For once potato growers and agronomists have little to complain about compared to last season, which is a relief. After the previous seasons experience it becomes easy to expect problems but, so far so good, with the possible exception of common scab.
Although emergence was delayed, root development was not, with some of best rooting systems I have ever seen. Canopy expansion has been fairly rapid, achieving a good size by tuber initiation. It is therefore unlikely seed and salad crops would respond to foliar phosphate applications this season. One exception is in seed crops where the centre of ridge is bone dry and phosphate uptake could therefore be limited, justifying technical grade MAP with blight sprays just prior to tuber initiation and a week later.
In un-irrigated ware crops, where the majority of the nitrogen has been placed and/or broadcast on post planting, if there has been insufficient rainfall to wash it down to the rooting system, then foliar feeding may be required in July to supply the crop adequately. This is unlikely to be wide spread.
The much publicised threats of blight, from seed and oospores, and the perfect aphid storm have not happened, which is no particular surprise. Highland Show week was the first real risk period for blight and it is likely the infection is now established somewhere and ready to spread with the next high risk period.
Canopy expansion is being covered by mandipropamid with the higher rate of dimethemorph + mancozeb used, if kickback is required. Last year demonstrated that no active ingredient can protect new growth adequately and kickback is key to protecting the crop during canopy expansion.
Aphid levels remain low and there has been no rush to start aphicide programs except in East Lothian, the Borders and the Black Isle. Rose grain aphid – metopolophium dirhodum – is now increasing with high numbers possible in mid-July, consequently pyrethroid is being applied. In areas where multiple Myzus persicae has been found in traps, then neonicotinoid should be applied.
The dry start to the season has been good news with regard to blackleg and powdery scab risk. Rooting systems should have reduced reliance on mother tuber, reducing the risk of blackleg developing, at least until after seed inspection. There are, however, reports of blackleg in England affecting Melody and Marfona, so it is possible we are not out of woods yet.
The sting in the tail this year is likely to be common scab affecting un-irrigated or poorly irrigated crops. Growers are better to prioritise scab regime irrigation to areas they can manage, rather than stretching intervals too far and being disappointed by the end result.