Maincrop potato planting has proceeded nicely over the last few weeks, and even the heavier, wetter soils are now going in well. Earlier plantings will be emerging sooner rather than later.
The next topic to consider is weed control. In recent years – with the loss of some actives and changes in approval and availability of others – weed control in potatoes has become more complex. It used to be simple, a good dose of linuron plus diquat/paraquat mixtures just prior to emergence was all most growers did. On the more organic soils metribuzin was incorporated prior to planting, but again it was still pretty straightforward.
The reduction in the rate of linuron has led to challenges in weed control, especially for managing black bindweed across many soil types. Also annual meadow-grass has become more of an issue, initially when paraquat was lost and more recently with the change in approval for glufosinate and its availability. Last season, with the patchy early senescence of many crops, annual meadow-grass became a real problem before and after haulm destruction. Glufosinate would have been the product of choice here, but the change of approval to only being used in a flail and spray system (and difficulties with product supply) meant there was nothing much growers could do to effect control.
Therefore we now have to consider not only the weed control in the growing crop but also post-burn-down in certain situations.
One element of good news is for the first time in a number of years we have a new herbicide active ingredient – metobromuron (Inigo/Praxim as product names). It will take a while before we know the most effective rates and mixtures to use for best effect with this new product, but it’s great to have a new active, especially for when linuron disappears in the next couple of years or so.
We’re planning to do further detailed trials this coming season to explore what we need to do to maximise performance, both in plots and as field scale trials. Metobromuron has shown excellent crop safety and weed control on light soils in our previous trials so it makes sense to use it here initially. In other situations on heavier soils it will probably be more of a look-see before more wide-scale use in 2016 and beyond, in order to ensure we have identified the optimum rates and mixes.
In Europe the trend for potato weed control is to apply the residuals soon after planting and then apply a contact such as diquat or carfentrazone just prior to emergence if needed. In the UK most is done just prior to emergence with a contact added to take out the emerged weeds. Many growers are now doing a bit of both and applying some of the residual, generally pendimethalin, soon after planting and then topping up with other actives and a contact if needed just prior to cracking. This seems to work well for many, especially where bindweed is an issue.
Also where three-way tank mixtures of actives including clomazone are used, the manufacturers will only support applications made within two weeks of planting to settled ridges.
Flufenacet (available with metribuzin) can help greatly on the meadow-grass issue and has even shown a benefit at the end of the season in our trials. Prosulfocarb brings control of some difficult weeds, especially fumitory, and like metobromuron it is safe on the lightest of soils. On the more organic soils metribuzin can still be incorporated, but check the rates approved as they have changed recently.
For our weed control plans there are plenty of different products around at the moment, each with their own strengths and weaknesses – make sure you read the label before use to gain the best results and to comply with all the necessary labelled legislation.