In the latest in our series on spray application developments Dr Mark Palmer, International Business Manager, Agrovista UK, Ltd., highlights key findings from pan-European trials to improve Fusarium control and reduce mycotoxin levels in wheat.
Fusarium epidemics occur once every few years in the UK, typically coinciding with warm, wet weather at flowering. When the disease does strike, the results can be devastating. Yield losses can be as high as 30%. But it is the production of mycotoxins by the fungus that can cause the most damage, as there are strict limits on levels of grain that, if exceeded on intake, can result in large tonnages being rejected.
Legal limits on grain intended for human consumption are particularly stringent and, in wet harvest years, significant amounts of grain can exceed them, particularly in the warmer East and South of England. The limits for deoxynivalenol (DON) and zearalenone (ZON), the two key mycotoxins, are set at 1,250 parts per billion (ppb) and 100ppb respectively on unprocessed wheat and barley intended for human consumption. There are higher guideline limits for mycotoxins in grains intended for animal feedstuffs.
Microdochium nivale is the main pathogen in the group. It causes seedling blight and death. Although this species can cause head blight, it is the true Fusarium species, the most common of which in the UK are F graminearum and F culmorum, that are usually associated with this symptom.
Head blight can hit yield hard, as a single spikelet infection can restrict nutrient and water flow to the rest of the ear, resulting in shrivelled grain.
In addition, F graminearum, which produces more mycotoxins than F culmorum, has a higher temperature tolerance and is displacing the latter in northern Europe.
The risk of Fusarium is increasing in the main grain-producing areas of the UK. Crop debris is the most important source of the fungus, so no-till systems, which are increasing in popularity, are known to be high risk.
The introduction of maize into rotations to feed anaerobic digestion plants also increases the risk, as it is a favoured host plant for Fusarium.
Wet weather at flowering greatly increases the risk of infection. Spores are splashed up from lower in the canopy and, if they get onto the ear during the start of flowering (around GS60), can rapidly infect spikelets.
Triazole fungicides such as tebuconazole, prothioconazole, metconazole and prochloraz can provide a degree of control. Timing is the most important factor in achieving the optimum result.
Go too early or too late and the critical window will be missed. Good application is also key. The ear is difficult to spray effectively, as it offers a small, vertical target. Ears are also exposed, so sprays tend to be more subject to drift than at other application timings, which reduces fungicide efficacy.
Control levels rarely exceed 60-65% even with a full dose of fungicide.
Agrovista’s work in Europe has shown that results can be greatly improved by tweaking certain areas of application technique to improve ear coverage and fungicide uptake.
Fusarium tends to be more severe in continental Europe due to the more widespread use of maize in the rotation, so it provides the ideal backdrop for these trials.
Over the past three years, several fungicides were evaluated in trials in Austria, Hungary, Poland and Ukraine. These included prothioconazole + tebuconazole, straight tebuconazole and tebuconazole + prochloraz applied at the manufacturers’ recommended rates, applied at different water volumes and nozzle types.
Percentage infection in untreated plots ranged from the high teens to 40%, apart from Ukraine where it remained in single figures. The average control achieved across the trials was 61%.
The same treatments were then applied with the addition of Velocity, a combination of fatty acid methyl esters, organosilicones and humectants that reduces drift and improves coverage of the leaf surface and uptake of active ingredient into the plant.
Velocity increased the level of control achieved in each trial. Overall, control rose by 17 points to 78%, and there was a consequent reduction in mycotoxin content in the harvested grain.
For example, in the Austrian trial, untreated winter wheat plots contained a not unusual 17% Fusarium infection four weeks after the other plots were sprayed. DON levels reached 1,590ppb, well above the permitted level of 1,250ppb.
Applying prothioconazole + tebuconazole (as Prosaro) at 0.8 litres/ha reduced the infection level to 6% four weeks after spraying, and the DON level fell to 401ppb. Adding Velocity further improved those results, reducing DON to just 314ppb.
In addition, adding Velocity to the fungicide treatments typically improves yield by 0.25 t/ha over the fungicide treatments alone, representing a return on investment of around six-to-one before considering any reduction in mycotoxins.
LOWER WATER VOLUMES.
As well as physically improving application, the European trials data has shown that water volumes can be reduced from the preferred 200 l/ha when treating difficult- to-hit targets, such as wheat ears, to 100 l/ha when using Velocity without affecting performance.
Halving the water volume to 100 litres typically increases work rates by a third, enabling more hectares to be sprayed at the correct growth stage, which is crucial in the control of Fusarium.
However, spray drift and rapid droplet drying can reduce fungicide efficacy.
Velocity reduces the amount of drift and it is a very efficient wetter and spreader, coating the ear and upper leaves much more uniformly than is possible with spray solution alone.
In addition, humectants in the product slow the rate of droplet drying. The combination of these three factors increases fungicide absorption into the cereal ear and leaf, preserving efficacy (see table) while enabling the sprayer to cover more hectares in a given time.
Angling the nozzle forward 30 degrees or using a twin-spray nozzle to ensure coverage on the difficult-to-hit wheat ears improved coverage and disease control.
In the Austrian trials, applying the fungicide using a standard flat-fan nozzle achieved 51% control. Adding Velocity increased this to 65%, while a combination of fungicide, Velocity and a twin spray achieved 82%.
This demonstrates the benefit of linking correct product choice with application technique and appropriate adjuvant.
The twin-spray nozzle used in the above trials was angled 30 degrees forwards and backwards. Some operators comment that the backward-facing fan can produce more spray drift, especially at higher forward speeds.
This season, nozzles producing two forward-angled sprays at 30 degrees
and eight degrees will be tested. The idea of the twin-angled nozzle is that it mimics a twin-line sprayer at almost no extra cost. By applying 200 l/ha we are delivering many more droplets onto the target, greatly improving coverage without increasing drift.
Velocity ensures these smaller droplets do not dry too quickly, minimising the chances of active ingredient drying on the leaf rather than being absorbed into the plant.
Agrovista trials show the benefits of adding Velocity hold true for other diseases and spray timings. In the case of the T3 spray, growers may well be looking to top up their triazole dose with a strobilurin if Septoria or yellow or brown rust is evident on the flag leaf or ear.
Getting good coverage to control these diseases late in the season is important, so even where Fusarium is not a threat it will still be worth adding Velocity to the tank mix to achieve optimum results.