Winter wheat growers are being advised to not only stay alert for Septoria tritici this season, but also for yellow rust risks at the upcoming leaf three (T1) spray timing.

Although Septoria is widespread, yellow rust can escalate more rapidly and the mild winter means the disease may have already progressed to younger leaves, even if not visible.

“Although Septoria will be the main wheat disease growers will focus on, it’s important not to let yellow rust slip through the net at the important T1 fungicide spray timing, which is typically during April,” said Syngenta area business manager, Peter Hawkins.

“The amount of yellow rust in the plant can be reduced by frosts, but temperatures need to be harsher than often realised – for example five days of continuous minus 5-6 deg C. Depending on the weather, yellow rust can bounce back quickly – going through its life cycle in just 10-12 days, compared with 14-28 days for Septoria tritici. This explains why it’s so important to halt it early. It can also cause big yield losses of up to 50%.”

In response, Mr Hawkins added that ensuring T1 fungicides target yellow rust and not just Septoria will be an important consideration.

“AHDB dose response curves show the SDHI fungicide Elatus Era has very strong yellow rust activity, with our own trial work showing T1 is the best time to apply it against yellow rust.

“If you check crops at T1 and think there’s no rust and don’t include a yellow rust active fungicide, you can find soon after T1 that yellow rust has suddenly appeared. You then have the conundrum of do I go back in with a T1.5 spray for yellow rust, which costs more, or not? If not, then it can cycle again before T2 in suitable weather, so you’re in a real dilemma.

“The main aim of T1 is to control disease on leaf three, which is effectively a stepping stone between any disease present on lower leaves and the upper yield-building leaves. These top three leaves contribute about 75% of final winter wheat yield,” he commented.

Mr Hawkins added that if a suitable T0 fungicide has not been applied before T1, or if there has been a long interval since T0, it could be particularly important to ensure good yellow rust activity is included in the T1 fungicide.

“Inspect crops regularly for signs of yellow rust and take into account variety resistance ratings, but remember that other factors can lead to its rapid flare up, even in more resistant varieties. With heightened Septoria tritici pressures this season, I would also urge growers to look at including the multi-site fungicide, folpet,” he concluded.