Offsetting waterlogging damage with careful management strategies – Farmers Guide
Early disease control and growth manipulation will play a crucial role in helping crops overcome a difficult start to the season ...
The widespread waterlogging and flooding seen over the autumn and winter has resulted in a huge variation in crop growth going into the busy spring months, and some careful management will be required to optimise yield potential, however high, or low, that may be.
At one end of the scale are early-sown wheats that went into good conditions last autumn, received a pre-em and escaped the worst of any flooding. These have generally put on decent biomass and show promising yield potential at the time of writing, although may inherently be at greater risk of other issues associated with more forward crops, such as septoria or lodging. At the other extreme are those fields affected by flooding or waterlogging, which have not been written off, but will require careful management to get the most from a compromised situation.
Manipulating rooting
One of the biggest issues facing crops that suffered flooding or prolonged waterlogging is poor root development, says Farmacy regional technical support manager for East Midlands, Alice Cannon.
In some situations, crops may have shut down completely, akin to a drought situation, which has consequences for photosynthesis, tillering, rooting and biomass growth.
“Potential fertile tillers are determined from the number of leaves present at stem extension, so keeping green area index going through March is crucial to building yield. Later-sown or backward crops have fewer leaves, so less potential for tillering.”
Roots often adapt to wet conditions by growing closer to the surface to facilitate gas exchange in anaerobic soils; however, this presents issues as the season progresses, especially when conditions turn dry and crops need more scavenging ability for water and nutrients.
Miss Cannon says that alongside a careful nutrition and disease control strategy to build healthy biomass, tillers and rooting, timely applications of plant growth regulators could play an important role in manipulating crops to offset some of the damage done by waterlogging or flooding.
“The power of PGRs is not just about straw shortening; the chemistry can manipulate crops in many other ways, on the product choice, rates and timing.”
Tramline and small plot trials last year, for example, showed early PGR applications at T0 (GS30-31) and T1 (GS 32) can significantly improve stem diameter and stem width, boosting the plant’s lodging resilience-something that will be particularly important in shallow-rooted crops that may be more prone to lodging as biomass develops, she says.
The same trial also found a benefit to tiller survival from early PGRs. “Tillers produced after stem extension usually abort, but that’s simply not an option this year given we’re already facing a reduction in tillering due to the compromised foundation period, so we’ve got to consider all available tools.”
Care is needed with product choice and rates on backward crops, she cautions, while more forward early-sown cereals might benefit from slightly higher rates. “Growth stage 30 will be an extremely important timing this season. It’s traditionally a disease control timing, but it’s just as important to manipulate crops at this stage to maximise their potential.”
Disease control
In terms of early disease risk, the variability in crop development, sowing dates, and uncertain weather outlook over coming weeks, makes for a complex picture, according to Farmacy’s head of integrated crop management, David Howard.
Though it is too early to ascertain disease risk for the main diseases, he anticipates that crop stress will have a huge part to play in disease pressure this year. Overall, pressure will vary depending on a host of variables, from drilling date, variety and disease pressure, to soil condition, time spent waterlogged and degree of crop stress.
“Ironically, we might see some benefit where flooding has taken away the lower leaves that can carry rust or septoria spores over winter, but that will be balanced against the damage flooding’s done to crop development and crop stress.”
Compromised rooting will reduce the resilience of affected crops to take-all infection – something that could have been spread within soils due to the very wet conditions. Eyespot could also be more problematic given the wet autumn and generally low varietal resistance is, he says.
Conversely, septoria pressure is likely to be lower in late-sown crops, but the disease will be more of a risk to anything drilled early with more advanced growth.
For crops sown later in the season, the main challenge is rust rather than septoria, especially as there has been a lack of hard frosts to kill inoculum. Furthermore, any stressed crops are generally more susceptible to many diseases, especially issues such as mildew, he says.
Indeed, research shows that abiotic stress, such as that caused by waterlogging, produces abscisic acid (ABA) within the plant that is known to reduce natural plant defence mechanisms. Chemical communication pathways within plants can also become “jammed” by abiotic stress factors, further hampering the response to any disease infection, he explains.
Relieving stress with carefully targeted early nutrition to improve green leaf area is the first step in effective disease management, and this should be supported with a tailored fungicide programme, from growth stage 30/31 (T0) onwards, Mr Howard says. It is particularly important that where high amounts of nitrogen are likely to be used early to restore plant growth, that this approach is matched by early fungicide management to reduce the risk of encouraging early disease.
“In difficult seasons, the T0 can be the first input to be removed, either due to adverse weather, rapid growth stages, or to allow more of the budget to go to the remaining disease management program. Although this might appear financial sense, it is important to consider what risks the crop will be facing.”
The GS 30/31 timing is becoming much more important due to the impact it can have on the rest of the spray program, particularly in a difficult rust season, he says. This is mainly due to the unpredictable and genetically diverse nature of rust since the first insensitive isolate races appeared some 12 years ago.
“Some of these more diverse isolates also appear to cycle more quickly, meaning rust epidemics can appear unexpectedly in crops.”‘
Indeed, a 2023 trial at Terrington, Norfolk, comparing a full programme (T1-T3) with and without a metconazole-based T0, found a 1.5t/ha yield benefit from the addition of a T0 in a high yellow rust pressure situation (KWS Kinetic, rated 4, and a high rust risk area).
T0 fungicide choices must be tailored to the specific needs of individual fields, Mr Howard says.
He also notes previous trials that have shown good results from using elicitors around GS 30 to increase energy uptake in stressed crops, thereby supporting natural disease protection. Products that mimic natural disease defence mechanisms are also worth considering for septoria and mildew protection, but more so as a preventative measure in healthier crops.
Looking ahead to T1
An effective T0 strategy can take the pressure off GS 32(T1) chemistry, which traditionally focuses more on septoria control, but again, should be tailored to the condition of crops nearer the time and not be too prescriptive, Mr Howard says.
He notes that recent years have seen a gap develop in the potency of new chemistry, such as fenpicoxamid + prothioconazole, fluxapyroxad + mefentrifluconazole, or isoflucypram + prothioconazole combinations, over older SDHI/azole fungicides.
For curative septoria control, newer chemistry is therefore favoured; however SDHI/azole products, such as bixafen, fluopyram + prothioconazole, can still be effective if timed well in protectant situations.
Where rust control is required, benzovindiflupyr + prothioconazole remains the best option, although Isoflucypram + prothioconazole+tebuconazole partners are a close second. Strobilurins could also be included at T1 as a protectant strategy against rust.
Previous seasons have shown variable responses from folpet, possibly reflecting the conditions, but long-term experience shows the multisite chemistry is a good addition to programmes, helping manage septoria risk, providing some effect on rust, and for resistance management.
Timing correctly
Perhaps the biggest challenge for disease control will be around spray timings in patchy crops, Mr Howard notes.
He advises growers to time sprays based on the parts of the field with the highest proportion of higher yield potential. “Don’t wait for poor areas to catch up and risk letting disease into the good parts.”
For T1s, GS 32 is the traditional timing, however growers must ensure the target leaf three is fully emerged before treating, usually between GS 31-33, but should be identified with careful plant dissection as early crop stress can alter leaf number and emergence timings.
He also reminds growers to be careful when going on with early nitrogen applications, especially to backward crops, as large doses can cause excess nitrogen in the leaf, potentially increasing disease pressure. A split dose approach may be more effective, both for efficient crop uptake and for minimising disease risk.”
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