Archive Article: 1997/07/19

19 July 1997

1Bacterial leaf spot, ramularia and powdery mildew are being reported in many areas and often symptoms are appearing earlier than is normally expected.

Leaf spotting is easily found in the field but is really not a problem. Symptoms show as black spots with black areas on the leaf and chlorosis around the leaf edges.

Although there is no approved chemical for controlling bacterial leaf spot, the disease isnt usually economically damaging in England and will not spread under warm conditions.

Ramularia normally doesnt appear until late August or early September but is being found early. The spotting differs from bacterial leaf spot by having pale centres with white spores visible with a lens.

It can be devastating when it spreads under wet conditions but growers should consider whether they need to treat for ramularia when they act against powdery mildew in a couple of weeks time. Rather than sulphur, it might be preferable to consider a broad spectrum triazole such as Alto 100 SL.

Our view would be that Alto on its own will give good control of mildew, rusts and other diseases.

Growers will have to weigh the disease risk against the cost of sulphur at about £8-9/ha and a triazole at over £20/ha. Protecting leaf may be particularly important for growers using beet lifters and if they are feeding tops.

Mike May,

IACR-Brooms Barn, Bury St Edmunds, Suffolk.

2We havent seen a Silver Y moth since early June and that was just an odd one that turned up because we were looking carefully for any kind of pest. Some Silver Y moths do appear to have overwintered in the UK although I havent seen any of those myself – only a photograph.

The winds during June were mostly from the north which is the wrong direction for the migration in large numbers that has occurred in other years.

Dr Alan Dewar,

IACR-Brooms Barn,

Bury St Edmunds, Suffolk.

A range of diseases, and even Silver Y moth, have been spotted earlier than expected in this years beet crop. Which should growers be most concerned about and when?

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