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Pre-em challenges for potato herbicide treatments

Weed free seedbed for clean and fast potato emergence

Potato growers and agronomists have a challenge for pre-emergence herbicide timings this season, with cold weather and cool soils delaying planting and emergence.

The overriding message is that pre-emergence residual treatments will need to be applied as soon as possible, with the focus on mixtures, stacks and rates to deliver longer lasting control, advocates Syngenta Technical Mananger, Michael Tait

Michael Tait

After the winter rains and then the unseasonably cold March and early April, growers have been waiting for heavier soils to dry out and to warm up for cultivations and planting. However with several weeks of little or no rainfall, particularly in large areas of the southern and eastern counties, herbicide timing decisions are still likely to be dictated by prevailing weather and soil moisture conditions.

Many agronomists are already looking at a split, or combination of contact activity herbicides with their weed control recommendations, if conditions will allow.

That is likely to potentially include pyraflufen-ethyl in tank mix with the pre-em treatment where any weeds are already present, with a follow-up of a second pyraflufen-ethyl, or possibly a glyphosate treatment where label approval permits, immediately prior to crop emergence.

Independent herbicide research has shown a simple pre-em mix of Defy with metribuzin + pyraflufen-ethyl achieved complete control of key potato weeds - black bindweed, fat hen, annual nettle and annual meadow-grass. Defy and a reduced rate of metribuzin was also equally effective when used in combination with metobromuron.

Weed free seedbed for potato emergence

However, whilst the combination of Defy (3.0 l/ha) + aclonifen (1.75 l/ha) + pyraflufen-ethyl (0.3 l/ha) did show a weakness on some key weeds, including black bindweed and annual meadow grass, adding metribuzin, at 0.3 kg/ha, to the stack, bolstered the mix back to full control.

Furthermore, the trials showed a Defy + pyraflufen-ethyl combination had the least impact on the emerging crop, with any transient effects quickly out grown.    

Potato growers and agronomists will need to make new choices with pre-em herbicide options this season

Where pre-emergence herbicides are applied at, or soon after planting, trials suggest higher rates of Defy can achieve longer persistence of residual activity for weed control.

Previous Syngenta herbicide research has highlighted Defy at 4.0 l/ha, for example, has shown a significant dose response increase in both efficacy and residual activity, compared to lower rates.

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