Putting the 'breaks' on - Technical Disease control - Crop Production Magazine
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Putting the ‘breaks’ on
Technical
Disease control
It might be tempting to focus has already got out of hand. Instead, before Christmas and it’s been a mild
most fungicide firepower on a good T1 has become increasingly winter. Later drilled crops may be at lower
important for keeping a lid on infection septoria risk, but they can be hit hard by
T2. But with unpredictable earlier, says Harry Fordham, new farming yellow rust because they’re so small.”
weather and disease risks, is technology lead at Syngenta. Paul Gruber, regional technical manager
for agronomy firm ProCam, agrees T1
this shutting the stable door Disease firebreak provides a crucial disease ‘firebreak’. He
after the horse has bolted? “Think of T1 as a disease firebreak. says the aim of an effective T1 when leaf
Although the primary spray target for T1,
CPM finds out. leaf three, only contributes about 8% to
yield –– compared with 23% for leaf two
By Rob Jones and 43% for the flag leaf –– its strategic
and Lucy de la Pasture importance goes well beyond this.
“By keeping leaf three clean with an
effective T1, it’s essentially ‘sanitising’ a
Few of us need reminding how stepping-stone that otherwise facilitates
unpredictable yellow rust has become disease transmission up the plant. It’s
over recent seasons –– including important because the tip of the flag leaf
growers in the west where yellow rust emerges from below leaf three and it
hasn’t historically been that much of a becomes even more so if you haven’t
problem. Septoria tritici also has a history got on top of disease at T0.”
which shows it’s becoming more difficult A big temptation at T1 can be to trim
to control. fungicide inputs if disease levels appear
Seasons such as the washout summer to be low at the time of spraying. But that’s
of 2019, when sudden weather changes a huge gamble, Harry stresses. “The
exposed any weaknesses in earlier impact of future weather on disease
fungicide inputs, have provided some development at that point is still unknown.
harsh lessons. So while the flag leaf Rusts cycle very quickly in favourable At T1 plants are growing more upright so you
remains the biggest yield contributor in conditions,” he notes. want the spray to penetrate down into the crop,
winter wheat, it’s no longer possible to rely “This season there’s been a wide range says Harry Fordham.
on a robust T2 to rectify things if disease of drilling dates, with yellow rust found
8 crop production magazine arable extra march 2021
Cereal diseases
“ If the
wheels come off early
three is emerged is to minimise latent
infection on leaf two above it, so that the
T2 spray can be applied to a clean flag
with yellow rust control,
leaf, to deliver its best results.
you never get the “Get T1 right and there shouldn’t be a
crop back.
” need for a T1.5 spray between T1 and T2,
apart from in exceptional cases,” says
Paul. “But get it wrong, and that’s when
you end up chasing your tail.
Varietal resistance
“If the wheels come off early with yellow
rust control, you never get the crop back.
Early yellow rust prevention has become Paul Gruber believes in keeping crops in a
even more pertinent, given how quickly preventative rather than curative situation
we’ve seen varietal resistance ratings when it comes to disease.
break down.”
Paul says that for septoria, curative prevention is also important at T1. “By
ability may potentially be improved with keeping the lower canopy disease-free for
new fungicide chemistry, but even with longer, there’s less of an infection source
this, he believes keeping crops in a to move upwards. This also gives some
preventative situation is still better than reassurance if there are delays to the T2.
a cure. We talk about maintaining a maximum
“The more we expose new chemistry three-week interval between spray timings,
to established disease, the sooner it will but we don’t always know if the weather
break. The cleaner we keep the crop, not will allow this.”
only the better the yield protection, but Trials at ProCam’s main hub at the
the longer the new chemistry will be Stockbridge Technology Centre in
preserved.” Yorkshire have shown T1 to T2 intervals
Allied to this, he says persistent disease vary widely depending on variety and
▲
Cereal diseases
“If there’s a hot spell between T1 and three won’t have emerged fully, so it won’t
T2, brown rust soon gets going. There be fully protected and there’s an increased
are plenty of varieties relatively tolerant to risk the treatment will run out of steam
septoria but not to brown rust. Solatenol is before T2. Spray too late and you
inherently strong on yellow and brown can miss the boat when it comes to
rusts and is persistent in its control.” maintaining preventative control.
