Farmers Weekly Interactive

Spud Special: Growers face herbicide conundrum

Further heavy showers has hampered planting progress, particularly for those with more bodied land, the dilemma being do you move soil to dry it out and run the risk of it getting wet again, putting you back to square one.

Conversely some growers in Cheshire are just about to start harvesting Maris Bard, grown under fleece. Quality and tuber numbers look good, the problem will be that crops not grown under fleece have a lot to do to follow on.

Applying pre-emergence herbicides in some parts of the country is proving challenging with regard to actually getting on to the fields. In some cases 100% emergence has occurred before application has been made. This can be risky as you are relying on the contact action of diquat or carfentrazone to take the foliage back to ground level to avoid residual uptake. Be aware that some varieties are extremely sensitive to metribuzin post emergence, so if in doubt use alternative actives.

I am being asked a number of questions regarding fertiliser rates and seed spacing as planting is delayed, however the answers are not always straight forward. My view is that you should take each variety and field separately, focusing on compaction in field and agronomic characteristics of the variety grown.

As a rule of thumb you might consider increasing spacing by 10% for main crop varieties, once the end of May approaches. However I believe that there is a limit, once you get to 42-43 cm (17 ins), any gaps or planter misses result in unproductive land impacting on overall yield.

Fertiliser is more challenging, as a rule of thumb you might consider reducing nitrogen by 10-15 kgs/ha for each week planting is delayed after the middle of May, but, once again this is not straight forward either. A shallow rooting variety, such as Estima or Innovator planted in less than ideal conditions is unlikely to be able to develop a root system capable of extracting all the nutrients it requires from the soil, if compaction is present. In this scenario you may be better off reducing the base fertiliser dressing and feeding the crop through the leaf.

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