Crop Watch: T2 spray decisions and leaf scorch problems

Crops are now racing through their growth stages, with winter wheat about to receive the key T2 fungicide sprays.

Disease levels are relatively low and fungicide programmes are keeping a lid on disease risk. In fact, in the dry East, leaf scorch from liquid fertiliser applications is the biggest problem for green leaf retention.

Looking further ahead, agronomists are not relishing the challenge of desiccation timings in flea beetle-ravaged oilseed rape crops.

Iain Richards

Iain Richards

South: Iain Richards

Agrii (Oxfordshire)

The first decent rain since my last piece – a good 15-20mm last week – has really lifted our spirits. Despite barely half this total falling in the in the previous four weeks, our wheats are full of promise as their flag leaves emerge. 

Our spring barleys are looking good too, approaching growth stage 31. Most of our oilseed rape has recovered amazingly from the most challenging of starts, with tremendous branching and overall pod set.

Of course, it’s early days yet. But providing things warm up from mid-May as we’re promised, we don’t get a repeat of last summer’s drought and we keep firmly on top of some key threats, we could be in for a  satisfying harvest all round.

See also: Farmer trials disease strategies in wheat variety Extase

Along with the dryness, a return to much cooler conditions since the Easter weekend has held back wheat diseases nicely. We’re also in a good place, with T2s set to go on to emerging flag leaves in decent weather within 21 days of T1s.

Therefore, the SDHI/triazole combinations we’re using – supported by chlorothalonil where needed – should continue to keep our crops clean as pressures grow, with more moisture and warmth.

Ringing the changes from the T1s as part of our anti-resistance strategy, we’re using fluxapyroxad where septoria and yellow rust are the key concerns, and Solatenol (benzovindiflupyr) on varieties with particular brown rust weaknesses, both with epoxiconazole/metconazole co-formulations.

Midge risk

After last year, we’ll be keeping a very close watch out for lemon blossom midge as the ears start to emerge from the boot. If necessary, we won’t be waiting for T3 to go in with a quality pyrethroid.

The right timing to deal with orange blossom midge is too late to deal with the earlier-emerging lemon midge, which affected some of our trials badly in 2018.

Having had all their nitrogen by two leaves and an early plant growth regulator to prolong tillering, our spring barleys have also coped extremely well with the dry April.

Both February- and March-drilled crops will be receiving their T1s from this week. These will be based on prothioconazole and trifloxystrobin, with the addition of folpet for the best defence against ramularia.

The crop that has raised our spirits most, though, has been oilseed rape. Under serious pressure from flea beetle larvae and not helped by the slow spring, it has shown truly miraculous powers of recovery in a dry, sunny flowering period.

It reminds me, more than anything, of DK Cabernet, which used to lose all the pods on its main raceme, but then compensate its heart out with side branch podding to deliver at harvest.

We haven’t been here before, so we have no idea how these crops will yield. Desiccation timing will definitely be an issue.

Sean Sparling

Sean Sparling

East: Sean Sparling

AICC/SAS Agronomy (Lincolnshire)

We have had 30.4mm of rain since my last report, making it 122.6mm so far this year. It is worryingly dry as we head into the heat of summer. Heavy dews have been a godsend.

Winter barley went from growth stage 31 to 47 in just three weeks but, despite the moisture stress and applied nitrogen sitting there waiting for the rain, disease levels remain manageably low, with abiotic spotting and nutrient deficiency the major concern. T2 fungicides are now being applied.

In wheat, there is more stem-based browning than I’ve seen for several years. The flag leaves on mid-September-drilled crops are emerging thanks to the recent warmth, although a week of single-figure temperatures has stopped them in their tracks, with a lack of any day degrees to accumulate.

Growth stage 37 fungicides are now being applied, but as with winter barley, disease levels remain unnervingly low.

Septoria in the base of these crops is widespread and not particularly variety specific, so well-timed and robust flag leaf protection, including chlorothalonil, will be crucial once again this year.

Leaf scorch

The single biggest problem for green leaf retention so far hasn’t been disease, but liquid fertiliser scorch.

Spring barley and spring wheat varies from growth stage 21 to 31. T1 mixes are being applied earlier than normal to take out the competition for water and nutrients from weeds, which are flourishing.

