Optimising the performance and benefits of take-all control chemicals

Abstract

Sequences and alternations of seed treatments (Jockey Flexi, based on fluquinconazole, and Latitude, based on silthiofam) were tested in field experiments in wheat or barley crops grown successively as second and third cereals (and in one case a fourth wheat) in eastern England. A spray treatment (Amistar, based on azoxystrobin) at growth stage 31 was tested in successive years, with or without seed treatment.

Seed treatment with Jockey or Latitude almost always decreased take-all and increased grain yield when applied to either second or third wheat crops. Yield increases, i.e. the differences between yields of treated and non-treated crops, were less at the Norfolk sites (where yield increase with Latitude was up to 0.42 t/ha in 2nd wheats and 0.54 t/ha in 3rd wheats) than at the Hertfordshire sites (up to 1.37 t/ha in 2nd wheats and 2.38 t/ha in 3rd wheats). Latitude decreased the amount of early take-all on roots, assessed in spring, more than did Jockey. Jockey usually controlled the development of severe take-all in the summer more effectively than did Latitude. Despite this, Latitude often increased yield more than did Jockey, although their relative effects were variable.

Each seed treatment applied to a second wheat crop delayed the development of the year-to-year epidemic, which affected the response to seed treatment in subsequent crops. A non-treated third wheat crop grown after a treated second wheat crop usually showed little or no benefit from treatment in the previous year (compared with no treatment in either crop), whilst non-treatment of a fourth wheat crop grown after one or two previous treated crops was detrimental, because the crop did not benefit from the take-all decline that developed in the fourth wheat in the absence of treatment. A treated third wheat crop grown after a treated second wheat crop often benefited from the treatment unless take-all was already becoming severe in the second wheat. The best yields in third wheat crops were obtained by treating the third crop with Latitude and the second crop with Jockey or Latitude, but were usually less than would be expected in the absence of take-all.

Amistar sometimes decreased take-all severity and increased grain yield in wheat but was very inconsistent. Information on the factors that influence its efficacy is required. Amistar sometimes added to the effects of seed treatment, especially Latitude. 

Take-all development was usually slight in barley crops with little effect on yield. It was usually decreased by seed treatment but Amistar sprays were inconsistent. Severe take-all is known to increase grain nitrogen concentration (because it decreases starch content) but, in the absence of severe disease, we found no evidence that take-all fungicides can help to regulate grain nitrogen concentration.