16 August 2002

Clean seed benefits too

Skipping a seed treatment

could be seen as a popular

path to cutting input costs

this autumn, particularly

where seed is tested first.

But soil infections could

still hit establishment. We

take a closer look

NEW work conducted at Harper Adams University College shows cereal emergence and establishment can benefit from seed treatment, even in the absence of seed-borne disease.

Soil-borne fusarium is thought to be the reason for the response seen in late-drilled clean seed, says HAUC fusarium researcher Martin Hare.

While direct proof is lacking, he suspects soil-borne inoculum is the most likely explanation. "At later drilling dates, seed can take up to 45 days to emerge, which provides plenty of time for infection to occur.

"And we know from previous work that fusarium is everywhere – all soil types are affected."

Post-graduate student Ian Haigh used clean and 30% M nivale infected Cadenza winter wheat seed to investigate four different drilling dates. The seed treatments used were Sibutol (bitertanol + fuberidazole), Jockey (fluquinconazole + prochloraz) and Anchor (carboxin + thiram),

Drilling took place on Oct 13, Nov 3, Nov 9 and Dec 13. Big differences were recorded in the rate of emergence – the earliest drilling date took 10 days to emerge, while the December-sown wheat took over 40 days.

"The seed treatments studied had no effect on the rate of emergence when compared with the untreated, they neither delayed nor speeded up emergence," reports Dr Hare.

But wheat drilled on Nov 9 came up sooner than plots drilled a week earlier, he says. "It is the soil conditions, in terms of moisture and temperature, which matter. People tend to focus on drilling date, when perhaps they should be paying more attention to the seed-bed."

In the untreated plots, the rate of emergence was related to drilling date and the severity of seedling disease. "Earlier drillings come through quicker, so there is less chance that they will succumb to fusarium. Seed that takes a long time to emerge is more likely to be affected."

Dr Hare believes growers should consider drilling date when choosing a seed treatment "All the seed treatments in our work had very good activity against fusarium, but there were differences in their performance, especially at later drilling dates.

"Anchor appears to be more robust as drilling gets delayed. When conditions cause the seeds to take longer to come through, it seems to work better."

Although Anchor did not speed up emergence, it gave the best reduction in seedling disease.

"The explanation for this may come from some research done in Italy, which shows that the chemistry in the treatment has an effect on seedling physiology and activates the plants natural defence mechanisms."

Disease assessments done after the post-winter establishment measurement backed up the initial results. "A seed treatment which does not look to be anything different on paper is performing very well in adverse conditions."

The effect that all the seed treatments had on clean seed was apparent at the later sowing dates, says Dr Hare. "We saw a fall in establishment as drilling took place later. This was reduced by the use of a seed treatment, even when there was no fusarium infection on the seed."

Assessments carried out on clean seed showed some disease on established plants. "It is probably due to fusarium in the soil. And it suggests growers should think carefully about trying to cut costs by not treating their seed."

Dr Hare agrees with HGCA-funded work highlighting the potential for savings on seed treatment where seed is tested first. "Treating according to need is fine if you are certain of drilling in good conditions. But seed-bed quality and the conditions within the seed-bed are all part of the picture."

The 5% infection threshold for fusarium could be a bit conservative, he believes. "Perhaps we should consider a sliding scale of infection depending on drilling date.

"But remember too that fusarium in seed is only one of the diseases that can affect establishment. If bunt was present, you would have to treat."

He also points out that the effect of cultivation technique and drilling depth on fusarium infection is still largely unknown. "There has not been enough work done in this area. We suspect that increasing the depth of drilling increases the likelihood of infection."

His final point is that growers should beware of making the management of crops too difficult. "This work showed that you can get a much reduced plant population in the spring if conditions are in fusariums favour. The cost of a seed treatment, especially at low seed rates, is very small." &#42