Peach-potato aphids are being found in traps across the sugar beet growing area, prompting experts to advise growers to check non-Cruiser-protected crops and apply a foliar insecticide where thresholds are met.

The British Beet Research Organisation (BBRO) has yellow water traps at its 12 trial sites and monitors aphids and beneficial insects at a further 34 locations across the sugar beet growing area.

BBRO head of science Mark Stevens says winged aphids are appearing at all trials sites and numbers of wingless aphids that transmit yield-damaging virus yellows through the crop are building.

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“Crops drilled with Cruiser SB [thiamethoxam] should have 10 weeks’ protection, and it should stop any wingless aphid activity during that time.

“However, crops that don’t have that protection will be under pressure over the next three to four weeks as temperatures rise and myzus numbers continue to build.”

Backward crops

Dr Stevens says aphid pressure is a particular concern this spring because the crop is behind where it should be at this time of year.

As plants are most vulnerable to virus infection when small, and the yield penalty is greatest when the crop is infected early in its development, it could have significant effect if left unchecked.

To minimise risk of yield losses, non-Cruiser-treated crops should be treated with a foliar insecticide as soon as the spray threshold of one green wingless aphid per four plants up to 12 true leaves is met.

Dr Stevens explains that one conundrum for growers is which product to use first.

Rapid knockdown

“As BBRO monitoring suggests beneficial insect numbers are generally low, it is potentially better to go with InSyst [acetamiprid] first for rapid knockdown of aphids in small, vulnerable crops.”

Growers can then follow up with Teppeki (flonicamid) if aphid numbers breach the threshold again.

This will maintain a period of systemic protection against aphids with a lesser effect on beneficials, allowing them to build and assist with pest control thereafter.

The BBRO has applied for access to a third insecticide active substance, spirotetramat, and it is hoped this emergency authorisation may come through in time for use in June.