Ear comes trouble
Ear comes trouble
For the second year running, theres a fusarium epidemic in wheat. What should be done about this underestimated disease?
ITS easy to spot the trouble: large numbers of white bleached ears – often with orange staining – are now becoming visible as wheat ripens. Reports are coming in of severely affected crops in East Anglia and the south west, despite robust ear sprays.
Warm, wet weather at anthesis is blamed – this begins the infection cycle by encouraging disease development on the ear. An extended flowering period has exacerbated difficulties with spray timings.
Theres some complacency about the sight of these bleached ears. Thats because its commonly held that the fusarium species responsible are not the same as those which can infect seedlings. And its problems with crop establishment which are likely to have a more damaging effect on returns – so why worry about the ear symptoms?
This is a dangerous misconception, says Dr Martin Hare of Harper Adams University College, Shropshire. His argument is that if youre seeing bleached ears, then its more than likely theres a lot of inoculum of the other fusarium related species about as well.
Risks
For crops now showing bleached ears, theres a risk to both yield and quality in terms of shrivelled grains, but its hard to quantify.
Worse is the risk to following crops, carried over either on seed from the affected wheat, or as soil-borne inoculum. Plants in following crops will die at various stages.
First, theres classic damping off, which can kill plants before they even emerge. Second is seedling blight, where attack occurs after emergence, leading to reduced winter hardiness and increased winter kill. Third, theres root rot. For those plants which do manage to reach adult status, key identification symptom is stem-based browning just above the root ball. Inoculum can then transfer from the stem base to the ear.
Fusarium is widely underestimated, according to a Novartis survey of independent advisers. Three out of four consultants have fusarium down as one of the most important threats to establishment – and yet one in four growers dont even know what this disease is, the survey finds.
For those who arent entirely sure, Dr Hare helps out with a reminder. "Fusarium is a complex disease. For a start, its not a single enemy. There are many fusarium species. The three most important are Fusarium culmorum, Fusarium olvenaceum and Fusarium nivale, now called Microdochium nivale."
Effects of all these organisms are similar, but the true fusarium species tend to be those which give bleached ear symptoms. Microdochium nivale sometimes doesnt show up as clearly in the ears, but still produces seed-borne infection and is the main seedling pathogen – which is why seed testing is so important.
According to figures from the Official Seed Testing Station, a staggering 99.5% of samples were infected. Of those, 94% were above NIABs 5% infection threshold for treatment. That said, most of this seed will have been treated before drilling – so blame should not be laid at the door of the seed merchant.
No guarantees
But buying certified seed offers no guarantees, says Dr Hare. "Theres no certification standard for fusarium. So you could buy certified seed and still have high fusarium – I know, Ive done it. And had 17% infection. Last year it was difficult to get hold of any seed without fusarium."
The lesson is: have seed tested, says Dr Hare. If infection is over the 5% threshold, use a seed treatment that will control fusarium already present on the seed, and prevent it coming in from the soil.
Researchers at Harper Adams investigated the activity of different seed treatment ingredients against the fusarium species, in work sponsored by Novartis, manufacturer of Beret Gold. In lab conditions, fludioxonil (Beret Gold) was the most effective at the lowest doses. As the activity of the treatment diminishes with time, this might indicate longer lasting protection.
Results from field studies pereformed by Neil Glynn, one of the Harper Adams reseachers, point to lasting protection from fludioxonil treatment – right through to the GS24 foot rot stage in the spring (see graph).
Also, applying fludioxonil to heavily infected seed, with just 68% germination, brought germination back up to 99% – which was a higher figure than that achieved with the cleanest seed sample the research team were able to find that year.
All the currently available seed treatments claim some control of fusarium, but Dr Hare would not recommend Baytan against this particular disease if seed infection was high.