23 February 1996

Weed-killers offer cost cuts – at the right time

Wheat prices are lower in real terms than a decade ago but input costs have risen considerably. Edward Long discovers if cheaper weed control can provide a route to help redress the balance

WEED control is one area where there is scope to cut input costs, provided grass species do not threaten, says Suffolk agronomist Johan Zethraeus.

"There is some room to consider cheaper options and cut rates, provided yields are not compromised." But the aim remains to prevent weed seed return, and each field must be considered individually, he adds.

Mr Zethraeus, an associate of Stowmarket-based Independent Agronomy, reckons there is little scope to cut costs in the autumn. Effective weed control is vital for crops to establish and to remove grass weeds. Flexibility comes with spring follow-up treatments, when herbicide costs can be as low as £17.50/ha (£7/acre) or less.

Diflufenican/IPU mixes (such as Javelin and Panther) backed by trifluralin to boost blackgrass control provide the base for his clients autumn weed control strategy. Other similar cost options include bromoxynil/ioxynil (Deloxil and others) + IPU which remove weeds poorly controlled by diflufenican.

Main weapon

Fluroxypyr (Starane) remains the main weapon for cleaver control. But over the past three years Mr Zethraeus has seen a big rise in shepherds needle, once thought to be extinct in East Anglia. Many fields are now swamped by it. Spreading hedge parsley, cranesbill and groundsel have also become more troublesome.

"East Anglia is haunted by thistles. Metsulfuron-methyl (Ally) is popular, as it can go on late in spring when most have emerged. But MCPA is a cheaper option costing no more than £2/acre. It does a decent job on thistles and I use it whenever possible." But it is weak on shepherds needle and spreading hedge parsley, he notes. And it is less flexible than dearer products, as it can only be used to GS30, although it is less temperature dependent than Starane.

CMPP is an ideal partner for Ally, as it suppresses ivy-leaved speedwell, but the price has doubled with the formulation change.

Although there are few other alternative products for anyone trying to make savings, there is scope for trimming costs by tailoring products to need. Half or third rates can be used, if care is taken to spray in the right weather, says Mr Zethraeus.

A reduced rate of Ally costs £5-10/ha (£2-£4/acre), and a half-rate Starane about £10/ha. Where autumn herbicide has worked but thistles have emerged early MCPA can be substituted at about £5/ha (£2/acre), about half the cost of the thistle rate of Ally.

"Wheat growers can be too fussy about weedy crops. If margins are squeezed much further lots of some common broad-leaved species could be tolerated. But highly competitive cleavers and rapidly spreading types such as shepherds needle must be removed. There is scope to cut costs but caution is needed, as one years recklessness could wreck seven years of prudence," Mr Zethraeus warns.

For the past two to three years autumn-applied pendimethalin (Stomp, Sovereign) and IPU have been popular with wheat growers in the West Midlands. They replaced diflufenican + IPU when resistant blackgrass appeared and to remove cranesbill which built up to problem levels. "Pendimethalin/ IPU is a robust and weather-proof combination which is streets ahead of anything else," says agronomist Peter Parr of Evesham-based Premier Crops. "It also offers scope for trimming herbicide costs.

Smaller targets

"Instead of using the full 4 litre/ha rate of pendimethalin with the 2 litre/ha rate of IPU, farmers could go down to 2-3litres/ha without comprising control of threatening weeds. But anyone adopting a reduced rate policy must be aware of weed growth stages. Targets must be smaller and younger than with the full rate."

Surviving weeds could otherwise add up to £7.40/ha (£3/acre) to the cost of spring weed control due to follow-up treatments. &#42


&#8226 Clean start vital.

&#8226 Reduce autumn spend with caution.

&#8226 Spring weed control cuts possible.

&#8226 Reduce rates of costly products.

&#8226 Use cheaper, often less flexible products with care.

Effective autumn weed control can give flexibility in the spring, says agronomist Johan Zethraeus. But watch out for competitive weeds.