GETTING the most out of the flag leaf spray and ensuring value for money out of the most critical application of the season
THERE IS far more disease on crops than at this time last year, and septoria levels are approaching those of 2002, warns UAP technical director Chris Bean.
“We have had a much wetter April. The rain is helping to move septoria up onto higher leaves and mildew is also coming back, having been present earlier on in the year,” he says.
“Varieties like Solstice and Einstein, which are more susceptible, are carrying mildew.”
The T2 – or flagleaf – spray is important for several reasons, Mr Bean explains.
“It gives the highest yield response of the three sprays – on average 1.4t/ha from our 2003 trials, which was a low response year.
“And if it‘s done right, it takes the pressure off the T3 spray. The better the job you can do at T2, the less relevant T3 becomes in terms of yield.”
Timing is critical and Mr Bean advises growers to spray within four weeks of the T1 application.
“Don‘t leave a bigger gap, especially where septoria is an issue.”
Most T1 sprays will have been a strobilurin/triazole mix with some chlorothalonil added or a triazole/chlorothalonil mix, he believes.
“The important thing is that growers followed the latest advice to use a higher rate of triazole. If they didn‘t, they will regret it.”
Growers must recognise potential levels of disease, he adds.
“If it becomes warm and wet, we could be in an explosive situation.
“Varieties like Consort, Riband, Solstice, Einstein, Savannah, Tanker, Malacca, early-drilled Claire, Dart and Access are all carrying high levels of inoculum.”
Fungicide rates are more important than ever, suggests Mr Bean.
“You must use the triazoles at realistic, not optimistic, rates. Don‘t go below half rates, and in more testing situations increase that to three-quarters.”
He recommends using a strobilurin at T2, regardless of the resistance situation.
“They are still very valuable, both in terms of yield response and disease control.”
In his view, trifloxystrobin and pyraclostrobin as the stronger materials at T2.
“On lower risk varieties, such as Robigus, there are other options. Landmark (kresoxim-methyl + epoxiconazole) might suffice.”
The best triazoles are epoxiconazole, metconazole and fluquinconazole.
“Final choice will come down to individual situations.”
Looking at Group 1 wheats, he encourages Xi19 growers to apply the best treatment they can afford.
“Malacca should have higher rates and one of the better strobilurins.
“But Hereward is less disease susceptible and has lower yield potential, so consider spending less on it.”
Group 2 varieties are all relatively dirty and may be suffering from mildew, he continues.
“Use both one of the better strobilurins and better triazoles.
“Keep rates up and consider adding fenpropimorph or spiroxamine for mildew and additional septoria activity.”
Where Solstice is being grown on the coast, there‘s a brown rust risk. “Make sure you use pyraclostrobin in this situation.”
With the exception of Robigus, none of the Group 3 varieties are brilliant against septoria, warns Mr Bean.
“Again, one of the stronger strobilurins and a good dose of triazole will be required.
“With Robigus, there is still a potential threat from yellow rust.”
The feed wheats, or Group 4s, are all high yielding but potentially disease prone.
“You will need higher doses and stronger chemistry with these,” he advises.
“Varieties like Tanker and Savannah really suffered in 2002, and without a good T2 programme were almost dead by the third week in June.”
The combination of residual nitrogen left from last year, robust fertiliser regimes and fast crop growth could encourage flat crops.
“Get your PGRs on at or before T2,” says Mr Bean.
Resist the temptation to combine the T2 and T3 sprays, he cautions.
“There‘s too much at risk. You lose as much as 0.75t/ha in a low disease year, so there‘s much more at stake this season.”
Apply the flag leaf spray at 100 litres/ha to get the operation completed in good time.
“Not all fungicides have the same drying time – they may vary by two hours.
“If you know it‘s going to rain, think about using adjuvants to reduce drying time.
“The flag leaf spray should cost you 50% of your total fungicide spend.
“Make sure you are putting enough fungicide on – you will often get a more cost-effective response by increasing dose rate.”
Look in the next issue of Farmers Weekly for the latest Baseline Advice.