“You can aid spray timeliness by using
Practical considerations drift-reducing nozzles to maximise spray
These are the biological arguments for windows. At T1 plants are growing more
effective T1 disease control, but what upright so you also want the spray to
about the practical considerations? With penetrate down into the crop.”
other inputs such as growth regulators, To these ends, for most situations Harry
herbicides and foliar nutrition also advocates Amistar nozzles for both T1
potentially going in the spray tank, and T2 sprays. As well as being 75%
Paul says good tank mixability of the drift-reduction nozzles, he says their
T1 fungicide is crucial. slightly rearward-facing spray pattern
“Opt for a fungicide that doesn’t move counters the sprayer’s forward motion, so
By achieving effective control at T1, latent
up the leaf rapidly and accumulate in the droplets travel more vertically into the
infection on leaf two will be minimised so that
leaf tip, which is what can cause scorch,” canopy for more even coverage on the
the T2 can be applied to a clean flag leaf.
he suggests. front and back surfaces of upright leaves.
Additionally, with the shape of the plant The coarser droplets they produce also
drilling date. And while brown rust is changing at T1 from its flatter T0 shape, aid canopy penetration, he notes.
▲
considered a later season disease, he and chances of catchy weather, Harry “Although the primary target at T1 is
says pressure can be building between says pay close attention to application, leaf three, a coarser droplet also helps
T1 and T2. For persistence and rust not only to get the maximum spray on the get spray down to leaf four and leaf five,
control he rates the SDHI Solatenol target, but also to achieve timely spraying. which can boost the firebreak effect. In
(benzovindiflupyr) highly at T1. “Spray too early and the base of leaf normal conditions, our guidance is to
▲
More than just disease control?
multisite fungicide still boosted A further disease-free occur in plants,” explains Tudor.
yield by 0.65t/ha, to 10.25t/ha. experiment also showed less water “This work has demonstrated
“At £165/t for wheat, that’s loss from the flag leaf and leaf two non-disease control benefits from
worth an additional £107/ha, so a in plants treated with Solatenol at Solatenol. It indicates that SDHI
significant return on the extra GS31, compared with an untreated chemistry may help plants to
investment. Being a dry year, this control. This was backed up by field conserve water, which could be
yield uplift was unlikely to have results in the low disease year of important in water stress situations.
been due to disease control, but 2020 in a crop under drought “The practical consequence is to
more likely physiological effects –– stress, where there was also less help the grower and agronomist
maybe increased rooting or better flag leaf rolling following a GS39 choose products that can exhibit
tolerance to drought,” he suggests. Solatenol application. non-disease control properties to
The physiological benefits of an “SDHI fungicides are very augment the returns from disease
early-season SDHI fungicide in effective at inhibiting processes control that fungicides offer, should
disease-free situations has also in fungi, but the same pathways disease not develop.”
been researched by Dr Tudor
Even in disease-free conditions, Dawkins at the University of Effect of SDHI on water loss
Tudor Dawkins found that flag leaf Warwick over the past two years.
greenness was boosted following A former agronomist, he’s well
an earlier application of the SDHI aware of the temptation to cut back Leaf 2
Solatenol at GS31. at T1 if disease pressure looks low,
Leaf layer
so was keen to understand what
The argument for investing at T1 fungicides do in addition to
may be convincing. But what disease control and to identify any
Flag leaf
happens if it turns into a low predictable and measurable effects.
disease year? According to Paul, Using a SPAD meter to measure
ProCam trial plots showed that leaf greenness in disease-free 0 5 10 15 20 25 30 35 40
Water loss per hour per cm2 of leaf
even in the low disease year of glasshouse conditions, he found the
2018, when T2 fungicides gave chlorophyll content of flag leaves was Reductions in water loss (mg water/hr/cm2) from flag leaves and leaf 2
only a modest yield increase, boosted by about 5% following an following application of Solatenol at GS 31.
adding SDHI plus strobilurin to earlier application of Solatenol at Source: University of Warwick, 2021
a T1 base treatment of azole plus around the T1 timing (GS31).
10 crop production magazine arable extra march 2021
Cereal diseases
Fungicide choice a factor in yellow rust control
Agronomist reports last season about the in disease levels between pyraclostrobin,
difficulties controlling yellow rust was put down to epoxiconazole, tebuconazole and prothioconazole
a combination of late drilling, winter weather and treated plots. But second assessments, one month
changes to the pathogen. But research by Bayer after application, revealed high disease levels in
at the Cawood trial site in Yorkshire suggests that strobilurin treated plots.
fungicide choice might have been a factor. “Strobilurin speed is an asset where the
A single application of various fungicide disease is established as the fungicide acts
treatments were applied to JB Diego and followed quickly against the pathogen. But for a fast-cycling
up with disease assessments approximately one disease like yellow rust it leaves plants exposed to Bayer trials illuminate the differences between
week and one month after application. The trial new infection,” says Rosalind. speed of activity in knocking down yellow rust
confirmed what had long been suspected –– that While strobilurins were at the bottom of and persistence.
