Top sugar beet yields require tip-top weed control. But with several spray strategies available, how should growers decide which is most appropriate? Andrew Blake relays Broom’s Barn advice

Whichever beet spraying programme you choose – FAR, conventional, or so-called “active” – be sure to stay flexible, urges weed specialist Mike May. “Always consider the conditions.”

In last year’s tricky spring growers who switched from phenmedipham-based FAR-type treatments to desmedipham mixtures, the basis of the “active” approach, achieved much better weed control in April. “That’s because desmedipham works better in dry weather,” says Mr May.

Choosing between the different approaches is all about balancing spraying capacity and costs, he says.

The FAR (phenmedipham/active/residual) system – involving four or maybe five weekly hits on weeds with relatively low doses at the early cotyledon stage – is usually cheapest in terms of herbicide costs alone. But by the time application costs are included the overall spend is likely to be much the same as with some conventional programmes (see table).

“With FAR you must also be spot on with the timings, so you need good sprayer capacity. Ideally, you need to be able to spray your whole crop in one day, or at most two. Poor soil conditions may mean having to fit low ground-pressure tyres, and if everything goes against you and you get delayed, you may need to revert to higher doses.”

There are no reliable statistics on the proportion of the crop that is FAR treated. But given the frequent washing out required if the same sprayer is used for other crops, and the extra management required, it is probably declining, Mr May believes. Sprayers have become much more sophisticated and fewer people have dedicated sugar beet sprayers these days.

“The other, non-FAR, programmes may cost a bit more on the sugar beet, but you have to decide what is best for the farm’s overall profitability. The key is to stay flexible. If you’ve opted for FAR and you get behind, you can always change. Equally, if a conventional approach seems to be working well you can always drop the dose next time round.”

Conventional programmes, which may or may not include a pre-emergence herbicide, can be reasonably economical, says Mr May. “I reckon that over 50% of the crop still gets a pre-em, not so much directly for weed control as for the flexibility it offers.”

His main caution is that the chemical mixes need choosing more carefully to avoid crop damage because the doses applied are higher than under FAR.

Growers should visit the BBRO Herbicide Selector site to help find the most suitable products according to the five main target weeds, soil type, condition and temperature, he suggests.

The “easiest” option in terms of herbicide choice and timing is the “active” route based on mixtures with formulated products such as Betanal Expert (desmedipham + ethofumesate + phenmedipham) or Debut (triflusulfuron-methyl).

Applied as soon as the first true leaves of the weeds are emerging, both offer good broad-spectrum control, the latter tending to be rather slower acting, but nonetheless effective. But such mixes cost more. “You should be prepared to spend up to 30% more than with the other systems.”

The big advantage is that the timing window is much wider. “It’s the simplest and best option if you are restricted on spray capacity.” Often just two treatments, costing no more overall than the conventional approach, will suffice.

But in Brooms Barn trials last year three passes with a sequence of Betanal Expert + Goltix, Betanal Expert + Venzar and then Betanal Expert + Goltix gave 13t/ha more than two (with the last Betanal Expert + Goltix omitted) even though it was hard to see any differences in weed control in mid-June.

“It suggests to me that anyone who is pushing hard for 70-80t/ha really does need very high levels of weed control,” says Mr May.

FW-WEED-CONTROL

Herbicide changes
There are two slight changes to the herbicide options in 2008, notes Mr May.

Ethofumesate (as in Nortron) is now subject to a lower maximum dose of 1000g of active ingredient a hectare over three years. “But not many people grow beet in successive seasons. But anyone using it pre-em could effectively be limited to one hit in three years, as the dose at that timing is high.”

Most growers use glyphosate to clean up land before sowing, but for those relying on paraquat (as in Gramoxone or PDQ) it’s worth remembering that it is being withdrawn by the EU. “The use-up date is 11 July 2008, so check your stores.”

Diquat, however, should continue to be available, he notes, in the form of a new product called Retro.