Be aware of higher risk disease threat to crops

This season’s lush, green crops have plenty of yield potential, but also plenty of potential for disease, Syngenta and Nickerson warn.

The good news is delayed T1 sprays should mean flag leaf sprays being applied in mostly protectant situations, provided growers are not tempted to delay timings.

“Crops look very happy with life at the moment,” Nickerson’s Bill Angus notes.

“That is a big difference from the last two seasons when we had either a dry April or a dry May and the crops were stressed, and looked very leathery.

Disease doesn’t like crops like that.”

But this year’s crops are ripe for being infected with disease, he says.

“They are perfect from a disease point of view.

Despite the perception that it has been dry, there’s been plenty of moisture around.”

Yellow rust is a particular risk, according to Syngenta’s technical manager David Ranner.

“There have been some pretty good dews, and temperatures of 10-15C have been perfect for the disease.”

Controlling yellow rust isn’t a big problem, Mr Angus stresses.

“For example, on Robigus where it develops late, it is totally controllable as long as you don’t give it a window of opportunity.”

This year’s delayed T1 applications – about one week later than usual – should help growers by keeping intervals short to flag leaf sprays, Syngenta fungicide product manager Matt Pickard says.

But they must use it an opportunity to continue with timely applications, he stresses.

“The temptation for some might be to push flag leaf sprays back, but everything suggests if growers get timings right they get rewarded.

Stretching timings is very short sighted for trying to capture a crop’s full yield potential.”

Applying appropriately timed protectant flag leaf sprays onto clean top leaves should also help growers get the most of strobilurins, Mr Ranner says.

“Our database suggests you get better responses from strobs where timing is good.”

The risk from both yellow and brown rust – last season’s breakdown in resistance from Claire, Istabraq, Alchemy and Glasgow to new races significantly increases the amount of at risk varieties in the ground – also makes a good case for using a strobilurin, he says.

“The average response from a strob doubles from 0.4t/ha when diseases other than septoria are present.”

Only two strobilurins are worth considering for rust control – azoxystrobin and pyraclostrobin, he suggests.

“The advantage for Amistar is its flexibility.”

In trials on spring barley there was little difference between Amistar and pyraclostrobin, each applied with epoxiconazole, when applied at the optimal timing, but Amistar was significantly better when timings were delayed for 10 days, he says.

“There is also the water volume factor – Amistar’s systemicity helps with low water volume sprays.”

Where brown rust is a risk Mr Ranner believes a strobilurin will pay at T3 as well as T2. “On brown rust risk varieties we’d recommend using Amistar on the ear.”