So far, 2017 will not be remembered as the worst year ever for cereal diseases and we are thankful for that. That is not to suggest that it has been disease-free, but it has not been bad for our usual wet weather problems.
For some, this will be the year of the rusts; for others, it will be powdery mildew. And the start of the year indicates a potential challenge from chocolate spot on beans.
The relatively dry winter was a bit of a help on septoria and rhyncho but winter weather does not matter that much on the lower leaves that will die off before spring growth cuts in. But having infection present in the crop does point to the potential for these diseases to move rapidly in springtime if conditions permit. Thankfully, this was not the situation in most instances and there is very little incidence of these diseases where fungicide was used sensibly.
While this is generally the case now (with winter crops being largely clean), there were some crops in early spring that had a worrying amount of septoria present. But the combination of the generally dry weather and good use of fungicides has held those problems and crops now look to have good potential.
Earlier drilling, geography and variety all influence what we see currently. Many winter wheat crops in the Leinster area have a full fourth leaf clean at the moment but further south this had been badly damaged on many crops.
In many instances, there is some evidence of fresh septoria coming though on leaf three but this has been at relatively low levels up to now. Some of the heavy rain in recent weeks may have further pressured the movement of infection but with the majority of fungicides applied at the correct stages these should help to protect our crops providing resistance has not become an issue. In general, resistance is much more likely to become a challenge in a high-infection year.
Yellow rust
However, low septoria does not equal low disease for many growers in 2017. The conditions that did not favour septoria seem to have greatly favoured either mildew or yellow rust or both. Yellow rust has been a particularly troublesome disease for some in 2017 and in particular on some of the varieties that are not recommended in this country.
The big difference with yellow rust is that autumn, winter and spring infection can cause serious damage and must be treated. This was the origin of the T0 treatment in the UK where an infected crop might not exist at T1 timing if it was not treated much earlier. Some growers with highly susceptible varieties told me they had already sprayed five times for yellow rust.
As with septoria, variety resistance must also be utilised against yellow rust. Some of the biggest problems encountered relate to varieties that were imported from the UK that were not fully evaluated here. But yellow rust evaluation is more troublesome than some other diseases because of the race structure of the population. A variety can appear to offer excellent resistance initially but when a new race appears it can collapse totally.
For similar reasons, variety resistance ratings can vary between here and Britain because of the make-up of the population. But an easterly wind can take races from there to bring new races into Ireland and make a variety with good resistance completely susceptible. Resistance to yellow rust is always a dynamic situation.
Crown rust
While crown rust on oats is an almost annual disease in many parts of the country, there are years when the problem is much worse than others. The planting of oats as a catch crop or green manure ahead of potatoes had been a factor in this regard. The early planting of such crops to enhance dry matter production can result in significant expansion of the disease long before the winter crop emerges.
This practice resulted in very high inoculum levels in spring 2016 and it will take a few years of control to wear down the population again. The problem with crown rust is that it is exacerbated by the low genetic resistance against the disease in current varieties. But, as with yellow rust, it is well controlled using fungicides in a programme and the major risk is early in the season ahead of the planned disease control programme.
Mildew
The other disease that caused a significant challenge in places and crops this season was powdery mildew. This occurred in all crops in the autumn and then transferred to spring crops. It has not been a universal problem in spring crops but it is present in some oat and wheat crops also.
I regard mildew as a nuisance disease because if it gets a strong foothold in a crop early you tend to have a battle for the remainder of the season. Husbandry, as in variety, seeding rate, planting date, early nitrogen, total nitrogen, elemental deficiencies, etc, all add to the risk of mildew infection.
Mildew can often come into a crop but never progress. This makes early and timely treatment somewhat questionable but if an early infection can be cleared up one seldom regrets that decision even if mildew does not progress in adjoining crops.
If an infection is allowed to progress, it becomes very difficult to clean up and treatment can involve two or three applications of a morpholine fungicide, plus possibly two applications of a mildewicide. These could amount to an additional €30/ac spend on fungicides over and above the normal disease programme and it is not always the most profitable element of the programme.
