N caution urged on strob-treated spring barleys

21 April 2000

N caution urged on strob-treated spring barleys

By Andrew Blake

BEWARE of over-doing nitrogen inputs on strobilurin-treated spring malting barleys, warns John Hughes of CSC Crop Protection in Scotland.

Mr Hughes believes HGCA-funded ARC trials could be misleading. "I am particularly concerned because the work is using only one variety, Optic. All our trials show it is an inherently low nitrogen variety."

Overcompensating in other varieties for the nitrogen dilution effect of strobilurins increased yields could cause growers to miss out on malting premiums, he suggests.

Although Optic occupies more than a third of the area in Mr Hughes region, from the River Dee to Sutherland, there are plenty of alternatives grown which could be adversely affected by incorrect N tactics, he says. They include Chalice, Chariot, Century and Decanter.

All five varieties were trialled by CSC under three nitrogen regimes last year (see table). All received the same dual Mantra (kresoxim-methyl + epoxiconazole + fenpropimorph) strobilurin fungicide programme. While Optic tolerated a high N input, returning a grain nitrogen of 1.64, Decanter with the same input ran up to 1.93 taking it outside maltsters likely requirements.

Even under the low nitrogen regime Decanter produced 1.8N. No variety, bar Optic, gave grain below 1.7N with the high N fertiliser regime.

Mr Hughes is also concerned at one maltsters recent statement that strobilurin use risks lowering grain nitrogens beyond acceptable limits. In trials with six spring barleys at Culbokie on the Black Isle last year, only on Prisma did strobilurins fail to be more rewarding than a conventional triazole-based programme.

"Its all about sensible nitrogen management and adjusting rates to varieties. If you are prepared to do that you should be OK.

"Thats easy enough with bag nitrogen. But you need to be very canny where there is likely to be any residual N. Lots of mixed farms up here still use low levels of farmyard manure.

"A little extra N for Optic might be OK, but not for varieties like Decanter." &#42

ARC stands firm

ARC director Mike Carver stands by the value of using Optic for the HGCA trial. "We are using it because it is one of the most important varieties being grown. While we appreciate that sticking to any individual variety could be criticised, we cant test them all. We believe Optic will prove a good benchmark."

Only at one of three ARC sites last year did Optic register the lowest grain N level compared with Chalice, Chariot, Century and Decanter, he says. At Caythorpe, Lincs, it measured 1.31 in a range running up to 1.45 (Decanter). In Hants and Glos Optic was about midway in the respective ranges covering the five varieties.

Nitrogen effect on strob-treated barley:Yield t/ha & (grain %N)

Optic Chariot Decanter Chalice Century

Low N 6.4 (1.64) 6.1 (1.73) 6.2 (1.80) 6.3 (1.67) 6.1 (1.66)

Med N 7.9 (1.41) 6.8 (1.55) 7.6 (1.54) 8.0 (1.48) 7.6 (n/a)

High 9.7 (1.64) 9.0 (1.76) 8.5 (1.93) 9.3 (1.75) 9.1 (1.7)

Source: CSC Inverarity 1999 trials

Spring barley crops, particularly those drilled more recently in the north, need extra care with strobilurin fungicide/N interactions to avoid losing premiums, warns John Hughes of CSC Crop Protection in Scotland.

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