Winter arrived last week, with temperatures as low as -12C near Market Rasen (a colleague at Holbeach recorded -16C). Unlike last year, there was very little snow cover to protect the crops.
The task of identifying light leaf spot in oilseed rape (OSR) crops will be challenging, as at first glance frost damage can appear similar. OSR leaf samples will be heading to my airing cupboard for incubation. This is unfortunate, as I have only just emptied the fridge of soil samples to be tested for soil mineral nitrogen. Who would marry an agronomist?
HGCA topic sheet 75, 2003 states if 25% of plants are infected with light leaf spot an appropriate fungicide should be applied at the earliest opportunity. With the current high value of OSR, and if the variety is susceptible to light leaf spot combined with the current cooler weather, I think we will be well rewarded for treating where infections are above 15%.
Most residual OSR graminicides appear to have worked well, but I will have one last field inspection with blackgrass control in my mind. We still have up to the end of the month to use carbetamide if appropriate.
As the frost and snow clears many cereal crops are looking stressed. Many growers are now keen to apply the first nitrogen dressing. My advice would be to look at each crop field by field, and not be too hasty. Despite having good PGRs available we need to be sensible.
Soil mineral nitrogen results, adjusted to give a soil nitrogen supply figure have been variable, which again justifies using the soil test. On average there is less N available than I had anticipated, though there has been a wide variation.
The fields prone to manganese deficiency will be receiving yet another top up of manganese imminently, with other trace elements added if a recent tissue analysis or field history has indicated a problem. With the anticipated high disease pressure and many herbicides to apply, good crop health is important.
Prior to the recent cold weather both yellow and brown rust could be readily found in wheat crops, but the frost has slowed development. With the most popular varieties being susceptible to either brown or yellow rust, and high levels of spores present, most wheat crops will be receiving a rust active T0 in early to mid March, depending on the weather.