Crop Watch: Rust alert in winter cereals and maize drilling

The recent warm weather has seen pest and disease pressure rise, with yellow and brown rusts being the current threats in wheat crops. This has led to tweaks to the fungicide strategy for the upcoming T1 sprays.

Brown rust pressure has also risen in winter barley crops in the north-west, prompting similar adjustments to the T1 spray. However, the more notable milestone is that the cut-off date for using chlorothalonil is fast approaching, with less than three weeks remaining for this key fungicide.

Maize drilling is now under way and thoughts turn to weed control, as early competition can have an impact on yields.

South: Iain Richards

Agrii (Oxfordshire)

A good 20mm of mid-April rain really helped crops deal with the late spring drought. It was just in time to help our spring barley establish in reasonable shape.

With linseed and spring OSR now in we are drilled-up with a far larger area of cropping than we ever thought possible a month ago.

See also: How ethylene can help control sprouting in potato stores

Spring barleys on our lighter ground are looking nice and even as they fair motor along, having received all their nitrogen and an early plant growth regulator to encourage rooting and prolong tillering. 

Giving us typical yield responses of 8%, early growth regulators will be even more important for the crops on heavier ground, only just coming through from mid-month drilling.

Equally vital here too will be phosphite, manganese where the seed wasn’t dressed, and magnesium.

T1s are imminent for our October-drilled wheats which are well into leaf 3 emergence and three weeks on from their T0s. This and the dry weather has kept septoria well under control.

Rust threat
However, both brown and especially yellow rust are easy to find and enjoying the dry weather and enough dew. With so many of our current varieties so susceptible, they are a major concern.

So we’re basing our T1s on our tried-and-trusted bixafen + prothioconazole + spiroxamine co-formulation, supported by a strobilurin in many cases.

As well as providing the best rust defence, of course, the combined physiological effects of an SHDI and strobilurin will be especially welcome if the dryness persists.

It also means we can save fluxapyroxad and Solatenol for our T2s, rotating our SDHIs and azoles and saving our main septoria guns for May so we’re well-prepared for the almost inevitable return to wet weather.

T1s for our later drillings – all of which were in by mid-December – are still a week away. As their T0s were focused on plant growth regulation and nutrition, and their lower leaves are so much more important, these may need to be more robust. But that all depends on the weather and the degree of potential they show.

In addition to the most appropriate fungicides, the balance of our plant growth regulator programme will be going on at T1, together with copper and magnesium in most cases.

Tissue testing has shown the lowest copper levels I’ve ever seen. With plenty of broad-leaved weeds coming through in open crops, many of our tank mixes will be fairly complex.

OSR continues to be a very mixed bag. The bulk is flowering strongly and has already set 15 good main raceme pods. The dry weather has enabled us to hold off on our mid-flowering spray, which could also be valuable in dealing with a recent build-up in seed weevils.

We’re less optimistic about the backward OSR that really hasn’t appreciated coming straight out of waterlogging into a bone dry, N uptake-restricting spring and has needed a pollen beetle spray to safeguard its green buds.

Even so, we have far lower levels of flea beetle larvae this season and we know how well the crop can compensate, given half a chance.

East: Sean Sparling

AICC/SAS Agronomy (Lincolnshire)

Since a torrential drizzle which soaked us with 0.4mm on the 20 March, I have recorded no wet stuff at all. Unsurprisingly, then, we’re moaning about how we could really do with a drop of rain.

In winter wheat, the yellow rust which is showing in some unlikely varieties takes no finding and is flourishing in the mild days and dewy nights.

Septoria is similarly moving and, like nits in children, will happily spread from leaf-to-leaf contact on the many and frequent windy days.

Growth stage 30 is now widespread even in the more backward-looking pieces (never assume!) and, with leaf 3 emerging quickly, T1 is upon us. Where epoxiconazole is used, as per Chemicals Regulation Division (CRD) guidance the 83g/ha maximum is being adhered to.

Direct drilling now appears to have been the way to put in spring cereals, with crops tillering evenly.

Where power harrows and the like were employed, we achieved little more than stirring golf balls in a bucket. A layer of concrete, a film of dust and assorted clods ranging in size from Brussels sprouts to cricket balls mean the latter are through in clumps, stripes and patches.

Not ideal, but we can only do our best with the conditions and timescale we’re given.

Unusually high numbers of winged barley yellow dwarf virus (BYDV) vectors have needed treatment in some areas, but with the spiders, ladybirds, hoverflies, wasps, lacewings and other predators building rapidly, further treatments will do more harm than good.

