Its all in the timing
Its all in the timing
Much of the success of the T1 spray relies on timing. Tom Allen-Stevens finds out how the A-team plans to get it right
THOUGHTS in the A-team plots at ADAS Boxworth are turning to fungicides, and theres a small quandary to overcome.
T1 is definitely looming, but harder to gauge is exactly when the ideal timing for spray applications will occur. The difficulty for plant pathology expert Bill Clark is that there is such a huge range of vegetative growth – from huge, well-tillered early-drilled plants to smaller, less prolific ones crowding out the later-drilled plots.
"You cannot infer growth stage from vegetative growth," he says. "If you look at some of these advanced plants, you may think that theyd already reached growth stage 31. But on closer inspection only leaf four, or even five has emerged – and so its not ready to spray."
The opposite can occur on later-drilled crops. The backward plants may look as though they are only at GS30, but leaf three may have been exposed to disease for nearly a fortnight. As with so much else this year, its a quirk of the season and reflects the vast range of dates and conditions encountered at drilling.
Knowing when leaf three emerges will be critical for the number one disease found in the plots: septoria. "The early-drilled wheats will have been exposed to septoria for longer, and the lower leaves will be plastered in the disease. That means the crucial leaf three may emerge into a pool of septoria and must be treated before it has been exposed for too long."
So, in terms of priority, early-drilled crops need attention first – less exposure time and faster growth means less risk for later-drilled wheats. Variety choice also has a bearing on how the disease develops. On susceptible varieties infection moves up the plant quickly, and leaf three can become infected on emergence. Slower disease development may lead to more of a delay on more resistant varieties.
But you shouldnt react to the amount of septoria you encounter in a crop, warns Mr Clark: "If you see it, your wheat is under pressure and will need to be treated. Triazole rate will depend on how long leaf three has been exposed."
So with a spot-on timing in a low risk situation a quarter rate of a good triazole will suffice. A half rate will be needed if the timing is way out. In the plots, the team are expecting to spray a higher rate on early-drilled, susceptible Consort, with a lower rate on later-drilled Claire.
As for which one to use, Mr Clark has his five favourites: "Epoxicona-zole is still the best, while tebuconazole, cyproconazole, metconazole and fluquinconazole are all useful. Well also be using a half-rate strobilurin at T1. Strob choice itself is all fine detail, theres little between them." Using them at the T1 timing has a big effect on greening of the lower leaves – these are especially important in thinner crops.
Any other additions to the mix will depend on other diseases. No eyespot has yet been found in the plots, although Mr Clark is keeping a check on the situation: "Its a first wheat, so we expect the pressure to be less, but we know that a one-year break is not enough for eyespot."
When deciding whether to treat for eyespot, Mr Clark advises growers to pick at random 20 to 25 plants from a field from about GS30 onwards and use a threshold of 20% of tillers infected with penetrating lesions. GS32-33 is about the latest stage you can sensibly treat for eyespot and you should drop the threshold down to 10-15% for this timing. Most at risk are early-drilled second wheats, although he has found some late-drilled Consort with a high level of infection elsewhere on the farm at Boxworth.
"Unix (cyprodinil) is the product of choice to treat eyespot. Landmark (kresoxim-methyl + epoxiconazole) can help suppress the disease, but you may lose your flexibility to vary the strob to triazole mix. Similarly, using Punch C (carbendazim + flusilazole) and Sanction (flusilazole)will compromise septoria control."
Mildew is less of a threat this year, says Mr Clark, and has not been a worry in the plots. Its usually carried on the lower leaves, especially in the later-drilled crops, and he believes septoria will swamp any incidence by T1. "Growers who find it should add a morpholine or spiroxamine to the mix. Dont rely on your strobilurin for mildew control: theres so much resistance around now youll need a different chemistry."