Finishing out
What happens for the reminder of the season remains to be seen. We could certainly see pressure from septoria, rhyncho, net blotch, etc, given the levels and intensity of recent rain events. Were we to move into a weather window of more broken and grey weather this may in itself be a partial trigger for ear blight infection. It is so pitiful when ear blight infects a crop (wheat or barley) that has been otherwise clean and is showing good yield potential.
Elsewhere in this publication, Dr Steven Kildea of Teagasc looks at approaches to finishing sprays on winter wheat and spring barley. If septoria levels remain low, this may result in lower selection pressure by septoria against the triazoles and this would be welcome. But with yellow rust present in so many fields, one would still need a good triazole loading to hold this disease and this may help the general economics of the T3 spray.
The T3 may be the most questionable of the three wheat fungicide treatments but one could not stand back and leave a crop uncovered against rust. If the weather were to turn hot and not so wet then brown rust could be an additional problem on both wheat and barley. While I have not seen any brown rust about, I have seen lesions that look too much like brown rust to be ignored.
The reason there is uncertainty is that the lesions have all the characteristics but the rust did not break through but this could be because it had been caught just in time by the fungicide. This comment about the risk of rust applies to all spring crops. Caution is needed and action may have to be considered.
On spring barley, brown rust is always a threat, especially on Mickle, Propino and Sanette. But of greater concern must be the potential impact of ramularia on the crop late in the season. As with the winter crop, the inclusion of either chlorothalonil or folpet is essential to help prevent this very troublesome disease.
But this final spray must also provide cover against the normal barley diseases of rhyncho, brown rust and mildew where it is present. In general, this will mean a triazole plus either a strobilurin or an SDHI along with the contact.
Different diseases have proven to be the main problems in this drier spring.Ear blight remains a significant threat to winter wheat but we have limited control ability using high fungicide rates of a mixed triazole.Ramularia is also a significant target for the final spray on spring barley. Read more
Special focus on sprays: crops and grassland
So far, 2017 will not be remembered as the worst year ever for cereal diseases and we are thankful for that. That is not to suggest that it has been disease-free, but it has not been bad for our usual wet weather problems.
For some, this will be the year of the rusts; for others, it will be powdery mildew. And the start of the year indicates a potential challenge from chocolate spot on beans.
The relatively dry winter was a bit of a help on septoria and rhyncho but winter weather does not matter that much on the lower leaves that will die off before spring growth cuts in. But having infection present in the crop does point to the potential for these diseases to move rapidly in springtime if conditions permit. Thankfully, this was not the situation in most instances and there is very little incidence of these diseases where fungicide was used sensibly.
While this is generally the case now (with winter crops being largely clean), there were some crops in early spring that had a worrying amount of septoria present. But the combination of the generally dry weather and good use of fungicides has held those problems and crops now look to have good potential.
Earlier drilling, geography and variety all influence what we see currently. Many winter wheat crops in the Leinster area have a full fourth leaf clean at the moment but further south this had been badly damaged on many crops.
In many instances, there is some evidence of fresh septoria coming though on leaf three but this has been at relatively low levels up to now. Some of the heavy rain in recent weeks may have further pressured the movement of infection but with the majority of fungicides applied at the correct stages these should help to protect our crops providing resistance has not become an issue. In general, resistance is much more likely to become a challenge in a high-infection year.
Yellow rust
However, low septoria does not equal low disease for many growers in 2017. The conditions that did not favour septoria seem to have greatly favoured either mildew or yellow rust or both. Yellow rust has been a particularly troublesome disease for some in 2017 and in particular on some of the varieties that are not recommended in this country.
The big difference with yellow rust is that autumn, winter and spring infection can cause serious damage and must be treated. This was the origin of the T0 treatment in the UK where an infected crop might not exist at T1 timing if it was not treated much earlier. Some growers with highly susceptible varieties told me they had already sprayed five times for yellow rust.
