Wheat flag leaf spray is extra important this year - farmers weekly

28 APRIL 2000 ------------------------- WHEAT FLAG LEAF SPRAY IS EXTRA IMPORTANT THIS YEAR By Andrew Blake WINTER wheat growers are being urged not to delay flag leaf (T2) sprays this

season, even where earlier treatments have been disrupted. This months wet weather means Septoria tritici could be hard to contain on the upper yield-driving leaves, warn specialists.

Uncontrolled the disease can halve yields, says Neil Waddingham of Novartis. Even with only a 10% yield cut, it could cost a 200ha (500-acre) producer normally expecting 8.5t/ha (3.4t/acre)

£11,000, he calculates. "It is a realistic scenario that is not very inviting. So fungicide choice, timing and dose at T2 will be critical." According to ADASs David Jones and

Morley Research Centres Doug Stevens, the key task at T2 is to protect the top three leaves. In many modern varieties these do not need rain splash to get septoria, picking it up by direct

transfer as they emerge. Up to 43% of yield comes from leaf 1, the flag leaf. Less than a quarter comes from leaf 2 and 9% from leaf 3. "That shows the vital importance of the flag

leaf," says Dr Jones. In thick crops leaf 3 may be heavily shaded and contribute little, notes Mr Stevens. "Conversely when the flag leaf rolls up in a drought, the lower leaves

become more important." No Recommended List wheat variety rates more than 7 against septoria, so in most seasons all merit treatment against it, he adds. The aim at T2 is protection and

short-term eradication in the flag leaf and longer-term eradication in leaf 2, says Dr Jones. That involves balancing different fungicides in a mix. Depending on dose, modern triazoles are

useful eradicants, whereas strobilurins are primarily protectant, he says. Morley trials with Opus (epoxiconazole) in 1997 highlight the importance of timing T2 sprays correctly. Where no

previous treatment was applied, a delay of 14 days beyond GS39 cut yield by over 0.5t/ha (0.2t/acre) irrespective of dose. Strobilurins at T2 are kind to crops and produce higher yields,

says Mr Stevens. "I think it is something to do with their control of secondary pathogens." Strob economic optimum dose is closely linked to variety and disease pressure, though

Claire did produce unexpectedly good responses last year, he notes. The work also suggests trifloxystrobin (as in Twist) combined with Opus at T2 is less sensitive to dose reduction than

Landmark (kresoxim-methyl + epoxiconazole). Other factors to consider are previous treatment and whether a T3 is planned. "Provided a good dose of protectant fungicide was used at T1,

there is some flexibility in the T2 timing." But for Consort, which was sprayed at T1 with a half-dose of Opus and strobilurin, with no T3 intended, mildew and rusts only low risk and

septoria the main threat there are two approaches, he says. "At the traditional timing at GS39 Id use 0.3 litres/ha of Opus with 1.5 of Twist. If you dont go until early ear emergence

at GS45 I would up the triazole to 0.5 litres/ha and reduce the protectant slightly to 1.2." &#42 T2 WHEATSPRAYS _&#8226 Guarding top 3 leaves._ _&#8226 Septoria main

target._ _&#8226 Use strob/triazole mixes._ _&#8226 Trifloxystrobin flexibility._