3 March 2000

New strob being tipped on rhyncho and septoria

Fungicides are vital inputs,

but top returns do not

necessarily come from top

rates. In this special,

edited by Andrew Swallow,

we ask where doses can

be cut, passes reduced and

when a robust strategy is

really the best bet. Barley

recommendations come

from the hot-bed of barley

disease, the south west.

Spring barley leaf spotting

is sorted out in Scotland,

and wheat is worked over

by experts in the east.

New triazole metconazole

is profiled, strobilurins

feature throughout, and

Amanda Dunn kicks off

with a north-to-south look

at trifloxystrobin, the

newcomer promised from

Novartis

TRIFLOXYSTROBIN – the Novartis strobilurin – looks set to find a role on rhynchosporium in the north and septoria in the west, but it is not without limitations, warn agronomists.

"Trifloxystrobin brings rhynchosporium control at a level better than anything we have seen so far," says Jim Rennie, managing director of Crop Chemicals, Scotland.

That view is echoed by Clare Bend, technical manager for Cheltenham-based Masstock group, which has been trialing trifloxystrobin for three years.

"It is definitely the best strobilurin so far for rhynchosporium in barley and in wheat it provides improved control for Septoria tritici. That is the main disease threat facing us in the south west."

Mildew control is better than azoxystrobin, at present, and trifloxystrobin appears to offer more rate flexibility than other strobilurins, potentially making it a more cost-effective choice, she adds.

But the new product is not without limitations. Control of stem-based diseases and rusts is questionable and tank mix restrictions and early access to the product may confine use this season, notes Ms Bend.

"I am yet to be convinced of trifloxystrobins control of yellow or brown rust in wheat, and it is poor on stem based diseases such as eyespot and sharp eyespot. But it is possible to work round these limitations and plug disease weaknesses using triazoles, such as cyproconazole or metconazole for rusts, and cyprodinil for eyespot," she says.

Lack of compatibility data means boosting plant growth regulator activity with adjuvants in tank-mix with trifloxystrobin will not be possible this season, though that may change next season.

For wheat crops, Ms Bend suggests flag leaf as the key timing for this new strobilurin, but Mr Rennie wants to see more work in his area.

"With this type of chemistry you learn once it is out in the field. While it is easy to identify clear targets for barley now, best routes for use on wheat are less obvious."

Rhynchosporium-prone varieties such as Regina, Chariot, Derkado and Optic should be treated at first or second node, possibly with a sec-ond application at flagleaf, he says. "At nodes one and two, control has been achieved with anything from 40-70% of a full dose rate.

"Rate decisions should be based on a combination of what disease you are targeting and how long you are expecting that crop to last, if you go in early use a higher rate, and later use a lower rate.

"To generate a yield kick, an aggregate of 80% of the full dose rate of strobilurin over the season should be applied."

TRIFLOXYSTROBIN TIPS

&#8226 Rhynchosporium boost on barley.

&#8226 Septoria strength for wheat.

&#8226 Mildew advantage, for now.

&#8226 Weaker on rust and stem-based disease.

Trifloxystrobin has a clear role on winter barley at T1, but more work is needed to see where it will fit for wheat, says East Lothian-based agronomist Jim Rennie. Masstock sees strong septoria and mildew control being an advantage in the west.