there are few ‘all-rounders’ in the yellow rust performance tables when it came to persistency,
fungicide armoury, with most actives ideally suited Elatus Era (prothioconazole+ benzovindiflupyr) tebuconazole, she says.
to protectant or curative situations, but rarely both. came out at the top of the list, offering protection Bayer-formulated Prosaro was also compared
How these curative and protectant fungicide over multiple-cycles, she says. However on with a generic prothioconazole+ tebuconazole
properties differed was quite marked. Strobilurins established disease Rosalind believes a strobilurin formulation. While they both performed well at the
stood out for their curative properties but proved or fast-moving azole is probably the best option. first assessment, the later assessment revealed
to have limited persistency. Some strong In addition to highlighting differences between 5% more yellow rust in the generic plots,
protectants offered little against established actives, the trial also confirmed the importance demonstrating its limited persistency compared
disease, says Bayer’s Rosalind Martin. of formulation. Bayer-formulated Folicur with Prosaro.
It all comes down to fungicide formulation and (tebuconazole) was compared to Toledo “Given the uncertainties and unpredictability of
the speed of active on the pathogen, she says. (tebuconazole) and the first assessment, factors affecting yellow rust, both tebuconazole
“It’s common practice to include a strobilurin in a just one week after application, found the and prothioconazole proved themselves as the
fungicide mixture to boost yellow rust control, but Toledo-treated plots had 5% more yellow rust best all-round actives against the disease,
their movement on and through the leaf means infection compared with the Folicur-treated plots. delivering a good balance of persistency and
they are short-lived on leaf surfaces. Our first This confirmed that SC (suspension concentrate) curativity, particularly when well formulated,”
assessments showed only small differences formulations don’t act as fast as Bayer-formulated she concludes.
Tailoring disease control to risk
Understanding risk based on early cropping automatically calculates which crops are at the
decisions, like variety or drilling date, and highest risk from disease, taking into account all
in-season monitoring of crops are key to using of the factors affecting disease developing in the
Integrated Crop Management (ICM) successfully. crop and allowing the user to tailor a fungicide
Many farmers may already be taking these steps approach accordingly.
without fully realising it, says Dave Howard, “It’s about being better informed to plan a
head of ICM at Hutchinsons. strategy. The job of the model is not to tell us
“ICM doesn’t require a drastic change from that disease is present, but rather to plan for
the norm, in fact many ICM principles have what disease will be more likely to develop in a
already been taken up over the years due to particular variety/field etc. This allows the user
the positive effect they can have on disease to temper that risk as much as possible, not
management. It’s simply a more strategic eliminate it, by tailoring a planned fungicide
approach when planning which crops and approach accordingly.”
varieties to grow, assessing where risks lie and The model takes into account the data
then adapting management and inputs in already entered into Omnia, like variety and Dave Howard explains that a new disease risk
response to changing weather patterns and drilling date, alongside the climatological data forecasting model within Omnia can help justify
disease levels –– or visualizing risk,” he says. provided by the Omnia Climate module. The fungicide applications.
“This can be more complicated than it output is a visual risk map across the farm,
sounds. Over the past two years growers have illustrating which fields pose higher risks and to be planned more effectively.”
juggled with a spectrum of drilling dates and where that risk is coming from, he explains. The risk is recorded though the season to
varieties across their farm, which makes “Users can allocate specific fields and are provide a record for justification purposes which
assessing which crops are at higher risk more presented with a sliding scale to access visual is something that is becoming increasingly
complicated. And that’s without the extremes of representations of crop growth and certain important, he adds.
weather to consider throughout the season.” growth stages. Likely spray days are then The Omnia team are developing a similar
So to make this process much simpler predicted and as the weather patterns model for barley and a lodging risk model for
Hutchinsons has developed a Wheat Disease change, the calculated risk constantly wheat, which are both being trialled this spring
Risk Forecasting model within Omnia. The model evolves, allowing fungicide programmes at Hutchinsons’ Helix farms.
crop production magazine arable extra march 2021 11
Cereal diseases
Brown rust can build between T1 and T2 so in “In conditions when drift reduction
susceptible varieties it’s wise to use a fungicide becomes even more important, consider
with both good preventative activity and 90% drift reduction nozzles but use a
persistence. minimum of 200 l/ha of water to
maintain coverage. Nozzle height
should be 50cm above the target, but
use Amistar nozzles at a water volume remember the target is higher than at T0.
