Increasing role for chlorothalonil predicted in wheat fungicide programmes this spring
63% of agronomists* who were asked, say they will use more chlorothalonil at T2 this season in wheat.
With reports of changes in sensitivity of Septoria to the triazoles and on the back of a difficult year for disease control, it is expected that the use of chlorothalonil will grow this year to bolster Septoria protection.
The SDHIs fungicides have now been introduced to support the azoles, but they come with a single site mode of action and are therefore at risk of resistance development. With limited new fungicide tools on the horizon, it’s vital that the industry protects existing chemistry.
Evidence suggests that by adding chlorothalonil to azoles and SDHIs, there is a strong likelihood that potential resistance will be slowed down. The 2012 HGCA FP trials confirmed chlorothalonil as the most effective Septoria multi-site partner for the SDHIs.
A recent model which was based on data generated as resistance developed to strobilurins, suggests that using even a low dose of a low risk product, such as chlorothalonil, could extend the life of the high risk partner.
In Ireland, where Septoria strains with reduced sensitivity to all the triazoles have been detected, the advice is to always include chlorothalonil at T1 and T2. “We see it as essential,” says John Spink of Teagasc. “The curativity of triazoles has been reduced and we need to keep the SDHIs working well and protect this group of chemistry for as long as possible.”
Jonathan Blake of ADAS agrees: “The addition of a multi-site product such as chlorothalonil in the early spray timings T0, T1 and T2 is very important in any fungicide programme, both in terms of increasing efficacy and reducing resistance pressure.”
“We know that the SDHI’s are at medium to high risk to resistance developing, and based on modelling work that we have done, the use of a multi-site partner could almost treble the time that the SDHI’s remain fully effective. “
With the price of 1L chlorothalonil around the £4 mark, its inclusion is fairly easy to justify. Peter Hughes, Product Manager, BASF says “We recommend chlorothalonil to be used at T1 with Tracker or Adexar. If your main disease priority is eyespot with Septoria and rusts as a concern, Tracker is the key product, but if Septoria and rusts are higher risk, go for Adexar as you’ll still get decent control of eyespot.
“If you want to use a new SDHI at T1, Adexar has to be the first choice as it’s fully compatible with chlorothalonil with no yield penalty observed. In many cases, our trials show a yield benefit of chlorothalonil’s inclusion with Adexar at T1 and T2..
“We must strive to maintain the effectiveness of the SDHI / azole chemistry for as long as possible and adding a third mode of action in chlorothalonil at T1 and T2 to the triazole / SDHI mixtures is a wise precaution to achieve this and one supported industry-wide.”
* Source: AICC Agronomists
