A well-timed T3 ear wash spray could hold the key to helping wheat crops fulfil yield potential in what has been a roller-coaster season for many.
The T3 is the final fungicide most crops receive, so getting it right is vital to protect milling or feed crops from disease and build yield in the weeks to harvest, leading agronomy firm Hutchinsons says.
The T3 serves three important roles which should be considered in any spray plans. These include controlling ear diseases such as fusarium, topping-up foliar disease control and extending green leaf retention (see below).
Product choice should be tailored to these factors, but perhaps more important is spray timing, says Leicestershire/ Northants-based Hutchinsons agronomist Sally Morris, who believes T3 fungicides are sometimes applied too late, reducing their efficacy.
“Some people wait until flowering is well underway before applying the T3, but it’s too late by then. Fungicides should be applied as soon as ears complete emergence and flowering is about to start.
“Flowering is variety-specific, but tends to begin in the middle of the ear and spread outwards.”
Extra vigilance is needed to monitor crops for the correct timing as many cereals have raced through growth stages in recent weeks as they make up for a slow start earlier this spring, she warns.
“In this region, T3s are normally applied around the Cereals Event in the middle of June, but we’re seeing a real mix of growth stages this year, more than normal, so decisions must be made on a variety and field-by-field basis.”
Controlling Ear Diseases
Where settled weather has allowed timely and effective T2 applications, the T3 can focus specifically on controlling ear diseases rather than topping-up flag leaf sprays, says Hutchinsons technical development director, Dr David Ellerton.
Fusarium and associated mycotoxins remain the priority, although disease development depends on weather during flowering, so asses the risks and tailor sprays accordingly, he advises.
Fusarium species are favoured by warm, wet weather during flowering, so where this is likely, he recommends products based on prothioconazole, tebuconazole or metconazole.
In contrast, cool, wet conditions promote Microdochium nivale, which although does not produce mycotoxins, can have a significant yield impact in bad years such as 2012, Dr Ellerton says. Prothioconazole is more effective than tebuconazole against Microdochium, he notes.
Other ear diseases such as sooty moulds, mildew, yellow and brown rust and Septoria nodorum should be considered, although these are generally controlled by fusarium chemistry.
Products based on phosphites applied at ear emergence have also been found to reduce DON production.
Top-up Foliar Disease Control
Although T2 fungicides (mostly based on SDHIs) have, or should, perform well given dry, settled weather around flag leaf emergence, T3s may still need to bolster foliar disease control, especially Septoria tritici, says Dr Ellerton.
The need will be greatest in susceptible varieties, where earlier sprays have been compromised, and/or where unsettled weather increases disease pressure in coming weeks, he notes.
“Where Septoria tritici has not been fully controlled at T2 ear sprays should concentrate on products containing epoxiconazole or prothioconazole.”
Despite dry conditions during much of May, Miss Morris says Septoria and mildew are still present on lower leaves near the base of some crops, so disease pressure may increase with wet weather.
“Likewise, if it remains warm and dry, brown rust could be a problem, in which case it may be worth including tebuconazole to target rust, alongside prothioconazole for fusarium.
“This adds another active ingredient to programmes [for resistance management] and may be slightly more cost-effective than straight prothioconazole.”
Finally, both agree there is value from including a strobilurin at T3 to help extend green leaf retention, especially as crops typically produce 60% of total biomass between flag leaf emergence and maturity.
During grain filling there is a large redistribution of nitrogen within the crop as proteins are degraded and nitrogen is transferred from the canopy to form grain protein, a process which progressively slows photosynthesis.
“Anything that keeps crops alive and green canopies working for longer, could make all the difference to yield by harvest,” says Miss Morris, who also recommends including magnesium with ear wash sprays where required.
- Apply at full ear emergence just before flowering starts
- Ear disease priorities include: fusarium (warm & wet), microdochium (cool & wet), sooty moulds, yellow & brown rust, Septoria nodorum
- Top-up foliar disease control (especially Septoria tritici)
- Tailor treatments to disease risk, variety and earlier chemistry - maximum of two SDHIs or strobilurins per season
- Consider strobilurins to boost green leaf area retention
Begin AHDB mycotoxin risk assessment before applying T3 - https://cereals.ahdb.org.uk/mycotoxins