Another good week
What an exceptional spell of weather we’ve been having, but we are now seeing the temperature dial being turned down at last. Recent crisp, frosty mornings will be welcome for those with forward crops, as they will slow multiplication of aphids and probably stop winged aphid production to transmit BYDV. But cold conditions will not kill aphids that are already in crops and these may continue to multiply if they get an occasional mild spell.
Herbicide: Most crops have received some herbicide at this point. If it was applied some time ago, this may be a good time to check on what has survived, to make a plan for the spring. In fields that were not sprayed before now, the choice should be governed by what weeds, if any, are currently in the crop.
Weeds can be slow to emerge with later sowing and so a residual like flufenacet or pendimethalin may still work very well. If there are broadleaved weeds present but no grass, then other products like DFF or Defy could help broaden the spectrum.
If there is already quite an amount of stronger meadowgrass or wild oats, then it may be best to wait until spring and consider options like Alister or Pacifica.
Most crops at risk from BYDV infection are likely to have been sprayed at least once with aphicide at this point and some have received a second spray. While the recent sharp drop in temperatures will certainly slow multiplication, you cannot depend on it to kill the aphids that are present.
If it has been a number of weeks since the first aphicide, a follow up insecticide (preferably from a different family) might still be applied when conditions are mild again.
They had been quite active when temperatures were higher, but now that things are cooler their pace of feeding will have slowed down. However, it is from here on that they will do the most harm, because they will still feed and the plant has no growth to help it recover.
They are unlikely to be in every field, so all crops should be inspected to identify a problem ahead of spreading pellets.
Treat if and where necessary. Apply a 50%-70% rate of products like Axcela or Metarex, or any of the other products with good formulations. Push application up to 100% rate in patches that are being worst hit. Some fields may only have patchy problems, but the whole field should be spread using a reduced rate.
With fertiliser prices gone through the roof, accurate soil tests are even more relevant to guide appropriate fertiliser spend. Take samples now if you do not have a recent test, or if you applied lime within the last few years following a previous low pH.
Soil tests are only valid for four years and a test result is needed for every 4-5ha. Where pH is low, the efficiency of all nutrients will be reduced, including applied fertilisers.