8 March 2002

Growers miss out on pre-em

By Andrew Swallow

MANY sugar beet growers would simplify and strengthen their weed control programmes if they used pre-emergence herbicide, says BASF.

"Over 50% of the UK area wont get a pre-emergence product – we think the farmer is missing out and running a risk," says the firms Stefan Hafner.

Morley Research Centres Martin Lainsbury endorses his comments. "About 70-80% of the UK crop is suitable for some form of pre-emergence herbicide, so yes, some growers are missing out."

Chloridazon (as in Pyramin) is the core pre-emergence herbicide, he says. "It is the broad-spectrum herbicide and has no seed treatment or soil type problems."

Most weeds are at least sensitised, if not killed by that residual, giving crops a head start. "Pre-emergence sprays really control the early emerging weeds, which are the most competitive."

In a wet year fewer post-em treatments are likely to be needed, saving money on sprays and probably increasing yield. In a dry year, while weeds may not be killed, they are checked and are more susceptible to post-em sprays.

"Once the residual is in the soil you limit the weeds root growth, so it becomes much easier to knock down post-emergence."

Pre-emergence treatment buys growers valuable flexibility with the first post-em spray timing, adds Dr Lainsbury.

"The ideal first post-emergence spray goes on at cotyledon to first true-leaves of the weeds. But if you have used a pre-emergence that may be delayed by up to 12 days with no loss of efficacy."

That allows growers to target sprays to the best days for phenmedipham (as in Betanal) activity, rather than being forced to go in poor conditions because weeds are getting too big, he says.

"Phenmedipham is an optical inhibitor, it works much better in warm, bright conditions."

Substantial savings and better control can result on key weeds such as fat-hen, which can grow from cotyledon to 4-6 true leaves in a week, he adds.

Introducing last years new sugar beet active ingredient, quinmerac, into the pre-em portfolio as Fiesta T (chloridazon + quinmerac) means growers can also combat cleavers and fools parsley with the pre-em pass, offering an alternative to post-em Debut (trisulfuron-methyl).

"The difference is with brassica weeds. If you have them I would use Debut. If not I would use Fiesta for cleavers," says Dr Lainsbury.

Only on organic soils, or land with a very low weed burden, is a pre-em spray not worthwhile, says Dr Lainsbury. "Or possibly when using the FAR-technique of weekly applications. But you have to know you can achieve accurate and timely sprays." &#42