Disease Management On Cereal Crops
Every year seems to be different when it comes to the challenges that face our cereal crops. 2012 was a difficult year disease wise, notably for Yellow Rust, Septoria & Fusarium Ear Blight.
2013 threw up different problems, not so much with disease but a shortened grain filling period and high temperatures. For crops to reach their full potential they need as much disease free leaf area to capture the sun’s rays during the important ear filling months of June and July, a good disease free crop will on average put on 200 kilos per hectare per day in grain yield over this period. Very high temperatures are detrimental to cereal grain yields.
Although grain filling increases as temperatures go up, when they reach 30 degrees C, starch deposition decreases rapidly. High temperatures do not compensate for a shortened period of good
TO SPRAY OR NOT TO SPRAY
In years when disease is forecasted to be high, the decisions of whether or not to spray are relatively easy to make. It is the years when low disease is forecast that can be tricky for the farmer and the tendency is to reduce disease control in an attempt to optimise returns. This can of course be very risky if the assessment is wrong and disease levels are higher than what had been forecast. Trials carried out by the NIAB showed that by using a full spray program in a year of low disease, it makes a marginal difference to the overall return for the crop but spraying in a year with high disease levels gives a far higher return on your investment compared to not spraying. Cutting down the application rates can also be risky as infection rates increase the lower the dosage with the amount of infection climbing steeply with application rates of 50% or less of the recommend dosage.
Strains of Yellow Rust are evolving all the time and are normally named after the wheat variety that the rust was first discovered on. In 1989, we saw it first appear on Slejpner, followed by Brigadier, Robigus, Oakley and recently, Warrior, a variety which until then had a resistance score of 9 on the recommended list.
Normally the disease has first shown signs in the UK and has then spread to mainland Europe however, the strain discovered on Warrior has come from outside Europe. Yellow rust is spreading around the world with infections found in New Zealand and Asia. One theory for the spread is globalisation and an increase in people travelling, carrying it across the world. Another theory is extreme weather conditions, carrying disease further. Mild winters have also meant that rust has managed to survive and not been killed off by cold temperatures.
SEPTORIA AND THE FUTURE
Septoria is probably the fungal disease which is causing the most concern. Whilst a spraying program can still give good control, the strains of Septoria are mutating all the time. Eradicant sprays seem to be becoming less effective to the new strains and more reliance will have to be given to preventative sprays with a program based around spraying at every leaf emergence stage to give full protection.
Future approaches may be:-
- Alternative Chemistry – slow coming forward at the moment with sprays being lost due to new EU regulations
- Better disease resistance in varieties through plant breeding
- Better disease monitoring/forecasting
- Biological controls integrated into conventional spray programs
- Agronomic interventions – drilling dates, regional strategies, cropping
All in all, the battle against fungal diseases on our present, high yielding but relatively low resistant cereal varieties will continue with new challenges emerging year on year