Management of Rhynchosporium in different barley varieties and cropping systemsManagement of Rhynchosporium in different barley varieties and cropping systems

Abstract

The barley disease commonly known as Rhynchosporium, caused by Rhynchosporium secalis, has become difficult to control with fungicides. In this project, Rhynchosporium was observed throughout the season in both winter and spring barley varieties and the importance of fungicide timing on disease control and yield recorded.  These trials also gave an insight into why variety resistance ratings for winter barley tend not to perform as well as expected in high disease pressure regions.  Rhynchosporium levels reached their peak in winter barley from boot growth stage (GS49-69) on the lower leaves. A second peak of disease was seen on the upper leaves at GS70-80. Variety resistance ratings are predominantly based on assessments carried out later in the season when disease levels can be lower than those seen at the boot growth stage.

The efficacy of individual barley fungicides was investigated before looking in more detail at fungicide mixtures, which achieved effective control of Rhynchosporium. The impact of the mixtures on protectant and eradicant control of Rhynchosporium was observed along with their effectiveness against other important diseases and yield. An experimental fungicide (HGCA3*) achieved the best control and yield benefits. Strobilurin fungicides were a useful component to control Rhynchosporium but their impact on green leaf area was less apparent compared to when they were first used on barley. Chlorothalonil had a positive impact on green leaf area, but little impact on yield, whilst cyprodinil had a greater effect on yield when applied early on winter barley than in spring barley. Morpholine fungicides had a negative effect on yield in spring barley, but this fungicide group has a useful short-term effect against Rhynchosporium.

Rhynchosporium isolates taken from trials were tested for their sensitivity to the fungicides epoxiconazole, flusilazole, carbendazim, cyprodinil and azoxystrobin. Patterns of sensitivity to epoxiconazole were also monitored over the three years of the study. The testing was carried out to see if the use of specific mixtures or if sequential use of the same fungicide influenced the sensitivity of Rhynchosporium as the season progressed.  Rhynchosporium isolates were found to vary in their sensitivity to epoxiconazole from site to site and the populations tested are starting to show a similar pattern of sensitivity to that seen with older DMI fungicides (triazoles) which are no longer important Rhynchosporium fungicides.

It was observed that Rhynchosporium isolated from the resistant variety Pewter appeared to be more sensitive to triazole fungicides than those taken from Riviera. This suggests that Rhynchosporium strains, which are able to develop on resistant varieties, may be easily controlled with triazole fungicides.

*HGCA3 refers to the code used in Winter Barley Appropriate Dose Project 2496