Beet those weeds…
Beet those weeds…
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WE KNOW how to control them. So why is the problem increasing? Weed beet were identified in three out of every five beet fields last year – thats an all-time high, says Mike May of IACR Brooms Barn.
These weed beet are a legacy of lack of control during the 1990s, he says. "Weed seeds can survive for long periods. And early March drilling exacerbates the problem, because bolters give rise to some plants which in turn will bolt in their first season of growth." Seed set in set-aside can also be a problem, he adds.
Just how quickly weed beet can build up is illustrated by Mr Mays calculations. Even with adequate weed control programmes in intervening crops, a modest population of 100 weed beet/ha left to set seed in 1996 can result in the headache of 5,000 weed beet/ha, by the time beet returns to the field in 2000. If these were ignored, and the rotation is repeated once more, then the number in the next beet crop jumps to an unmanageable 250,000 weed beet/ha.
So it is imperative to take control early on, to prevent the population explosion. But even at low numbers, weed beet have a serious impact on yield, says Mr May. Each plant/sq m can cut yield by 12% – worth about £150/ha in lost revenue. Competition from weed beet is worst on light soils, where moisture is more limiting.
Weed beet are less intrusive if the rotation allows a six-year gap between beet crops. The annual mortality of weed beet seeds in the soil is about 50%/year. However, widening the rotation isnt possible on most holdings. So other techniques of tractor hoeing, hand pulling, weed wiping and cutting must be employed. The table below gives the cost thresholds for each approach.
Mr Mays tips for reducing the weed beet seed burden are:
• delay cultivation and ploughing of infested fields to reduce seed return; birds and mice will eat seeds left on the surface
• plough deep – weed beet will not emerge from depths greater than 10cm – and then leave deep buried seeds undisturbed by using shallow ploughing in subsequent seasons
• most weed beet will germinated in open spring sown crops, so use a stale seedbed to stimulate germination and kill off before establishing the spring crop
• spring linseed sown into a fine seedbed in March will encourage weed beet germination – these can be controlled later with a sulphonyl-urea herbicide such as Ally.