As with septoria, variety resistance must also be utilised against yellow rust. Some of the biggest problems encountered relate to varieties that were imported from the UK that were not fully evaluated here. But yellow rust evaluation is more troublesome than some other diseases because of the race structure of the population. A variety can appear to offer excellent resistance initially but when a new race appears it can collapse totally.
For similar reasons, variety resistance ratings can vary between here and Britain because of the make-up of the population. But an easterly wind can take races from there to bring new races into Ireland and make a variety with good resistance completely susceptible. Resistance to yellow rust is always a dynamic situation.
Crown rust
While crown rust on oats is an almost annual disease in many parts of the country, there are years when the problem is much worse than others. The planting of oats as a catch crop or green manure ahead of potatoes had been a factor in this regard. The early planting of such crops to enhance dry matter production can result in significant expansion of the disease long before the winter crop emerges.
This practice resulted in very high inoculum levels in spring 2016 and it will take a few years of control to wear down the population again. The problem with crown rust is that it is exacerbated by the low genetic resistance against the disease in current varieties. But, as with yellow rust, it is well controlled using fungicides in a programme and the major risk is early in the season ahead of the planned disease control programme.
Mildew
The other disease that caused a significant challenge in places and crops this season was powdery mildew. This occurred in all crops in the autumn and then transferred to spring crops. It has not been a universal problem in spring crops but it is present in some oat and wheat crops also.
I regard mildew as a nuisance disease because if it gets a strong foothold in a crop early you tend to have a battle for the remainder of the season. Husbandry, as in variety, seeding rate, planting date, early nitrogen, total nitrogen, elemental deficiencies, etc, all add to the risk of mildew infection.
Mildew can often come into a crop but never progress. This makes early and timely treatment somewhat questionable but if an early infection can be cleared up one seldom regrets that decision even if mildew does not progress in adjoining crops.
If an infection is allowed to progress, it becomes very difficult to clean up and treatment can involve two or three applications of a morpholine fungicide, plus possibly two applications of a mildewicide. These could amount to an additional €30/ac spend on fungicides over and above the normal disease programme and it is not always the most profitable element of the programme.
Finishing out
What happens for the reminder of the season remains to be seen. We could certainly see pressure from septoria, rhyncho, net blotch, etc, given the levels and intensity of recent rain events. Were we to move into a weather window of more broken and grey weather this may in itself be a partial trigger for ear blight infection. It is so pitiful when ear blight infects a crop (wheat or barley) that has been otherwise clean and is showing good yield potential.
Elsewhere in this publication, Dr Steven Kildea of Teagasc looks at approaches to finishing sprays on winter wheat and spring barley. If septoria levels remain low, this may result in lower selection pressure by septoria against the triazoles and this would be welcome. But with yellow rust present in so many fields, one would still need a good triazole loading to hold this disease and this may help the general economics of the T3 spray.
The T3 may be the most questionable of the three wheat fungicide treatments but one could not stand back and leave a crop uncovered against rust. If the weather were to turn hot and not so wet then brown rust could be an additional problem on both wheat and barley. While I have not seen any brown rust about, I have seen lesions that look too much like brown rust to be ignored.
The reason there is uncertainty is that the lesions have all the characteristics but the rust did not break through but this could be because it had been caught just in time by the fungicide. This comment about the risk of rust applies to all spring crops. Caution is needed and action may have to be considered.
On spring barley, brown rust is always a threat, especially on Mickle, Propino and Sanette. But of greater concern must be the potential impact of ramularia on the crop late in the season. As with the winter crop, the inclusion of either chlorothalonil or folpet is essential to help prevent this very troublesome disease.
But this final spray must also provide cover against the normal barley diseases of rhyncho, brown rust and mildew where it is present. In general, this will mean a triazole plus either a strobilurin or an SDHI along with the contact.
Different diseases have proven to be the main problems in this drier spring.Ear blight remains a significant threat to winter wheat but we have limited control ability using high fungicide rates of a mixed triazole.Ramularia is also a significant target for the final spray on spring barley. Read more
Special focus on sprays: crops and grassland
This is a subscriber-only article
SHARING OPTIONS: