12 April 1996

Knock couch grass regrowth on the head this season

USING Roundup Biactive (glyphosate) can boost control of couch regrowth by almost 40% compared with original Roundup, says maker Monsanto.

Rhizomes were sampled two weeks after treatment with 4 litres/ha (2.8pt/acre) of product. Individual sections of rhizomes each containing a single bud were then tested for germination.

Only 2.7% germinated after a Biactive application compared with 4.43% of those sprayed with the original formulation. Nearly 32% of rhizomes from untreated plants germinated.

That seemingly small difference between the two products amounts to £16/ha (£6.50/acre) loss in the first season after treatment, rising to £49/ha (£19.80/acre) in the second, says technical manager Colin Stride.

That assumes an average wheat yield of 7.5t/ha (3t/acre) at £110/t and a couch infestation of 30 shoots/sq m at the time of treatment, he adds.

Biactives better performance is due to more active adjuvants which improve spray retention on the leaf, speed uptake and boost distribution within the plant, says Mr Stride.


That also improves the rainfastness, he adds. Trials show that at 4 litres/ha, light to moderate rainfall four hours after application gave no loss of control on couch.

On cereals and wild oats, a 1.5 litres/ha (1pt/acre) rate was unaffected by light to medium rainfall just two hours after application.

Although Biactive appears to give a slower kill then the original formulation, it also gives a more thorough one, Mr Stride maintains. &#42