Disease levels remain low, although net blotch and rhynchosporium are just starting to appear. I am using chlorothalonil while I still can to thwart ramularia.

Sugar beet ranges from emergence to six leaves. Even the most robust cover crops couldn’t stop the need for redrilling in some fields following the gale-force winds of a couple of weeks ago which, in the arid conditions, shot blasted a significant acreage out of existence.

Weed control is going well, with the weeds as stressed as the beet. Flea beetle damage is having to be treated for the first time in many years, but as yet there have been no Myzus persicae issues – the British Beet Research Organisation website is a great help.

Linseed is being hit hard by striped flea beetle, while peas and beans are facing an onslaught from weevils. Pyrethroids are variable in their efficacy, so we can only hope the recent rain and a warming forecast will get these crops growing away from the damage.

Agronomist Helen Brown

Helen Brown

North: Helen Brown

Hutchinsons (Cumbria)

In my opinion, May is the best month on the farm, and I was reminded why when the countryside burst into life over the past couple of weeks.

Winter barley crops are starting to push awns out and will soon be ready for the final fungicide, which will be aimed predominantly at ramularia and rhyncosporium.

Although ramularia risk is relatively low at present, as temperatures increase into summer, the risk will also rise. Therefore, I will be including chlorothalonil in my T2 winter barley spray as a preventative control. I am starting to consider how we are going to control this disease next year when we lose this active.

At present there are no ratings for ramularia tolerance, but I will be looking out for the varieties that perform well in the untreated plots in our Cumbrian trial site to help choose more tolerant varieties as part of an integrated management plan for this disease.

Silage time has begun in Cumbria and it is key that after-cut fertilisers are applied as soon as possible. It is worth noting that for every day after-cut fertiliser is delayed, about 150kg/acre of fresh grass is lost, which can soon add up to big losses.

Spring barley

Spring barley crops are now beginning to tiller and in general are looking very well. Growers are starting to apply weed control in fields with a high abundance of broad-leaved weeds, especially where there are significant numbers of polygonums.

In fields where weeds are yet to emerge, herbicide will be delayed and applied alongside the first fungicide application.

Maize is also emerging and is at the two- to three-leaf stage. In Cumbria, most of our maize is under film, so a pre-emergence herbicide is key to weed control.

Our maize demonstration site is now drilled and this year we have some interesting work with varieties, plastics, fertiliser and undersown grass.

Stephen Harrison

Stephen Harrison

West: Stephen Harrison

Avon (AICC/Southwest Agronomy)

Crops are racing away and even on the thinnest brash soils, last week’s welcome rain has boosted growth and leaf emergence. 

Crop biomass is generally high and investment in growth regulation has therefore been higher. Use of ethephon growth regulators is up.

Many applications have been made as a single shot between the T1 and T2 timings to avoid complicated tank mixes and any compromise of flag leaf fungicide timings.

I always have a debate with my clients over the use of plant growth regulators and straw yield. I must say I have never seen high straw yields scraped off the ground. Just remember to only use these products on vigorously growing crops with high yield potential.

Septoria is still confined to leaf four and below. On thicker crops there is an element of leaf blotching, which I am sure is leaf necrosis linked with shading rather than disease as – even with a hand lens – pycnidia cannot be seen. The rain splash of the past week will heighten risk. 

T2 sprays

With a large area of wheat to treat, be prepared to start the T2 at growth stage 37-38 on the least-resistant varieties. Where most of the wheat can be sprayed in one day, it is preferable to treat at GS39 (flag leaf fully emerged and ligule visible).

Ideal timings of leaf three applications mean we have not needed to apply any intermediate T1.5 treatments. All flag leaf sprays will be based on azole, SDHI and chlorothalonil, with the SDHI rate adjusted by variety.

All field operations on winter barley are now complete and the crop looks as well as I have seen for several years.

The patches of soil-borne cereal mosaic virus look better now the upper leaves have emerged. This year we should get a better idea of the effect of this virus by overlaying early spring drone footage on yield maps.

Spring barley is doing its usual impersonation of Usain Bolt and is rocketing towards growth stage 30.

I am bracing myself for the nightmare task of timing desiccation on flea beetle-ravaged oilseed rape crops. For many crops, the best timing for pre-harvest glyphosate would have been March.

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