Minimum tillage systems appear to exacerbate slugs and mycotoxins, delegates at a Controlled Traffic Farming conference in York heard.

Easy solutions to the problems caused by slugs and mycotoxins to crops established by direct drilling or non-inversion tillage were in short supply at the conference, organised by CTF Europe.

Both were exacerbated by establishing crops using those techniques, delegates were told by researchers.

Slugs, in particular, would be difficult to overcome, particularly where oilseed rape was in the rotation, David Glen, an independent consultant said. The crop was particularly vulnerable to slugs, especially without the natural glucosinolate defence mechanism that had been bred out of modern varieties. It also provided good feeding conditions for slugs, meaning populations always grew in the crop, leaving following crops vulnerable, he said.

Research had shown that cultivation, particularly in the dry, reduced slug numbers, he said. “Slugs are also favoured by leaving crop residues on or close to the surface.”

It left growers direct drilling, and those only employing minimum non-inversion tillage, with a difficult problem, he admitted. “One of the keys for slug control is to do some cultivations.”

Some growers have been finding success by discing and rolling oilseed rape stubbles immediately after harvest, and then applying two half-doses of slug pellets three weeks apart, while Yorkshire farmer Andrew Manfield suggested spreading low rates of slug pellets into standing crops of oilseed rape around the time of late foliar nitrogen applications to try to reduce slug numbers. “Last year by the time the combine went through the ground was paved with live slugs and eggs. It felt like fighting a losing battle, so I think we need to manage that population.”

But it wasn’t a strategy Prof Glen believed would work. “I sympathise with his problem, but it just leaves too much time for slug numbers to recover following treatment. If we had summer weather like this year you wouldn’t see any benefit.”

But drilling into a fine, firm seed-bed would help, he stressed. It minimised the chances of slugs attacking seed and maximised plant growth allowing the crop to grow beyond the early susceptible stage.

If seed-beds were cloddy, then drilling a little deeper to find a finer tilth could also help, he said. Vulnerable seeds could also be protected by pellets drilled with the seed.

Generally, slug pellets should be applied shortly after drilling, he advised. “The effects from pellets applied before drilling can wear off before you’ve drilled if it’s too far in advance,” he warned.

But if populations were very high post-oilseed rape that strategy might provide some help, as long as the ground was left undisturbed for three days after application.

Direct-drilling

As with slugs, the past season had also proved to be challenging for mycotoxins, Simon Edwards from Harper Adams University College said. Initial sampling suggested levels of two key mycotoxins, DON and zearalenone, were much higher than at any time in the past eight years.

Nearly a third of samples tested were over the 100ppb legal limit for zearalenone for wheat destined for human consumption, while about 15% had failed the DON limit of 1250ppb, he said. That compares with just 2% on average since 2001 failing for DON and 2.5% for zearalenone.

The high level of zearalenone was due more to the delayed harvest, while DON was a factor of that and a band of wet weather around flowering across central England, he said.

Trash-borne fusarium infections, which led to mycotoxin production, were affected both by previous cropping and cultivation regime, he told growers. “Maize carries the highest risk, although any host crop increases the risk. And the more chopping and mixing you do when cultivating the better.”

That favoured growers with more intensive non-inversion systems. Growers could also minimise their risk when growing wheats intended for human consumption by removing straw and reducing the intensity of cereals in the rotation, he suggested.

• The 13 December issue of Crops will feature a Yorkshire farmer’s experiences using controlled traffic farming.

Non-inversion tillage risks

  • Slugs and mycotoxins
  • Both favoured by less tillage
  • Oilseed rape problem with slugs
  • Removal of straw helps guard against mycotoxins