Exploiting new fungicides and varieties to reduce fixed costs

Abstract

This three year project set out to examine how the introduction of the new strobilurin fungicides, coupled with the introduction of winter wheat varieties with superior disease resistance could be exploited to reduce the fixed costs of wheat production by reducing the number of fungicide applications from three to two whilst maintaining disease protection throughout the season.

The project was conducted at Morley Research Centre, Wymondham, Norfolk in the 1999 to 2001 seasons on crops of Riband and Claire, representing disease susceptible and disease tolerant varieties respectively.  Landmark and Mantra were used to test the hypothesis but in 2001 two other strobilurins (Twist and Amistar) were also tested.

The disease pressure in the three seasons varied considerably, with 1999 being typified by early intense pressure from Septoria tritici, which was sustained throughout the season and later from brown rust.  In 2000, disease pressure built during the season and was mainly from septoria.  The 2001 season was typified by low disease pressure.  These three seasons tested the treatments under varying situations and provided added confidence to suggest that the results were robust.

The untreated yields of Riband in the three years 1999 to 2001 were 5.07, 6.04 and 9.19 t/ha and of Claire, 8.65, 8.70 and 11.17 t/ha.  The difference in untreated yield between the two varieties underlines the benefit in selecting a variety with inherent disease tolerance.  Yields from the benchmark three-strobilurin programme for the same period were 10.81, 10.38 and 11.12 for Riband and 12.40, 10.91 and 11.96 t/ha.

In Riband, a three-spray programme was necessary in the first two years, when there was high disease pressure, to achieve maximum margins.

With Claire, a two-spray programme of Mantra starting at GS 32 (final leaf three emerged) at 0.5 l/ha followed by a 1.0 l/ha dose at GS 60 (onset of flowering) gave the highest yield and thus proved the most cost effective treatment.  This was even when compared to a programme containing three applications of strobilurin fungicides or a FRAC-compliant mixed programme of triazole followed by two strobilurins.

This project has demonstrated that the combination of improved disease resistance and more effective fungicides calls in to question the need for the traditional three-spray approach to control diseases in modern, disease tolerant winter wheat varieties.  Savings in time and application costs are important for growers who have taken on larger acreages often at some distance from their base.  Any Additional cost in fungicide when employing a two-spray strategy over that used in a conventional three spray programme is offset by the convenience of a reduction in passes through the crop and the simplicity the two-spray strategy provides in terms of crop management. Adopting the following sequence of spray priorities could provide appropriate protection to a range of crops:

         GS 30-31 - include specific treatment for mildew or yellow rust if required, with early growth regulator or herbicide.

         GS 32 - treat varieties that are very susceptible to Septoria tritici. This could be combined with some late herbicides.

         GS 32-33 - treat more disease resistant varieties (there will be scope for dose reduction in some cases). This could be combined with some late herbicides.

         GS 39-43 - apply second fungicide to susceptible varieties.  This could include a late growth regulator where needed.

         GS 55-61 - apply second and final application to more resistant varieties.  This may be the appropriate time for aphid control.

         GS 65 - apply final ear treatment to susceptible varieties. This may be the appropriate time for aphid control.

 This will go a long way towards providing a uniform requirement for spraying from GS 30-31 (mid April) to GS 65 without the current peaks at GS 32 (early May), GS 39 (late May) and GS 65 (second week in June).

The doses used in these experiments were robust.  Work started in year three of the project to refine the system to use the latest strobilurin products and reduced doses.  This work is continuing under Project 2669