8 March 1996

Cocktails top the tariff…

Last seasons ultimately low disease pressure in cereals surprised many in the industry. But lowering ones defences could be asking for trouble. In this special focus we ask specialists at each end of the UK for their thoughts on this years strategies. We also examine protection for oilseed rape, peas and potatoes. Edited by Andrew Blake

NO ONE can accurately predict which diseases may pose problems this season. But growers should not want for choice of chemical solutions, says ADAS pathologist Bill Clark.

"There will be a flurry of new or little-known products on the market in 1996, but few are based on new active ingredients," he says. "ADAS experiments confirm the outstanding performance of Opus (epoxiconazole) on both wheat and barley."

Mr Clark believes the trend towards mixtures, particularly of triazole/triazole and triazole/morpholine, will accelerate in the next year or two.

"Some of the mixtures are as good as the best straights weve got. Although not necessarily offering great steps forward in the level of activity, they do provide very robust products."

1995 results confirmed Opus as the "number one in terms of efficacy and cost-effectiveness" for controlling septoria in wheat, says Mr Clark.

There is still, however, a place for Bravo (chlorothalonil) used early season (GS31/32) and late (post GS37), he reckons. "ADAS Rosemaund trials found Bravo mixtures were particularly beneficial when sprays were applied before the target flag-leaf was fully emerged."

So far ADAS has no evidence that triazoles can be translocated into emerging leaves at high enough concentrations to control Septoria tritici.

The diseases disappearance in the dry weather after stem elongation in 1995 should have been predictable, he maintains. "Check for inoculum, ie active, sporulating lesions, at GS31/32. If there are none on the upper two leaves, the risk is small and GS32 sprays less critical, unless the weather at that time is very wet."

To ignore yellow rust would be "tempting fate", warns Mr Clark. "The race which can attack Brigadier is not very common, but the variety is. The race will soon spread with the variety so widely grown. The potential for damage is high if the weather is cool and moist."

Growers in traditional high yellow rust risk areas round the Wash and coastal Essex will be prepared, he believes. But those in lower risk areas could be "caught out" if the weather is favourable.

1995 was potentially a very high risk year for eyespot. Dry weather checked the diseases development, but cannot be guaranteed to do so again this year. "The current season has potentially moderate risk and growers should have been checking crops from the end of February. Its wise to keep checking until GS32. If the treatment threshold of 20% tillers with penetrating lesions hasnt been reached by then you can forget it, except on Soissons where a 10-15% threshold should be used."

"Some early drilled crops last year gave a 20% yield response to eyespot control so you cant be complacent, particularly on early drillings or on very susceptible varieties like Soissons."

Net blotch in barley has become a severe problem in parts of the UK, especially the south and west, comments Mr Clark. "The disease seems to be with us now on a regular basis. The French have had it for a few years but now have Unix (cyprodinil) to expand their fungicide armoury.

"Opus is probably our best weapon against net blotch, but we welcome the imminent arrival of Unix, probably next season."

Early treatment is "crucial" and follow-up sprays are often needed to keep on top of disease, he says.


&#8226 "Flurry" of new products expected.

&#8226 Opus (epoxiconazole) "outstanding".

&#8226 Check wheat for Septoria tritici at GS31/32 (first/second node).

&#8226 Dont ignore yellow rust potential.

&#8226 Keep checking for eyespot until GS32.

&#8226 Unix (cyprodinil) useful weapon against barley net blotch.


ADAS ON FUNGICIDES

Dont be complacent about

eyespot, says Bill Clark.

Decision time for fungicides?Watch out for yellow rust, says ADAS.