Low wheat prices should have little impact on how much growers spend on fungicides this season, and they are being advised to “tweak” inputs rather than making full-blown cuts to keep up profit margins.

Falling grain prices prompted Niab-Tag’s technical director Bill Clark to develop a new computer model for 2016 to show growers that they don’t automatically need to cut their fungicide spend.

Mr Clark says this new tool shows that choosing optimum fungicide levels to suit this year’s disease risks is a smarter choice than a knee-jerk reaction to scrimp and save as wheat prices linger around £100/t.

See also: Disease alert as yellow rust builds on winter wheat

Bill Clark

The model uses variety yield data from official trials and combines this with the wheat price of the day and the disease pressure to give an optimum fungicide spend to maximise profits.

“This model shows that your fungicide costs need only change very slightly with a change in wheat price,” says Mr Clark.

“Prices would need to be well below £100/t – probably around £70/t – for this model to tell you to change your fungicide strategy radically.”

“Many growers think they can spend less money, but that is a risk because nobody can predict what the future disease pressure is going to be like.”

He estimates that margin loss from spending too little on fungicides in a high disease year is three times the margin loss from over-spending in a low disease year.

Fungicide savings

When it comes to maximising profits, Mr Clark says growers should be adjusting dosages rather than dropping relatively expensive SDHI fungicide products from a T1 or T2 spray.

Not only will this help growers stay in budget but it will also go some way to ensuring the curative ability of the SHDIs is preserved and disease resistance is not allowed to build up.

“If you don’t use an SDHI at T1 and you get to a bad stage at flag leaf you will be putting a large amount of pressure on the eradicant capability of the SDHI chemistry if you only use it at T2,” explains Mr Clark.

“Savings should be made by dropping from a three-quarter dose to a half dose, for example, not by dropping a product. I stress that in a high disease year you will need to use an SDHI at T1 and T2 for septoria control.”

See also: Increased threat of SDHI-resistant septoria in UK

He advocates using two SDHIs in a fungicide programme to alleviate the risks of resistance, which he says is “waiting in the wings”.

Preventative approach

Iain Hamilton

Syngenta field technical manager Iain Hamilton warns that growers’ ability to effectively treat a wheat crop for septoria has diminished with reduced sensitivity to azole fungicides, making an even stronger case now for prevention instead of cure.

“With septoria we cannot clear an infection once it’s started so we must adopt a preventative approach.”

“T0 and T1 fungicides are especially important, not only for protecting the lower leaves, but also for reducing over-wintered septoria and rust innoculum, and then in restraining disease progression up to the flag leaf,” explains Mr Hamilton.

He points to Adas trial work which found crops with a T0 application yielded 0.36/ha more when a chlorothalonil and two different azoles were used. 

Mr Hamilton adds that there has been a rebalancing of the importance that a T1 and T2 each play in a fungicide plan, with the T1 now being viewed as a “firebreak” against disease and a need for the T2 to be more adaptable to a season’s disease pressure.

“We see the T1 spray as increasingly important over the past few years to stop disease transfer up the plant, while the T2 serves to keep the main yield-building leaves clean.”

Bill Clark and Iain Hamilton were speaking at a wheat fungicide press briefing held at Syngenta’s headquarters in Whittlesford, Cambridgeshire.

Bill Clark’s fungicide top tips

1. A mild winter means some wheat crops are looking very advanced but growers should not confuse development with growth and go in prematurely with a T1 spray. This would mean a long wait until T2 and risks leaf two getting infected, with disease then able to spread to the flag leaf once it emerges.
2. SDHI resistance is waiting in the wings so timing is vital to ensure growers are not putting too much pressure on SDHIs.
3. Using a different SDHI product will not help the risk of resistance developing in the future. The best thing to do is to follow the stewardship and only use an SDHI in a three-way mix.
4. Make the most of the protectant opportunities at T0 and T1.
5. Make savings by reducing fungicide dose rather than dropping a product from a T1 or T2 spray.
6. Don’t be surprised to see yellow rust developing on disease-resistant varieties already. The varietal resistance can kick after T1, so don’t let the plant struggle early on or let innoculum build up for other less-resistant varieties on the farm.