Take-all control with silthiofam (Latitude); Economic implications from a six-year rotation experiment

Abstract

The aim of this project was to assess the effect of silthiofam (Latitude) seed treatment on a range of wheat crops grown in different rotational positions.  Effects on disease progress, take-all decline, as well as on the economics of rotational options, were assessed.

Field experiments were undertaken in each of six harvest years 1998,1999, 2000, 2001, 2002, and 2003, at ADAS Rosemaund in Herefordshire, a site characterised by moderate to severe take-all infection.

In all experiments autumn plant population, grain yield, specific weight, and thousand grain weight were measured. Take-all incidence, index, shoot number and number of clean and infected roots, were also assessed at least four times each season, with the timing and intensity of monitoring depending on take-all progress. In the first five seasons cereals were grown both with and without Latitude seed treatment. In the last year all cereals were sown without Latitude to assess effects on take-all decline.  

The results demonstrated the classical pattern of initial rapid yield loss and subsequent recovery when entering a long run of consecutive wheat crops. The initial yield loss at 3.5 t/ha was much greater than has been found in other work, the average yield loss in a second wheat compared to a first being closer to 1 t/ha.   The subsequent yield recovery in 3rd and 4th wheat crops of about 1.5 t/ha still left a yield deficit compared to first wheat of 2 t/ha.  The magnitude of the yield effects observed may be related to the use of Equinox, a variety considered to be a particularly poor non-first wheat.

Second wheat crops showed a consistent benefit from use of Latitude. In the four years when these crops were grown with and without Latitude, the seed treatment reduced take-all indices and increased yield by an average of 0.47t/ha. Some positive effects of Latitude on take-all progress and yield were observed in third and subsequent wheats, although these tended to be less consistent.  Results indicated that take-all decline may be mediated by factors that only have a significant effect on the secondary phase of disease progress during the spring and summer.  This contrasts with the timing of the effect of Latitude, which has been shown to impact solely on the very earliest 'primary' phases of the epidemic in the autumn. Results from the final season indicate little or no evidence of a direct or indirect effect of seed treatment on the development of take-all decline.  It has previously been reported that a severe take-all infection is needed before significant take-all decline can develop.  It may be that, as the effect of Latitude is to delay the take-all epidemic, there are sufficiently high levels of take-all late in the life of the crop for the development of take-all decline.

Substantial increases in take-all severity were observed where the third cereal in a run of four was winter barley. This contradicts other findings on which previous advice has been based - that suggests growing winter barley as the second and third cereal to avoid the worst take-all years and then reverting to wheat. 

Making the decision whether or not to use Latitude will ultimately be a financial one. Given the average responses to Latitude use reported in this study of 0.19 t/ha for all non-first wheat crops the blanket use of Latitude would not be economic.  A more targeted approach would, however, be economic and using Latitude on all second wheat crops where the average response was 0.47 t/ha would provide an average return of £14/ha. This work was conducted on the take-all prone, silty clay loams at ADAS Rosemaund. The economic benefits of Latitude use may be greater where non-first wheat is grown on lighter soils, as take-all epidemics may be expected have a greater impact on water availability and yield under these conditions.