Yield responses from controlling powdery mildew with flag leaf sprays can be as much as 0.7t/ha, according to research carried out by a leading farming company last season.
The very cold frosts earlier this spring has kept mildew levels in check so far this season, Velcourt technical director Keith Norman says.
“However, it can come in later on, and even mildew on the ear can be very damaging to yield.”
Last season mildew levels of 5-15% were evident in the Velcourt trial on the uppermost leaves as T2 approached, he recalls.
“It was clear something had to be done.”
Three mildewicides were tested: Fortress (quinoxyfen), Flexity (metrafenone) and Talius (proquinazid).
In addition morpholine fungicide Tern (fenpropidin) was added to each mildewicide to assess its curative control.
“When used alone, in a single application at flag leaf, Fortress showed no yield response over the untreated, Flexity gave an additional 0.36t/ha while Talius gave a staggering 0.73t/ha extra,” Mr Norman says.
However, all three treatments gave a 0.65t/ha response when Tern was added to each.
Mr Norman also tested each in split applications made three weeks apart.
“Talius and Flexity performed equally, ahead of Fortress. Fortress appears to be losing its edge.”
Again, putting in a half rate of Tern evened things out, he notes.
“Tern’s curative activity came to the rescue.”
The trials show morpholines still have a place.
“Talius and Flexity are both good protectant fungicides with some knockdown of established disease, while the morpholines have curative properties but are short lived.
So where the disease is already present, a morpholine may be required.”
Eight weeks’ protection is needed to keep crops clean from T2 until harvest, DuPont’s Mike Ashworth notes.
“If there isn’t much mildew present, Talius alone will be sufficient.
“But where there is a significant level of mildew, then it’s sensible to include a morpholine with Talius.”
Where Talius has already been used at T1, it should be mixed with another mildewicide with a different mode of action if it’s to be used again at T2, he adds.
“The rates can be tailored to suit the circumstances.”