1 December 1995

Cocktails control OSR volunteers…

CONTROL of volunteer oilseed rape in peas with pre-emergence herbicides may be unreliable, particularly in a season like 1995 when lack of rain to trigger activity compromised its performance.

But recent trials at the Processors and Growers Research Organisation suggest two post-emergence mixtures used for follow-up treatments can give good control of the damaging weed.

Rape volunteers have become a major weed of peas. A recent survey of 17,700ha (44,250 acres) of the vining crop showed 25% was infested with unwanted rape plants, which can contaminate the sample at harvest. In dry harvested peas they hinder combining.

Farm experience suggests rape seed can remain viable in soil for at least five years. As it emerges over a long period, the timing of post-emergence herbicides is difficult.

"Pre-emergence materials, such as Monarch and Reflex T, may work well against rape emerging from shallow seed but are less good when it comes up from seed deeper in the soil," said PGROs Cathy Knott.

"So it is best to control rape volunteers with a cheap follow-up post-emergence treatment. Over the past three years half-rate doses of Pulsar and Fortrol have worked well if applied at the 2-node stage of crop. But if peas are more advanced the full rate is needed.

"Skirmish and Basagran has also given excellent results, but this combination is not as cheap as Monarch."