.

marion self

marion self

East: Marion Self

Prime Agriculture (Suffolk)

This autumn growers have worked hard to create false seed-beds, which have been very effective and we are pleased by the amount of blackgrass controlled by glyphosate before drilling. 

I have never seen this amount of blackgrass flush before drilling, But Adas hasreported that the seed shed in 2017 is of moderate to high dormancy. 

This causes me concern; it suggests much of the emerged population has come from seed shed the previous year and there may be significantly more to emerge from seed shed this summer. 

So, a word of caution, the “big chit” so far is not a reason to switch planned spring cropping to autumn drilling and those still intending to drill autumn crops in high blackgrass situations should hold off drilling as long as they dare.

Growers have paid close attention to seed-beds and spray operations to maximise the efficacy of the pre-emergence herbicides.

Conditions are moist, so we have the best chance for the big, expensive stacks and sequences to work well.

Many rapeseeds have high populations of blackgrass, more crops are already receiving post-emergence blackgrass control – for example, with Centurion Max (clethodim) – than ever before.

The next few days will reveal how effective these sprays have been. In the worst situations I’m expecting to have to sequence carbetamide ahead of the propyzamide applications.

Aphid reports suggest relatively low numbers of migrating BYDV vectors (mainly the bird cherry aphid).

Despite these low numbers, non-Deter (clothianidin)-treated crops will need protection at the two-leaf stage with pyrethroid – a follow-up treatment will be required.

Aphid monitoring also shows moderate numbers of those thattransmit the turnip yellows virus (Myzus persicae).

Continue to monitor these surveys and your own crops to decide when treatment is required.  

These aphids are widely resistant to carbamates (for example, pirimicarb) and or pyrethroids (such as Lambda-cyhalothrin) so treatment with another mode of action is recommended e.g. pyridine (for example, Plenum) or neonicitinoid (for example Biscaya).

Mary MunroNorth: Mary Munro

AICC/Strutt and Parker (Perthshire)

This is an autumn of struggles and frustration. In the north-east of Scotland farmers are still battling with harvest and heading towards a salvage situation with increasingly wet and flat crops.

Further south and east the cereal harvest is nearly all done, but autumn sowing is a very stop-start affair and ploughing too far ahead of the drill is definitely not to be recommended. 

Potato lifting is managing to continue, mostly thanks to self-propelled machinery, but the price is causing misery.

On the plus side, crops that have been sown are progressing nicely  – the wet, mild conditions are ideal for plant growth.

There is a bit more slug activity though, and it is worth setting up bait traps in newly sown fields.

This is much better than watching bare patches appear in an emerging crop. Care must be taken with metaldehyde, to prevent contamination of watercourses, and the ferric phosphate alternatives are effective and safer.

There have been just enough suitable spraying days to keep up with the workload.

A lot of my growers apply early post-emergence cereal herbicides rather than pre-emergence ones,  which provides an opportunity to deal with aphids at the same time.

I don’t recommend insurance insecticides, but we did see a bit of barley yellow dwarf virus in crops as they approached harvest, so there will be infected aphids about on the green bridge of grass margins.

I am targeting the high-risk sites with early-sown crops. Aphid activity tends to cease by mid-October, when it is just too cold, wet and windy for them.

This year we have the new option of hedges for greening in Scotland and the multiplication factor seems generous enough to be worthwhile.

Green cover after harvest seems to be gaining popularity too, as it fits between two crop seasons.

The need to sow by 1 October means it won’t suit everyone –  there will have been some sown on the last possible date this year.