Foliar disease control crucial after late start
Foliar disease control crucial after late start
Effective disease control in sugar beet will be more
important than ever this year. Our baseline agronomy article
takes a timely look at what sprays will pay this summer
LATE drilling means it will be more important than ever to maximise sugar beet growing potential throughout the season this year, says Dr Mike Asher of IACR-Brooms Barn.
"Compared to last year, when most of the crop was in by the end of March, we are behind by a month. And we know that there is major yield loss with late drilling, which is anything drilled after mid-April."
To be sure of reaching quota, growers must make up for this delayed start by maintaining a healthy crop, he says.
"Foliar disease control will be a key feature of this. Over the last five years, nearly half of the national yield has been accrued from the beginning of August onwards. The late summer and autumn period makes an important contribution to final yield."
However, no matter how good the disease control, with more than half of the crop drilled in May it is inevitable growers will see some yield reductions, he adds.
Mildew
Growers should plan to apply a triazole fungicide in late July/early August where mildew threatens, says Dr Asher.
"The forecast this year is for 40% of the national crop area to be affected by mildew by the end of August, which is fairly similar to last year."
Most of that will be in East Anglia, but if the summer is dry it could spread rapidly to the midlands and north of the Wash.
"Crops affected by mid-September are still worth spraying, even at C prices, unless they are destined for an early harvest."
Punch C (flusilazole+carbendazim) is preferred by Dr Asher for mildew control, because of its persistence. "But it must be applied at least seven weeks before harvest."
Last year, when disease levels were low, it increased yields by 12% compared to untreated plots. "Much of this yield increase was due to its effect on maintaining green leaves and keeping photosynthesis going late into the season," he adds.
Sulphur products are also known to give effective and persistent mildew control. "But last year, mildew failed to develop much due to the wet conditions, so we only recorded a low yield response to a sulphur treatment."
Rust
Growers wont know whether rust is going to be a problem if the sprayer is out early for mildew.
"Unfortunately its impossible to forecast rust long-term," says Dr Asher. "If rust does come in, the first signs will generally be noticed at the end of August."
Crops on low-lying ground, near inland water or the coast, are prone to the disease. Irrigated crops and areas where the disease has previously struck are also at risk.
"Growers will know if they are in a rust-prone area. Warm, moist conditions help to encourage rust, so if warm weather is combined with water on the leaf surface, then it might be worth controlling. But the economics are marginal."
Alto (cyproconazole) is the best product for rust control, and is a better choice for mildew where a short harvest interval is needed.
"But we havent seen rust for several years now and most varieties have reasonable resistance to it."
Feeding sugar beet tops or top lifting can improve the case for targeted rust sprays, Dr Asher adds. *
DISEASE CONTROL
• Max yield needed from late start.
• Mildew: Punch C preferred.
• Mildew spray pays at C price.
• Check rust-prone crops in August.
• Alto best rust control.
Fungicide margins
1999 2000
Cost (£/ha) Yield increase Margin (£/ha) Yield increase Margin (£/ha)
(t/ha) A/B C (t/ha) A/B C
Sulphur 6 4.4 113 29 1.8 43 8
Punch C 16 9.7 246 62 8.8 222 54
IACR-Brooms Barn. A/B beet price £27/t. C beet price £8/t.