What’s the optimum timing for T3 fungicide spraying in wheat and barley? T3 spraying is effective in Fusarium head scab (head blight) control.
Fusarium Head Scab is not only a yield robbing disease in wheat (and barley), but it also produces Mycotoxins on the grain that can be harmful to human health. Fungicides can effectively control it in most seasons, but appropriate doses have to be used.
When To Spray Wheat For Fusarium Head Scab
The recent data from several years and 7 different sites across the UK and Ireland collected by the AHDB in high rainfall environments makes fascinating reading, and dispels the common myth that very high (often twice the legal rate) doses of a cheap fungicide (tebuconazole) are the most cost effective way to control the disease.
The researchers there are suggesting that 140-200g/ha of prothioconazole is needed to effectively control the disease (note that this in excess of the approved label rate here in Kenya).
Fusarium Head Scab Fungicides
However, if you look at the light blue line below which shows the dose response to Proline (straight prothioconazole sold in Europe), and compare this to the pink line for Folicur you can see that even at 2x the legally approved rate of tebuconazole (500g a.i.) the researchers were not getting a response.
In fact, there wasn’t a response above 0.75 l/ha of tebuconazole 250, although remember that we often apply a full rate for Stem Rust control.
Also look at Caramba 90 which is straight metconazole – available here in mix with epoxiconazole. This is no more effective than Folicur and is more expensive on a rate for rate basis.
A few more comments on disease control…
Take away messages from the AHDB Agronomists’ Conference last month:
- Chlorothalonil is working well in protectant situations against Septoria and is very low resistance risk. I would be adding it to more Septoria prone varieties like Robin or Gregory in wet seasons.
- Epoxiconazole is still as good as Prothioconazole on Septoria – go to know as it is very well priced and adds variation to our fungicide programs to minimise fungicide resistance.
- Strobilurins azoxystrobin and pyraclostrobin continue to provide the best persistence against Rust.
- Tebuconazole noticeably behind epoxiconazole and prothioconazole on Septoria – no surprise there – but still very effective on Yellow Rust.
- In a protectant situation (fungicides applied before the disease arrives) triazoles are not losing their efficacy. Curative activity is still declining however – the message as always is get in early before disease is established.
- The researchers all voiced their concerns that wherever you look around the world, resistance to the SDHI fungicides (e.g. Skyway) is a very real threat. Use no more than two per crop.
- Net Blotch in barley – this is a worry. In 2015 field performance from SDHI’s (Bixafen, isopyrazam, fluxapyroxad, benzovindiflupyr) were ALL superior to the triazoles. In 2017, monitoring across Germany, France, Ireland Denmark and the UK all suggested that their efficacy had declined and was now LESS than prothioconazole. They are still worth using, but we need to be very careful not to overuse them as an industry.
Our trials are examining some of the other actives that are showing less of a decline in performance against Net Blotch, so that we have alternatives, again to add variation to the programs and improve disease control.
Until next week!
David Jones is the Broad Acre Specialist at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). David has a keen interest in soils and no till farming systems where he has undertaken work looking into weed levels and changes in soil structure, and has extensive experience in field trials and in the development of precision farming techniques. In his spare time he enjoys playing rugby.