Spud Special: Long days but short on sun

Having passed the longest day, I can count on one hand thenumber of open crops I have seen in Scotland that have achieved the yieldpotential benchmark of reaching full canopy. Key to this season is the rootsystem. In many fields compaction and/or waterlogged subsoils are reducingrooting to 30-40cm (30-40% less than usual).

Tuber initiation is occurring very rapidly (5-10 days) afteremergence. Recent rains have mostly covered scab control but seed and saladcrops are going to have small canopies reducing their potential for solarradiation interception. That will also mean root systems and P uptake could belimited which are needed to maximise tuber numbers.

It may be beneficial applying foliar phosphate in the firstthree blight sprays to boost the plant prior to and during T1. For some warecrops (e.g. Estima, Marfona, Osprey, Saxon, etc…) with restricted rooting,nitrogen is being increased by 20kg/N/Ha by using foliar urea. Foliar nutrientsneed applying early in the morning or evening to maximise the time on the leaf whenstomata are open to maximise uptake.

Blight pressure has been high and we could be set for arepeat of last season with untreated fleeced crops a prime inoculum source. Toprotect susceptible crops during canopy expansion use a seven-day program ofalternating mandipropamid and cyazofamid with cymoxanil added if risk periodsoccur more than three days after application.

The rain has meant a temporary decline in aphid numbers.Pyrethriod programs have commenced and myzus persicae has been caught in trapsin the south of Scotland prior to the rain.  A neonicotinoid insecticide will beadded in the next spray in the south if it stops raining and as soon as theyare caught in the north. Slugs are also a major risk and have been on thesurface so one full dose equivalent of methiocarb will be applied tosusceptible crops prior to canopy closure. 

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