Spud Special: Loss of pesticide actives gives challenges

The time has come yet again for all true potato enthusiasts to start getting excited, planting time is here or fast approaching, its stopped raining, for the time being at least, and seed is being delivered on to farm.

This season is not going to be without its challenges, no Vydate (oxamyl) for free living nematode (FLN) control, no methiocarb for slug control and no fluazinam for powdery scab control in seed, yet I am still relishing the prospect of helping to grow fantastic crops of potatoes.

The Vydate issue is high on the agenda of all the conversations I have had with growers so far this spring, with field and variety selection crucial if spraing caused by tobacco rattle virus (TRV) is to be avoided, although it is the early grower who will suffer the most, as Vydate has an 80 day harvest interval. Mocap (ethoprophos) offers an alternative for early crop FLN and potato cyst nematode suppression, as it also has an 80 day harvest interval, but – and it’s a big but – supply is always tight and it must be applied as an overall application, not down the spout on the planter. Nemathorin (fosthiazate) also has to be applied as an overall application and has a 119 day harvest interval, thus limiting its availability for early growers. It is worth remembering that there are lots of weeds that carry the TRV virus, amongst them groundsel, chickweed, pansy, fat hen, mayweed, which are all familiar sights in overwintered stubbles.

I am also concerned about feeding damage caused by free living nematodes. If they are in sufficient numbers they can invade the roots and cause significant damage not just through feeding, but by providing an entry point for other pathogens such as rhizoctonia and verticillium. It is always worthwhile making sure you know what you are dealing with.

In my opinion ferric phosphate will provide a suitable alternative to methiocarb, there are no buffer restrictions for starters. Remember the timing of the most cost effective application of slug pellets is just prior to canopy closure.

It will be interesting to see how the loss of the Extension of Authorisation for Minor Use (EAMU) for fluazinam for the control of powdery scab on seed crops affects the quality of susceptible varieties. Once again field and variety selection will be crucial. One other point to make about fluazinam is that it now comes with buffer zone restrictions when spraying, the extent of which differs from one product to another, so check before use.

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