Kestrel fungicide provides disease control in cereals

The introduction of broad-spectrum foliar-applied azole (DMI) fungicides in the 1970s has since resulted in the azole, or DMI group of fungicides, becoming the cornerstone of cereal fungicide programmes. However, repeated use of fungicides from the same chemical group year-on-year has led to resistance of the pathogen to products or groups of products.

One of the most important diseases of wheat is Septoria Tritici, also known as speckled leaf blotch, a wet weather disease that spreads and kills leaf tissue and reduces green leaf area. This leads to a reduction in the photosynthetic area and in yield and grain quality.

Azole fungicides are systemic in their mode of action (MOA), so when applied to the leaf, they move within the plant protecting it as it grows. All azoles have the same MOA inhibiting sterol 14α-demethylase (CYP51). Over 100 mutations in the azole target site protein have now been identified and so sensitivity to older DMIs has declined since the mid-90s and field performance, particularly at reduced doses, has also. 

With the declining activity of the two most active DMI’s, Epoxiconazole and Prothioconazole, Bayer mixed DMI’s from two of the groups shown in Table 1, Prothioconazole and Tebuconazole. Mixing them in a 50:50 mix of 125 g per L each gave greater disease control and yield than either straight Epoxiconazole or Prothioconazole.

Table 1: Work carried out in Europe and the United Kingdom identified that sensitivity of the Septoria isolates to DMI fungicides can be separated into three groups of comparable sensitivity.

Source: Fungicides Resistance Action Committee.

As Prothioconazole is more active on Septoria than Tebuconazole, Bayer refined the formulation to contain two-thirds Prothioconazole and one-third Tebuconazole; 160 g per L to 80 g per L. Sold as Kestrel, this mix contains Prothioconazole to control Septoria, yellow stripe rust and Fusarium spp. and Tebuconazole for Septoria, yellow and brown leaf rust and Fusarium spp control.

Tips on using Kestrel:

• Mix azoles with fungicides with different MOA in repeat spray programmes with, for example, SDHIs or QiIs.
• Use appropriate doses to ensure effective disease control.
• Azole insensitivity appears to be driven more by application number and less by dose. Reduce resistance risk by minimising the number of applications. Fewer high-dose treatments are
  preferable to multiple low doses.
• CYP51 mutations affect DMI fungicides in different ways, meaning it is possible that mixtures of azoles could slow further shifts in sensitivity. However, the number and complexity
  of mutations are dynamic, making it difficult to predict the performance of multiple azole products.

If you’re growing cereal crops and need assistance forming a fungicide programme, contact your local PGG Wrightson Technical Field Representative.

 Written by Gary Bosley on behalf of Bayer

Registered pursuant to ACVM Act 1997, Kestrel #P009531. Always read the registered label before use.