Seeing might be believing, but for Septoria tritici infections, seeing can also mean it is too late to get effective control. But is being able to detect whether a leaf is infected before disease symptoms are visible of any value to growers when making spray decisions?

That’s what 200 growers and advisers are trying to determine this spring when trialling BASF’s improved septoria test kits, which the firm claims can detect latent septoria infections in the leaf. “I think it could be a really helpful tool,” says Margaret Lawrence, who makes the agronomy decisions for husband Nigel, farm manager of the 500ha Shirburn Farm in Watlington, Oxon.

“Most wheats have Septoria tritici on the older leaves [at this time of year], but knowing whether it has spread onto newer leaves is visually very difficult to know.”

Using the test kit is straightforward, says Mrs Lawrence. “It takes no longer than 20 minutes and, while I’ve done my tests so far in the kitchen, they could very easily be done out in the field. The only tool you need is a pair of scissors.”

So far Mrs Lawrence has tested two varieties – septoria-susceptible Tanker and Robigus, which is relatively resistant. In initial tests on Apr 7, both varieties were positive for septoria infection on visually clean leaves, although the most recently emerged leaf on Robigus tested negative a week later.

“That initial result on Robigus was a real eye-opener,” says Mr Lawrence, although reacting by spraying a T0 spray was never considered. “In the current financial climate, any sprays have to be carefully thought about.”

However, the test kits could influence T1 spray decisions, says Mrs Lawrence. “Other factors such as the weather will obviously be taken into account as well. The kits can only ever be a guide.”

But a positive result on the newly emerged leaf, which will be tested just prior to T1, would require a fungicide re-think. “Last year we targeted eyespot with Poraz, and added chlorothalonil as a septoria protectant. Our strategy is to keep it simple.

“A positive result would mean we would need to add a better eradicant.”

Helping with that decision is where the test kits could be really useful for growers and agronomists, according to BASF’s Tony Grayburn. “If growers are picking up latent septoria infections it could mean they will need to put a curative material in.”

That could be particularly crucial on a variety like Robigus where growers may be tempted to go just with a chlorothalonil at T1, he says.

The kits are more useful just before flag leaf sprays, according to ADAS fungicide expert Bill Clark. “Testing leaf 3 is really useful – knowing how effective T1 sprays have been, and whether lower leaves are infected gives a good guide to how much of a dose of eradicant will be needed.”

Mrs Lawrence is planning to use her remaining tests – each kit comes with 10 tests – to do exactly that, including evaluating small test areas of the new T1 fungicides available this season.

“We”ll definitely try some Proline and Tracker. For the first time we have a yield monitor on the combine so we”ll be able to check their effectiveness.”

But Mr and Mrs Lawrence are conscious of not overspending on fungicides. “Our chalky loam soils dries out badly in the summer, which restricts yields. We’re aiming for 7.5t/ha so it’s important we get the spend right for the maximum yield,” concludes Mrs Lawrence.

mike.abram@rbi.co.uk

[Box] Active ingredients Poraz – prochloraz Proline – prothioconazole Tracker – boscalid + epoxiconazole [Panel] Six steps to septoria diagnosis Take 10 similar leaves [eg all final leaf 3s] from 10 different plants Cut middle 5cm of each leaf Chop roughly and put into provided buffer extraction fluid Shake vigorously for one minute Discard 1.5ml of solution using provided pipette Place test strip in solution for 10 minutes Read off result – positive result = 2 pink lines on strip; negative = 1 line (control) ENDS (692 WORDS)