Continued studies on the use of reduced fungicide doses

Summary

Sector:
Cereals & Oilseeds
Project code:
PR97
Date:
01 October 1992 - 30 September 1993
Funders:
AHDB Cereals & Oilseeds.
AHDB sector cost:
£40,625 From HGCA
Project leader:
Part I. S Wale SAC-Aberdeen S Oxley SAC-Edinburgh Part II. O W Jones ADAS Starcross

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About this project

Abstract

This report represents part of a larger overall programme of work on reduced fungicide doses. Project Report No 104 reports work which precluded that reported here and [as of January 1996] two projects are continuing (0051/1/92 on winter wheat and 0052/1/92 on winter barley).

Summary - Part I.

Four trials were carried out, two each on winter barley and winter wheat. Each trial evaluated a series of fungicide programmes using different fungicide doses at standard timings on two contrasting varieties. A prototype Integrated Disease Risk (IDR) Strategy was evaluated in the winter barley trials.

Both winter barley trials were sown late and yields were modest but contrasting disease epidemics occurred. At the SAC Edinburgh site disease developed only after GS 49. Despite the limited and late disease epidemic yield responses up to 1.0 t/ha (cv. Willow) and 1.4 t/ha (Pastoral) resulted. On the Rhynchosporium-susceptible variety (Willow), a single application of ¾ dose at GS 31 was the most cost effective treatment although two ½ doses at GS 31 and 39 was similar. On Pastoral (a mildew susceptible variety), a two spray programme at GS 31 and 39 of ¼ doses was most cost effective. At the SAC-Aberdeen site infection was first recorded at GS 31 and developed thereafter. Yield responses up to 0.87 t/ha (Willow) and 1.36 t/ha (Pastoral) were recorded. The most cost effective responses on Willow were from two ½ doses at GS 31 and 39. On Pastoral, a three spray programme of ¼ doses at GS 30, 31 and 39 was the most cost effective. The IDR strategy proved to be effective only in one trial. In part this could be attributed to the use of severity rather than incidence of disease as one criteria in deciding dose. It also lacked sensitivity, failing to recognise that responses were likely even at low disease levels.

Yield responses on wheat were large with the Septoria tritici susceptible cultivar Riband (up to 3.2 t/ha) but much smaller on Apollo (up to 1.05 t/ha). Timing and dose were shown to be crucial in control of S. tritici. At both sites, delaying the GS 32 application to GS 33 improved disease control and yield. Using quarter doses proved ineffective in disease control. Three half doses at GS 33, 39 and 59 were highly cost effective at both sites. At the Aberdeen site reducing the GS 33 dose or increasing the GS 39 dose gave similar margins. On the cultivar Apollo at the SAC Edinburgh site where mildew development was limited, a two spray programme at GS 32 and 59 of ¼ doses was most effective. At the Aberdeen site where mildew arrived later but developed to a greater extent a single application of a half dose at GS 39 or two half dose applications at GS 39 and 59 were most cost effective. Acceptable mildew control was achieved by reduced doses but like S. tritici treatment early in disease development was crucial.

Using reduced fungicide doses on winter cereals requires a higher level of management and technical expertise. In order to use the minimum fungicide dose timing is crucial, yet management of all crop inputs (as well as farm management) involves a continuous series of compromises. Sub-optimal fungicide timing is a factor all growers and those who advise growers have to face. Any decision support system needs to be flexible, permitting the dose to vary with changing circumstances.

Strategies such IDR which has been developed on wheat have the potential to give guidance on dose. There is scope for refinement to encompass other factors that might influence dose. One of these factors is yield potential. The trials on winter barley demonstrated how this factor is important.

To fully implement a decision support system like IDR, more information is required on dose response curves and the interaction of fungicide dose and disease resistance of cultivars. Experimentation on

this and evaluation of fungicide programmes comprises the appropriate fungicide dose projects on winter wheat and winter barley initiated in October 1993.


Summary Part II.

Two fungicides, propiconazole as Tilt and fenpropimorph as Corbel, were evaluated as single sprays at four different doses against foliar diseases in winter barley at three Westward Arable Centres trial sites in Devon and Cornwall.

At the Devon site, brown rust was significantly controlled in Pastoral for five weeks by all dose rates (full, 3/, 1/, 1/,) of both fungicides, with full recommended doses giving best control. This was reflected in yield increases of 26% for full dose propiconazole and 22% for fenpropimorph. All treatments significantly increased yields, but for both fungicides, use of full recommended doses produced significantly higher yields than lower doses.

At Trerulefoot, East Cornwall, Rhynchosporium was significantly reduced on Halcyon by all treatments for seven weeks, with propiconazole at half recommended dose and above giving out-standing control - 7% compared with 34% on flag leaf. Although all treatments significantly improved yields, the superior control of Rhynchosporium with propiconazole was reflected in higher yields with this fungicide.

Net blotch was the major disease on Pastoral in West Cornwall and was well controlled for seven weeks by all doses of propiconazole. This resulted in significantly increased yields with half recommended dose of propiconazole and above.

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