With warmer conditions said to be on the way, wheat crops will quickly move to stem extension and beyond.
With this comes the appropriate timing to begin your 2022 disease control programme.
While it can be difficult to get the timings spot on due to normal weather constraints, my money is on being a slight bit late on T1 if it can’t be spot on, rather than being early with this timing. But, first, where should these programmes start?
It is surely more than two decades since we began to designate useful disease control programmes as requiring three treatments or applications which became known as the T1, T2 and T3 timings.
Perhaps it would have been better if they had been called F1, F2 and F3 to designate the fact that we are talking about fungicides as we now also have a programmed treatment approach to nitrogen, growth regulation and even herbicide at times.
But let us stay with what we are used to and designate them as treatments.
For a chunk of the early 2000s the precise T1 timing recommendation was often ignored in favour of just getting the job done when weather permitted
At the time of the original three “T” advice, the timings recommended were GS32, GS39 and mid-flowering. These remain the main target timings today with a little additional refining.
The first and last treatments are a little bit less precise but for a chunk of the early 2000s the precise T1 timing recommendation was often ignored in favour of just getting the job done when weather permitted.
The T1 is the first treatment which automatically affects, or should affect, the timing of all following applications.
With an average of about 10 days for full leaf emergence, the timing between the third-last leaf fully emerged and the last leaf fully emerged should be around 20 days. This is also regarded as the period of effective cover or protection from a fungicide treatment. So, if you get the first one right, the subsequent treatment should follow effectively.
The second node fully developed, or GS32, is taken as the correct timing for the T1 fungicide.
At this stage, it is assumed the third-last leaf is fully emerged. This may or may not always be the case as planting date can influence the number of leaves (and nodes) produced on the main stem in spring.
So, it is important that the emerging leaves are checked to see how many more remain to emerge.
This is done by unfolding the leaf sheaths and checking on the other leaves rolled up inside the emerging one.
If the third-last leaf is emerging/emerged, the last or flag leaf will be big enough to find.
Having the third-last leaf fully emerged at the time of application will mean the fungicide can be applied to all of that leaf because and some of the second leaf which is already emerged but still rolled up.
Either way, part of that leaf will also be protected by fungicide, helping to protect an important part of the overall canopy. While the third-last leaf is not hugely important for grain fill, it is important that the progress of developing disease from the base to the top of the plant is halted for as long as possible.
The gap to when the flag leaf is fully emerged will be greater than three weeks and this may allow disease progression up the plant
If the T1 is applied prior to the third-last leaf being fully emerged, this leaf itself will not be fully protected by fungicide.
The gap to when the flag leaf is fully emerged will be greater than three weeks and this may allow disease progression up the plant, which may be too advanced to be halted by subsequent fungicides at T2. For this reason it may be better to be slightly late than too early with the T1 timing.
Low temperatures can also slow leaf emergence and extend the period to the T2 timing.
However, when this happens, the development of the disease will also be slowed, as will plant growth and the increase in bulk which dilutes the effective concentration of fungicide active in the plant tissues while also slowing its degradation.
One important element in targeting the actives to use is to know the diseases that you need to target. This is primarily based around septoria but there are three others which must also be considered. These are yellow rust, eyespot and mildew.
Where mildew remains a target, the addition of fenpropidin (Tern or Winger) will generally be necessary for knockdown, with prothioconazole possible doing enough thereafter on wheat. But where a persistent mildew problem is expected, the addition of Talius might be considered.
If eyespot is a major target disease because lesions can be easily found in the crop then the T1 should contain high rates of prothioconazole or be in a mixture with an eyespot-active SDHI ingredient and many of them claim this.
Where yellow rust is a major target at T1, it is likely that Elatus Era is the strongest of the SDHI mixtures to consider but others also claim to have a strong impact on that disease.
However, where yellow rust is both very active and very prevalent in a crop at the time of spraying, the inclusion of a morpholine like Tern should help to speed up the knockdown of this very aggressive disease.
This would also apply at any other time of the season when yellow rust is very active.
Other active ingredients do work but they are slower and the disease can continue to develop in the interim.
Then on to septoria. Control of this disease forms the basis of all programmes. In recent years, this has involved the application of a triazole plus an SDHI with chlorothalonil added into the mix.
We are seeing a weakening of the SDHIs, prothioconazole is now the only long-serving triazole left and chlorothalonil is gone.
Thankfully, we have seen the introduction of two new actives, Revysol and Inatreq, which add considerably to the control of septoria but they must be minded by the addition of folpet.
The presence of any of the other diseases may influence the choice of product at T1, as might the apparent pressure from septoria in the crop. But assuming that septoria is the only serious disease, then the T1 choices tend to involve Lentyma, Elatus Era, Ascra, or combinations of similar actives at doses that may be more appropriate to individual situations.