Ground conditions

The extraordinary weather and ground conditions of recent weeks have led to many growers being out on the land doing jobs from ploughing, planting, spraying and even fertilising. While the correct advice in such extraordinary conditions is impossible, January planting has given both good and bad outcomes in the past.

So if you are planting don’t plant too much and only do it in safe fields. Also, if you feel the need to spread fertiliser, given ground conditions now and the fear of what might happen in February/March, the advice must be to keep the total N down to around 10 units/ac. That will supply the needs of the crop for the next few weeks or so.

Arguably the return of cold non-growth conditions for a few weeks might be best for winter crops.

Aphids and BYDV

One of the very common questions at the moment is BYDV risk given the mild conditions. This is a really awkward situation because normal colder conditions minimise this risk.

There are many different scenarios. We know there is higher risk in September and early October sown crops and we expect low or no risk in November emerging crops. But the very mild winter must alter these generalisations.

There are a few technical points worth considering. There is no assessment for BYDV risk so we use aphid numbers as an indicator of risk. And temperature is possibly a better indicator of risk than our ability to see or count aphids.

Temperatures in recent days and weeks were suitable for the multiplication of aphids. Temperatures have to drop to around -8o C to kill grain aphids which transmit virus.

In situations where aphids and BYDV existed following mild winters, aphicides sprays in January have been very successful and recent research bears this out. So if someone believes they have a high risk situation then spraying an aphicide must be a sensible thing to do because high pressure is high pressure. However, very many fields may not be in high risk situations.

Aphid counts at Oak Park increased last week. This is a consequence of the mild conditions but we do not know what exactly this means. There are no established thresholds to compare this to. Add to this the fact that some families of aphids are not able to transmit the virus even if they carry it.

So crops planted which received no insecticide at all might benefit from an aphicide spray shortly. This might also apply to late sown crops as this has been an exceptionally mild winter to date. Cold weather will stop the spread for the time being but it can recommence.

The decision to apply an aphicide now, or not, needs to be considered for each individual field. Sprays will be beneficial where they are needed. But the general advice is that two treatments (Deter + aphicide) is still optimum for early sown and one treatment (Deter or an aphicide) should still generally be enough for late-sown crops. Only very high risk situations will need more.