Dissection is sure fire spray guide
Dissection is sure fire spray guide
By Andrew Swallow
HOW sure are you of correctly identifying critical cereal growth stages? Fail to get it right and you could jeopardise crop profits, as many growers did at T1 this season, visitors to Morley Research Centres Growth Stage Clinic heard last week.
Many growers went too early with their first main fungicide application, raising disease risk and probably fungicide cost, it says. "Year on year a good proportion of crops nationally, probably at least 50%, receive T1 sprays too early," says researcher and agronomist Ben Freer.
This year will have been no exception, with many growers tempted to get on in good weather before the main T1 target, final leaf three, had started to emerge.
Now, with flag leaf still a fortnight away on most crops and some October-sown wheat only just ready for T1-sprays, early April treatments will be running out of steam.
"If thats the case you will need to go back before flag leaf. Recent showers mean there is a serious septoria risk."
For some growers impatience or the practicality of getting round large areas of crop is to blame for the premature T1 tactics. But for others it is because they still struggle to correctly identify the critical final leaf three emerging growth stage, he believes.
"Accurate identification of growth stages is vital. It enables the grower to get the most out of his fungicides and crop, and spend as little as possible on it. When you are bang on time with applications you can be more economical with the dose."
Arguably, a late T1 application is less costly than going on too early. "If you are a little late getting on at least you can recoup the situation by using a spray with more kick-back. But if you were too early leaf three will have emerged unprotected and, if it remains untreated, will act as a vector moving disease onto the flag leaf."
Mr Freers comments are echoed by crop physiology expert Margaret Appleyard. "The growth stage to understand is final leaf three."
All you need to identify that is a good pair of fingernails to tease the leaves apart and peel them back to the embyro ear (see panel on left). *
Accurate growth stage identification is essential for effective fungicide management, says Morley Research Centre. Here, adviser Margaret Appleyard helps Morley member David Hurn get to grips with mainstem dissection – a key to timing T2 sprays accurately.
Dissection advice
First find the mainstem, usually the largest stem with the remains of the seed attached to the base. Tear off tillers, peal the fully emerged leaves off the mainstem and discard, including leaf sheaths as far down as the top node. "As soon as you can see the ligule a leaf is fully out," says Margaret Appleyard. Then remove each remaining leaf in turn, counting down to the ear. "If the emerging leaf is the only leaf left then clearly, that is the flag leaf."