4 June 1999

Late season spraying pays

By Andrew Blake

PROTECTING sugar beet from late season diseases boosts yields by 7-11% and is cost-effective even at C-beet prices, says Mike Asher of IACR-Brooms Barn.

Growers should inspect crops weekly for disease from late July.

"The national forecast is for 37% of the total crop to be affected by powdery mildew by the end of August. This suggests much of East Anglia is likely to benefit from treatment. But areas north of the Wash and the West Midlands may not see the disease until well into September."

Where mildew is first spotted in August, fungicide should be applied within seven days. "Where mildew appears later, treatment is still worthwhile up to mid-September, providing there are at least four weeks until harvest."

Ramularia leaf spot is impossible to forecast because it is not influenced by the severity of the previous winter, says Dr Asher.

"It is a wet weather disease. So the succession of dry autumns has almost eliminated it as an economic problem in the UK over the past 10 years. But its effect on sugar content can be devastating, as seen in 1987."

The main products for foliar disease control are sulphur or triazoles. "Sulphur products give excellent and prolonged control of powdery mildew at low cost, but they have little effect on rust and none at all on Ramularia leaf spot.

"Alto (cyproconazole) has given very good control of rust in Brooms Barn trials and was also more cost-effective on mildew than sulphur, though part of this may have been due to enhanced green leaf retention."

Another triazole for sugar beet, Punch C (flusilazole + carbendazim) should be approved in time for use on this years crop, he believes. "It gave by far the best control of powdery mildew with at least seven weeks persistence. The yield response to a single application was over 8 adjusted tonnes/ha.

"And data from Irish trials indicate it is also very good at controlling rust and Ramularia, so it will be a useful addition to the armoury."

Despite reports of substantial yield responses to mildew control using sulphur/triazole mixtures, there is no evidence from Dr Ashers trials that mixes are superior to a full rate Alto. &#42

Foliar disease control products

Active ingredient Product Dose Approx cost (£/ha)

Sulphur Various 10kg/ha 8

Triadimenol Bayfidan 0.5 litres/ha 12

Propiconazole Tilt 250 EC 0.5 litres/ha 13

Cyproconazole Alto 240 EC 0.25 litres/ha 19.50

Flusilazole + Punch C* 0.625 litres/ha 20

carbendazim

*Subject to MAFF approval.