West: Rapid growth and spray timing decisions

Crop growth has continued without missing a beat, unlike previous springs, when we have had periods when growth has been checked at some stage. This time of year nodal growth stages on wheat become slightly irrelevant, it is all about leaf emergence and phyllochron, which was ably described by my magician colleague Sean Sparling in last week’s blog.

Leaf rolling tests the patience, making me wish I didn’t bite my finger nails so much, but it is critical to get the correct leaf layer targeted. This, for me, is as important as fungicide product choice and rate. Some believe that the “normal” flag leaf emergence date of May 16will still be achieved, with leaf emergence on forward crops slowing down. However, having done crop physiology experiments for many years, growth stages can still be significantly different at flag leaf and only really concertina by the time of ear emergence and flowering. There are already reports of winter barley with awns showing, so it is going to be an early season.

In my area development of wheat is tracking sowing date, with early September sown wheat already with eventual leaf 3 fully emerged and leaf 2 emerging. These will have had T1’s the week before this blog. As expected these crops also have the highest septoria levels – which in west is always our main disease control focus – and the concern shared by others is how high up the canopy we have disease with up to 30-40% of the tip of leaf 5 with lesions. On some of these crops I have upgraded to an SDHI rather than a three quarter dose of triazole plus chlorothalonil mix which would be my standard at T1 on most wheat. Late September/early October drilled crops will get T1’s around the Easter weekend and later drilled than that will be post-Easter.

Winter barley crops look very promising, with good tiller numbers that we know are critical to sustain high yields. Hybrid crops of Volume and Galation are looking particularly promising, with their larger leaf area looking impressive and with less rhynchosporium than Cassia. Hence pints of beer have been wagered with clients on eventual yield and I’m sure this will pursued with more enthusiasm than any yield guarantee. The mild winter has allowed low levels of brown rust to survive, which is unusual for this part of the country, but T1’s – which have included SDHI – have all been applied in the last 7-10 days. With the crop rapidly growing and flag leaves starting to emerge, T2 will be needed by the end of April.

Oilseed rape crops are well into flowering and yield potential is starting to look much more promising now. At early in stem extension they seemed to be very mono-stemmed with just a terminal raceme, despite a fungicide with PGR activity being applied. Recently there has been branching and this may have been a function of nitrogen management, which caused some problems. Wet field conditions in March and large crops delayed first splits, followed by rapid growth and tall early crops meant that  the planned three split strategy was adapted to two applications. However, there is excellent light penetration through the canopy, which is critical to the yield that is all formed post flowering. With good healthy leaf area retention I am optimistic about yield potential, but sclerotinia needs to be protected against to ensure this potential is achieved and I usually plan for a two spray strategy. A triazole at yellow bud and half rate boscolid (Filan) at mid-flowering. These have been deployed and it is now a careful watch on timings and how long the flowering will continue.

So, as is often at this time of the year, crops show excellent promise, but we are now entering the critical time where the weather has the greatest influence on whether we achieve this potential. Oh how I wish for an accurate crystal ball!

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