Sugar beet growers who aim to lift their crops after the
first week of November can help to reduce the risk of frost damage
by ensuring their crop is free fromrust. But action may be needed sooner
than usual.
Signs of the disease are already starting to show due to the
warm and damp weather over the past couple of weeks, says Mark
Stevens of
Broom's
Barn.
"Rust usually appears in late August or early September, but
recent weather has brought many foliar diseases forward and the
first case of rust was spotted last week," says Dr Stevens.
Trials conducted last year at Broom's Barn found that of all the
foliar diseases, rust had the greatest effect on the susceptibility
of beet to subsequent frost damage, while presence or absence of
powdery
mildew was shown to have little or no impact.
"The run of frosts we had between October and December in 2008
caused plants infected by rust to sustain high levels of
defoliation; the higher the level of infection, the greater the
damage became," says Dr Stevens.
Once significant defoliation had occured, the crown was exposed
and the root was vulnerable to further frost damage. "Crops with
poor green leaf cover would have been particularly prone to damage
when later frosts came in."
Lessening the effects of these later frosts is therefore
essential for any grower storing crops in the ground later in the
season.
"If beet is going to be lifted late, good rust control must be
achieved to maintain healthy green leaf cover," says Dr
Stevens.
"Growers should also be looking out for powdery mildew,
cercospora and
ramularia and adjusting their fungicide strategy to suit.
"If we are going to see several of these diseases, which we
could, we would recommend a broad spectrum fungicide strategy such
as
Escolta (cyproconazole and trifloxystrobin),
Spyrale (difenoconozole and fenpropidin), priori Xtra
(azoxystrobin and cyproconazole) or
Opera (epoxiconozole and pyraclostrobin)."
"It is important to keep a close eye on the crop and take
appropriate action as diseases start to develop."
If powdery mildew and rust are present, a sequence of
flusilazole
(
Sanction or
Punch C) followed by cyproconazole
(
Centaur) will give good control at a lower price, he says.
First sprays should be applied at full rate to ensure optimal
control and offer some flexibility on timing if a second
application is required, he adds.
"Early-lifted crops may get away with one spray, but given the
weather should be monitored closely, although harvest interval
should be noted; late-lifted crops will probably need a second
application in the latter part of August, which should not be
applied any later than mid-September." The extent of disease
development will be regularly updated in the weekly
BBRO
bulletins, he adds.
During trials, ramularia-resistant varieties such as Bullfinch,
Goya and Bobcat showed the greatest susceptibility to rust and
subsequent defoliation, said Mr Stevens.
Bob Rush farms 240ha of beet near Bury St Edmunds,
Suffolk and has had good results applyingEscolta(cyproconazole and
trifloxysrtobin) to Goya and Bobcat in late July/early
August.
Any crops lifted after the first week October also receive a
second dose at the end August/early September.
"We have adopted this strategy for the past few years and have
found it gives good protection against foliar diseases and
maintains good green cover right up to the point of lifting," he
says.
"We are on heavy ground and try not to lift anything after the
end of December, but at this point green cover has looked very
strong since we adopted the two-spray Escolta programme."
Neil Thompson, product manager for Bayer, says the ability for
Escolta to maintain green leaf cover is not just down to disease
control.
"When tested, crops treated with Escolta showed a higher
chlorophyll content than crops treated with other fungicides such
as Spyrale," he says.
"The increased chlorophyll content shows that the product
promotes healthy green leaf cover and development, in addition to
controlling disease."