Crop Watch: Growth regulation in barley and a leaf wax warning

Fungicide sprays have gone on in good time, and even in Scotland there have been few unsuitable spray days, with disease largely being suppressed in cereals.

However, recent rains have seen a surge in growth, which has forced some agronomists to change their growth regulator plans to limit the risk of lodging.

Some of this rain was in the form of heavy bursts of hail, which may have dewaxed some pulse crops, increasing the risk of scorch from herbicides in spring bean crops.

The rain has also caused flushes of broad-leaved weeds.

Mary Munro

Mary Munro

North: Mary Munro

AICC/Strutt and Parker (Perthshire)

The crop protection season is a bit of a rollercoaster, but suddenly we are over the hump and the midpoint of peak action is past.

The weather has been kind and there have been very few days unsuitable for spraying. We have also had a decent amount of rain to keep things growing.

The awns of winter barley are well out and, apart from a few specks of mildew and the very occasional bit of rhynchosporium, there has not been much disease around.

We are fortunate that the SDHI fungicides are very effective on the main barley diseases. Ramularia could still develop, but by adding chlorothalonil to the second fungicide application, I hope to control it.

Winter wheat has had its T1 and the T2s are planned – if not quite on yet. I used Adexar (epoxiconazole + fluxapyroxad) – or boscalid in second wheats – at T1 and will be using Ascra (bixafen + fluopyram + prothioconazole) or Elatus Era (benzovindiflupyr + prothioconazole) at T2.

These recent rainy days will have increased the disease pressure from septoria, and the crops are generally looking full of potential, so the rates will be kept up.

Yellow rust is never far away and with susceptible varieties, it has to be kept in mind in the programme.

Cleaver control

Some growers will have a final run around the headlands to tidy up cleavers and/or bromes. The choice of cleaver control is wider than it used to be and we are not totally reliant on fluroxypr, which is helpful and allows a change from year to year to combat resistance.

I find Pacifica (iodosulfuron + mesosulfuron) good for bromes, and the aim – as with cleavers – is to stop the population getting a foothold in the crop.

Spring cereals have come on well, and there are some fantastic spring barley crops in the Lothians. Crop protection will be based on two treatments of Siltra (bixafen + prothioconazole), with chlorothalonil added in the second one for ramularia.

Flowering in oilseed rape has been protracted, but most crops are losing colour now as the later petals fall. My crops have had one mid-flowering application of Proline (prothioconazole) and the gate is shut, bar pre-harvest desiccants.

Antony Wade

Antony Wade

West: Antony Wade

Hillhampton Technical Services (Herefordshire/Shropshire)

The month of May is often a time when crops can look full of promise, but kind weather is still needed for crop potential to be realised.

Winter barley crops have finally woken up from their reluctant growth pattern earlier in the season.

However, assessing them before the T2 spray, I felt my robust T1 plant growth regulator strategy had done a good job in stiffening them up. So, I decided not to apply a late growth regulator, apart from to the hybrids. I’m hoping the possible bounce-back we get doesn’t make them too prone to lodging.

In grower trials, I have seen a positive reduction in brackling from using a fluxapyroxad-based SDHI at T2, so this was my choice, along with chlorothalonil for ramularia.

As we have had good tiller numbers since the autumn, I am quite optimistic about yields, as long as lodging doesn’t come back to haunt my T2 decisions.

Winter oats have been similarly slow to get going this spring, but are now growing fast. In some cases, contact herbicide applications in April have affected quite a lot of crops, with the typical reddening, hypersensitive reaction that oats express.

Wheat crops generally are looking very promising in my area. As mentioned, we have been fortunate to have enough rain to make the early fertiliser applications available to crops, so we have good tiller numbers and green area index.

Septoria threat

Septoria is present on lower leaves and you can find lesions on the tips of leaf four and three. With about an inch of rain in early May since the T1 spray – plus recent showers – robust SDHI co-form rates will be deployed.

Flag leaf emergence has been fairly leisurely, but is not far from the normal 15-22 May timing. So, by the time you read this, much of the crops will have been sprayed.

All the promise May brings is being countered by the disappointment of seeing blackgrass and brome heads poking above crops, despite the best efforts with herbicide strategies.

While it is impossible, in my opinion, to predict eventual oilseed rape yields, they look promising as they start to come to the end of flowering – unlike in other areas of the UK.

Early pod set looks good and they are holding onto green leaf area, which is vital to fill the pods.

Sclerotinia-conducive conditions haven’t really sustained high risk levels for significant periods of flowering, so the cost-effective single mid-flower strategy has been stuck to.