▲
of 100 l/ha and 12 km/h forward speed. “Overall, it’s well worth investing in
In an especially thick crop, a higher water getting T1 right. You still need to do a
volume won’t harm, but don’t simply good job at T2, but it may be possible
increase the pressure to achieve this to use a less expensive T2 fungicide
–– the finer droplets produced won’t because of reduced need for curative
penetrate and will be more prone to drift. control.” ■
Biofungicides can take pressure off chemistry
Disease control is all about about 10 weeks and helps protect registration for barley is anticipated
prevention these days and this new and developing plant tissues.” in the future after trials have shown
is where early use of the The difference between a promising reductions in net blotch,
elicitor-based biofungicide, Iodus conventional T0 and an elicitor is rhynchosporium and ramularia.
(laminarin), provides an added ‘same time, different place’ –– the
dimension to septoria control target is leaf four but the Iodus Sticky sulphur
strategies, says Greg Hanna, trials provides systemic protection for the Sulphur is something that’s been
manager at UPL. whole plant, including the leaves used for decades for its fungicidal
“When used at 0.75 l/ha, yet to emerge, explains Greg. activity. It’s now available as
Iodus triggers the self-defence “Traditionally a fungicide applied biofungicide Thiopron, a liquid
mechanisms within the wheat at the T0 timing aims to protect the formulation with enhanced sticking In trials Iodus has reduced the
plant. Normally it takes 48 hours basal leaves that have just capabilities due to its formulation incidence of septoria by a
for these defences to be activated emerged and can contribute up which includes Xanthan gum. It also similar level to both folpet and
after a pathogen has invaded plant to 5% of the crops yield. Iodus has good compatibility with other chlorothalonil, providing another
cells, but Iodus causes them to be provides protection to the basal fungicides. tool for tackling disease,
‘switched on’ in advance of a leaves along with a reduction in Elemental sulphur is effective says Greg Hanna.
fungal attack so the plant is already the inoculum that would spread when formulated as a fungicide due
prepared to fight it.” upward, but also confers benefits to a process known as sublimation, future establishment of spores.”
Laminarin, the active ingredient to the upper canopy that isn’t the transition of a solid substance Thiopron can be used as an
in Iodus, is a natural metabolite present at the time of application. to a gas state without passing alternative multisite at T1 and T2
extracted from a special species of This ‘priming’ of the upper leaf through a liquid phase, explains and in trials provides equivalent
seaweed, Laminaria digitata, found layers against subsequent disease Greg. levels of control to folpet when
in the North Atlantic Ocean. can help reduce the pressure “Atmospheric hydrogen binds used at 2-3 l/ha. On the label
“Laminarin is a protein which on the T1 and T2 fungicide with the sulphur active and forms approval is for powdery mildew but
mimicks a protein found in dead programmes.” Hydrogen Sulphide (H2S) gas in Greg says trials have provided
fungal cells and this tricks the plant In trials Iodus has reduced a surface layer on the leaf. This good efficacy data for septoria in
into thinking that a pathogen has the incidence of septoria by a gas layer is toxic to fungal wheat and for rhynchosporium and
invaded,” explains Greg. similar level to both folpet and pathogens, providing curative ramularia in barley, where it has a
“The plant responds to this chlorothalonil, with an average effects but also toxifying the particularly good fit because of its
elicitor action in three ways. It yield response of 0.3t/ha across surface of the leaf to prevent the disease profile.
increases the thickness and the trials which is comparable with
lignification of cells walls to provide the multisites. Greg emphasises Main contributors to yield
a barrier to invading fungal hyphae. that as an elicitor, the biofungicide
Ear
The plant also produces isn’t actually acting on the
phytoalexins which circulate in pathogen so is a parallel product Flag leaf - Leaf 1
the vascular tissues and bind to multisites, providing another tool Leaf2
to pathogens, inhibiting their for managing disease. Lea 3
development –– producing The reduction in disease burden
Leaf 4
a vaccine-type effect. that Iodus brings to the party is
“As well as phytoalexins, the plant something that Greg believes can Leaf 5
produces pathogenesis-related (PR) play a key role in supporting other 0 10 20 30 40 50
proteins in response to cell-to-cell fungicides as they come under Contribution to yield (%)
signalling as part of the systemic increasing pressure due to the
Iodus switches on the plant’s systemic acquired resistance pathways so
acquired resistance (SAR) evolution of resistant pathogens.
protects leaves yet to emerge.
response. This is maintained for Currently only approved in wheat, a
12 crop production magazine arable extra march 2021
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