Spud Special: Planting turns into a long slog

A month is a long time in potatoes and what promised to be a short planting campaign has turned into an increasingly frustrating long slog that looks like continue for another week to 10 days for some growers. North of Aberdeen was generally finished in record time, but constant rain showers or, in Perthshire and Kinross and some areas of Fife, downpours, means that some large growers are only just over half way, even planting in all conditions.

Damp conditions have slowed emergence, but this week should see the majority of early April planted crops emerge. Weed flushes on ridges are very variable, although annual meadow grass is quite prominent again on light land. Where this has become established in ware crops, some pre-emergence glyphosate is being applied when sprouts are at least 2in below the surface. For seed crops 3-4l/ha diquat is being applied with the pre-emergence herbicide. Rain has settled the ridge nicely and weed seedlings are close to surface, so it will be an easier year for weed control hopefully.

Rain has also meant that the majority of ridges are now saturated, so at least this will take the guess work out of at which point to start irrigation scheduling balance sheets and enable the soil full point to be determined if you are using probes. There should be a good soil to seed contact and no matter how dry it gets from now on, 15mm should be adequate to wet up the ridge prior to tuber initiation (approx. three weeks after emergence).

One of the biggest challenges to seed crops this season could be virus. There has been some early cereal aphid activity in traps, with unsurprisingly Morayshire and Black Isle looking to be earliest area, matching temperature and good weather conditions. Growers need to ready to start programs when the weather improves, as this likely to trigger the flight. At present aphid pressure does not justify the use of oils, but May planted seed crops are likely to emerge into high aphid pressure and varieties susceptible to PVY may justify the phytotoxicity risk associated with oil use, particularly if last years crop was known to be carrying virus.

Finally, while low night temperatures have prevented Smith periods being triggered, we are definitely getting the humidity for late blight risk. Growers need to get dumps sprayed off and blight programs will commence between full emergence and rosette stage with either fluazinam or mancozeb, plus cymoxanil if fluazinam has been applied to the soil for powdery scab.

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