Crop Watch: T0 cereal spray strategies and variable oilseed rape

The effects of the unseasonably warm spell in February are now being seen, with wheat crops motoring on and oilseed rape starting stem extension. 

It means agronomists’ thoughts have now turned to T0 fungicide strategies in wheat and barley, including whether a T0 is needed with forecasts of cold weather and frosts to come.

For oilseed rape, a key headache for some is the extreme variability because of cabbage stem flea beetle and how to manage these in the coming weeks.

Agronomist Giles Simpson

Giles Simpson

West: Giles Simpson

Pearce Seeds (Somerset)

The false spring in the second half of February is now making us pay. Some spring crops were drilled and are now suffering from the wet and cold, and slugs are causing a problem.

Quite a big area of grass was fertilised in that dry period and is now growing away nicely. It will need its second dose in the next couple of weeks if the weather allows. Most winter barley and second wheats were also fertilised at that time and they are now looking well.

See also: Why ramularia is so difficult to control in barley

Most of the winter wheat is yet to be fertilised, as it is looking extremely well. However, it will need its first dose as soon as we can.

Oilseed rape crops are very variable, with some growing away nicely, but others are full of flea beetle larvae and looking sick. The good crops are going to receive a fungicide shortly, as stem extension is well under way, with some green buds just appearing on the most-forward crops.

Forward crops

Some crops of winter oats and triticale are very forward and will need a plant growth regulator and fungicide shortly. Thankfully, none of these have received any nitrogen and we will try to hold off with any for now.

I have seen a lot of winter wild oats in fields where we don’t normally see them – the dry summer and mild winter may have had an effect. These will be dealt with in the T0 spray application, which will happen shortly.

Many cover crops have now been sprayed off, ready for applications of muck in front of cultivations for maize drilling. Some of the cover crops have been extremely large and have not died back due to our lack of any significant frosts.

If you haven’t ordered your maize seed, I would suggest you do, as mesurol-dressed seed may start to get short now.

Agronomist Kevin Knight

Kevin Knight

South: Kevin Knight

Zantra (Kent)

Oilseed rape has moved rapidly following the warm spell, leaving precious little opportunity for thistle control given calendar and growth stage restrictions (after 1 March, but before buds visible).

Adequate boron levels during bud initiation and early flowering are crucial, with the stem extension timing most critical, so a top-up will be included with the mepiquat-based growth regulator plus fungicide at the next spray window. There has been some light leaf spot locally, so I’m including prothioconazole and tebuconazole in the mix.

Pollen beetle panic has set in early this year. While I do worry about the purple sprouting broccoli I advise on, I’m not overly concerned about OSR.

Early-drilled winter wheats are doing a passable impression of stem extension at present, though when dissected the nodes aren’t moving much. It’s the basal meristem – pseudo stem extension, if you like – and leaf four is not yet emerged.

We will be getting there in a week or so, but do mark that applying the T0 too early can leave a gap of more than four weeks to T1, which is a riskily long time without protection.

T0 fungicide

Given the mild winter, the T0 will need to suppress eyespot and mildew as well as septoria and rusts. Epoxiconazole and metrafenone are a likely combination with a multisite, plus some growth regulator and a foliar nutrient top-up.

In the meantime, we have been tidying up weeds and including an aphicide to try to limit the spread of yellow diamonds (barley yellow dwarf virus) where they have occurred due to missed autumn opportunities.

Resistant ryegrass is becoming a significant issue in places. Don’t be complacent if some gets through your spring graminicide – ruthless control by spraying out or rogueing at the earliest sign of infestation will save a lot of headaches in the long term.

Spring cereals and beans have gone in well on the “boys ground,” while those with less-forgiving soils are still exercising patience until conditions are right.

Agronomist Patrick Stephenson

Patrick Stephenson

North: Patrick Stephenson

AICC (Yorkshire)

What a difference a few days make. Having been basking in the heady heights of 18C for five days, we have now plunged back to more typical temperatures with some frost thrown in.

