Spud Special: Dry soils influence herbicide choice

Warm weather has finally arrived with recently planted crops emerging very quickly. Some early growers in Cheshire rapidly removed fleece which was covering their early crops and have started harvest. A late frost just a couple of weeks ago resulted in some damage to foliage but not enough to impact on yield.

Herbicide choice is being made all the more difficult by the dry soil conditions. In some cases I suggest keeping the cost of the residual element down, whilst making sure that the contact element is robust enough to see the crop through the ground in the knowledge that a post emergence application of Rimsulfuron (Titus) will be required. This is not an option for seed growers however.

My thoughts are now turning towards Irrigation and Blight control. For the control of Common Scab the timing of irrigation is crucial. Tuber initiation usually starts 2-3 weeks after 50% emergence and as a rule of thumb I aim to keep a soil moisture deficit (SMD) of no more than 15-18mm through this period. Scheduling of irrigation is vital especially if over watering, which is not only wasteful but can cause problems with Powdery Scab, is to be avoided.

Make sure that irrigation applied is effective and is getting to where it is needed. Under dry conditions some soils may require an initial application closely followed by another to achieve this. Rain gauges should be used across each irrigation run to see how much water is actually getting to the ground.

Blight control on early crops started as soon as the weather warmed up or fleece was removed. Usually I like to start blight spraying at 100% emergence with the aim to keep application intervals to 7 days. Product choice is very much determined by weather conditions, potential risk and growth stage of the crop. My colleague Dr Rairidh Bain at SAC Auchincruive carries out trials every year on behalf of both PCL and individual companies so I get a good look at what is working well. Two such products Mandipropamid (Revus) and Cyazofamid (Ranman Tp) give excellent protection during the rapid growth stage of the crop, whilst also offering excellent rain fastness.

The warm weather has also resulted in high numbers of aphids being seen flying over crops, especially those in close proximity to oilseed rape. I shall be watching crops closely for aphids in the coming weeks, with treatment warranted when there is a significant increase in numbers on leaves in ware crops with seed crops getting an insecticide every 7 days.

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