Crop Watch: Beans and linseed face pest onslaught

As June arrives, the disease and pest threats continue to occupy our agronomists’ minds with concerns of brown rust growing in the South.

Flea beetles are hammering linseed crops in the East and weed control is proving tricky in beans.

One rare bit of good news has been the recovery in barley in the South West, as warmer temperatures and rain arrived back in May.

Iain Richards

Iain Richards

South: Iain Richards

Agrii (Oxfordshire)

Brown rust is one of our key concerns as most wheats receive their flag leaf sprays.

Sticking to our T0 guns and maintaining robust T1s means we’ve yet to see significant signs of infection.

However, the worrying number of reports we’re getting locally show the cold, late spring hasn’t done the job we hoped it might.

With Agrii research showing about 70% of the main varieties in the ground at high risk from brown rust and the sheer amount of Crusoe being grown, we’re not taking any chances here.

It’s a disease we cannot afford to be chasing. 

See also: T3 spray tips for battling ear blight in wheat

So, Solatenol (benzovindiflupyr) is our T2 SDHI of choice wherever we have any varietal concerns.

Supporting this with an epoxiconazole/metconazole co-formulation and a multisite protectant should give us the peace of mind we need in our septoria management as well.

Dry weather has kept infections nicely confined to the base of most crops so far. However, we know how rapidly things can change especially in light of forecast rainfall.

Green leaf area

Crop performance this season will be all about working hard on maintaining green leaf area to compensate for the very slow start to spring growth.

This will be particularly important for crops on heavier ground, which didn’t get their nitrogen nearly as early as we’d have liked.

Many of these are decidedly thin when you get into them, having lost many tillers, making the contribution of their lower leaves to grain fill more vital than ever.

Maximising grains/ear will be crucial too. So we’re including more magnesium in our T2s to encourage both photosynthesis and N use. With the weather as dry as it has been, minimising stress in the run-up to flowering is key.

We will also be keeping a very close eye on orange blossom midge levels. Reports suggest adult midges are emerging at about the same time as crops are susceptible for the first time in recent years.

There’s a brutally short control window, many varieties aren’t resistant and our chemical armoury is limited to say the least.

Sean Sparling

Sean Sparling

East: Sean Sparling

AICC/SAS Agronomy (Lincolnshire)

T2 fungicides are now being applied across winter wheats and barleys and judging by ear size, there’s potential for a good harvest.

However, with noticeably shorter crops and late spring cereal drillings, straw may be in short supply. The implications for livestock farmers are concerning – isn’t it time they took priority over power stations?

Septoria has been held back by T1s, but lurks in the base and remains the significant threat, although on Reflection wheat, yellow rust continues to frustrate. Mildew is widespread, but, where a prothioconazole-based T2 is used, the need for additional mildewicides reduces.

Blackgrass levels are low where crops were drilled late and robust pre-emergence herbicides were applied, despite few contact herbicide applications.

Most spring barley is receiving T1 fungicide/herbicide mixtures. Rhynchosporium and net blotch is always threatening alongside low levels of mildew and abiotic spotting.

Spring wheat woes

Overall, spring barley is lush and vigorous – more than can be said for some spring wheats, which have whined since the day they went in.

Oilseed rape is largely out of flower, but with the weather we have seen, protectant sclerotinia sprays have been vital.

Seed weevil numbers are moderate on headlands, but minimal within the field. Therefore, that situation is still being monitored.

Winter beans display high levels of chocolate spot due to early season stress and initial bruchid beetle migration coincided with first pods being set.

Pea and bean weevil continue to assault both winter and spring beans as well as peas, but with warm soils and some welcome rain, crop growth is rapid and notching is being outgrown.

Flea beetles are hammering some linseed crops, but the sugar beet is growing almost as fast as the weeds. However, with near constant winds, it’s proving a challenge to get the required fine quality sprays applied when required.

Stephen Harrison

Stephen Harrison

West: Stephen Harrison

AICC/Southwest Agronomy (Avon)

Thundery rain has eased drought stress on crops. I was concerned for the security of some heavy hybrid barley crops during the deluges, however, a walk around a few local fields shows that they are still standing. 

Earlier in the spring, I bemoaned the state of barley on heavy wet soils. Their recovery, as temperatures improved and rain fell, has been dramatic. I am so pleased we did not succumb to the temptation to write off or redrill these fields.

Decision-making on poor crops is invariably tricky, as there is always a temptation to take no chances and destroy the evidence. The early Victorian naturalists had a saying: “What’s shot is history, what’s left a mystery.”

Wheat is now approaching ear emergence. Disease is largely confined to leaf five with more susceptible varieties showing a little septoria on leaf four. 

While disease is never welcome, this lower canopy infection combined with a clean leaf three suggests most of the T1 fungicides went where they were intended.

Mosaic virus

The only yellow rust prone variety we grow is Zulu, being resistant to soil-borne cereal mosaic virus. Despite a relatively low rust risk, spring spray misses in this variety have been taken out. 

Our only other mosaic virus resistant varieties are Cordiale and Claire.  Frequent questioning of plant breeders suggests there is little or no new material coming through.

On the subject of viruses, we are also seeing resistance breaking strains of barley yellow mosaic virus appearing. Varietal resistance to the virus is a single gene, so it is not surprising that other strains are infecting crops.

If you have unusual symptoms in winter barley I suggest you have the presence of virus confirmed or refuted by Fera. The virus is carried by a soil fungus, so care should be taken not to spread infected soil.

Of further concern in barley is the appearance of loose smut on crops grown from treated seed.

On the positive side with viruses, the barley yellow virus tolerant variety, Amistar, looks to be performing well in our second year of field-scale trials.

Andy Goulding

Andy Goulding

North: Andy Goulding

CAS/Hutchinsons (Cheshire)

A familiar tale of one extreme to the other: we started the year with an awful winter and early spring, but we are now leaving behind an exceedingly hot and dry May.

The residing moisture is available for established autumn-sown and early sown spring combinable crops (of which there are few).

There doesn’t look to be many lazy rooting spring crops, but none the less, a little flurry of rain has just kept everything establishing.

Wheat T2 is on the last leg of the run and crops are still all over the place, with the seasonal calendar unable to get things to an equilibrium due to the huge array of planting dates and poor early growing conditions.

We’ve gone from exceptionally high septoria pressure to low, and rates have been tuned accordingly.

Moisture for establishment is not an issue with potatoes that have been planted late, as it can be found around the seed tuber, and there’s plenty of energy left in there yet.

Ridge moisture may reduce efficacy of the residual herbicides, which we so majorly rely on.

However, with little moisture in the outermost part of the ridge, weed emergence is also delayed.

Product selection and rate is going to be geared around the half-life of the active ingredient, as we strive for persistency for when the flushes come.

Weed challenge

Beans have also been subject to the same dilemma, with residual herbicides not achieving the desired control.

In instances where broad-leaved weeds will become competitive, post-emergence products are being used. Be mindful of the narrow application window and potential for herbicide damage – these are best applied during the cooler part of the day.  

Despite mainly being late drilled, maize is mostly up and away, and looking good with no cold snap to hold it back.

Post-emergence herbicides are a little off yet, but I will be using other chemistry as terbuthylazine starts its phase out from the market.