After writing this column for a year this will be my final article and it starts as my first one began; on the subject of flea beetle and the dry weather. It almost feels like the OSR crop is a repeat of summer 2018.
The crops drilled early which caught the moisture are now romping away and many have had the grass-weed herbicide Centurion Max (clethodim) applied for the ever-troublesome black-grass before the canopy closes over.
At the other end of the spectrum, the typical August bank holiday drillings are suffering from very dry seedbeds and significant pressure form CSFB.
If there is one thing that farmers are noticing more and more is that OSR can leave an unacceptable level of black-grass lurking below the canopy which will then rear its head again in the first wheat situation. On this note it is also worth casting your mind back to the spring of this year when poor OSR crops failed to grow away in the spring due to high levels of CSFB larvae.
I would urge growers to remember that a poor looking crop going into the autumn/winter will not necessarily recover to perform well and in addition could lead to knock on weed issues in the following wheat crop.
On the cereal front, my growers had generally finished harvest by the end of the first week of September and wheat yields were generally very pleasing with some crops hitting 12tonnes/hectare.
Quality was generally good, but it is noticeable now going around farms which varieties shed before the combines were able to arrive due to catchy weather conditions. This should be taken into account when choosing varieties for the coming season.
With attention now turning to winter cereal drilling many thoughts are turning towards the threat of BYDV in the coming autumn. Controlling the spread of BYDV with the loss of neonicotinoid seed treatments is turning reliance back onto the use of pyrethroids.
To avoid increasing pyrethroid resistance amongst aphid vectors an integrated approach must be used to avoid selecting for resistance. It is mainly the bird cherry oat aphid and grain aphid that carry the virus, with resistance being found in the grain aphid to pyrethroids.
BYDV can start to be tackled by a few cultural controls before we turn to pyrethroid applications.
Aphids can survive on a green bridge from the previous crop or migrate into the crop from surrounding habitats.
To limit survival between crops green bridges should be sprayed of before cultivating at least five weeks before drilling. Delaying drilling is another tool that can be incorporated into an integrated approach.
Aphid migration starts in warm temperatures but slows when temperatures drop below 11degC, meaning later drillings may not experience aphid migration if we experience a cold start to winter.
It is also useful to look at Rothamsted’s aphid monitoring results which uses suction traps to monitor aphid migration.
To help determine whether a pyrethroid spray should be applied the T-sum temperature should be calculated to determine risk. This measurement is calculated by monitoring daily temperatures above 3degC and adding them together – when the sum reaches 170 there is a high risk of aphid pressure and spraying should be considered.
The presence of aphids and use of thresholds to help determine spray timings must be adhered to to ensure pyrethroid use is limited to prevent resistance.
With the threat of BYDV likely to rise in the coming years due to the loss of neonicotinoid seed dressings, together with milder winters and resistance to pyrethroids much research needs to be directed into this area to help us overcome this threat.
Yield loss as a result of BYDV infection in wheat can be as high as 60%, a worrying statistic which poses a real threat to the future of wheat production in the UK.
However, while research into control options of the virus and decision support tools are being developed, we must in the meantime safeguard what control methods we have by implementing both cultural and chemical control in a responsive and effective manner to ensure their longevity.