10 August 2001


This seasons boosted set-

aside area, up 20-25%,

provides a unique

opportunity to get on top of

grass weeds, particularly on

heavier soils and land

otherwise used for

continuous wheats.

Wendy Owen reports

THE agronomic benefits of set-aside are tremendous and farmers have had the chance to achieve a total kill of all difficult grassweeds, says Bryan Pickles, Fieldcares northern technical manager.

"I encourage my clients to make the most of non-selective herbicides like Roundup (glyphosate) pre-drilling. This will avoid transplanting large weeds during drilling which will not be controlled by selective products."

Many growers plan to drill set-aside early this autumn so seed-beds on difficult land can be prepared before bad weather sets in. "That requires a high level of weed control," warns Mr Pickles.

"If there are more than 5-10% of blackgrass survivors in any one season, the population can spiral out of control, leaving resistant strains to multiply for future years." With up to 400 heads/sq m blackgrass can shed huge numbers of seed.

Pre-emergence herbicides are essential in early drilled crops where blackgrass or brome is present, he believes.

The two main choices are Avadex (tri-allate) and newcomer Crystal (flufenacet and pendimethalin). Costs will be similar though Avadex requires pneumatic application.

Controlling sterile and soft brome with Avadex alone has been difficult, so lately he has favoured a sequence with Monitor (sulfosulfuron) + adjuvant at growth stage 29-31.

For post-emergence treatment, Mr Pickles advises full spray doses and alternating chemicals from different groups to discourage resistance. On sites known to be herbicide-resistant, an effective treatment is a tank mix of Hawk (clodinafop-propargyl + trifluralin) and Lexus (flupyrsulfuron-methyl + metsulfuron-methyl + adjuvant oil).

"Timing and application are crucial," he says. "With crops being drilled early this year you can throw the rule book out of the window. I prefer to apply post-emergence treatments as soon as the most advanced blackgrass reaches three leaves; that could be as early as September this season. Particular attention should be paid to application and the best way is to use a fine spray.

"If I see blackgrass or ryegrass surviving any treatment I immediately suspect resistance," adds Mr Pickles. "For many years we have collected mature seed heads before harvest and tested them for tolerance to a range of products. Once we know the results we can target inputs appropriately, saving costly oversprays or disappointing control."

Ryegrass has become a problem in the past decade, due to increased populations of resistant plants. But some exciting new products have come on to the market recently and more await approval, he notes.

"Last year I had great success with chlortoluron mixed with Ingot (diflufenican + flurtamone + IPU). Rates will vary according to application timing and it is important to consider varietal tolerance, because some crops are susceptible to chlortoluron." &#42

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