13 November 1998

Still plenty of time to spray for blackgrass

HGCA researchers took to

the road last week to relay

results from work growers

have paid for. Andrew Blake

relays the key messages

delivered at Salisbury

DONT panic if you havent yet sprayed against blackgrass. That is the reassuring news for winter cereal growers from Jim Orson, weed specialist and director of Morley Research Centre.

Provided crops are treated before February, yield can be maintained, he told HGCAroadshow delegates last week. "There is a lot of flexibility." Trials at ADAS Boxworth in 1996 and 97, when blackgrass populations at treatment were 224 and 191 plants/sq m, showed no yield reduction until spraying was delayed beyond Feb 2 and Jan 31 respectively.

Lighter infestation

In 1995, on a much lighter infestation of nine plants/sq m, treatment could safely be left until April 12 before yield was cut, he noted. Mr Orsons main concern is that growers be aware of the costs of blackgrass resistance given current low cereal prices.

Temptingly economical minimal cultivation systems and early drilling are ideal for blackgrass, he said. Even with wheat at £100/t the cost of resistance can be up to £180/ha (£73/acre).

"Make sure you have a sound anti-resistance strategy in place now. You will need it in future. Think about drilling date, make sure you kill all emerged blackgrass first with a broad spectrum herbicide, and monitor, monitor, monitor to make sure any resistance is picked up as soon as possible."

The Weed Resistance Action Group is working on guidelines to pinpoint which of several resistance tests is most relevant in particular cases, he noted.

New herbicides, JV485 from Monsanto and another from AgrEvo, could be a great help in future. "But dont count on it."

Mr Orson challenged the view that growers should always aim for 95% blackgrass control. "In many cases we are only talking about containment and 70-80% control is often enough to live with it." Only on high or hard-to-control populations should the target be higher, he suggested. "In reality there are lots of areas of the country where lower levels are acceptable."

Isoproturon is valuable as part of a herbicide resistance strategy, but growers must handle it more responsibly to retain it, he warned. "There was a lot of ipu in water last autumn and the water authorities are beginning to run out of patience." New health limits on the amount of bromate in water, which is formed during decontamination, could put extra pressure on ipu.

AUTUMN HERBICIDES

* Dont panic on untreated crops.

* Beware blackgrass resistance.

* Assess control required.

* Handle ipu more carefully.

AUTUMNHERBICIDES

&#8226 Dont panic on untreated crops.

&#8226 Beware blackgrass resistance.

&#8226 Assess control required.

&#8226 Handle ipu more carefully.