24 May 2002

Zero tolerance needed to beat weed

ONE years seeding; seven years weeding, goes the saying.

For weed beet that could read 20 years weeding, judging by the experience of Peter Wright of Brettenham, near Thetford and Mike May of IACR-Brooms Barn.

"It sort of crept up on us without us realising it," recalls Mr Wright. "One field suddenly became quite bad in the mid 1980s. It has been through four rotations since then and we are only just getting on top of it."

Hand rogueing is his preferred control method. Every beet field is walked twice, once at the beginning of July and again in August.

"It takes priority over everything else. We pull up the plants and break them in half, then leave them in the field. It is very important to make sure you get them before they set seed."

Each time across his 170ha (420-acre) crop takes about one and a half weeks and the average annual cost is about £10/ha, he calculates. But the 15ha problem field is the one that takes the time.

"There are two or three patches – about 5ha – affected. That field can take us three or four days."

Hoeing is shunned for fear of reducing weed control. "We do a small amount of weed-wiping but you cant beat hand weeding."

IACR-Brooms Barns Mike May echoes that up to a point (see box). "Hoeing is always worthwhile if you have more than a few/ha as it takes out 70% of the weed beet and will make hand-pulling much more manageable. But it may not be worth it where there are only a few weed beet/ha if it means you have to apply an extra herbicide."

Weed wiping or cutting come into play on higher infestations, roller or moving rope weed wipers being the simplest to operate. "Wicks need to be constantly adjusted as the temperature changes."

Wipers must not be used from mid-August for fear of herbicide-laden weed beet roots being big enough to be harvested and raising a residue risk, he warns.

Cutting should start in late July before seed sets. "The trick is to do the first cut 10 inches above the crop, the second 5in, and trim the crop with the last one. That should give 95% control."

Whatever method is used growers are unlikely to see a yield return benefit greater than the control cost in that crop, warns Mr May. But zero tolerance is required if they wish to keep fields in beet production, he stresses.

"If you do not remove them they will shed seed and multiply. One weed beet can lead to a field having to be taken out of production within three rotations."

&#8226 Zero tolerance needed.

&#8226 Hand-pull if less than 1000/ha.

&#8226 Wipe at 1000-10,000/ha.

&#8226 Cut x 3 if more than 10,000/ha.

&#8226 Hoeing removes 70%.