Spring cereals and pulses have established well and weed control is being completed following significant flushes of broad-leaved weeds. Maize crops are emerging well and pre-emergence herbicides went on in good conditions.

All this optimism with crops in my region is all well and good, but now it is in the hands of the weather. We need good light levels and adequate moisture so we can fulfil all the potential the crops promise.

Marion Self

Marion Self

East: Marion Self

AICC/Prime Agriculture (Suffolk)

Winter wheat flag leaf sprays have been well timed and we have managed to maintain a tight gap (three to four weeks) between the T1 and T2 fungicide sprays.

Robust sprays will protect the emerging flag leaf and keep the top three yield-building leaves clean. Septoria levels on lower canopy leaves clearly reflect the varieties’ disease ratings and the time of drilling. 

Dirtier varieties drilled in September are evidently carrying a higher level of disease. Yellow rust remains a threat, but is currently well controlled by the recent robust and well-timed applications.

As temperatures warm up, insect pest and beneficial numbers will increase. Sugar beet crops are being monitored carefully by the British Beet Research Organisation, agronomists and growers alike for the increasing presence of aphids that transmit viruses, such as the peach potato aphid.

Aphid numbers are increasing, and in some crops the economic threshold has been reached, triggering treatment with an approved foliar insecticide such as Biscaya (thiacloprid) or Teppeki (flonicamid).

As a reminder, the threshold for treatment is one green wingless aphid for every four plants up to the 12-leaf stage. It is also helpful to visit the BBRO website to view aphid trap catches near you.

Pest pressure

We are also monitoring pea crops for pea aphids and waiting to see if orange blossom midge will be a significant threat to susceptible wheats when ears start to break boot and florets are exposed. 

The timing of the midge emergence will depend on soil temperatures, following rain earlier this month. Mealy aphid populations are visible on the headlands of rapeseed crops. Populations appear relatively high this season, but treatment is rarely required.

Spring cereals are at various stages of development, most nitrogen applications have been completed and T2 fungicide treatments will be applied soon.

Now is the time to map grassweed populations. Start thinking through your control strategy for the coming season, make cropping and rotational decisions to combat these weeds.

Late drilling and spring cropping really does work, although persistence is required.

Richard Harding

Richard Harding

South: Richard Harding

Procam (Sussex)

Recent rain – while useful – seems a distant memory already. It probably wasn’t enough to completely resolve the concerns about some spring crops on the Downs.

Looking at wheat crops last week, the flag leaf has now fully emerged in those fields drilled in mid- to late October. The rain also switched the yield potential back on and increased the disease risk, suggesting it’s vital not to let timings slip.

Most T2 fungicides have now been applied to winter wheat and barley. They consisted of an SDHI plus azole partner, or strobilurin plus azole, along with chlorothalonil – while we still have it – depending on yield potential.

Well-timed nitrogen applications, followed by the rain, will have helped make a lot of that nutrition more available and has certainly stimulated a surge in growth, dramatically improving some crops.

This growth surge has also necessitated the need for some late plant growth regulators on high-yield sites consisting of mepiquat chloride + chloroethylposphonic acid or prohexadine + triexapac ethyl.

Last week, when I looked at wheat crops drilled in mid- to late October, leaf two was half emerged, which would suggest a T2 flag leaf timing in about seven to 10 days, depending on temperatures.

The rain will have switched the yield potential back on and increased the disease risk, which means no holding back for the T2 application.

For spring crops, the rain has stimulated some broad-leaved weed emergence that will need to be addressed in the next few weeks, along with T1/T2 fungicides on spring cereals.

Leaf wax issues

Some of the rain has been in the form of heavy showers, including bursts of hail. These will have dewaxed affected pulse crops, especially peas. So, it will be important to make sure leaf wax is checked with a crystal violet test before contemplating herbicide applications in spring beans.

Where bentazone is planned, an interval of at least seven days will need to be observed before applying a post-emergence grass herbicide. This is generally preferable to leaving an interval of 14 days after applying a post-emergence grassweed herbicide.

There may be some increase in sclerotinia risk following the rain – not least as the cooler temperatures of last week may prolong the flowering period in what appears to remain very variable oilseed rape crops.

This month has pleasingly seen the culmination of a 12-month joint project with Weston Park Farm to grow and manufacture a batch of no-till potato crisps.

The aim of the project is to raise awareness and question current soil management techniques. The crisps will be presented to attendees at this year’s Groundswell Conference.

With assistance from Whitewater Potatoes in Hampshire, Fairfields Farm crisps in Essex, and the very willing team at Weston Park Farms, I am hugely grateful to all involved.