Archive Article: 1997/11/08

8 November 1997

IN THE south, some wheat crops have emerged patchily. Upon closer inspection, the seeds which didnt produce a plant lie hollow and seedlings are struggling. The damage looks familiar, but there is no sign of slugs or frit flies. What could be responsible?

1SLUGS are active where seedbeds are moist enough for them to move unhindered. In late sown crops, they are hollowing out seeds and grazing the seedlings, leaving them ragged and often unable to recover.

But there is another enemy whose damage appears similar at first glance. The wheat flea beetle first came to our attention last year, and this autumn is taking a few growers by surprise.

Early last month, we found several crops in Hampshire, Berkshire and Dorset with large bare patches in them. When we looked closer, seeds had been hollowed but through a more defined entry hole than slugs produce. There were bronze-coloured adult flea beetles inside the seeds, giving us unequivocal proof that this was the guilty party.

Something had also eaten through leaves before they unfurled, producing a symmetrical pattern of damage. It could have been the larvae which hatch out through the autumn and winter from eggs laid in grass.

If your crops are still at a vulnerable stage, check the damage symptoms carefully to identify the culprit. Dig down the profile for slugs before jumping to conclusions and spreading pellets about. Its all to easy to assume you know what it is, but this pest isnt familiar to most growers, yet.

This may sound like scaremongering, but the damage is bad enough in patches to warrant redrilling. It may even be worth drilling seed treated with gamma-HCH, usually used for wireworm control.

Tod Hunnisett,

Crop Management Services, Hampshire.

2WHEAT flea beetle can cause quite serious problems, particularly after grass leys or where stubble has regrown. I have seen some fields wiped out by this occasional pest.

The adult dies off in mid-autumn, once it has laid eggs and the weather starts to turn against it. But its larvae can damage plants right through until the late spring.

They cause typical deadhearts, much like the symptoms of several other pests appearing at this time. Since their first sighting in the 1970s, their damage has been mistaken for frit fly, wireworm and caterpillar grazing. But unlike frit fly larvae, which destroy just one shoot, wheat flea beetle larvae can eat up to 15 shoots in one winter.

Theres no mistaking the pest itself – its a dirty white grub with a dark head and dark plate at the rear end, typical of flea beetle larvae. Frit fly and wireworm larvae are yellower. But if you arent sure, ask your adviser for a second opinion.

Its only worth treating if you believe there are enough to cause bare patches and necessitate redrilling.

I would try an insecticide approved for leatherjacket control, such as the gamma-HCH products Lindane or Gamma-col. If frit fly or caterpillars are your problem, chlorpyrifos is a better option.

Jon Oakley,

ADAS Bridgets, Hampshire

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