Pests fight back in grain crop

Changes in how fungicides are registered and the development of fungicide resistance in their target pathogens, are severely undermining the future success of fungicide- dependent disease control strategies, the Teagasc National Tillage Conference was told by Steven Kildea, of the Teagasc Oak Park research staff.

Even though their efficacy is under threat, fungicides must continue to be relied on, until varieties with robust levels of resistance and yield become available.

Research is also ongoing to provide more integrated disease control approaches, such as matching the fungicide programme to variety and disease risk.

Mr Kildea described the continuing slide in the efficacy of the main fungicides for control of septoria disease in wheat.

However, he pointed out that disease control is possible, if sprays are well timed to leaf emergence, combined with careful product selection and sequencing.

And an extra application of chlorothalonil (when leaf two is fully emerged) may be justified if there is any compromise on the main spray timings.

Under Irish growing conditions, if left unchecked, foliar and ear diseases have the potential to severely restrict the yield potential of cereal crops.

The Teagasc National Tillage Conference also heard that grain growers must adopt measures to retain the efficacy of insecticides, because resistance is developing in grain aphids.

Researcher Lael Walsh (Teagasc Ashtown and UCD) said tests of grain aphids in winter barley showed evidence of the mutation for knock down resistance to pyrethroid compounds in the aphid. But results also strongly suggested a second enzyme-based pyrethroid detoxification mechanism for resistance to the insecticide is present in some Irish field populations.

These findings reveal that continued over-reliance on pyrethroid insecticides is likely to further exacerbate difficulties in controlling both grain aphid and its transmission of Barley Yellow Dwarf Virus (BYDV).

“Growers must adopt cultural control options such as sowing date changes, use of varietal resistance etc, to reduce the pressure on insecticides. In the near absence of alternative pesticide chemistry, it will become essential that non-chemical options are explored as part of a wider integrated pest management strategy,” said the researcher.

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