BCPC Diseases Review 2022 – Changing Challenges and Changing Tools for Integrated Crop Management

Abstract

John Lucas, Editorial Board Member and Jon West, Rothamsted Research suggested that the threat posed by Fusarium is likely to increase due to a number of factors including maize crops extending further northwards. The second presentation, given by Derek Croucher, focused on the impact of mycotoxins on producers. The main processor focus on mycotoxins both in the field and during storage is compliance with current legislation, including the ability to test effectively and analyse samples, as well as mitigation measures. There are parallels with legislation of plant protection products, and concerns about potential changes due to exit from the EU. To date these have not occurred, but there is the possibility of GB adoption of EU rules by retailers to facilitate trade. The Food Standards Agency have a priority list of contaminants with maximum limits for mycotoxins in particular foodstuffs, exemplified by current permitted levels for T-2/HT-2 toxins in unprocessed and milled oats. The primary problem in UK oats is Fusarium langsethiae, which causes a mainly symptomless disease, varying in incidence from year to year, with some "high" years, especially in Scotland. There are no commercially viable field mitigation measures. Milling reduces contamination, but this varies and is not batch to batch predictable. There is no reliable rapid test for toxin contamination in oats, and testing by LC-MS/MS is expensive and takes time. In severe years, around 10 – 30% of unprocessed oats would be non-compliant, and as much as 20% of processed products. Identification of compliant versus non-compliant products is challenging and poses a significant risk of recall and reputational damage. The 2022 Diseases review was held at the NIAB Park Farm, Cambridge on October 19th 2022 with a mix of in person and online delegates. The meeting was chaired by Jenna Watts, Head of Plant Health and IPM at the Agriculture and Horticulture Development Board (AHDB). She outlined the current issues and challenges for crop production including climate change, the evolution of pathogen populations to overcome host resistance and pesticides, alterations in the regulatory framework, and changing consumer priorities. New tools are available for disease diagnosis and control, but how can they be most effectively used for integrated crop management? The first two presentations dealt with the issue of mycotoxin contamination of small grain cereals. Professor Simon Edwards (Harper Adams University College) described the various mycotoxins in cereal crops infected by different Fusarium species causing the head blight complex. On wheat the main problems are deoxynivalenol (DON) and zearalenone (ZON) produced by F. graminearum and F. culmorum, while HT-2 and T-2 toxins produced by F. langsethiae and F. sporothrichioides are more of an issue in oats. Mycotoxin profiles vary by cereal, region and season, and exceed permitted regulatory limits in some crops and years. Risk factors for head blight are well known and include crop debris (the main source of inoculum), a warm spring, and heavy rainfall with high humidity in summer. In experimental trials, agronomy accounts for relatively little of the variation in mycotoxin levels. Maize as the previous crop is a major risk factor, along with min tillage and direct drilling. Ploughing or chopping and mixing of debris reduce mycotoxin levels in the crop. There is limited current varietal variation in resistance to head blight. Some fungicides including prothioconazole, metconazole and tebuconazole applied at T3 can reduce DON levels, while Adepidyn (pydiflumetofen) a new but not yet registered SDHI shows some promise for head blight control and toxin reduction. Integrated management to minimize Fusarium mycotoxins in milling wheat therefore combines the use of less susceptible varieties, avoiding high risk crops such as maize in rotations, intense cultivation if a high-risk previous crop has been grown, application of an effective fungicide (or mixture) at T2 and especially T3, and ensuring a timely harvest as late harvesting is associated with higher mycotoxin levels. It was noted that these recommendations are not easy to reconcile with some crop management trends such as reducing cultivations. Professor Edwards also presented some data on HT-2 and T-2 occurrence in oats, and tactics for reducing risk such as switching to spring varieties, or taller more Fusarium resistant varieties, long rotations, and the use of cultivations. Climate change models suggest that the threat posed by Fusarium is likely to increase due to a number of factors including maize crops extending further northwards,