Yellow is a fashionable colour in cereal crops this spring

Fife Monitor Farm meeting

Crops at the “well on” stage

Following an exceptionally mild and wet winter, and a slow start to crop development in the early spring, many crops are now reaching the famous “well on” growth stage. There is much anguish over yellow rust, where the offending fungus has enjoyed the mild wet winter, doing what fungi do over the winter months – reproducing and  taking advantage of the cooler wet weather to attack crops. Unfortunately, the same weather meant crops were slow to grow away in the cold spring.

Disease ratings are good at representing what has happened in the recent past, but once you have used them to help identify which variety to grow, it is essential all crops are monitored. This is because disease-causing fungal populations can change, and varieties differ in their susceptibility to the disease at different points in their development. So, when does a variety move away from juvenile susceptibility to adult resistance? Sounds like a grim exam question with no clear answer.  What is also likely to happen is the appearance of different populations in different areas and fields. Markets may dictate that we  drill a single variety over a large area, but this approach exposes our single variety to a diverse population of fungi ready to attack it.

Yellow rust monitoring Alkerton May 2016

Yellow rust monitoring Alkerton May 2016

 

I’m sure the discussion about the merits of drilling a diverse selection of varieties to improve stability and minimise disease risk and 101 reasons why the market is less than happy with this approach will continue, but it is clear that a single stand of one variety in large blocks is a sitting duck when the pathogen, weather and declining fungicide activity conspire against it.

It is clear that some varieties have been hit harder than reflected in their resistance ratings, requiring protectant fungicides to be applied in the early spring. Now the focus for wheat has moved on to protecting crops from septoria tritici, azoles and SDHIs applied to this end will effectively protect crops from yellow rust, assuming doses and timings are well timed.

Another ‘yellow’ to look out for is Barley Yellow Dwarf Virus (BYDV) in wheat and barley. BYDV is a virus disease spread by aphids.  It attacks many cereals, not just barley, and may not always cause yellow leaf symptoms – sometimes red, and late infections may not even cause shortening of the crop. Why is it so severe? The mild  winter, once again, was the start of the woes, with weather conditions enabling the aphids to overwinter in cereal crops after migrating from grass, feeding on the emerging cereals, transmitting the virus. Patches of stunted plants with yellow or red tips to otherwise healthy leaves gives a clue to this migration. Later infections appear as aphids fly into crops, leading to random plants evenly affected through the field.

The bad news is there’s little that can be done now to  treat affected crops. The good news is that it  isn’t transmitted by seed, so you can plan ahead for the autumn and look at integrated management to reduce the risk. Early sown cereals following grass or grown in fields where volunteer cereals are common will be at greater risk.  As far as Recommended List variety trials are concerned, we do apply a seed treatment to minimise early infections, but getting some trials with symptoms helps us to identify any varietal differences based on visual  symptoms. The yields from our trials are a more important indicator of variety performance in a season where levels are higher than average.

Hopefully we will soon leave the yellow spring and, being positive, enjoy a healthy green summer.  Septoria tritici and fusarium may yet come and spoil the party to give us a brown (septoria) then pink (fusarium) summer.

 

 

SimonOxley

SimonOxley

Simon Oxley spent 20 years in Scotland carrying out applied research and giving integrated pest management advice to advisers and growers on a wide range of agricultural and horticultural crops. Simon currently manages the cereals & oilseeds Recommended Lists and agronomy projects at AHDB. Simon has worked on a wide range of research projects including Scottish Government funded advisory activities in plant health focussing on the monitoring pests and disease activities, and identifying unusual pest, disease and weed outbreaks. Cross institute research projects include cereal pathology projects, in particular work on barley disease epidemiology and management. Simon has been involved with training activities to both agricultural students and BASIS training to agronomists.

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