7 May 1999

Blackgrass meets its match

By Andrew Blake

WHEAT growers plagued by hard-to-control blackgrass can look forward to some highly effective herbicides based on new chemistry, if a Cyanamid trial in Cambs is anything to go by.

Two of the companys latest products, ACH 210 and a development chemical further from commercial launch, helped kill up to 99% of the blackgrass in plots this season at Tony Webbs 162ha (400 acre) Grange Farm, near Lutton.

Autumn use

Provided ACH 210 meets PSD requirements it could receive approval in time for autumn 2000 use, says the firms herbicide marketing manager, Rob King.

The two materials were tested alongside a range of industry standards and another well-trailed newcomer from a different company, both with and without pre-emergence Avadex (tri-allate) treatment.

The trial, in a field of mid-October drilled Abbot, provided a stiff challenge, says technical services manager, Peter Tayler.

A history of minimal cultivation meant there was a heavy population, on average 194 plants a sq m by early January when post-emergence treatments were applied. By the beginning of last week the wheat in the untreated plots was well swamped.

The site is also affected by resistance, which probably accounts for the relatively poor performance of both isoproturon and some newer products like Hawk (clodinafop + trifluralin) and Lexus flupyrsulfuron-methyl), he says.

"Our rapid resistance tests showed there was not any target-site resistance, but there was moderate enhanced metabolism resistance which can affect a wide range of herbicides."

With Agenda 2000 about to bite, all the signs are that there will be more wheat grown, which will increase the pressure for good blackgrass control, says Mr Tayler. "We will need better performers than we have now.

"Even the best of the current chemistry is struggling here." That includes Hawk early post-emergence and a standard residual Stomp (pendimethalin)/ipu treatment both of which gave no more than 75% control, even with the backing of Avadex.

But even alone the three novelties, all applied pre-emergence, achieved a 90-95% cut in weed numbers, says Mr Tayler. After Avadex they came within a whisker of total clean up. Main reason for the survivors is probably clods at application, which allowed some seeds to escape the chemicals, he believes.

Besides highlighting the potential of the new chemistry, the trial also showed how relatively little extra control – about 10% – is provided by adding trifluralin to ipu, says Mr King.

ACH 210, for use also on winter barley, is not targeted solely at blackgrass. "It is a very good annual and rough-stalked meadow grass treatment."

It is also active against Italian rye-grass, loose silky bent, fescues and several broad-leaved weeds including chickweed and speedwell. "Wild oats are not its forté. You could expect 85% control of autumn germinators."

75-80% control of sterile brome can also be anticipated, says Mr Tayler. "It is as good as the standard approach, which includes Fortrol and which can be a bit hot on the crop." &#42

"We have used Hawk on its own before and it has not been very successful," says farmer Tony Webb. "Neither has Lexus."

A multi-pronged approach using full rates of both herbicides in a mixture on Nov 11 after pre-emergence Avadex on most of the trial field gave acceptable blackgrass control. "It seems reasonably successful, but it has cost us a fair bit."

Peter Tayler believes the result may be due to the earlier spray timing and the combined attack from the Hawk and Lexus. "But its not a strategy I would recommend." In the trial the products were used individually, he notes.

Adjuvant aids control

MIXING a low rate of sulfonyl-urea herbicide with a new adjuvant can provide better weed control than some full rate herbicides used alone, according to trials conducted by SAC-Edinburgh.

The trials compared combinations of new adjuvant Torpedo from Newman Agrochemicals with Ally (metsulfuron-methyl) and Quantum (tribenuron-methyl) at 15g/ha, a Deloxil (bromoxynil + ioxynil) and Ally reduced rate mix and full rates of the herbicides alone.

Full-rate Ally gave 70% control of knotgrass, while a reduced rate plus Torpedo gave 100% control. Forget-me-not control was 88% and just under 100%, respectively. Similar effects were seen with reduced rate Quantum.

Use rate is 0.1% of the spray, costing £2.50/ha (£1/acre). &#42