Concerns over pesticide losses comes out repeatedly as one of the industry’s main issues when it comes to managing plant health issues going forward.
Vegetable and soft fruit production are particularly at risk, because of the limited number of existing actives and the high risks posed by pests and diseases. Alternatives such as increased use of physical barriers, nets and biological agents will be costly but necessary for the industry to pick up quickly, along with enhanced methods of monitoring and predicting pest and disease risk so that sprays can be targeted to maximize effectiveness and profit.
Losses in broad-acre crops also pose concerns and in cereals, the scheduled withdrawal of chlorothalonil in May 2020 coupled with the potential withdrawal of at-risk azole fungicides would make the management of diseases such as Septoria leaf blotch on Scottish winter wheat crops harder. Looking at some of the actives most used in Scotland, it has been estimated that the withdrawal of prothioconazole alone would reduce the annual £120M Scottish Total Value of Output of winter wheat by 2% or £2.40M. The additional withdrawal of chlorothalonil adds another 2% reduction, reducing the value of Scottish wheat by another £2.4M.
Spring barley, worth £274.83M annually, will also be impacted by the withdrawal of prothioconazole resulting in a possible £2.74M reduction in value if alternatives such as new actives and more resistant varieties are not picked up. The withdrawal of the insecticide chlorpyrifos in 2016 has raised the risk of leatherjacket damage in spring barley, potentially taking 0.5% (£1.37M) off the Scottish crop’s value. There are currently no pesticide options available to manage this pest, growers having to rely on techniques such as rolling the crop. Due to the revocation of the neonicotinoid cereal seed treatments at the end of 2018, there will be a predicted increase in the use of pyrethroid insecticides to manage aphids and Barley Yellow Dwarf Virus (BYDV). The potential withdrawal of lambda-cyhalothrin (medium risk of withdrawal) and other pyrethroid insecticides, coupled with limited alternatives could see a resurgence of BYDV and significant yield losses – estimated to be in the region of 1% or £0.47M for winter barley, £1.2M for winter wheat and £2.75M for spring barley, particularly in light of grain aphid resistance to pyrethroids..
The recent reprieve of metaldehyde from its previously proposed withdrawal in 2020 is likely to be temporary, and it is probable that this molluscicide will be lost in the next year or two. The withdrawal of metaldehyde is mitigated by the availability of ferric phosphate as a straight (if not more expensive) alternative. Whilst some herbicides used in cereals are at high or medium risk of withdrawal, there are several alternatives available and economic impact on cereals is likely to be minimal.
Alternatives which include new fungicides such as Inatreq and Revysol and increased use of biologicals will add to cost and require better ways of predicting pest and disease risk so that usage can be more targeted than currently. More robust varietal resistance is a key strategy in reducing reliance on pesticides and the acreages planted to more resistant varieties of cereals continues to increase which is a positive. More use going forward of integrated pest management techniques (IPM) is crucial and should be supported by advice and training.
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