The dry and warm conditions played a part at keeping our main wet weather diseases at relatively low levels in 2017. However that did not mean that there were no problems and diseases like mildew, ramularia, yellow rust and brown rust took over as the main disease threats in some crops.

But diseases were not the only problems encountered by some growers. It seems that a few growers had a really big issue in spring oats with some sort of allergic reaction following fungicide application. This was made known to me recently by one north Galway grower . He said that there were at least seven other growers with a similar problem within six miles of his location, plus at least one other in Roscommon.

Gerry Heavey from Moylough in Co Galway only stumbled across the problem on his own land because he happened to use two different product combinations in the same field. Basically it looks like one of these combinations caused significant premature senescence of the crop. This seems to have destroyed the bulk of the green leaf area.

The crop was sprayed initially at GS32 on 25 May. This was to target mildew and crown rust using fenpropidin (0.31 l/ha), plus tebuconazole (0.63 l/ha) plus CCC (1.2 l/ha) for growth regulation. Gerry said that there had been a significant adverse reaction to that application at the time but the crop grew away from the symptoms after about 10 days or so as new leaves appeared. So the crop recovered then but only because the damaged leaves were covered up by new foliage.

The T2 treatments

The next fungicide treatment was applied at full ear emerge on 5 July. The initial tank of spray was applied to the headlands and a number of the tramline runs. These were sprayed with epoxiconazole plus fenpropidin (0.78 + 0.38 l/ha). This was applied to about 16ac of the field while the remaining 24ac in the field were sprayed with a tebuconazole (250g/l) plus fenpropidin mix at 0.625 + 0.38 l/ha respectively.

This latter treatment was similar to that used by all the other growers who now report a similar problem. Gerry said that the day in question was dull and that temperature was relatively low. He used 200 l/ha of water.

This time a similar reaction appeared but it was more severe. Because the flag leaf and ear were emerged at the time of application the consequences had the potential to be more damaging.

Initially, reddish blotches appeared on the leaves and the ears took on a bleached appearance, Gerry said. There were also some blind grain sites visible in the head but these can be seen in most crops, especially at the base of the panicle. Whether or not this problem is worse in the damaged area is not possible for me to say.

A few weeks ago the area sprayed with the epoxiconazole plus fenpropidin combination was perfectly green but there was substantial damage visible on leaves and spikelets in the areas and field sprayed with tebuconazole plus fenpropidin, which then looked light brown in colour.

The crop now looks like the damaged area is nearing ripeness, while Gerry suggested that the part of the field that did not suffer this damage could be 3-4 weeks later maturing.

When asked about sprayer hygiene or the chance of having something else in the tank that could cause that damage, Gerry said that he is very particular about same.

Triple rinsing is the minimum, with even more after certain products. And there was no sign of damage in the first tank applied to the field, which would be the most likely place that damage would be seen if there was a carryover of spray involved.

Photo tells the tale

Recent aerial photographs show the difference between the areas of the field treated with the different mixes in the second spray. Even the areas that were over-sprayed on the ins-and-outs show the damage clearly. Damage was even evident where the washout from this tebuconazole mix was over-sprayed on tramlines initially treated with the epoxiconazole mix. This would have been a diluted concentration of the mixture but it still seemed to have caused damage.

The instant reaction is that the problem seems to relate to the inclusion of tebuconazole. The whole field received fenpropidin and it was only the area that received tebuconazole in the mix with fenpropidin that showed the symptoms and early senescence.

There may well be other fields around the country that suffered a similar reaction in 2017. However, growers may be unaware of an issue because there is nothing to compare it to. I had seen other fields in other counties where different brands of tebuconazole were used with other actives and damage was evident, but at a much lower and possibly insignificant level.

There can be little doubt about the level of damage caused in these instances. And the evidence appears to point to the inclusion of tebuconazole in the mix. The earlier treatment used in this same field also caused damage so might there have been some sort of negative compatibility between the two actives? Indeed could either chemical have been part of a bad batch that had a problem? Shouldn’t be, but…

Fungicide should not kill foliage

Whatever the reason it would seem that everything was done properly and crop death should not follow the application of a fungicide mix which was applied to keep leaves alive. This may not be a simple issue but crops have been damaged and it would not appear to be the fault of the grower.

Products that might generally be regarded as fully compatible are in some way responsible for these problems, even if it is in association with unusual weather patterns. There needs to be some formal way of dealing with such issues where the cause is purely related to the products in question and where other factors are unlikely to be involved.