Improving resource use efficiency of barley by protecting sink capacity.

Abstract

The aim of this project was to identify how fungicides increase the resource use efficiency and yield of spring barley so that fungicide strategies can be tailored more effectively to account for the disease resistance of the variety and the potential physiological response of the crop. Specifically, three broad research questions were addressed which have scientific and commercial relevance.

1) What duration of protection of canopy light interception is required post-anthesis to maximise yield?

2) How do fungicides increase yield where visible disease severity is low or absent?

3) How should fungicides be timed in low disease risk situations?

Detailed physiological measurements were made in experiments conducted by research partners at two main sites, ADAS in Herefordshire and SRUC in Edinburgh. Experiments by industry partners tested the validity of the findings over a wider range of varieties and sites differing in disease pressure.

Results showed that light interception by the canopy must be protected for approximately the first 75% of grain filling in order to maximise yield; a period of 3-5 weeks from 50% ear emergence depending on the site and year. After that period yield is insensitive to major reductions in light interception, probably because grain filling can be completed using dry matter from storage reserves.

Treatment of disease-susceptible varieties with prothioconazole plus pyraclostrobin (products Proline and Comet 200, respectively) at the start of stem extension gave adequate protection of the canopy over the critical first 75% of grain filling when disease pressure was low.

Under higher disease pressure an additional treatment during booting was needed. Although later applications after ear emergence protected the canopy for longer, they had no effect on yield because the additional protection occurred late in, or after, the critical period.

Field experiments over a wide range of varieties and sites showed that, on average, yield responses in the order of 0.3-0.4 t ha^-1 were obtained from treatment with Proline and Comet in the absence of visible disease.

The yield increases were largely the result of an increase in the number of grains produced m^-2. A comparison of the effects of Proline and Comet with that of chlorothalonil (product Bravo 500) indicated that the grain number response was not the result of the control of visible disease, the control of symptomless pathogen infection and leaf saprophytes, or a delay in leaf senescence.

It appeared to result from a direct effect on plant metabolism which occurred before flowering. A single application during booting was sufficient to elicit the response. The results have implications for fungicide treatments in low disease risk situations, e.g. where resistant varieties are grown or where the disease pressure is low.

If there is no disease present at the start of stem extension, fungicide treatment can be withheld. However, an application of prothioconazole plus pyraclostrobin at booting can be justified economically as it will provide insurance against late season disease and will result in yield enhancement, even if disease fails to develop.

It can be further justified in terms of improvements in N use efficiency and reduced greenhouse gas emissions per tonne of grain yield.