Complete: Control of late season foliar diseases

Timescale: 2000 - 2007
Project Lead: M Asher
Project Sponsor: BBRO

Project Summary

In recent years, a significant proportion of the growth of the beet crop has taken place during the late summer and autumn and it has therefore become increasingly important to maintain the crop in a healthy condition during this period. The most important foliar diseases are powdery mildew and rust. Up to 1998, mildew had been almost exclusively controlled with sulphur. However, two new triazoles have been introduced since then which give good control of both diseases and, according to preliminary observations, could offer additional yield benefits by delaying leaf senescence

Main Objectives

The objectives of the project were to (a) examine the yield and hence economic benefits to be obtained from the effective control of powdery mildew and rust with these new triazoles during this autumn period and (b) to establish whether additional yield benefits, over and above disease control, can be obtained with these products. To achieve this, field trials were conducted over the four years of the project to study the efficacy, yield responses and cost effectiveness of the new products applied on one vs two occasions, and harvested either early, mid-campaign or late. In addition, to achieve a representative overview, products were compared in a series of trials sited in the different beet growing regions of the UK.

Outcomes / Key Message For Growers And Industry

Key findings

● During the period 1999-2003, 5 fungicide trials were carried out at Broom‟s Barn; 2 were severely infected with powdery mildew (30-60% leaf area infected on Untreated controls) and 2 were moderately infected (18-25%). Only very low levels of disease were encountered in 16 trials conducted on outside sites over the years 2001-2003.

● Under moderate/severe disease pressure the triazoles Punch C (flusilazole + carbendazim) and Alto/Fort (cyproconazole) gave average yield increases over Untreated plots of 8.0 (11%) and 5.3 (7%) adjusted tonnes per hectare, respectively. This difference reflects the greater persistence of Punch in controlling mildew.

● In low/no disease situations, Punch and Alto/Fort gave average yield increases of 5.3 and 4.2 adj. t. per ha, respectively. These yield benefits are likely to be due largely to direct physiological effects on the plant, investigated in an associated project “Physiology of beet growth in the autumn”. ● Using these data cost-benefit analysis indicated that margins of £160-£215 per ha could be obtained with a single triazole spray in the presence of moderate/severe disease, at the prevailing A/B quota price of £30 per tonne. At a „C‟ price of £5 per tonne, small net margins were still obtained.

● In the absence of disease, the yield boosting properties of the triazoles produced margins of £100 - £125 per ha at the A/B price and no net loss at the „C‟ price. 2

● Recommendations to growers arising out of this project include the following conclusions : (a) Except for the earliest lifted crops, control of disease appearing up to the middle of September will almost always give an economic return when triazoles are used, even at „C‟ prices. (b) Even where disease risk is low, a triazole fungicide can be part of a managed strategy to ensure quota and maximise yield.

● Benefits to the industry from triazole use in 2003, a low disease year, have been calculated to be an additional 360K tonnes, worth £11M nationally.

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We are set up jointly by British Sugar plc and the National Farmers' Union.

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