Barley leaf spot strategy
Barley leaf spot strategy
By Andrew Swallow
GROWERS in the north and Scotland should look at tolerance to light induced leaf spotting when choosing spring barley varieties this spring and be ready to fine-tune strobilurin use at GS39, says Teagasc scientist James Burke.
"Variety choice makes a very big difference to the amount of damage. Then it is down to fungicide choice and timing. A strobilurin at GS39 is essential."
The phenomenon, widely labelled ramularia in 1998, is now known to be a combination of non-parasitic spotting, linked to intense light, and parasitic spotting.
"The non-parasitic spotting generally comes in first, followed by ramularia. We do see some instances of ramularia on its own, but they are not so severe."
Fungicides, strobilurin or otherwise, have had limited control on non-parasitic spotting, but by limiting parasitic infection, notably ramularia, and increasing green leaf retention, strobilurins have increased yields in susceptible varieties substantially.
In 1999 responses to a GS39 application reached 1.75t/ha (0.7t/acre) but in 2000 spotting incidence was less and responses fell to 0.7t/ha (0.3t/acre).
"But it could be back next year and yields might be 2.5t/ha down. You have to plan your programme according to that.
"While days are dull you can afford to wait to make applications, but if crops have a sudden burst of sun get out there early the following morning," suggests Dr Burke.
Of common UK varieties, Chariot is most susceptible, Optic and Prisma intermediate, and Decanter more resistant, he says.
SACs Simon Oxley, one of a consortium of scientists working on the phenomenon, echoes Dr Burkes comments.
"Decanter is pretty robust, and chariot is the worst for both parasitic and non-parasitic spotting. Pewter is poor for ramularia but does not score so badly for non-parasitic spotting."
But he urges growers not to get hung up on the cause of spotting.
"The key thing is that a strobilurin plus opus will reduce both ramularia spotting and non-parasitic spotting."
Applications should be made at anytime during GS39-45 when it is fit to spray, he says.
"Once crops get to ear emergence and flowering then, bang, the spots appear."
Varietal susceptibility
Variety % spotting
Lux 2
Tavern 5
Optic 9
Century 11
Cooper 29
Teagasc untreated plots, % non-parasitic spotting on leaf 2.
Sunshine plays a key role in spring barley leaf spotting, according to Teagascs James Burke. Strobilurins are a must.