1 August 1998

GET TO GRIPS WITH TALLS

Weed beet is on the up and up. Gilly Johnson asks how to best to tackle this seasons growth of bolters.

THERES no disguising a problem with weed beet: the evidence grows above the crop for all to see. This season looks to be the worst for many years. Tell-tale talls are most visible in the Eastern counties, where nine fields out of 10 have some weed beet.

The last seriously bad year was in 1984, when 70,000ha (173,000 acres) were affected. Simon Fisher of British Sugar reckons this seasons figure might be higher – though the official BS crop survey has yet to be made.

Growers shouldnt blame seed stocks or early drilling this spring, he says. Both 1997 and 1998 were low bolting seasons, so the problem is a legacy of poor bolter control in previous years.

It doesnt take many missed bolters to sow the seeds of a problem. Each plant is capable of leaving behind 2,000 viable seeds – and these can remain dormant in the soil for more than 20 years.

If weed beet are uncontrolled, theres a risk to both yield and quality. Four plants per square metre can cost 1t/ha (8cwt/acre) in beet yield. At double that population, half the crop might be lost. Even at C beet prices, thats perhaps £300/ha (£120/acre) – which puts the cost of control (see table) into perspective.

Much weed beet occurs in discrete patches, so such high populations are more common than growers might think, says Mr Fisher.

The message is to take every opportunity to control weed beet, insists Mr Fisher. Tractor hoeing will clear 90% of the weed plants, but leaves those within the row. These days fewer growers have tractor hoes available, he adds.

In the worst scenario, the rows vanish and there are too many weed beet even for tractor hoeing.

Hand pulling remains the most effective, as long as weed beet populations are not too high. And pulled weed beet should be removed from the field, if they have set seed. But finding reliable gang labour can be tricky.

Using herbicide with weed wiping equipment is fast, covering perhaps 12ha (30 acres) or more a day. But it takes two passes, in different directions, to kill what can be rather woody stemmed plants. And some weed beet now appear to be flowering low, out of reach of the wipe. Is it a case of repeated weed wiping and/or cutting practices giving selection pressure for shorter weed plants?

For large acreages with bad infestation, cutting could be the fastest, fire-brigade answer. But whichever route is chosen, timing is critical. If pulling, the advice is to remove all bolters up to the end of August. Wiping should be done as soon as the first flowers open (early July), and repeated every 10-14 days. Wiping should be stopped in early August to prevent rotting roots being harvestable, which can affect beet quality in the clamp. Cutting needs to start 3-4 weeks after the first flowers appear, with repeat cuts every 2-4 weeks.

The BS survey shows that 65% of growers are taking control measures against weed beet. But that leaves 35% who arent – a worrying statistic, reckons Mr Fisher. "Once youve got weed beet, you sit up and take notice. No-one is complacent when it appears. The trick is to try and prevent a weed beet problem starting in the first place."

THREAT

THE problem is as bad as it has been for a long time, according to British Sugar surveys. More than 60,000ha (148,000 acres) could be contaminated this season. But bolting has been low for both this year and last. The high populations of weed beet are likely to be a result of seed carried over from the previous beet crop in the rotation.

Control is a must, because each weed beet can leave 2,000 seeds, capable of surviving 20 years. A population of eight weed beet a square metre can halve beet yield. At four weed beet a sq m, expect to lose 1t/ha (8cwt/acre) in beet tonnage. Weed beet will also exacerbate nematode problems.

THERE are four control measures:

* tractor hoeing

* hand pulling with gang labour

* using herbicide with weed wiper machinery

* cutting Timing is critical, to avoid shed seed.

Other helpful strategies are:

* longer rotations

* harvest crops with bolters first, then shallow cultivate after harvest to encourage weed beet seed germination, then eliminate

* use incorporated trifluralin in May-June on sandy soils, to control later germinating weed beet seed as well as other weeds

* control weed beet elsewhere in rotation with herbicides

THE most cost-effective solution to bad weed beet is hand pulling, reckons Peter Browne (right) of Moseleys Farm, Fornham All Saints, near Bury St Edmunds. "And weve a weed wiper in the shed! Hand pulling worked out last year at about £3.65/acre. Taking a tractor across would be more expensive." However, finding the labour is becoming more difficult, he says. About a quarter of his 263ha (650 acres) of beet requires attention this season. "The problem is a result of the way the fields have come round with the rotation," he believes. The first pull will take just over a fortnight. A second trip is planned with the pulling gang to take out the later developing plants in the worst spots.