Spud Special: Ideal conditions for applying residual herbicides

This time last year clients in Cheshire were harvesting their first earlies, not a chance this year with crops at least three to four weeks behind, down to cool temperatures and lack of warm sunshine.

In general, crops seem to be taking up to six weeks to emerge, even recent rainfall has not been particularly warm, soil temperatures within potato ridges in the middle of May were only 6-7C.

Recent moisture has provided ideal conditions for the application of residual herbicides, it’s worth remembering that residuals have different solubility. Metribuzin and clomazone are the most soluble with prosulfocarb and pendamethalin the least soluble therefore mixtures are often best.

Once crops emerge and temperatures warm up, I expect growth to be rapid, therefore, keeping this lush new growth protected from blight will be important. In my opinion, mandipropamid is the best product to use at this stage and it is extremely rain fast.

Blight inoculum has to come from somewhere; some may come from seed infection, particularly after last years’ difficult season, although I haven’t seen any seed tuber infection.

The biggest source of infection is always from out grade piles and ideally these should be covered up completely with black plastic to avoid haulm development. Reglone can now be used to treat haulm on out grade piles using a knapsack sprayer under an Extension of Authorisation for Minor Use (EAMU) arranged by the Potato Council and SRUC.

Two applications are approved with a maximum individual dose of 0.4 ml of product per square metre (same as 4 litres/ha).

Water volumes between 200 and 400 litres/ha are acceptable, but the out grade pile must be on a permeable surface. Growers who use Reglone for this purpose must have a copy of the EAMU authorisation.

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