Oilseed rape has shown the most amazing transformation, with the first nitrogen being the catalyst that sent crops from hugging the ground to stem extension and flower buds visible. We are now past Galera (clopyralid + picloram) timing and even late-applied graminicides are unlikely to hit the target.

This rapid burst of growth has certainly focused my attention on growth regulators for OSR. We now have a multitude of different products to select from. I will admit to being a bit of a dinosaur, preferring the dual approach of light leaf spot and growth regulation.

There is no doubt that the further north I travel, the more light leaf spot can be seen. I feel this completely justifies my approach. But further south, it is harder to justify, with little or no disease evident.

We did not totally escape the ravages of cabbage stem flea beetle in the autumn, with several crops being redrilled. However, we appear to have escaped the worst of the larval damage, which is terrorising the country.

Main nitrogen dressing will be applied before the month’s end, and I certainly subscribe to the biomass theory in rapeseed, so large canopy crops will receive less nitrogen.

Septoria

It has been fascinating to see the latent levels of septoria in the crops. Siskin, Sundance and Costello show markedly less septoria than Barrel, Diego and Leeds, confirming the AHDB ratings.

A return to much cooler weather will, I hope, temper everyone’s enthusiasm for imagining growth stages and a desire to get spraying. Examining plants and announcing they are at growth stage 30 is a fool’s game, dissect the plant and identify each leaf layer, which means putting on your glasses.

Unfortunately, I did not need to put on my glasses to see the yellow rust in two crops this week. Despite this observation, I will not be indulging in a T0. The forecast of frost and colder weather will do better than a fungicide at the moment.

Winter barley has also responded to the early nitrogen and is no longer lime green. There are still high levels of mildew and brown rust present. To compound this the recent wet weather will further increase disease pressure, meaning that the first robust fungicide will be targeted at the end of the month.

One major concern I have is the size of the overwintered wild and tame oats. Normally, products like Broadway Star (florasulam + pyroxsulam) and Monolith (mesosulfuron + propoxycarbazone) in wheat would tidy most infestation of oats up, but these are monsters.

If these are present in winter barley, then the cost could be eye-wateringly high to control them.

Agronomist Marcus Mann

Marcus Mann

East: Marcus Mann

Frontier (Essex)

The recent warm spell resulted in an early-season growth spurt with oilseed rape beginning stem extension and some wheats beginning to reach growth stage 30.

T0 applications in winter wheat are starting to be discussed. Septoria remains present in most crops with low levels of yellow rust being found in the more-susceptible varieties.

Where active rust is present, it will be important to add an azole such as tebuconazole to a chlorothalonil base treatment. 

Low levels of brown rust are present in winter barleys. Where crops are a long way from a T1 fungicide, an earlier T0 is being used to help control this and to allow for a well-timed T1 later on. 

Oilseed rape has begun stem elongation and growth regulators as well as boron applications are being planned. For more forward crops, metconazole is being used with the addition of prothioconazole for light leaf spot and phoma control.

For those that are more flea beetle larvae damaged, tebuconazole is being used just to stop apical dominance and encourage further branching to help counteract some of the damage.

Pollen beetle

Pollen beetle has begun to migrate after the higher-than-usual temperatures in late February. They are present at low levels and will require temperatures above 15C before damaging activity can occur. Forward crops this year will be more likely to grow through the susceptible stage much sooner and could flower earlier this year.

During flowering, the pollen beetles become beneficial for pollinating, as they congregate on the flowers. However, the flea beetle larvae-ridden crops will be more of a concern due to stunted growth and will need to be monitored. 

Sugar beet and the loss of neonicotinoid seed dressings is a major concern to potential virus yellows infection this year. The British Beet Research Organisation has forecast high level of virus and if conditions remain mild, we could see an earlier migration of peach potato aphids.

This will make sugar beet establishment ever more important in order to ensure crops rapidly reach 12 true leaves. It would also be prudent to ensure Teppeki (flonicamid) is on farm and ready, as this is currently the only authorised insecticide for these aphids.