So far in March I have recorded just 8.2mm rain, but recent warm days – despite night frosts – mean soil temperatures at 4″ of 7.2C and so spring growth is well and truly under way. All outstanding herbicides such as Atlantis, Unite, Broadway, Fox, Galera etc has now been applied and all winter cereals have had 50-80 kg/ha of N. The oilseed rape has also had its first N plus SO3 and by the look of the speed at which it’s shifting – 6 inches in 48 hours – it won’t be long before it gets the rest!
We’ve had several days in the last fortnight with temperatures over 15°C, explaining the sudden appearance of pollen beetles on headlands of several OSR crops around March 14. It’s easy to overreact when you walk into a rape field and find what looks like scores of pollen beetles on every plant. Move into the field and away from the headlands though and they’re still hard to find. Insecticides should only be applied against this pest if thresholds are reached.
Current guidelines are that for <30 plants /sq m = 25 pollen beetle per plant; 30 to 50 plants /sq m = 18 pollen beetle per plant; 50 to 70 plants /sq m = 11 pollen beetle per plant; >70 plants /sq m = 7 pollen beetle per plant. We have pollen beetle thresholds for a reason and they should always be used – remember that in about four weeks time when OSR crops are beginning to flower, we’re going to need pollen beetles to help with pollination, so just spraying because you’ve found a few headland plants at threshold isn’t how the job should be done. If you reach threshold and do have to spray, wherever possible use products like Mavrik (Tau-fluvalinate) which is kind to non-target species such as the pollen beetle’s natural predators – of which there are many, bees, parasitic wasps etc.
In the winter wheat, thanks to a benign winter, the older leaves which were covered in yellow rust before Christmas have not been killed off and are therefore once again plastered in it. Rust is easy to find even for the most sedentary agronomist – particularly in the usual suspect varieties, but this more aggressive “Warrior” race is also attacking hitherto bullet-proof varieties like JB Diego.
With conditions and disease levels such as they are, T0 fungicides are now being applied across my area. I’m using strobilurin/chlorothalonil or strobilurin/chlorothalonil/triazole mixtures, depending upon variety. Strobilurin use at this stage gives the crop a useful kick up the backside and both strobilurin and triazoles will easily control rust and protect against reinfection. Chlorothalonil is vital at T0 and is in there to protect the canopy against the spread of the Septoria – also widespread on the older leaves. It may not be raining at the moment, but when it does come it’ll quickly splash that Septoria around any unprotected canopies.
Spring bean and sugar beet drilling is under way in earnest, the top inch or so of fields is largely dry but go much deeper on the heavier soils and plasticine is still the comparative medium. Patience is a virtue.