2 March 2001

Choosing right partner is vital strob decision

WITH little eradicant activity, strobilurins need mixing with a triazole fungicide for optimum disease control and yield. Deciding which triazole to use and at what dose will be an important decision this spring.

According to David Jones, plant pathologist at ADAS Rosemaund, a big factor in fungicide choice this year will be the requirements of the tank-mix.

"Because of the very wet weather, there is a lot of spraying to do in a limited time," he says. "Some growers may find that their choice is dictated by the other components of the mix."

Opting for kresoxim-methyl, as either Landmark or Mantra, means the decision on partner product has already been taken, as both come co-formulated with epoxiconazole.

Choosing Amistar (azoxystrobin) or Twist (trifloxystrobin) requires choosing the best triazole partner, says Dr Jones. "Much will depend on when you are going to apply the strobilurin. One of the two permitted treatments per season should be made at flag leaf, but the other application could be at either T1 or at T3."

He recommends a strobilurin at T1 on high risk varieties, especially in the south-west where septoria pressure is high. But in the north, where there is less disease pressure early in the season and grain filling can be prolonged, it is often better to use it at T3.

"As a rule of thumb, if you are growing a susceptible variety in the south-western half of England, use the strobilurin at T1 and T2. But with a quality breadmaking variety, go for T2 and T3."

A potential exception to the T1 application is where eyespot is a concern and Unix (cyprodinil) is needed for high risk crops, he says. "But a Unix/strobilurin mix is expensive and offers no eradicant activity. So in that situation, the T1 spray should be a Unix/triazole mix."

Due to resistance concerns, strobilurins should also not be used for mildew control in wheat, so alternatives have to be sought where the disease threatens.

Where varietal susceptibility and site history indicate a high mildew risk, a low rate, insurance treatment at GS 30-31 with quinoxyfen often proves cheaper than a fire brigade approach with fenpropidin, says Dr Jones.

STROBPARTNERS

&#8226 Spray timing influence.

&#8226 Eyespot & mildew concern at T1.

&#8226 Epoxiconazole more robust at T2.

&#8226 Triazole choice wider at T1.