2 March 2001

Timings need to be spot on

With the extremes of early and late drilled wheats on farm

this spring fungicide timings will need extra care, say

agronomists. Andrew Swallow reports

TUNING fungicide timings to drilling date and crop state will allow savings to be made this season, but care must be taken to avoid costly gaps in protection, say agronomists.

Late drilled crops offer the biggest chance to cut inputs, says AICC agronomist Steve Cooke, of Hampshire Arable Systems.

"You will probably be able to cut back to two sprays. But the T1 will need to go on at GS31 rather than GS32 as leaf three will be emerged from GS30."

That means some triazole kick-back will be needed to keep latent disease at bay. But the strobilurin rate can be substantially cut, perhaps to a quarter, he says.

UAPs Chris Bean echoes Mr Cookes comments. "In November or January drilled crops GS31 to flag leaf emergence only takes two to two-and-a-half weeks." (see chart.)

Combine that reduced interval with lower septoria pressure and eyespot risk and growers can use much lower inputs on such crops.

"I would suggest a half-rate of Landmark or possibly lower depending on the site and the variety."

A non-strob approach such as metconazole plus chlorothalonil could prove equally as effective, he suggests. But mildew must be watched as the rapid growth of late sown crops makes them very vulnerable to the disease. Adding quinoxyfen or a morpholine may be necessary.

While extreme wet weather has held back late sown crops, early drilled wheat has generally established well. Here, an early T0 spray may be needed, as rain and recent mild conditions have led to high disease pressure, especially in over-thick crops.

"We are seeing higher levels of septoria than last spring. The tips of the leaves are turning yellow and it is pure Septoria tritici.

"On septoria susceptible varieties a T0 spray last year added 1t/ha," he adds.

Consort, Tanker, Deben, Riband and Savannah all fit in that bracket and a mid-March application buys insurance if true T1 sprays are delayed.

"Last year sprays that should have gone on in the first week of April ended up going on at the end of the month or even the first week of May."

Landmark (kresoxim-methyl + epoxiconazole) at 0.5 litre/ha provides a good range of control at T0, he says.

"It is good enough on eyespot, very good on septoria and helps to take care of rust and mildew."

If mildew is considered a severe risk then quinoxyfen should be added, or perhaps a morpholine where rust is active too, he suggests.

If a T0 has been made, then T1 can be timed at GS32 and 0.5 litre/ha of Landmark should suffice. But, where no T0 is made 0.75 litre/ha plus a morpholine is recommended.

Due to the time from T1 to T2 in earlier drilled crops, T2 sprays should be made with the flag leaf half-emerged. But in later-drilled crops growers can afford to wait until full flag-leaf emergence.

"And you could argue if the crop is only for feed you could delay to ear emergence," he adds.

But for most crops Mr Bean suggests a stand-alone T3 to coincide with flowering at the latest.

"Typically that is 15-18 days after T2, it does not want to be much longer. If you are not on before flowering finishes then you might as well forget it." &#42

TIMING TIPS

&#8226 March T0 for early drilled wheat.

&#8226 Late drilled wheat GS30-31 T1.

&#8226 Two-spray option on late drillings.

&#8226 Beware mildew on late drillings.