31 August 2001

Fusarium seed treatment could be waste of cash

By Charles Abel

SOWING untreated cereal seed could be an option for more growers than usual this autumn, according to survey data showing the most damaging fusarium species may be totally absent.

The Central Science Laboratorys DEFRA-funded survey of winter wheat suggests Fusarium ear blight is at its lowest level for four years and Microdochium nivale, the main fusarium species to hit crop establishment, is totally absent.

But seed treatment suppliers say the extra cost of a fungicide is small compared with the potential benefits for establishment, yield and quality.

The CSL survey of 450 crops showed fusarium affected 19% of samples this year, compared with 61% in the bad fusarium year of 1998 and over 30% last season.

More importantly M nivale, which dominated last year, was totally absent, probably due to dry weather during flowering in June. Instead F poae dominates, but poses no threat to establishment.

"The need for treating seed for fusarium is significantly reduced compared with other years," says Judith Turner of CSL York. "There is the potential to adjust seed treatment choices to take account of that."

NIABs Jane Thomas agrees. "For growers saving their own seed the chances of not having to use a seed treatment are looking good."

Dual-purpose seed treatments typically cost £40-£45/t, so growers could save £4-£10/ha (£1.60-£4/acre), depending on seed rate.

But sowing untreated, untested seed is not an option. Seed must be tested for M nivale and bunt, says Dr Thomas. Testing by NIAB Labtest is likely to be cost effective where seed lots exceed 2-2.5t.

For certified seed the logistics of processing in time to meet drilling demand leaves little scope for firms to test and treat seed accordingly, Dr Thomas adds.

That could change if a major HGCA-funded project to develop treatment thresholds and faster seed testing proves successful.

Uniroyal, which supplies Anchor (carboxin + thiram), admits the use of untreated, tested seed is rising. But soil-borne fusarium and bunt can still be a risk, particularly with later sowings. Furthermore, disease expression is not always consistent with test results, says the firms Malcolm Tyrrell.

Ian Hamilton for Syngenta, which supplies Beret Gold (fludioxinil), adds that the extra costs of testing and the need to use a higher seed rate if drilling is delayed while results are awaited could largely offset any untreated seed saving.

M nivale may also be more widespread than CSL and NIAB data suggest. "Levels will be lower than last year, because there was less rain in June. But our own testing in July found 20% of samples were still infected," Mr Hamilton concludes.

lAlthough the risk of fusarium seedling blight appears low, several traders fear fusarium ear blight has hit grain quality this harvest (see harvest reports p50-55). &#42

UNTREATED SEED

&#8226 Fusarium low in CSL survey.

&#8226 No M nivale seedling blight.

&#8226 Test seed and avoid treatment?

&#8226 £4-£10/ha cost saving.

&#8226 Consider other benefits.

Ultra-low disease

The CSL survey confirms that 2001 was largely a disease-free season for winter cereals. Leaf disease levels in winter barley in England and Wales were the lowest on record. Levels in winter wheat were the lowest since 1995 and the second lowest since records began in 1970. Rhynchosporium was the only disease to significantly affect barley and even Septoria tritici in wheat was at very low levels.