16 March 2001

Be cool to hot herbicide mix

By Andrew Blake

AVOID hot herbicide mixes if you are trying to control big grassweeds in cereals, but cannot get crops walked first because of foot-and-mouth restrictions.

That is the message from agronomists in the west, including Agrovistas Shropshire-based Neil Buchanan. Many mixed farms have meadow grass infestations in untreated crops fast passing the stage when herbicides can be expected to control them.

"The problem is that we are virtually grounded by the foot-and-mouth." That means individual crop inspection merely to contain, let alone control, burgeoning grass weeds is impossible. Sickly crops are not helping.

Isoproturon is the only realistic herbicide option for tackling meadow grass, he says. "Normally I would use 1000g/ha in the spring. Now I will probably have to apply the maximum of 1500 allowed in mixes under stewardship guidelines."

But that alone is unlikely to be sufficient. "We need to tank-mix other hormone type products such as the HBNs to improve the IPUs contact action. But that can be risky to crops, and some are not particularly healthy anyway."

Stewardship advice not to apply IPU to waterlogged soils and being unable to walk fields means he cannot decide on the most appropriate mix. "It is a real dilemma. I cant afford to wipe out a crop, so I will be cautious – which will probably be the wrong course of action."

At best only 30% of cereals in Mr Buchanans area had been herbicide-sprayed by last weekend. Untreated annual and rough-stalked meadow grasses in early sowings are already at mid to late tillering demanding urgent attention.

"Annual meadow grass has always been regarded as fairly uncompetitive. But in places it is like a green carpet with 200-300 plants/sq m. We reckon the estimated yield loss from 100/sq m is 7-8%."

Flurtamone (as in Ingot) and simazine (as Protugan Plus) have both boosted annual meadow grass control from IPU in the far south-west, notes Agrovistas Cornwall-based Martin Stuart. &#42

Pre-em catch-up for autumn?

A significant return to pre-emergence herbicides for cereals next autumn is on the cards, predicts Mr Buchanan.

With hindsight he believes older, often cheaper, pre-emergence chemistry such as trifluralin, terbutryn and chlorotoluron, where varieties permit, could have avoided this springs problems.

"A decade ago we used to do a lot of pre-emergence spraying. We then moved to post-em, mainly because of BYDV, and tried to do the two jobs in one. But we really cannot continue in similar vein."

Returning to pre-em treatments, at least for early sown cereals, would help prevent annual meadow grass running riot, he reasons.

WESTERNWEEDCONTROL

&#8226 Growing meadow grass problem.

&#8226 Foot-and-mouth preventing field inspection.

&#8226 Hot mixes could hit crops.

&#8226 Seek advice and consider return to autumn pre-em.