Let the predators do their job. 

Slowly emerging fields of peas and beans were also savaged by pea and bean weevils, but now as long as crops are outgrowing the adult feeding damage, bravery and constraint should be exercised.

Sugar beet is emerging well with the early drillings now sporting four leaves. Herbicides seem to be doing little to the emerged weeds, but a drop of rain would change that overnight – pre-emergence herbicides have come into their own and fields are noticeably cleaner where applied.

There is no sign yet of the dreaded one myzus persicae nymph per four plants threshold.

But as I once again spend the spring crawling about on my hands and knees in every beet field I walk, I find myself wishing I’d worked harder at school!

West: Stephen Harrison

AICC/Southwest Agronomy (Avon)

Spring 2020 has certainly proved the need for field-specific advice. A host of growth stages and plant populations means that fungicide and plant growth regulator recommendations have rarely been so varied.

Septoria pressure is currently low following the dry April. T1 mixtures have centred on an azole plus chlorothalonil on later-established high-resistance varieties. More forward crops are receiving an SDHI component in the treatment. 

Growth has been slow with a lot of applied nitrogen yet to be taken up. Do not be lulled into a false sense of security regarding growth regulators: the forecast rain will cause a huge growth spurt much as we saw in the brown rust spring of 2007.

The ramularia threat has led to a change in strategy in winter barley. It has become our standard approach to apply a second plant growth regulator and chlorothalonil at the early flag leaf stage. This fits usefully with any necessary wild oat treatments.

Maize drilling
Maize drilling is well under way. However, will drill operators please heed the personal protective equipment (PPE) requirements for handling maize seed with ziram anti-bird treatment. 

Pre-emergence treatments largely based on pendimethalin are planned. Early weed competition is challenging to maize and even in dry times we see consistently good effects on fat hen and chickweed.

The earliest spring barley is approaching mid-tillering. Few broad-leaved weeds have emerged in the dry conditions, so a single spray of fungicide and herbicide will suffice. 

Second fungicide timings will be beyond the 19 May chlorothalonil cut off. Therefore we will adopt a similar ramularia strategy to winter barley.

Ignoring the usual grassweeds, one of the more challenging weeds in winter cereals has been groundsel.

Sulfonylurea herbicides control it well while small, but it grows so quickly that any slip in timing, thereby letting it flower, means control is next to impossible.

I started my agronomy career in 1980 and throughout the years, chlorothalonil has been a great ally. It seems unbelievable that this article is the last time I will ever write about it.

I do not expect the new fungicide actives on offer will remain as cost-effective as chlorothalonil in another 30 years.

North: Helen Brown

Hutchinsons (Cumbria)

Who’d have thought a month ago that my next Cropwatch piece would be a cry for some rain? But here we are after an extremely dry April shouting for rain and I am eagerly watching the forecast in hope that by time you read this we will have at least had enough to settle the dust.

Winter crops are varied from growth stage 31 up to 39 in some winter barleys. Lack of rain has reduced rhyncosporium risk in winter barleys.

However, the recent warm conditions are ideal for brown rust which I have spotted in many winter barleys. I have edited my T1 fungicide applications to account for this shift.

Brown rust on a barley leaf

Brown rust in barley © Blackthorn Arable

We are starting to see some big differences in wheat varieties at our regional trial site, which was drilled late into poor conditions and then struggled through a very wet winter.

This is giving us a great opportunity to see how the varieties perform under pressure. There are some stand-outs for vigour – which for me include Extase, Skyscraper and Gleam.

Spring drilling
Spring drilling is fully under way in Cumbria. Spring barleys are varying from being still in the bag up to 3-4 leaf stage.

Reducing the amount of soil movement and trying to cultivate/drill and roll in one day where possible is essential to preserve moisture when establishing spring barley crops in these conditions. There is limited spring weed germination in crops so far due to lack of moisture.

Maize drilling is also under way and soil conditions are nice and warm. However, the dry seed-beds bring concern over pre-emergence efficacy, which is important when using film. Where growers are not using film, I have moved towards a post-emergence herbicide programme, since the pre-emergence will have limited efficacy in these dry conditions.

Docks are currently around the ideal size for control in grass swards and, due to their large taproot, are still reaching water and actively growing.

However, the hot, dry conditions mean grass may be stressed and making sure to use chemicals which are softer on the grass, for example fluroxypyr, is beneficial in this situation.