14 May 1999

Trials show when use of strobs is cost-effective

By John Burns

CONDITIONS under which the strobilurin fungicides are cost- effective are becoming clearer, thanks to HGCA-funded trials.

Making use of that knowledge will be essential to realising the full potential of this new chemistry, plant pathologist David Jones of ADAS Rosemaund Hereford, told a breakfast meeting of Somerset cereal growers this week.

Strobilurins only have protectant action and so must be applied before diseases arrive, he stressed.

They are also unlikely to be used alone on cereals, except possibly Amistar (azoxystrobin) to keep ears clean in milling wheat in the east of the country. Full benefit from strobilurins in other situations will only be achieved if the level of the supporting fungicide in the mix, usually a triazole, is enough to ensure a high degree of overall disease control, he noted.

It also needs to be remembered that strobilurins appear to work by maintaining the green canopy longer. That means they will only be cost-effective on crops of suitable structure on land capable of providing enough moisture throughout the growing period.

Anybody on good land where wheat yields are never under 7t/ha (2.83t/acre) should try strobilurin fungicides to see how they work under their conditions, he advised.

But where the early wheat market is the target also be wary of using too much strobilurin on the ear, which could delay harvest, he said. Use on the flag leaf should not cause such problems, he felt.

Decisions need making in the next week, so it is necessary to predict the possible consequences of a dry June, he noted.

Most of the HGCA funded trials have been on wheat. But there is also a place for strobilurins on barley. Amistar, for example, is good on net blotch, a disease to which some of the malting varieties are very susceptible, said Dr Jones.

Amistar is very good on net blotch and brown rust but needs a triazole mix partner to give good rhyncho control, Dr Jones noted. He felt it was likely that there would be greater varietal differences in response to strobilurins in barley than in wheat, because of the greater differences in varietal resistance to barley diseases.

Zeneca now accepts that Amistar is not strong enough to cope with Septoria in most years, he said.

&#8226 The HGCA breakfast meetings for farmers to hear about results of topical HGCA trials are a new venture this year. The Somerset group felt they were a good idea and the 8am start ideal. &#42

Strob responses

Rosemaund Somerset

(t/ha) (t/ha)

Untreated control 5.76 3.68

Opus 10.54 9.4

Landmark 11.35 9.81

Amistar 9.14 7.18

Amistar + Opus 11.06 9.67

NB. Riband trials 1998