T2 disease control
After a recent period of warm and unsettled weather most growers will have come to the conclusion that their T2 applications will need to be based around strong septoria activity. The question then is: which product combinations provide the most reliable control.
The situation is further complicated by the variable growth stage of many crops. Drilling date and variety have both contributed to this variability.
The cold snap in March resulted in T0 sprays being delayed and in some cases T1 sprays were further delayed by the weather and slow final leaf 3 emergence. In some cases the gap between T1 and T2 may be less than 3 weeks but this is no reason to make false economies when it comes to product choice.
The use of an SDHI at T2 is now a routine treatment. Independent trials by AHDB Cereals & Oilseeds supports this observation as treated crops have regularly out-performed those treated with either a straight triazole application of prothioconazole or epoxiconazole.
There are several SDHI products available to growers. Those based on fluxapyroxad or bixafen have often given the best control. Other products can also perform well if the timing is right and dose is not compromised. Even with bixafen and fluxapyroxad based products, when risks are high, rates should not be cut too much. When it comes to curative activity fluxapyroxad chemistry may have an edge but wherever possible it is best to try and avoid over using them as curatives. The triazole partners have already succumbed to performance change, especially as curatives and we do not want the same to happen to SDHIs.
The above images from NIAB TAG trials show the value of varietal resistance when spray timings are compromised.
If the weather delays timing then an increase in dose may be sensible.
Curative action will be important in many cases but the need for prolonged protection should not be overlooked and tank mixing with a protectant such as chlorothalonil will be worthwhile.
Not all products have a recommendation for such a tank mix at T2.
Whilst Septoria is the main target at T2 topping up yellow rust control is also important and where control has proved difficult earlier in the season or on very susceptible varieties the addition of a rust active strong strobilurin such as pyraclostrobin would be a good idea.
Brown rust susceptible varieties might also benefit from a similar approach.
No sooner have T2 sprays been applied then attention turns to T3 treatments.
Where Fusarium control is required especially on quality wheats or if we get rainfall around flowering then a triazole active against that disease will be important. Prothioconazole, tebuconazole and metconazole are the most likely choices.† Control can be variable, dose and precise timing holds the key. Topping up foliar disease at this time will also influence product choice.