11 June 1999

Precision weed control

TRIALS at Morley Research Centre are showing the scope for improving beet weed control by considering dose, formulation and herbicide interactions more carefully.

A series of trials at Manor Farm, near Wymondham, Norfolk, is testing Debut (triflusulfuron-methyl) at a range of rates with various product partners. The most striking finding is that the highest rates do not always give the best weed control.

In some sequences and mixes very low rate Debut is more effective than full rates. "But a lot depends on the weed spectrum and the choice of partner product," stresses MRC herbicide specialist Martin Lainsbury.

To investigate interactions further a set of plots was sown with spring rape to provide an even weed infestation. Mixes with high rates of Betanal Progress (desmedipham + ethofumesate + phenmedipham) have proved disappointing, which is possibly due to rapid leaf scorch limiting Debuts translocation, notes Mr Lainsbury.

Another trial on the site is testing the effect of omitting the T1 spray. "We wanted to see if we could avoid the early knock to the beet crop that a first herbicide application can cause, but still control weeds with a hotter spray applied a little later."

In terms of weed control and crop vigour results look good so far, and the plots will be taken to yield to check the outcome. "But it would be a risky strategy. If bad weather delays T2 spray applications, weed control could be compromised," notes Mr Lainsbury.

The trials are seeking to identify dose response curves for a range of beet herbicides used in mixes and sequences. Due to various levels of antagonism and synergy response curves can be markedly different, depending on partners used Once complete, the work will help growers identify the most effective programme for a given weed situation. &#42

Check AIrates

How much active ingredient is your chosen product mix really supplying? A striking example of the need to maximise the key ingredient is seen in black-bindweed control at Morley. Using a relatively expensive mix of 30g/ha Debut, 1.25l/ha Betanal Progress and 0.4l/ha Venzar (lenacil) gave less control of bindweed than a far cheaper mix of 1.25kg/ha Goltix (metamitron) plus 1.2l/ha Betanal Flo. "The difference is the phenmedipham rate," explains Mr Lainsbury. "Betanal Progress supplies just 100g/ha, whereas Betanal Flo provided 200g. Other plots showed how using Pyramin DF pre-em compensated for week bindweed control from the post-em programme on this site."