Wheat crop diseases – a lull before the storm?
Spring is has sprung but night frosts over the past few weeks have put the brakes on crop growth and disease after the mild winter. However, it won’t be long before the season lives up to its name and warmer soils, moisture and nitrogen kick in to encourage a flush of new growth. As new leaves develop (potentially final leaf 4 at this time) they are likely to get a dosing of rain and disease causing spores. This situation means growers and agronomists have to weigh up the odds as to whether to leave crops to the mercy of weather and varietal resistance to manage disease for a little longer, or to give them a helping hand with an early protectant fungicide. All of this, of course, to be considered with an eye on input costs, ability to travel, and other pressing priorities.
Fields should now be full of squatting farmers and agronomists looking to see what diseases are out there and which leaf is emerging so they can come to a decision as to when they start the treadmill of fungicide treatments on their crop.
When I was in Scotland, some regions had the luxury of waiting to see what was happening in other areas of the country. Yellow rust outbreaks in Wisbech meant it was time to look a little more closely at wheats in East Lothian. Pity the growers in Wisbech who don’t have a similar early warning system, so it is no surprise that your perception of disease risk and the action you take will vary on your circumstances.
Twitter is good for alarmist images of diseased crops. I’m guilty of this myself. Clean crops don’t necessarily make good pictures for tweets about disease. That is why monitoring varieties – the resistant ones as well as susceptible ones – is so important. Recommended List trials do have their uses at this time, since at many sites we have untreated trials or disease observation plots which are monitored regularly for presence of disease. It is just another small piece of information growers can use to determine when their nerve breaks and their treatments should start.
We also provide weather information, which for the nervous agronomist around Wisbech shows that there have been plenty of frosts over the past few weeks. Our disease monitoring shows these frosts have either worked wonders keeping yellow rust at bay on resistant and susceptible varieties, or the disease is yet to establish.
This information is no substitute for looking at your own crops, which may have been drilled earlier than ours, or which may be in a microclimate conducive to disease where frosts are minimal. Yellow rust isn’t the only consideration. Eyespot was the subject of an earlier blog. The main concern, however, is likely to be septoria tritici which is present on all varieties. Interpreting the weather data as each new leaf emerges may help you measure when septoria starts to develop unseen inside new growth. The warmer the temperature, the faster the disease develops.