Outstanding wheat flag leaf sprays will almost certainly require higher doses of triazole fungicides to control a heightened threat from Septoria tritici, agronomists warned on Monday (22 May).

The dismal weather forecast for what would have been the optimal week for applying flag leaf sprays left agronomists fearing few would be applied before this weekend.

“The prospect of a week’s delay is very serious,” ADAS plant pathologist Bill Clark said.

“It has turned a moderate risk year for septoria into a high risk year.”

The recent warm, wet weather had been “superb” for spreading infection, added UAP technical director Chris Bean.

“Disease is on the move. Septoria is easy to see on leaf four at our Kent trials site – it is quite dirty – and there is established disease on leaf three.”

Leaf two could have been infected for at least 10 days by the time growers spray, which could cause real problems, Mr Clark noted.

Only about 10% of T2 treatments had been applied so far in North Yorks AICC agronomist Patrick Stephenson’s area.

“I left a lot of recommendations on-farm 7-10 days ago for 0.5 litres/ha doses of Opus on resistant varieties.

I’ll be spending all week going round upping the dose to 0.75 litres/ha.”

It was advice Mr Clark would also be giving growers.

“Growers will have to review doses. Last week, most would have been using half doses if they could have sprayed, now it needs to be three-quarters on high risk crops.”

That included more varieties than just Consort.

“There are a whole lot of [varieties rated as] fives and sixes at risk.

There are not many varieties apart from Alchemy that can get a half dose.”

The delay could favour using Opus (epoxiconazole) rather than Proline, Mr Stephenson said.

“It probably gives the edge to Opus, because it possibly has more kickback.”

Strutt & Parker agronomist Will Gemmill agreed, but said if ears were showing on feed wheats Proline, as the better fungicide on ear diseases, might be an alternative.

Switching to a combined flag and ear spray strategy would be dependent on the farm’s spraying capacity and whether the crop was for feed or milling markets, he continued.

“I might be looking to combine the two, if the ears were out, on a feed wheat, but on a milling wheat I am still looking to do an out and out ear spray.”

The decision needed to be done on an individual field basis, Mr Bean said.

“Quality wheats, the likes of Solstice, Malacca and Hereward rather than Einstein, probably need to be covered as a separate operation.

“But our experience in trials and on farm is that for a feed wheat, T3 application is less important.

It is possible to maintain yields by putting a decent dose on at T2 as it is by doing a separate T2 and T3.”

Combining the two sprays could make a substantial saving on application costs, although not necessarily on input costs, he said.

“So, yes, it is perfectly practical.”

But TAG agronomist Andrew Blazey was less convinced.

“It is probably achievable on resistant varieties, but trials indicate a yield loss on dirtier varieties.

It is also too early for optimum ear disease control on quality wheats.”

mike.abram@rbi.co.uk