13 March 1998

Septoria is Number One enemy for now

SEPTORIA rather than eyespot should be uppermost in wheat growers minds at first fungicide timing.

"Septoria is a yield robber even at T1. Eyespot is far more sporadic and even where it occurs septoria is still more of a threat," says ADAS fungicides specialist Bill Clark.

"Get control right now and you can create a barrier of clean foliage which moves up the crop and protects the flag leaf as it emerges later on."

Andy Selley of Du Pont echoes those views. He is working with NIAB and IACR-Long Ashton to get a better understanding of the disease and develop regional early warnings. Diagnostic testing and monitoring of untreated plots at eight NIAB sites show that Septoria tritici is already well established.

Septoria nodorum is also common and regionally significant, he adds. In Shropshire, for example, S nodorum infection levels are already well above those at the same stage last year.

It is still too early to predict the threat from eyespot, he maintains. But Du Pont monitoring has shown that only 10% of crops have been at high risk over the past five years. Eyespot should not be forgotten but must be kept in perspective, he maintains. Depending on varietal resistance and disease pressure, Septoria tritici control can be worth £77-£315/ha (£31-£127/acre), according to NIABs Richard Fenwick. But the cost of control in NIAB trials has been £66/ha (£27/acre) at most.

With septoria already in the crop, a fungicide with both curative and protective properties is needed, Mr Selley maintains.

Evidence of the value of ELISA diagnostic tests in determining when to spray against septoria later in the season is growing, says Long Ashtons Shiela Kendall.

A treatment threshold of 5 antigen units on leaf three of Riband has given good results in trials. The same work highlights the benefits of using mixtures rather than straight triazoles against the disease. &#42